Quorn Tool and Cutter Grinder

A "Very Much Improved"
Quorn Tool and Cutter Grinder
PART I
by Walter B. Mueller
Photos and drawings by Author
A
pparently, the Quorn Tool and Cutter Grinder was
born in controversy, in 1974, with inventor
Professor D. H. Chaddock being almost immediately
attacked by a vociferous detractor, Mr. Thomas, who
took exception to nearly every idea of the professor.
What prompted the brouhaha may never be known (or
be important), but even to this day, it seems
unfortunate and unnecessary. In a fraternity built on
amicable interrelationship, animosity surely has no
place.
Anyway, I hope the issue is dead, as the 1974 Quorn
design is no longer the best thing around to argue about.
I make this statement with some amount of confidence,
as I intend to show that there is a legitimate
improvement possible on the 1974 Quorn design that
renders much of the Chaddock/Thomas debate passe.
This is the "VMI Quorn," the design named in the title
of this paper, and I think even the most hard-toconvince old-timer will agree that newer may be better,
at least sometimes.
Maybe the Mark 2 Quorn was protected by patents, but
I am surprised that nobody picked up the ball after
Chaddock left the field. The Quorn was a tidy little
machine, but I don't think anyone who built and used
one should feel disloyal for thinking it might be
improved. When ! first built nunc, I bad the strong need
for a machine that would easily resharpen end mills. For
me, immediate disappointment ensued. The end angles
2 A rear view of the VMI Quorn tool ans cutter grinder.
30
1
A front view of the VMI Quorn tool and cutter grinder.
were easy enough to grind, but OD grinding was
decidedly "iffy." Proper setup of the lip support finger
was difficult to get right, and then came the problem of
getting the lip to be ground on the lip support rest and
keeping it there while the flute was being drawn across
the grinding wheel. There's a lot of friction in the world,
3 A rear view of the VMI Quorn showing the surface ground
baseplate and the vernier height gage used to make quick machine
setup
adjustments.
T H E
H O M E
S H O P
M A C H I N I S T
PARTS LIST
PART NO.
QTY.
1
1
Base Plate
2
1
Lip-Support Bar
3
1
Lip-Adjust. Screw-Guide
4
1
Top Guide
5
1
Bottom Guide
6
1
Adjusting Knob Assembly
7
1
Height Adjusting Screw
8
1
Slide Clamp Screw
9
1
Lip-Support Guide
10
1
Slide Positioning Screw
11
1
Lip-Support Lock-Nut
12
1
Lip-Support Finger
13
1
Adjusting Screw Bushing
14
1
Adjusting-Screw Retainer
15
1
16
17
4 The vernier height gage in use to determine the center line height
of the air spindle.
and most of mine was located in the fit between the
work spindle and its mating housing diameter.
Fiddle with the adjustment of the ball handle on the
spindle housing as I might, I could not achieve a
condition of low enough "stick-and-slip" friction to
keep the flute being ground on the lip support rest.
Immediate disaster was the usual result, leaving me
with a low opinion of Chaddock's design choice in this
area. If this is what Thomas was incensed about, I think
he had a very valid point, if not the right decibel level in
his criticism. I put the machine in a back corner of my
mind and left it there, but I didn't forget it.
If Chaddock could have been reincarnated, I think a
Mark 3 Quorn would have appeared. I also think that
Chaddock, with all of his academic titles, knew about
the mechanical "coefficient of friction." In all
mechanical assemblies with mating surfaces in
intimate contact, friction is unavoidably present. The
only way to lessen the friction is to interpose a
lubricating film of something between the two surfaces.
This is usually oil, but oil is a big N O - N O when sliding
surfaces and grinding grit coexist in the same
mechanism. Externally pressurized air-lubricated
bearings are a successful alternate to conventionally
lubricated bearings, but since high-speed air-lubricated
grinding spindles first appeared in Germany in the '60s,
Chaddock might not have wanted to consider including
such a thing in his thinking. Hence, he settled for the
"stick-slip," high-friction condition that his design
dictated. But you and I can do in 1999 what Chaddock
wouldn't/couldn't do in 1974, so if you are willing to
unstiffen your lips, and do the few simple things I will
suggest, we can have a superb little tool grinding
machine that will WORK!, and (don't worry) will still
look British.
N () V E M B E R / D E C E M B E R
I 9 99
PART NAME
Air-Spindle
2
1
18
Clamp Collar
Air Bearing
3
Ball-Handle
19
1
Adjusting-Screw Retainer
20
1
Brass Gib
21
1
Clamp Screw (purchase)
22
1
Lip-Support Clamp-Plate
23
1
Rear Bar Hook
24
1
1.0" Micrometer Head (purchase)
25
1
Clamp-Plate
26
1
1.0" Travel Dial Indicator (purchase)
27
1
Indicator Mtg. Bracket
28
1
Guide-Lip Support Bar
5 The vernier height gage in use to determine the center line height
of the wheel head spindle.
1 came to my present state of enlightenment in two
steps. I bought my kit of Quorn castings in 1984,I
think, and started building the machine per Chaddock's
instructions. In about five or six months, I had a usable
but unfinished Quorn grinder. The machine was
grinding things but was unfinished in the respect that
31
6 The vernier height gage in use to make a correct height setting for
the lip support finger.
all the degree (numerical) markings were left off the
scales, as I didn't think Chaddock's instruction, to take
a hammer and hand stamps and punch the numbers in,
would give me a satisfactory result.
And when I ran into the friction problem, I put the
machine aside and started doing other things.
On December 12, 1988, my son died, and after several
months of misery, I knew I had to do something to
preserve my sanity, so I started working on another
problem. This was the engraving machine I needed to
finish my Quorn. After about 600 hours of design and
build time, my engraver was finished, so I engraved all
my Quorn dial rings and scales. I should have been
extraordinarily happy; how could it be that I wasn't? A
nice new dial engraving, a spiffy paint job and all - and I
still couldn't make the Quorn do what I wanted most,
which was sharpen end mill flutes. In spite of the
verbiage and the pictures presented in the "Operating
Instructions" manual that came with the casting set, I
(at least) could not get the easy results Professor
Chaddock predicted. The "coefficient of friction" value
- of about 0.15 that Chaddock had accepted - had to be
reduced. The best way to do that was by the air spindle
approach, where the coefficient of friction value would
be closer to 0.001" than 0.15", so I went to work.
First, I built the air spindle/spindle housing assembly;
and while I was at it, I added the Blanchard-ground
baseplate, fixed up the lip support finger problem (to a
degree), and added the long travel indicator to help ease
the setup difficulty I felt should be addressed. That was
the (improved) Quorn project published in the May/June
1998 issue of HSM.
My latest version of the Quorn (Very Much Improved)
machine arrangement I now offer for your
32
7 The dial indicator showing the correct wheel head elevation setting
for a 6.0° clearance angle, with a 2.25" diameter grinding wheel.
c o n s i d e r a t i o n . T h i s p a r t i c u l a r little b e a u t y has been
active in my shop for over four years now, and I am
happy to report that my entire opinion of the Quorn and
my sharp end mill inventory have been dramatically
improved.
But, after all of this verbiage, what is a VMI Quorn?
Shown in Photo 1 is a full frontal view of what I now
think is (Yank-enhanced) British excellence. Maybe
you'll pardon me for privately thinking of this as my
machine, but I acknowledge it would not exist if it were
not for the solid spade work of Professor Chaddock. If
he had lived to design a Mark 3 Quorn, it might well
have been a first-born precursor of the VMI Quorn, and
then there could not have been the bitter controversy
between Chaddock and Thomas.
But, on to the changes that make the VMI Quorn a very
good tool grinder to have in your shop. Listed and
described below, but in no particular order of
importance, are all the "fixes" my Quorn now enjoys.
1) "Blanchard-ground" baseplate: The Blanchard rotary
grinder is used most often to produce flat surfaces on
large pieces of "hot rolled and unflat" metal plates. A
very obvious addition to the pictured Quorn is a
12 X 18 X 3/8" steel baseplate that is flat to within
maybe 0.002". This additional member provides a
reference surface from which to execute all the
quickly-made machine setup adjustments. The
baseplate appears in Photo 1, with the basic Quorn
machine sitting on top of it. Also appearing, just to
the right of center, is what one might rightly surmise
to be a micrometer spindle. This member fits into
Mr. Chaddock's item No. 301 casting and, along with
my item 23, replaces his items 308 and 309, which
were his method of controlling the depth of grind
T H E
H O M E
S H O P
M A C H I N I S T
and, hence, the diameter of the end mill he was
sharpening.
I think my scheme beats his, because the micrometer
gives easier and finer diametral control and my item
23 prevents the top-heavy work spindle assembly
from doing heart-stopping back flops when you least
expect them.
2) The air spindle assembly: As explained at length
earlier, the Mark 2 Quorn grinder suffered from the
large amount of friction in the close fit of the sliding
work spindle/work spindle housing, and that made it
hard to use. The air-lubricated work spindle is free to
move in its housing with virtually no friction and
makes the sharpening of miniature end mills only a
question of operator skill. If any one thing is
revolutionary about the changes I recommend on the
Quorn, it is the externally pressurized air spindle. It
makes the machine a joy to use.
3) The lip rest mechanism: I think Professor Chaddock
would agree that the lip support rest is in the wrong
place, and that it needs to be designed so it can be
adjusted more easily and quickly. In addition, since
the lip support rest is used mainly in the
resharpening of end mills, it should be "married" to
the air spindle and housing assembly. In short, the
entire mechanical structure of the end mill
sharpening device should become a "stand-alone"
kind of machine attachment that can be easily
removed and quickly reattached to the Quorn main
structure, to be used when it is needed. It is this kind
of stand-alone assembly that I have designed and
present to the reader.
4) Long-travel dial indicator to position the grinding
spindle head: This machine feature makes it easy to
properly set the height of the grinding spindle the
required distance above the cutter center line to give
the needed clearance angle to the cutting edge of the
end mill. Used in conjunction with the vernier height
gage, it provides a quick and foolproof method of
machine setup.
5) The micrometer head and way bar hook already
described in item 1 above.
These five additions to the Quorn are shown in the
layout drawing. I would be the last person to claim that
what I have assembled is the ultimate tool-grinding
machine, but I think it's safe to say that, now, the
grinder is closer to the ideal that Chaddock intended.
This machine has ended a major source of frustration
for me and lets me derive a lot more enjoyment from
my hobby.
Since one picture is supposedly worth 1,000 words, let's
not waste a lot of time talking and look at a bunch of
pictures. Photo 1 is a frontal view of my machine as it
now looks. You can certainly see the air spindle and air
spindle housing on the right end of the machine; they
are items 15 and 17, respectively, on the parts list.
Directly under the left end of the air spindle is hung a
N O V E M B E R / D E C E M B E R
19 9 9
9
A close-up view of a dull end mill in the process of being ground.
mechanism that has a pointed finger sticking upward,
angled to the left. That's the lip support mechanism,
and it's fastened to the end of a stiff slide member (item
2|, the lip support bar. Additionally, just above the
grinding spindle housing is suspended a long-travel dial
indicator and its mounting arm (items 26 and 27),
which are not shown on the layout drawing due to lack
of space but which provide the vertical grinding spindle
offset measurement needed when the machine is being
set up to grind the flute clearance angle (usually 6°) on a
dull end mill.
Photo 2 exhibits the rear of the machine and shows the
backside features of the things mentioned in Photo 1; it
also pictures the way the lip support bar is mounted on
the. air bearing housing, as well as the dial indicator
support mounting to the column of the machine. It also
shows the air inlet plumbing on the air bearing housing,
and the way the micrometer head is positioned on the
33
rear way bar of the machine and is able to control the
amount of "rocking" motion imparted to the work
spindle assembly during the lip clearance grinding
operation. It also shows how the entire lip
support mechanism is "married" to the air
spindle and the mating spindle housing, so
the end mill always stays on the lip
support finger during grinding and also
when the work spindle is "rocked"
away from the grinding wheel as
the cutter is being rotated to
present a new dull flute to
the wheel.
reading, as it is a 0.500" diameter half pin.
Then, I write that value on a note pad so I
don't forget, because I will shortly need the
number again.
In Photo 5, the height gage is being used to
determine the actual height of the grinding
spindle center line. If that number is any different
from the measured value of the work spindle center
line, I adjust the grinding spindle center line height to
be the same as the work spindle center line height.
With the center line height of both the grinding spindle
and the air spindle measured to be the
same, the height of the lip support
finger is set to coincide with
the height of the center lines of
both the work head and
grinding head spindles (Photo
6). Here, I take the actual
measured value of the air
spindle and grinding spindle
center lines and subtract 0.250"
from
the measured height. Then I
10 A detail view of the air spindle and
set the lip support finger height to the
clamp collars, with a 3/8", reducer
bushing installed in the air spindle bore.
computed value.
Photo 3 shows the vernier
height gage (with a 4"
long, ground, 1/4 X 1/2"
tool bit attachment), to
determine the height
of the work spindle
center line, the lip
support finger height,
and the grinding
spindle center line
""^^^
height. This height
measurement is the key to the rapid
setup for the end mill flute grinding operation. If such a
thing as a "secret weapon" is involved in this whole
grinding operation, this is it. It quickly gives the vital
information needed for foolproof setups.
The vernier height gage is being used in Photo 4 to
measure the height of the air spindle center line. It
shows the measurement being made to the rounded
diameter part of the half-pin tool. The reason is that it
is easier and faster to set the height gage to just touch
the top diameter of the half-pin tool than to find the
accurate height of the flat surface part of the half pin.
Since I need the actual height of the work spindle center
line, what I do is subtract 0.250" from the vernier
When all the center line measurements and
adjustments are completed, what remains is to zero out
the long travel dial indicator, then elevate the grinding
spindle center line by the amount calculated from the
expression:
Elevation distance = sin (desired clearance angle) X
grinding wheel radius
For a 2-1/4" diameter wheel and a 6° desired clearance
angle, the elevation distance becomes:
Elevation distance = 1-1/8" X sin 6° (0.1045)
Elevation distance = 0.117" (Photo 7).
With the machine center line adjustments completed,
you can now insert a dull end mill in the work spindle
and set the stop collar (item 16) adjustments and
advance the dull cutter to the wheel. It is probable that
at this point you will need to adjust the micrometer
head position and rear way bar hook to get the required
work head movement toward and away from the
grinding wheel. This is a quickly made setting and
when it is done you are ready to make your grind. The
grind always starts at the shank end of the flute (Photo
8), proceeding toward the tip end of the cutter. Go easy
on the amount of stock removal.
A grind of .001" is plenty heavy. Photo 9 shows the
shiny grind area on the flutes of a dull end mill being
reground. It might be a narrow looking land on the
periphery of the cutter, but nonetheless the cutting edge
is razor sharp.
11 A detail rear view of the air spindle housing assembly showing
the air inlet for the air bearing housing.
34
With the main features of the machine well in mind, we
can now look at the specific elements that make up the
assembly. The air spindle itself and the air spindle
1 3 A general view of the air spindle assembly, with the entire cutter lip support
mechanism in its operating position.
1 2 A rear end view of
the air spindle housing,
showing the lip support
bar guide and clamping
arrangement.
housing were described in the May/June 1998 issue of
HSM, which details the specific technique used to make
an air spindle and its mating air bearing housing. The
air spindle (item 15) and the stop collars (item 16) are
shown in Photo 10. The general details of the air
bearing housing are apparent in Photos 11 and 12, with
Photo 12 showing the particulars of the lip support
guide (item 20). Photo 13 is a rear view close-up shot of
the manner in which all of these diverse elements come
together to form the "stand-alone" assembly that can be
added to or removed from the Quorn structure as the
particular grinding problem dictates.
14
This view illustrates how the grind of the dull cutter starts at
the top end of the flute.
The flute grinding operation is designed to happen as
shown in Photos 14 and 15. As in Photo 14, the grind
always starts at the top end of the flute and progresses
to the tip (Photo 15). That way, with downward
rotation, frictional force at the cutting point of the
wheel, the cutter is always held down on the lip support
rest, and can be moved across the face of the wheel by
the slightest rightward pressure of the finger on the air
spindle. When first experienced, it is an amazing
sensation.
Next time we'll get underway with the making of chips.
15
This view shows how the grind progresses to
the tip end of the flute, with the end mill still
being supported by the lip support finger.
N O V E M B E R / D E C E M B E R
1 9 9 9
35
A "Very Much Improved"
Quorn Tool and Cutter Grinder
PART 2
by
Walter B.
Mueller
Photos and drawings by Author
P
hoto 16 shows where all the action really occurs on
the grinding machine. This close-up view shows
the lip support finger with its vertical positioning and
clamping mechanism, as well as the horizontal, sliding
member controlled and locked by the two knurled
finger knobs that appear on the left end of the assembly.
Of course, the air spindle and housing also appear on
the upper right, along with the lip support bar, to
complete the picture.
Photo 17 is just an auxiliary rear view of the entire lip
support positioning apparatus. The two half-pins
Professor Chaddock required as necessary for his
machine setup procedure are shown in Photo 18; I use
them as full diameter pins for a considerable saving of
setup time. The photo also shows a 3/8" diameter
adapter bushing for the air spindle. I also have 1/2" and
5/8" diameter bushings, all of which go into the 3/4"
diameter hole in the air spindle with a nice, snug fit,
which allows me to use and regrind all end mills with
the listed shank sizes. I have no need to make my air
spindle accept collets of any type, thereby
compromising the great rotational
accuracy I now enjoy.
Photo 19 shows the wheel and
spindle adapter mounts that I
generally use for all my OD grinding
on end mills, and Photo 20 is the "secret weapon"
height gage that makes the setup procedure on the
VMI Quorn the "piece of cake" it is. I use a dedicated
Chinese import for this job, because the grit that
unavoidably occurs in any grinding operation is bound
to affect the absolute accuracy of the instrument.
My more expensive vernier height gage can safely
remain on my surface
plate and not undergo
any degradation in
accuracy, but I use
my shop vacuum
before and after
every grinding session
because, inevitably,
grit happens.
18 A detail view of an air
spindle bushing and the two half-pins called for as setup tools by
Professor Chaddock (see text).
J A N U A R Y / F E B R U A R Y
2 0 0 0
16 A front view of the adjusting mechanism needed
to position the lip support finger in the correct
relationship to the grinding wheel.
17 A rear view of the lip support
finger positioning
mechanism.
19 The two wheels I generally use for grinding the peripheral and
end clearances on dull end mills.
39
With all the preliminary chit-chat out of the way, it's
probably time to get down the business of making
chips. Even though the May/June '98 issue described the
business of making the air spindle/air spindle housing and
the July/August '98 issue the rest of the parts, the area can
be profitably revisited because changes were made; and
then, undoubtedly, there will be the folks who tuned in
late who will want the whole story, all in one piece.
The air spindle is shown in Photo 10 with its mating
collars; those members remain common to both
designs. They are detailed as item numbers 15 and 16.
The air spindle housing (item 17), however, changes in
some details. Since there can be no VMI Quorn without
these vital parts, the manufacturing story starts here.
My air spindle started life as a rusty, 11.0" length of 1-1/2"
diameter hot rolled steel. Hot rolled (unattractive as it
is) is the best material because it is less apt to have large
residual stress levels when you remove the bark from
the bar, and good dimensional stability is what we need.
1 center drilled the (outboard) end of the bar, rechucked
the piece taking a short grip on the un-drilled end,
engaged the centered end on the ball bearing center in
the tailstock, and I was off to adventure. Several turning
passes later, I was down to about 1.320" diameter, so I
stopped peeling and mounted my home-built grinding
attachment on the lathe, also draping the machine with
an attractive assortment of old towels, etc., that I
filched from my wife's rag bag.
40
What I wanted now was not so much an absolute size
on my air spindle, but as true a diameter as I could
achieve. After several grinding passes to clean up my
rough-turned air spindle, I found my lathe was not
turning a taper but was generating a barrel-shaped bulge
of 0.0002" on the diameter of my workpiece. The time
had arrived to outwit the first problem, so I removed the
workpiece from the lathe and chucked up an unemployed
cube of steel about 2.5" on a side. After I poked a hole
through this, I bored the diameter to a size about a halfthousandth over the bulge diameter of my air spindle.
Then I cross-drilled and tapped the block for a 1/4-20
NC pinch bolt, after which I slotted the block, cutting
through the drilled and tapped hole, so I could change
the size of my big hole by tightening the pinch bolt.
What I had now was a ring lap, as pictured in Photo 21.
It's not pretty, but it works well.
One last statement about the air spindle. The detail
drawing of this part calls for a 0.7500" diameter hole, on
the geometric axis of the central diameter, within 0.0002"
TIR. This is important, if you expect good grinds from
the machine. When machining this hole, chuck the air
spindle (protected with aluminum scrap) in your fourjaw universal chuck. Then take the time (maybe hours)
to indicate the air spindle outside diameter to 0.0000"
TIR concentricity. In toolmakers' parlance, that is
"dead nuthin" or "dead nuts" perfect concentricity.
Then drill and bore the hole to the 0.7500" diameter.
T H E
H O M E
S H O P
M A C H I N I S T
Don't trust the drill to hold the concentricity you need.
If you don't trust your lathe to produce a 0.7500"
diameter on demand, then you may consider reaming
the hole. But first, ream a test hole so you have some
notion of what size it is actually going to cut when you
get up the nerve to operate on your air spindle.
About 35 years ago, I built an 8.0", f6.3, reflecting
telescope. I ground and polished the mirror, built all the
telescope hardware, and had great fun until atmospheric
smog and light pollution put me out of business. However
(since I never throw any good stuff away), I still have a
stash of optical abrasives left from my mirror grinding
days, including 1000-grit (and finer) polishing compounds.
So, rechucking my bulgy air spindle on its unturned end
portion, I attacked the bulge with my new lap and a pinch
of 1000-grit aluminum oxide and a little oil. Again, I
attired my lathe in a collection of my wife's castoffs to
be grit safe, and myself in a pair of stout leather gloves
to be injury proof. Then, running my lathe at its slowest
speed, I lapped the air spindle until it showed a uniform
end-to-end diameter of 1.3122" - as close as I can read a
mike. At this point, I was not attempting to hit an exact
diametral dimension. All I wanted was a uniformly
sized, round geometry. With a slow-acting lapping
process, this was easy to achieve.
20 The "secret weapon" tool that makes the VMI Quorn
setup such an easy job.
Now, I was ready to make the air spindle housing. I had
on hand a chunk of what my friendly scrap dealer
supposed was mild steel. I took the air spindle
housing out of a 24-lb. hunk of this stuff.
I have no idea what it actually was,
but it was not "mild" in nature.
When I machined it, I thought it was
feisty steel because it fought back
hard, but I finally won.
Next, I had to consider how to
make the air spindle housing.
I had on hand an air spindle of
1.3122" diameter. I had
determined I wanted a bore size
of 1.3135" diameter, giving a
I sawed it; I ran it through my shaper;
spindle-to-housing clearance of
I milled, drilled and rough-bored it
0.0013". The best way for me to
and was finally ready for the finish
do this job, I knew, was to make
boring. I took the precaution of
a plug gage to tell me when I had
getting some M-42 cobalt boring bits
achieved a bore diameter of 1.3135".
because I knew the 4.0" long finish
A plug gage will tell you with great
bore would prove too tough
21 The ring lap used to do the for regular high speed steel
truthfulness if you have a tapered bore or
final sizing of the air spindle.
do not meet a m i n i m u m size. If used
(I didn't have anything in
judiciously, it will also give you an estimate of a
carbide that was long enough to reach the
maximum diameter size, because I know from
bottom of the hole). But the stuff finally
experience that you can insert (if you know how) a plug
knew when it was licked. I expected I
gage that is only .00001" smaller than a straight, round
would have a tapered hole and that's what
hole. So I set out to make such a plug gage. Photo 22
I got, but when I got to the point where
shows what it looks like.
my "no-go" gage finally just started in the
hole, I was finished boring.
Before I pulled the workpiece out of the
chuck, I formed the annular air grooves
in the bored diameter. This is not a
hard job. All it takes is a little hand
grinding of a radius-nosed form tool
on a tool bit that is sized to fit into a
stout boring bar. Locate the grooves
as best you can ;
2 2 The double.ended
its not necessary
plug
gage used- to
to work to 0.001".
J A N U A R Y / F E B R U A R Y
2 0 0 0
determine bore size
when boring and
lapping the air spindle
housing bore.
41
42
T H E
H O M E
S H O P
M A C H I N I S T
Now, comes an embarrassing
question. Do you know how to
grind a fairly small drill - a No.29
(0.136" diameter), in fact? Don't
try this next operation if you don't
have a sharp, correctly ground drill
to work with. What you arc now
going to do is drill two 0.136"
diameter holes, each from the
opposite end of the air spindle
housing, and hope they meet in the
middle. Each hole will be about 21/4" deep, so if you are not certain
of your drill grinding prowess, I'd
advise buying a new drill.
Additionally, you have to drill an
intersecting hole into the junction
point of the other two long holes.
When you drill these holes, clear
chips from your drill
frequently and use
plenty of a good drilling
lubricant, such as
Tapmatic. If you pay
attention and do your
job right, you have
every reason to expect
good results.
After this step, there is
just the drilling of a few
more miscellaneous holes
remains, as do the
drilling and tapping of the
1/8-27 tpi pipe thread and
the 8-32 NC threads that
plug the air holes. One
more caution: make
awfully sure
you have done
an accurate
layout job on the
location of your air
holes. It pays to
double check!
23 The lapping tool used
to bring the bore in the air
spindle housing to its
proper
diameter.
As you can see from Photo
23, a lap doesn't have to be
fancy or look like it was made
in a tool room. Mine was made
out of a rusty, pitted bar of some
ferrous material that was 1-3/8" in
diameter (at least in some places).
I turned the OD to 1.3135" diameter for a
length of about 2-3/4", drilled and tapped the
outboard end for a 5/16-18 NC expander screw,
and put a generous 60° chamfer on the threads.
Then I modified a 5/16-18 NC socket-head cap screw
to have 60° taper to match the threads. Finally, I saw-slit
the lap lengthwise (by eye), into four segments, got rid
of the burrs, and file-formed a lead-in radius on the end.
Nothing fancy here - in fact, it looks like a mud fence,
but it works and sure didn't cost much.
I chucked the lap in the lathe and made sure I was in the
slowest speed at which I could run. I oiled the lap and
added an oily fingertip's amount of 1000-grit abrasive to
it, then put on my gloves and started lapping. When you
are just starting out, you don't run the lathe under
power. You lap with a dead lathe spindle until the air
spindle housing is moderately free on the lap. Then, you
can power the lathe and run the air spindle housing
back and forth on the lap. Turn the workpiece end-for-end
on the lap frequently, and use paper towelling to clean
out the bore so you can regularly use your plug gage
to check your bore size. Lapping is not a high-speed
operation, but it is all too easy to open the bore up too
much, so check your progress often.
At this point, not much is left to do on your air spindle
housing: the drilling and reaming of the 0.625" diameter
hole through the mounting boss; the drilling and tapping
of the two 1/4-20 NC holes into the backside of the
mounting boss and into the 0.625" diameter hole; and
the milling of the 0.30 x 0.25" cutout in the front end of
the mounting boss. After you take care of these details,
get your 0.625" diameter reamer again and
carefully clean out the burrs that resulted from
the drilling and tapping of the 1/4-20 NC holes.
After doing a little corner break and cosmetic
filing, sit down in a comfortable chair with a
cold one and your newest and greatest finished
part. You deserve the applause of the crowd,
but lacking that, give yourself a pat on the back.
Items 15 and 17 are finished and have been
put into inventory!
Next time, we'll put together the three-way
adjustable lip rest support.
J A N U A R Y / F E B R U A R Y
2 0 0 0
43
A "Very Much Improved"
Quorn Tool and Cutter Grinder
PART 3
by Walter B. Mueller
Photos and drawings by Author
CORRECTION
An editing misconception emerged in the first
installment of "A Very Much Improved Quorn Tool
and Cutter Grinder," in the November/December 1999
issue of HSM. It is not a serious problem, but I am sure
it will cause questions and comments from readers who
have an in-depth mechanical engineering education.
The difficulty appears in the text on page 32 of the
November/December 1999 issue where I wrote, "The
'coefficient of friction' value - of about 0.15 that
Chaddock had accepted - had to be reduced. The best
way to do that was by the air spindle approach, where
the coefficient of friction value would be closer to 0.001
than 0.15 [not 0.001" than 0.15"], so I went to work."
What I must explain is that the "coefficient of friction"
value is a dimensionless number, that cannot have a
trailing dimensional suffix, such as "inches" or "ounces"
appended to it. This dimensionless character of a
number can come about in the following way:
In any engineering calculation, if a product or a quotient
is formed, the resulting figure is a combination of
numbers and dimensions. Non-technical individuals
may not generally know it, but if numbers can cancel
each other out, so do dimensions. To wit, a velocity
calculation may be:
velocity (ft./sec.) = acceleration (ft./sec/sec) X time (sec)
Then, dimensionally: ft./sec. = ft.sec. on both sides
of the equation, and the calculation is said to be
"dimensionally consistent," or homogeneous.
M A R C H
/ A P R I L
2 0 0 0
Similarly, a ratio such as 20 ounces / 5 ounces = 4,
which is a pure or dimensionless number, since the
dimensions in the calculation cancel just as readily as
do the numbers.
I sincerely hope the two examples given above clearly
show how dimensions and numbers are handled in any
engineering calculation, and I also hope any confusion
that has been generated is cleared away.
W
ith the conclusion of the air spindle and the air
spindle housing discussion, the time is right to
get to the other things needed to make our Quorn
perform its intended task. What we will do now is get
out the hardware we need to put together the three-way
adjustable lip rest support. For the major components of
this assembly you are asked to procure a length of 1/2
x 1.00" cross-section, cold rolled steel. If you will
measure the actual size of the nominal 1.00 dimension,
you will likely find that it measures maybe 0.998".
Whatever width it is, this width will have to be
accommodated by the cross-slot that is milled to the
0.300" depth near the end of the bar.
We'll take an 8.6" length of this stock and turn it into
item 2, the lip support bar. There isn't much machining
required on this part. Just machine it to length, then put
in the 0.998" wide (or whatever your bar width
dimension is) cross slot at the 0.06" dimension from the
end of the bar. Make the 0.998" (or whatever) slot width
a 0.001" slip fit for the piece of material you are going to
use for detail 5, which is the next part you will make
37
from the 1/2 x 1.0" stock you have left. With the part
still in the mill vise, get your edge finder and locate the
geometrical center of the slot you have just made and
measured. Center drill this geometrical center location.
Now you can remove the lip support bar from the mill.
It's not complete, but you are finished with it for now.
It's also of interest to see if the section of raw stock you
are going to use for detail 5 will fit in the slot you
milled for it in detail 2.
The next item on the agenda is detail 5, the bottom
guide. It is made from the same kind of material as the
lip support bar, previously machined. Get out a piece
of 1/2 X 1.00" steel, long enough to finish out at 2.50"
long. Set it in your milling vise (that has previously
been indicated to parallel the long axis of table travel),
and mill the end surfaces of the bar to give a finished
length of 2.50" to the workpiece. Install an edge finder
in the milling spindle collet and locate the long edge
of the work.
Remove the edge finder and install an undersized 3/8"
diameter end mill in the spindle, and move the table of
the machine to place the center line of the workpiece
directly under the center line of the cutter axis.
Mill the central slot in the workpiece to a finished
depth of 0.188". Start widening the cutter track in the
workpiece by a small increment, each in turn on each
side of the slot. Measuring carefully, widen the slot in
this manner until a finished width of 0.375" is attained.
Next, remove the workpiece from the milling vise, and
try to remember where you stashed your lip support bar
(detail 2). When you have found it (whew!), take it to
the drill press and drill a No. 7 (.201" diameter) hole
through at the center drilled location.
38
After breaking the edges of the No. 7 hole to remove
burrs, find detail 5 and install it in the cross slot of
detail 2 so when the slots in both pieces face upward,
the assembly resembles an elongated "L," with the long
shank of the "L" out to your right and the short tongue
away from you, and with the end edge of detail 5 flush
with the near side of detail 2. Clamp the two pieces
together in this orientation and transport the assembly
to the drill press, where you will transfer drill through
the hole location in detail 2 into detail 5, using your
No. 7 (.201" diameter) drill. Unclamp the two
workpieces; then, using a 1/4" diameter drill, enlarge
the No. 7 sized hole in detail 2 to 1/4" diameter
through. Turning detail 2 slotted side down,
countersink the 1/4" hole to a diameter that will accept
a 1/4" diameter, flathead Allen cap screw. Finally, tap
the No. 7 (0.201" diameter) drilled hole in detail 5 to
1/4-20 NC, through, and stash the parts in your
swelling treasure trove.
Please turn your attention to detail 4, the top guide.
This part is made from your last remaining piece of
1/2 X 1.00" rectangular bar stock. Cut off a piece long
enough to finish out at 2.50" long, and clamp it in your
(carefully aligned) milling vise. Mill it to length and
again find the edge of the workpiece with your edge
finder. Move the machine table over half the width of
the workpiece so the spindle center line and the
workpiece center line are coincident. Remove the edge
finder from the work spindle and install an undersized
3/8" diameter end mill; as with detail 5, mill a slot
down the entire length of detail 4. Deepen the slot to
0.188" and then, as before, widen the slot by a small
increment, taking the same amount of stock off each
side of the slot, in turn, until its width is 0.375".
T H E
H O M E
S H O P
M A C H I N I S T
Now, remove the end mill from the spindle and
reinstall your edge finder. Find the right-hand end of
your workpiece and zero adjust the table X position.
Using the edge finder again, find the "farthest from you"
long edge of the workpiece, and zero adjust the table in
the Y position. Move the table in the Y direction to
position the spindle center line 0.156" from the long
edge of the part. Similarly, move the table in the X
direction to position the spindle a distance of 0.500"
from the right end of the workpiece. Now, replace the
edge finder with a small center drill and drill the first
No. 21 (0.159") diameter hole. From this location, move
to the coordinate locations of the remaining three No.
21 holes and center drill each in turn.
Remove the part from the milling vise and turn it over,
so the central slot is facing down. Then, with your edge
finder, again locate the right-hand edge of the part and
move the machine table in the X direction to bring the
spindle center line a distance of 0.250" from the righthand edge of the part. Remove the edge finder from the
spindle and install your smallest diameter center drill.
Center drill at this location (the machine table should
still be in the same Y coordinate location as when the
hole pattern was center drilled on the opposite side of
the part) 0.156" from the long edge of the piece. Then,
move the machine table a distance of 0.688" in the Y
direction and spot drill the remaining No. 43 (.089"
diameter) hole. Finally, move the machine table in both
the X and Y directions to bring the spindle to the
coordinate position of the central No. 21 (0.159"
diameter) hole, and spot drill at this location. For now,
you are finished working on this part, so pull it from the
vise and store it in your stash.
M A R C H / A P R I L
2 0 0 0
The next job will be to make the lip support guide (part
9). We will make this item from a 3-1/2" length of 1.00"
diameter cold rolled steel, in a somewhat sneaky
manner. The first parts of the process are simple lathe
jobs, and I expect you will have a three-jaw chuck, so
chuck the raw stock with 2-3/4" protruding from the
chuck. Take your first OD machining pass on the
workpiece, removing only enough material from the bar
to clean up the diameter about 75% or 80%. Then face
the end of the bar and center drill; the center drilled
hole is now concentric with the cleaned-up diameter
of the bar.
Drill the central, long hole No. 7 (.201") diameter to a
depth of 2-3/4", and tap the hole 1/4-20 NC to a depth
of 3/4". Reverse the part in the chuck, making sure that
each jaw of the chuck grips on the machined diameter
of the workpiece, and redrill the central hole to 0.257"
(letter F) diameter, to a depth such that 5/8" of the 1/4-20
NC thread remains. Cut off the chucking lug end of the
bar and face the end to a total workpiece length of 2.63".
You are finished in the lathe and will move to the mill.
Since it is vital to have the axis of the drilled and tapped
hole central to the 0.375" square tongue, it is necessary
to mill only to the proper depth at this point. So, now,
measure the cleaned-up diameter of your workpiece,
and if that diameter is only 0.988" diameter, it is now
necessary to mill the blank to a finished thickness of
0.682". The dimension is figured thus: 0.988/2 = 0.494
- 0 . 1 8 8 = 0.306". Then 0.988 - 0 . 3 0 6 = 0.682".
When that dimension has been successfully attained,
the blank is flipped over in the mill vise and the top
side is milled, the important dimension to hold being
the 0.375" thickness of the tongue for a length of 2.50".
39
With that done, the blank is again turned 90° in the
vise, and a flattened dimension of 0.682" is again milled
along the side of the tongue for a distance of 2.50". All
that remains is to again flip the part 180° in the vise and
mill the remaining material away for a distance of 2.50"
to a final squared dimension of the tongue of 0.375".
With some burr removal done and maybe a little
cosmetic filing to remove tool marks, the part can be
stood on end in the mill vise and the location of the
4-40 NC holes spot drilled.
If you do not have a thin, small square to use to set the
part vertical, you will have to take the time to make a
small square from a piece of 1/4 in thick scrap, 3 X 2"
long and wide. Just grab a substantial piece of rectangular
cross section steel about 6" long in your mill vise with
about 3" protruding from one side of the vise. Clamp
your 3 X 2" piece of scrap to the protruding end of
heavy stock in the vise, and use the X and Y table feeds
to make your little square.
With that small diversion out of the way, you can now
set your real workpiece vertical in the mill vise to spot
drill for the 4-40 holes. Since your blank diameter was
0.988" and the desired hole spacing is 0.687", use your
edge finder to locate the center line of the part. Having
done that, it is a simple matter to move 0.343" to each
side of center to center drill your exact hole spacing.
With all that accomplished, you can take the part out of
the vise and see how it fits into the slots you have
previously milled down the middle of items 4 and 5. If
they are not a free sliding fit, you have a little filing to
do. Other than that, you can add the lip support slide to
your growing stash.
Eventually, we arc going to need something to hold the
lip support bar, and guide its travel. This, item 28, is
logically called the "guide lip support bar," right? And it
is the piece we are going to attack next. This part is
made from a chunk of hot or cold rolled mild steel, and
is mostly a milling machine job. Get out the raw stock
on your power saw and leave it about 0.1" oversize on
all dimensions. Then, in the mill, square up the block
in your well-aligned milling vise and try to hit the
1.735" length, the 1.050" thickness, and the 1.560"
height dimensions.
Still in the mill, flip the part so the long (1.735")
dimension is oriented vertically, with the short edges of
the piece parallel to the Y-axis of the machine. With
your edge finder in the milling spindle, locate the center
line of your part and position the machine spindle on
the center line and 0.688" from either edge of the part.
Now you can pull the edge finder out of the spindle and
install a center drill. Center drill and drill a 3/8"
diameter hole at this location through the 1.735" length
of the part, trying hard to avoid drilling a hole in your
milling vise. (I've done it, so don't get mad at me for the
admonishment.) With all this work done, you can now
pull the part out of the vise and proceed back to the
band saw, where you will saw out the "slot section" of
40
your workpiece. Of course, you could mill out the
sawed section, but I'm presuming that until you have
this project finished, you are on "short rations" as far as
your end mill usage is concerned.
Anyway, now, using an undersize 7/16" diameter end
mill in your milling spindle, you can finish your slot
width to its requisite width of 0.001" more than the
measured thickness of your detail No. 2 lip support bar.
When you have milled the slot to its requisite depth,
you can retire the end mill and again install your trusty
edge finder in the spindle. You should be getting good at
the practice of edge finding by now, so I'll abbreviate the
instructions and just tell you to pick up the center line
and find the location of the t w o 1/4-20 NC holes, which
you will now want to center drill. In like fashion,
proceed to the hole pattern of the four 10-32 NF holes
and center drill their positions. When this is done, you
can pull the part from the mill vise and amble over to
the drill press. Here, you will drill and tap the four
10-32 NF holes and drill and counterbore the two
1/4-20 NC holes in the bottom of the slot.
After a little filing to remove burrs, break corners, and
improve the cosmetic appearance of your part, you can
retire it to your stash, and enjoy the comforting knowledge
that you have one more major piece in the bank.
Now you can start to put some things together. Get
items 4, 5, and 9 out of the safe. None of t h e m are
finished, so that's what we will do. Take item 4 first and
proceed to the drill press. Previously, we had spotdrilled a number of holes we will now finish up, so
install a No. 21 (0.159" diameter) drill in the drill chuck.
Drill the No. 21 holes at the five locations indicated.
Deburr the part and p u t a No. 43 (0.089" diameter)
drill in the chuck and drill the No. 43 holes to the 3/8"
dimension called for.
Now, retrieve items 5 and 9. Fit them together in their
proper orientation with item 4, and secure them in
place with a small parallel clamp. Put a No. 21 drill
back into the chuck and drill the four No. 21 holes
called for into item 5, using the four holes (to be
counterbored) in item 4 for location. Unclamp the
assembled parts, and deburr item 5. Now, put a No. 11
(0.191" diameter) drill in the chuck, and open up the
four holes (indicated to be counterbored) in item 4 to
the 0.191 clearance diameter needed. Counterbore
0.328" diameter X 0.187" deep (from the unslotted side)
to accommodate four 10-32 NF fillister head Allen
screws. Then, tap the four holes in item 5 through, and
tap the central hole in item 4 through, using a 10-32 NF
tap. Next, using a 4-40 NC tap, carefully tap the two
0.089" diameter holes in item 4. Deburr all the tapped
holes using a 90° countersink and run some 1/4-20
screws into the counterbored holes to hold the parts
together. How does everything fit together? Is item 9
"sticky" in its slot? Maybe a little file work is needed,
but you're getting there!
Next, at the drill press, using your handy little
homemade square, put item 9 into an upright position
T H E
H O M E
S H O P
M A C H I N I S T
in the drill vise and clamp it securely. Install a No. 43
(0.089" diameter) drill in the chuck and drill the two
holes to be tapped to accept a 4-40 NC screw. By the
way, here is an excellent place to take the time to make
a simple tapping aid. Just take a 4.0" length of 3/4"
square scrap material and scribe a longitudinal center line
on it. Prick-punch four locations on the centermost
length of the piece at 3/4" intervals. Then center-punch
to give a good drill starting point at each location and
drill four holes of 0.141", 0.168", 0.193" and 0.255"
diameter. These four holes will accommodate the shanks
of all the taps from 2-56 to 1/4-20 thread size. If, later on,
you wish to expand the usefulness of the tool, you can
add holes to accept the shanks of 0-80 and 1-72 taps.
Install a 4-40 NC tap in the chuck of a small tap
wrench, lubricate the tap, and insert it into your tap
starter tool. Bring the first drilled hole of your item 9
workpiece snugly into contact with your tool, start the
tap into the hole, and carefully tap the first hole. That
done, shift to the second hole, relubricate your tap and
tap the second hole. You will find you will now break
very few taps because you can tailor the size of the tap
wrench to suit the size of the tap, and you will also
enjoy a sensitivity of feel you have never felt before.
It's all so easy, if you just know how. Anyway, your
item 9 (lip support guide) is done and can be stashed
in your secret cache.
Your next item of manufacture is going to be item 3, the
lip-adjusting screw guide. This oddly shaped part is
quite easy to make if you will first make an accurate
layout on your workpiece blank. Of course, this starts
with a blued, steel blank, so get out your can of layout
blue and do it. When you have, it is relatively easy to
make the setups required to get the outline shape
milled to the lines, and the 0.40 X 0.20" ledge milled on
the top edge of the piece. With all that done, the next
thing to do is swing the vise to a 30° offset angle and
M A R C H / A P R I L
2 0 0 0
mill the 0.250" wide slot that accommodates item 7
(height adjust screw).
At this point, you are all set to employ your edge finder
to locate the edge of the slot you have just milled. When
you have done that, make the table moves you need to
bring the centers of the two No. 43 (0.089" diameter)
holes under the spindle center line. With that done,
replace the edge finder with a small center drill and spot
drill the two 4-40 NC hole locations. You are then able
to swing the vise back to its original (indicated in) 0°
orientation, and once again employ your edge finder to
nail down the location of the two No. 33 (0.113"
diameter) mounting holes. When these are in their
proper location, you can remove the part from the vise
and stash your treasure for later finishing operations.
The next candidate for consideration is item 25,
the clamp plate.
Again, the piece is oddly shaped, so is better started as a
bench layout operation. Blue up a piece of steel, make
the required layout, and start milling to the line. When
that series of milling cuts has been done, the part can be
mated to the profile of your newly machined item 3,
and clamped in place. Thus located, it is now easy to
match drill the location of the two No. 33 (0.113"
diameter) holes to No. 43 (0.089" diameter) by drilling
through the existing No. 43 holes in item 3.
After that is done, the parts can be separated and the
No. 43 holes in item 25 can be redrilled to No. 33
(0.113" diameter). Finally, the location of the 10-32
hole can be determined from the position of the two
No. 33 diameter holes, and this feature can be drilled
to No. 21 (0.159" diameter) and tapped through with
a 10-32 NF thread. Voila! Another job has been
completed. What fun!
Next time, we'll complete all the parts and discuss
knurling.
41
A "Very Much Improved"
Quorn Tool and Cutter Grinder
PART 4
by Walter B. Mueller
Photos and drawings by Author
T
he next parts scheduled for completion arc items
14 and 19 - both called adjusting screw retainers.
These items may have different dimensions, but they
have the same name and function and they arc made
by exactly the same series of operations. On the
assumption that one picture is worth ten thousand
words, I'm going to show you four pictures (Photos 24
through 27), and save everybody the pain and eyestrain
of absorbing 40,000 extra words. All you need to know
is that both pieces start out as 1.0 x 1.0" angle iron
42
for material with a generous clamping length of stock
held in the vise, and the workpiece length protruding.
From there, everything proceeds as in the photographs.
All that is left to your imagination is how to put in
the holes and the slots, and as is written in the
Constitution of The United States of America,
"we hold these truths to be self-evident."
The ball handles (item 18) should be mentioned. I give
you the manufacturing data required to make them
because of a regard I have for classic machines. The
American machines, such as the Moore jig borers,
Monarch lathes, Excello boring machines, and others
T H E
H O M E
S H O P
M A C H I N I S T
24 The first step in making the adjusting screw retainers - squaring
off the sawed end of the angle iron raw stock.
25
The second step - cleaning up the inside angle of the angle iron.
26
The third step - machining the outside dimensions of the
retainer after the workpiece has been sawed from the bar.
27
Finish the last sawed end of the adjusting screw retainer.
M A Y / I U N E
2 0 0 0
43
will always be associated with excellence, as are the
British Myford lathes and the Crystal Lake cylindrical
grinders. Of course, these machines were mostly
intended for industrial use, not home shop amusement,
but I have a feeling that borders on reverence for these
creations, as I have firsthand knowledge of what they
can do. I feel the same way about Professor Chaddock's
Quorn grinder. He died before he could supply the
finishing touches to make it a true classic, but the
machine, with its presently proposed improvements,
is now certainly in a class by itself.
piece, center drill, and drill it, hopefully with a drill of
the exact diameter of my noted dimension. If I have to
slightly file-dress each corner of my square piece, I do
that - to achieve an exact fit to the size of drill I have
available. Then, I drill that size of hole in the end of my
drive bushing, going through the entire bushing length.
I install a 10-32 NC setscrew in the hole. Then I insert
my file-flatted workpiece in my square stock driving
dog with only the end protruding. I face it and turn the
end to a diameter of about 0.250" (bigger than the minor
diameter of a 5/16-18 NC thread) for about a 3/8" length,
and I counter-drill the turned end.
I loosen the setscrew and extend the square stock to
the length I want to thread, plus about 1/4". Next,
I put my 5/16-18 threading die in a die stock and start
it onto the turned diameter, and engage the part on my
ball bearing center. Would you believe it is possible to
thread four-cornered square stock with a four-cuttingtooth button die? Try it if you don't believe it's possible.
28 See! It is possible to make good knurls. The top knurl has 65
"points" and the bottom knurl has 66, all perfectly formed.
Therefore, as a tribute to Chaddock, I continue to show
his ball handles on my machine. It gives his creation a
deservedly classic look. But, if you do not want to add
a ball turning tool job to the present project, they are
commercially available for $65 from OMW Metalcraft,
27 Ross Valley Drive, San Rafael, CA 94901. This tool is
a little on the small side, but it can turn 3/4" diameter
balls, so it should work.
Before I forget, another item should be discussed - item
7, the screw with the (would you believe) square cross
section. It might look stupid, but there's a reason for it.
It fits in the square groove of detail 3, and can only slide
lengthwise, but not rotate, when its knurled adjusting
knob is turned. How does one make a square screw?
First, I cross-drill a No. 21 (0.159" diameter) hole in a
short piece of 3/4" diameter, say, round stock, about
1/4" from the end, and I tap it 10-32 NC.
Then, I chuck the cross-drilled piece in my three-jaw
chuck with the drilled and threaded end protruding.
I measure the diagonal dimension of the piece of 1/4"
square key stock I intend to thread and I note that
dimension. Next, I lightly face the end of my drive
44
29 A 1.250 length of high-carbon steel drill rod, knurled with 82
"points," also all perfectly formed.
The minor diameter of the die is about 0.240", while
the smallest diameter of the square stock is 0.250",
so the die is always engaged by its minor diameter, and
it always stays centered and on its correct lead path. It
feels rather odd when you are cutting the thread, but
who cares as long as you are getting nice threads?
The actuator screws for the Y- and Z-axis adjustments
both have knurled finger wheels to aid in their
adjustment. Did I just hear a chorus of curses when
I mentioned the word "knurl"?
I've never seen it written in a book, but a foolproof
way exists for making perfectly knurled parts every
T H E
H O M E
S H O P
M A C H I N I S T
time you try. For instance, I have three knurling
tools, and when I bought them, I specified that I
wanted " m e d i u m " knurl wheels. Maybe I am lucky,
but it so happens all three of these tools have 0.625"
diameter knurling wheels, and all of them have 40
teeth on their periphery. I know this because, one day,
I took the time to count them. I did it because it
occurred to me that there should be preferred outside
diameters that could be knurled easily and there
would be other outside diameters that would be
difficult to knurl without mistreating your lathe or
the part being made.
this system. Photo 28 shows two knurls, one on a
1.0157" diameter that has 65 "points" and the other
on a 1.0313" diameter that has 66 "points." Photo 29
shows the 1.2813 diameter knurled with 82 "points."
Each knurling job was perfect and each knurl was
If a threaded rod can be visualized next to a knurl
wheel, it will be easily seen that the thread crests can
be compared to the crests of the teeth on the knurl
wheel. If you have 16 threads/in., the pitch of the thread
is 0.0625", and if you have 40 teeth on a 0.625" diameter
knurl wheel, the pitch of the knurl wheel is 0.04909".
This formula can then determine any preferred blank
diameter: Pitch (of your knurl) X Number of teeth
to be knurled / 3.14159 = Pref. Diameter of blank.
Thus, a 1.2813" diameter blank can be exactly divided
into 82 knurl points, if you are using a 40-tooth knurl
of 0.625" diameter.
30
My knurling tool (see text).
completed in less than two minutes.
My "magic" knurling tool is shown in
Photo 30.
As can be seen from the drawing sheet,
there are also threaded bushings that get
super glued into the knurled knobs in a
specific way (also detailed on the drawing),
using details 14 and 19 as spacers. The
detailed process information is provided
on the drawings, further verbal details are
not needed.
Photos 31 and 32 show the component
parts of the Y- and Z-axis subassemblies,
31 The collection of individual parts needed for the Y-axis adjusting
mechanism of the lip support finger assembly.
Similarly, a 1.0157" diameter blank can be exactly
knurled with 65 knurl points. There is no mystery to
this; if you use this procedure, you can perfectly knurl
any preferred diameter with no sweat and - this is
important - you can knurl any malleable material
without putting great stress on your cross slide
screw or nut.
I constructed a table of preferred blank diameters
for myself, ranging in size from 0.500" to 1.250"
diameter that has saved me much time and frustration.
Photos 28 and 29 show sample knurls I made using
M A Y / J U N E
2 0 0 0
32
The collection of parts needed for the Z-axis adjusting
mechanism of the lip support finger assembly.
45
34
33
The front view of the lip support finger adjusting assembly.
and Photos 33 and 34 picture the front and rear views
of the assembled mechanism. Photo 35 shows the lip
support bar and Photo 36 pictures the component parts
of the lip support guide assembly. Photo 37 shows the
dial indicator mounting bracket (item 27) and the
(item 26) long travel dial indicator itself.
A rear view of the lip support finger adjusting assembly.
plate, and item 27, the indicator mounting bracket. You
know enough now to build a very slick tool that will
augment your shop to a degree that's hard to believe.
For those of you who have also subscribed to Projects
in Metal magazine (now Machinist's Workshop), you
may remember the article "A Small Tool and Cutter
Grinder," authored by Glenn L. Wilson and published
October 1991, Vol. 4, No. 5.1 read that article
A few other simple
parts are needed to
complete the air
spindle assembly,
but no mysterious
technology is involved
in their manufacture.
These are detail 20,
the brass gib, detail 22,
the lip support clamp
35
46
The lip support bar.
T H E
H O M E
S H O P
M A C H I N I S T
voraciously, and
undertook to build a
version of the Wilson
machine. I say it was
a "version" of that
design because my
machine is bigger
than the Wilson
design, I needed to
grind end mills of
3.0" flute length and
1-1/8" diameter. This
made my machine
grow in size, and that
caused me difficulties
f
111
36 The collection of parts that makes up the
"guide lip support bar" assembly.
r
in duplicating the
Wilson wheel head
design; I had only
an 8.0" diameter
turntable - too small
to manufacture his
item 22 (wheel head
support) members for
my larger machine.
So, my wheel head
design departs from
his, but in many
respects our machines
37 The dial indicator
mounting arm and the long
travel indicator assembly.
M A Y / J U N E
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47
are quite similar. My version
of the Wilson design is shown
in Photos 38 and 39.
I tell you all of this because now
I am in a position to compare
the Professor Chaddock VMI
Quorn design with what
I consider to be the more
conventional (Wilson) type of
machine. Quickly, the Wilson
design is usually set up to grind
end mills only (although it will
grind some other tools), so it is
quicker to put into operation
than is the VMI Quorn. But the
Quorn, with the newly designed
air spindle attachment and its
other features, is far more
versatile because it is also a
toolmaking grinding machine,
as well as an efficient milling
cutter sharpener.
The Quorn needs more initial
setup time, but once set up, it
is just as able as the Wilson
design. My Wilson modification
offers the undeniable bonus of
being built mostly from locally
38 A general view of
available, surplus (low cost)
material, while the Quorn requires a kit of purchased
castings (which arc available today from Power Model
Supply Company).
my "Glenn Wilson type" tool and cutter grinder.
Both of my grinding machines will sharpen the largest
cutters my milling machine can use, but for home shop
machinists like me, the Quorn can also easily grind
cutters for my engraving machine, or supply special
toolbits when I turn my South Bend shaper into
an involute gear-shaping machine. It is almost
unbelievable for me, an individual who was dependent
on commercial grinding services for so long, to now be
free of the expense and delay formerly endured. It is a
new freedom, made sweeter by the knowledge that it
was won by my own ingenuity, and the payoff is the
total independence I now feel.
But, if the VMI Quorn is as good a machine as I say, just
how good is it? I took the trouble to make some simple
measurements that may serve to show you what you
can expect, if you build this machine pretty much to
the size and specifications I used. First of all, I operate
my compressor at about 6 lbs. (gage) pressure. I can't tell
you what my compressed air usage is, but my 5.0 cu.
ft./min. compressor does not run continuously. My air
spindle (measured) weight - with two stop collars - is
1,795.6 grams, or 3.995 lbs., and is 9.5" long. The
maximum travel of the air spindle is about 4.4".
Using a 0.0001" dial indicator, the measured downward
drop of the air spindle is 0.0007" at the full outward
48
extension from its housing. With the air spindle leveled,
stationary and floating, a measured two grams of
endwise force, exerted by a + / - 10 gram, spring gram
gage (Photo 40), would cause endwise motion of the air
spindle from a stationary position. Using the expression,
m u = Ff / N,
where:
mu = coefficient of friction;
Ff = force of friction (2 grams);
and
N =
the downward force of the air spindle in its housing
(1795.57 grams),
then:
mu = 2 grams / 1795.57 grams mu = 0.0011.
This coefficient of friction is 135 times less (0.15/0.0011
= 135.14) than Professor Chaddock could realize (0.15)
for completely dry steel-on-steel contact.
Additionally, the 0.0007" measured drop in the air
spindle center line height over its 4.4" travel would
generate a tapered grind on a 1-1/8" diameter end mill of
only 0.4 micro inches (0.0000004"), if the flute length
of the cutter were 4.4", and correspondingly less if the
cutter were shorter. This is a totally insignificant error,
which would be even less if the -4.0 lb. air spindle were
reduced in weight. With these results, it would seem
my initial complaints about the Quorn have been
adequately resolved.
T H E
H O M E
S H O P
M A C H I N I S T
A drawback is common to both machines, however.
Each machine requires compressed air for its operation,
and this means one needs a compressor, probably of 4.0
cu.ft./min. capacity. Additionally, each machine has to
have dry compressed air for its operation. This is no
problem if you live in a desert atmosphere, but most
people contend with periods (maybe extended periods)
of rainy, moist conditions. In accordance with the
and those that have an oil filled crankcase. You are lucky
if you have an oil-less compressor so you do not have to
worry about oil droplets getting entrained in the air going
to your air spindle. If you have the oil-using compressor,
you will have to install a coalescing oil filter (about
$100) and a replaceable filter another ($30), or conduct
a housecleaning operation, should your air spindle
start to get sticky in its housing.
These are the advantages
and drawbacks to having
an air spindle type of tool
grinder in your shop. But the
disadvantages of not having
any tool and cutter grinder
are so bothersome that
if you ever achieve the
ownership of this kind of
machine, you'll wonder
how and why you ever did
without it.
REFERENCE:
(2) Marks' Mechanical
Engineers
Handbook:
4th edition, 1941, page 233,
Table, edited by Lionel S.
Marks; McGraw Hill Book
Company, New York and
London.
39
A close-up of my Wilson-type grinder in action.
laws of thermodynamics, when one compresses air, it
becomes heated and can hold more moisture, but even
then you come up against the dew point of the warm,
moist air, when the excess water vapor will condense
into water - the stuff that gets into your air spindle and
hampers its operation. This means each compressorto-air spindle air line must have at least one water
separator included in its makeup, and that this water
separator must be drained periodically. So, I will include
this caveat. Install your water separator in the air line
as close to the air spindle as you can put it, and in an
accessible location, because with an air spindle, you
will be draining off accumulated water.
Another way to go, however, to get dry, compressed
air, is the way I have chosen - by making use of a
refrigerated air dryer. This is the way industrial shops
keep water out of their air lines. My unit is a Deltech
Refrigerated Air Dryer, which works on the high-pressure
side of my compressor by cooling the hot, moist
compressed air down to a temperature of about 35° F.
This condenses most of the water out of the compressed
air and drains it away, before it can get into the air
spindles of either of my machines. I bought my air dryer
"used" for $250, and I think this is the way to go.
Also, there are two varieties of air compressors, oil less
M A Y / J U N E
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40 The +/- 10 gram, gram gage I used to measure the residual
friction present in my air spindle/spindle housing assembly.
49