Mounting a new lathe chuck for use on a screw

Newsletter # 7
Welcome to another Model Engine Builder Newsletter
Mounting a new lathe chuck for
use on a screw-thread spindle
Space to 3-hole punch
I
have been very happy with my Logan 10" lathe (OK, Power-Kraft since it
was sold by Montgomery Wards way back in the 1940's) which I purchased
at an estate sale. I'm going to call it a Logan!
When I asked the price of the lathe, the widow
said $600. I just about broke my thumb getting
my billfold out of my pocket. Furthermore,
she said, I was to take
anything that suggested
it belonged to the lathe.
The accessories to the
lathe included a full
3AT collet set, a frontmount collet closer
(never have been able
to ID the collets) with a
front closing handle for
production work, a brand
new automatic fivestation turret, a cross-cut turret plus steady and follower rests and a three- and four-jaw chuck.
I did explain to the lady that the price she was asking was way too little but she said she'd
worked 10 extra years so her late husband could have all the toys and she wanted them out.
Now! Yes ma'am!
I either overlooked or there never were a set of outside jaws for the three-jaw chuck and I
thought I'd never be able to get along without a set. Unfortunately, Logan had their chucks made
by the leading chuck manufacturer in the U.S., but production had ceased and the jaws were
unavailable at any price.
Enter Enco, stage left. They had a great sale to get rid of all the store inventory when MSC
purchased Enco where I was able to purchase a backing plate and three-jaw, 5" Bison brand
chuck for a very nice price indeed. And there my bargains sat on a shelf for 15 years as I allowed
the metals to 'properly' age.
Last month, in a fit of cleaning up the workshop, I decide to mount the chuck to the Logan,
something I'd done before to my previous lathes.
As a preface, I have to say that I do not think that the chuck register really centers a chuck.
I think that the cone formed by the spindle threads work to form a nice compact 30° taper (½
the 60° thread) that largely centers the chuck on the spindle. The position of the chuck backing
plate on the spindle is determined by the contact between the threads and position is fixed by
the face of the backing plate collar contacting the face of the lathe spindle and stopping rotation.
Page 1 of 16
© 2013 by Elmwood Publishing, Inc.
This is a very repeatable
Register
condition and only changes if
the contact surfaces wear or
are contaminated. I have used
this method to make backing
plates for a 6" Craftsman, 14"
Rockford (six-jaw, 8" AdjustThread
Tru chuck) and an ER-25 collet
adapter for the 6" Craftsman
and now this Logan-built lathe.
In all cases, the run out of work
in the chuck and collet jaws
Spindle face
was minimal and extremely
repeatable over the years.
Logan 10" spindle nose
The register and threads of a
purchased backing plate may
already be cut so you have to
work with whatever dimensions
the manufacturer delivers.
I have made my own backing
PROCEDURE LIST
plates by welding a mild steel
PREcollar onto a mild steel plate
STEP
WELD-UP
UN-MACHINED
MACHINED
of about 1/2" thickness (for a
4" chuck) on my Craftsman 6"
1
Optional
Optional
Optional
lathe using a MIG welder. (MIG
2
Optional
Optional
Optional
weld cuts better than leaded
3
YES
X
X
steel in my opinion.)
4
Yes
Yes
X
The decision to buy or make
5
Yes
Yes
X
your own backplate should
6
Yes
Yes
X
depend, among other issues,
whether you are willing to cut
7
Yes
Yes
Yes
the backing plate from a solid
8
Yes
Yes
Yes
piece of metal or weld one
9
Yes
Yes
Yes
(only if your welds will be safe,
10
Yes
Yes
Yes
however).
11
Yes
Yes
Yes
Below are the steps I followed
12
Yes
Yes
Yes
to make a backing plate for a 5"
13
Yes
Yes
Yes
three-jaw chuck on the Logan
lathe. I wrote a slightly older
version of this process back in 1997 which you can find it at MetalWebNews.
Step 1
Precisely measure your spindle nose—diameter, length, length of thread, diameter of spindle collar. Use
an accurate method to measure the threads such as a thread micrometer or a three-wire method.
Page 2 of 16
© 2013 by Elmwood Publishing, Inc.
Step 2
Make a dummy spindle nose. This will be quite useful for
other applications so leave a little extra metal in back of
the nose collar so you can easily mount it. This Step is
not absolutely necessary but unless you have a large
(read expensive) go/no-go thread gauge, it does
make measuring the internal threads (using the
dummy spindle as a thread gage) much easier.
Note that this dummy spindle has both a set of
holes in its mounting plate so it can be mounted
on a board and a spigot on the backside so it can
be mounted in a vise. Either one is optional. A dummy
spindle is valuable for centering parts in a 4-jaw chuck,
etc.
Note - if you have a tap of the proper size you
don't have to worry about this step. You can use
the tap to finish the threads. However, a 1-1/2" X
8" tap is expensive, MSC quotes approximately
$225 U.S. The 1" X 8" tap for my 6" Craftsman
was about $75 twenty years ago. (I tried a
cheaper tap but it took three cooks and five small
boys to turn it. A U.S.-made high-quality
1 x 8" tap cuts with very little force).
Logan 10"
Dummy spindle
This computer
rendering of a
working dummy
spindle nose
is two-colored
to differentiate
between the
brass-colored
spindle nose
and the greencolored part of
the dummy that
makes handling
the dummy
spindle much
easier. It is a
single piece of
metal in this
design
STEP 2
Mounting plate
Chucking/
vise
spigot
Step 3
Either weld up a plate and bar stock (works really well for
smaller lathes) to make the backing plate
blank, purchase a cast iron blank from your favorite supplier, or start with a thick
Fill in with weld
billet of stock of the appropriate diameter and cut it down (a lot). Drawing
of a welded plate arrangement for the Logan 10" lathe at the end of this
newsletter.
Weld
joint
Welded
backing
plate
STEP 3
Note: I've taken all three approaches and I prefer the cast iron blank for
speeding the process and for the vibration dampening effects of cast iron.
Cast Iron also has the benefit of usually deforming before it damages the
threads on your steel spindle.
Step 4
If your backing plate is not bored and threaded, grab the chuck-side of the
blank in a 3- or 4-jaw chuck (or bolt it onto a face plate) and bore a hole frontto-back through the center of the blank at the spindle-thread root diameter
(you can get this value from Machinery's Handbook). It is also possible to
thread it directly onto the spindle with the hub outermost if the blank was
pre-threaded as was the backing plate for my chuck.
Page 3 of 16
© 2013 by Elmwood Publishing, Inc.
Step 5
Computer rendering of purchased
backing plate with pre-machined
threads and register
Collar
Thread
Register
bore
Face
Bore the hub section that will cover the spindle register to
a close but not tight fit, about 0.005" larger. In the case
of my Logan lathe, the Register is the same size as
the major thread diameter. This section on a prethreaded backing plate may be much larger but
this condition will not cause a problem.
Then cut a thread relief groove. This will
make cutting the internal threads easier
because you will not have to stop quickly and
precisely when cutting the threads on the
backing plate. It is possible that the register
bore will be so much larger than the thread
root diameter that the groove is not needed.
Remember to not leave any sharp inside
corners anywhere to prevent possible stress
cracks from forming.
Step 6
Without removing the
backing plate, cut the internal
thread to specification, to a nice
fit with the dummy spindle nose or by finishing the thread you started with
a single-point threading tool with a tap. If you do not have a dummy spindle
or a tap, you can unscrew the chuck or face plate from the lathe spindle
and turn the assembly (do not remove the backing plate from the chuck or
face plate) around to check the fit on the lathe spindle. This works very well
and the chuck or face plate will go back to the same position every time.
Chamfers
Step 7
Take a facing cut on the face of the backing plate collar that will bear
against the spindle face. Then cut chamfers on all outside corners and
chamfer the threaded bore.
Thread
relief
groove
Step 8
Take a deep breath and remove the backing plate
Backing plate after all
from the holding device and remove the holding
machining is finished
device from the spindle (assuming you have
only one lathe). Now thread the backing plate
Faced
onto the spindle. It should go on smoothly and
bottom out on the spindle face.
Now take a trueing cut on the face
Radius
of the chuck plate, the face upon
which you will mount the chuck.
Step
Face of backing plate trued
Also take a light cut on the O.D.
Page 4 of 16
© 2013 by Elmwood Publishing, Inc.
of the backing plate. This will true it up so you don't have a not harmful but visually annoying out-oftrue condition on this plate. Make this entire area look nice because that is what people will see.
Step 9
Cut the required step in the face of the chuck plate to fit into the recess on your chuck. This must be
a good fit or you will have a bit too much run out when you get done. Go slowly because a problem
at this point can ruin your day not to mention the backing plate. The
recessed surface of the chuck should not contact the backing
plate. Only the mounting face (the rim) should contact the
Step cut on backing plate
backing plate.
Some people advocate making the step in the face plate a
slight interference fit into the chuck register recess and then
heating the chuck so that when it expands, it will fit tightly
onto the backing plate. This may be an OK idea but it makes
it very difficult to remove the chuck from the backing plate
should you need to do so. It will probably also make a mess
when the chuck lubrication melts during the heating.
On the backing plate I machined, the fit was tight
enough that it took tightening the bolts holding the
chuck to the backing plate to pull the two pieces
completely together. A light press fit is about as good as you can get here. Sometimes I get lucky.
What can go wrong here?
You can cut the step O.D. too small and the chuck will have too much run out. You cannot depend
upon the bolts holding the chuck to the plate to hold everything true and the hold-down bolts should
not come into shear (side) stress, that is the purpose
Mounting
of the register recess. If you get the register on
face
the backing plate undersize and the backing
plate is of steel, run a bead of weld around
the step and cut it again. If the backing plate
is cast iron or you don't want to weld on it,
cut the diameter of the recess step even
Back of chuck
further down and epoxy a tight-fitting ring
that you then re-machine to the proper fit
with the chuck.
Step 10
If necessary, cut the diameter of the backing
plate down to smoothly meet the diameter of
the chuck.
Register recess
Step 11
Place the chuck on the backing plate and use
transfer punches to mark the hole locations for the
hold-down bolts. If this is a new chuck, they usually come with bolt-pattern dimensions.
Page 5 of 16
© 2013 by Elmwood Publishing, Inc.
At this point, take a good look at the chuck. Some, especially four-jaw chucks, have bolt holes that
go all the way through the chuck and the bolts have to screw into the backing plate.
This is the point at which you determine if you are drilling and tapping the backing plate or drilling
through-holes for bolts that thread into the chuck body. In both cases, with new chucks, the bolts
normally accompany them. If you are dealing with a used chuck, make certain you use good bolts.
You don't want the chuck coming off the backing plate if a bolt fails. I would use grade 5 or 8 bolts for
this purpose.
If you made your dummy spindle, this is a good use for it. You could also use a rotary table or a
bolt-pattern coordinate set calculated with Machinery's Handbook (Jig-Boring section). This is a
noncritical area of the backing plate as long as the holes are pretty well aligned. Drill and tap the
holes to match the supplied bolts.
A bar clamped in the
chuck jaws makes a good
handle
Step 12
Wood to protect the
lathe ways in case the
chuck is dropped
Uniformly torque the bolts holding the chuck to the backing plate
tightening the bolts using a crossing pattern like you would on
an automobile wheel. It is best to use a torque
wrench for three reasons:
1.The chuck should be pulled evenly onto the
backing plate.
2.The bolts should be properly torqued, not too
tight or loose. Use tables in a reference book to
decide on the torque you will apply. Use a torque
table for material matching the weakest part of
the threads–either the bolt, the backing
plate or the chuck body.
3. If the bolts are properly torqued, they will not come loose although you could use a
thread-locking compound if you wish.
Step 13
Put the newly mounted chuck on the lathe
spindle, chuck a piece of good quality round
bar stock in the chuck and measure the runout
2 inches out from the front of the chuck jaws.
The bar should run within 0.002 TIR at worst,
probably 0.001 at best. If the run out is too
large, it is time to return the chuck or, if you are
brave, fix the chuck.
Measuring runout
Fixing a chuck
Back when I was learning to abuse metal and didn't know a cheap lathe chuck was not a good buy,
I bought one. It certainly looked OK but when I started checking it, the back was not square with the
Page 6 of 16
© 2013 by Elmwood Publishing, Inc.
chuck jaws and the periphery of the chuck was a bit wobbly too.
What to do? Brilliant idea # : turn a bar between centers so it is running true. Clamp the new chuck
to the bar with its chuck jaws and with the backside of the chuck towards the tail stock. Spin the
assembly up to a reasonable speed and take a trueing cut on the backside of the new chuck and on
its periphery as well.
Then I made a backing plate by welding a collar and a plate as described and mounted the chuck.
Much to my satisfaction, it was a good chuck from then on. It delivered a few thousandths run out on
the work piece but even expensive chucks will do that. I don't know how long the chuck maintained
its accuracy because I foolishly sold the lathe when I bought the Logan. Little did I know that small
lathes are very useful for small work pieces. Fortunately I now have a Sherline lathe that does the
smaller jobs very well.
Note: I do have a financial arrangement with Sherline. I made a DVD on how to set up and use their
lathe and they buy the DVD for resale. But I like the lathe for small parts because of its precision and
the ability to get my head down close to the parts I'm machining.
Conclusion:
This is a workable method for mounting chucks. I made a collet adaptor for my Craftsman using this
technique and its run out is about 0.0002" (≈.005mm) when measuring a piece of drill rod 2" out from
the collet. I used ETR double taper collets because of their short length and wide clamping range
compared to 5C or R8 collets. And it left the spindle bore open too.
BTW
I am certain there are ways to achieve the Adjust-Tru capability with a shop-made backing
plates and perhaps one of you readers will take the time to write and tell me of it.
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Engineering Show
September 21 & 22, 2013
Fine Arts Building ,Pennington County
( Central States Fairgrounds)
Rapid City, South Dakota
Oregon GEARS
September 28 & 29, 2013
Oregon Rail Heritage Center
2250 SE Water Ave
Portland, OR 97214
26th Estevan Model
Engineering Show
October 19 & 20, 2013
Wylie Mitchell Building, Estevan Fairgrounds
www.estevanmodelengineeringshow.com
Estevan, Saskatchewan, Canada
Midlands Model
Engineering Exhibition
October 17 to 20, 2013
Warwickshire Exhibition Centre
Fosse Way, near Leaminton Spa
Junction of the A425 and B4455
MidEast Model Engineering
Expo
October 18th & 19th 2012
Muskingum County Fairgrounds
Cabin Fever Exposition
April 11th to the 13th, 2014
York County Fairgrounds Expo Center
York, PA
North American Model
Engineering Expo.
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Southgate MI
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WEME 2013
Show Report
T
he Western Engine and Model Exhibition (WEME) was another great success with visitors again
claiming that WEME was the hit of the Goodguys Hot Rod show. For those of you who do not
know, Goodguys provides the Bay Area Engine Modelers (BAEM) with a 7,500 square foot airconditioned pavilion in which to hold the WEME exhibition.
Dwight Giles and his
line-up of engines
This year we were again pleased to have several headline exhibits including Jim Moyer's collection
of 1/6th scale engines including his 1/6th scale Chevrolet Small-Block shown below. The V-8 took
V-8 close-up
1/6th Scale V-8
7 years to complete during which time Jim learned
to make parts in many different disciplines. Even the
spark plugs had to be custom made.
Page 10 of 16
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The Bay Area Tankers 'planted' their model village out in the agricultural garden behind our pavilion.
Not only were their tank battles interesting, they also had a course set up so the young visitors could
drive a tank. As the tankers soon found out, the youngsters would drive off their course and head to
the village for their own version of tank vs. tank. Fortunately these tanks only shoot low-power lasers
at each other.
The Village
Lots of interest in tanks
Not to be outdone, the San Francisco Model Yacht Club displayed several boats including John
Garris' four-cylinder powered yacht that is towed by a radio controlled truck, launched into the water,
started and run around, then brought back to the trailer and recovered and the truck then tows the
yacht off into the sunset. This is all done with no hands touching the yacht, truck or trailer. John has
a video of the sequence and kept it running during the show. Next year we hope to have some water
John Garris from the San Francisco Model Yatch Club
and his completely radio controlled model yatch
for him to play in. By the way, the San Francisco Model Yacht Club was formed in 1898, the same
year as Model Engineer started publication and the Society of Model and Experimental Engineers
(SMEE) was founded. Check their Web sites for more information.
Page 11 of 16
© 2013 by Elmwood Publishing, Inc.
In the category of unusual models and exhibits, we had Michael Cooper with his truck, his go-
cart and his all-wood tricycle. Michael was giving demonstrations on how he goes about making
his unique wood models. Almost
all of the wood in the tricycle and
the orange seat of the go-cart are
made of thin strips of wood epoxied
together in the rough shape of the
part. Michael then shapes the rough
shape by hand, using the largest
collection of sanding tools this writer
has ever seen in one place.
To see more of Michael Cooper's
talent, please go to his Web site.
Michael Coooper
We were also fortunate to
have Paul Knapp with about 60
model engines from his Miniature
Engineering Museum. Paul has collected many
prototype model engines from model engineers
around the world. He also manufactures the
miniature spark plugs used by many of us. His
plugs were used to spark the first radio controlled
model airplane flight across the Atlantic ocean a
few years ago.
For you Chevrolet Small-Block lovers, on the left
is a picture of Paul's ¼-scale casting set for the
engine. Someday we'll see it run.
Steam engines were on display and ranged from
the small wobbler types to a steam locomotive.
Page 12 of 16
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The wobblers to the right
were built by Yuan Mogle, a
13 year old student who is
being mentored by Dwight
Giles.
The locomotive below is
demonstrated by its builder,
Roy Anderson. Locomotives
take a very long time to
build, usually a number of
years and this one is no
exception. They are also, in
this large scale, very heavy
and special handling equipment has to be built and employed to move them around. Roy is leaning
on his locomotive lift which elevates the locomotive up to trailer height and down to near ground level
when he needs to place or remove it from the tracks.
Many of the hundreds of model engines that were present at the exhibition are not shown
Page 13 of 16
© 2013 by Elmwood Publishing, Inc.
Forest Edwards
5-cylinder engine
John Meredith's radial engines
Wright J5 9-cylinder engine
here because the space required would be
enormous. If you would like to see some of the
best model engineering in the world, I invite
you to attend the 2014 WEME show which will
be held August 22,23 & 24, 2014. The location
is the Alameda Fairgrounds in Pleasanton,
California. For more information, go to the
Goodguys' Web site.
The Bay Area Engine Modelers (BAEM) meet
on the third Saturday of the month at 10 AM at
Chabot College, Bldg. 1500, 25555 Hesperian
Blvd., Hayward California. For a campus
map, please click here. No charge to attend a
meeting. For the WEME exhibition web site,
click here.
Paul Knapp's Pratt & Whitney
R-985 Wasp Jr. Radial engine
THE
END
George Gravatt and a few of his engines
Page 14 of 16
© 2013 by Elmwood Publishing, Inc.
Page 15 of 16
© 2013 by Elmwood Publishing, Inc.
BREAK OR DEBURR
EDGES UNLESS OTHERWISE SPECIFIED
DIMENSIONAL TOLERANCES UNLESS
OTHERWISE SPECIFIED
IMPERIAL
METRIC
2 PLACE ±0.01
1 PLACE ±0.3
3 PLACE ±0.001
2 PLACE ±0.03 4 PLACE ±0.0005
3 PLACE ±0.005 n3.000
n2.400
n1.813
wn.531 X 82.000 
4x n.250 x THRU
.063
.627
.826
EDITED BY
MIKE REHMUS
DO NOT SCALE
NOTE THAT THE REGISTER
IS THE SAME DIAMETER AS
THE MAJOR THREAD
DIAMETER 1.5" ON THIS LATHE
WARDS POWER-KRAFT 10" LATHE DUMMY SPINDLE
STEEL, 1 REQ'D
1.5
PROJECT
© 2012 BY
ELMWOOD
PUBLISHING, INC.
DRAWN BY
2
3RD
ANGLE PROJ.
Mike Rehmus
PROJECT
DWG # 1 OF
Logan Actuator
DESIGNED BY
.375
Logan Lathe Spindle
2.8
Page 16 of 16
© 2013 by Elmwood Publishing, Inc.
n5.000
n2.020
n1.250
n2.000
n2.750
45 
.200
45 
Section A-A
.500
.650
DIMENSIONAL TOLERANCES UNLESS
OTHERWISE SPECIFIED
IMPERIAL
METRIC
2 PLACE ±0.01
1 PLACE ±0.3
3 PLACE ±0.001
2 PLACE ±0.03 4 PLACE ±0.0005
3 PLACE ±0.005 NOTE:
NO CHAMFER ON DISK OR COLLAR IF BRAZING,
LEAVE 0.002" CLEARANCE FOR BRAZE
BETWEEN THE COLLAR AND THE DISK
USE A KNOWN WELDABLE STEEL.
DIMENSIONS ARE FOR A 5" CHUCK USED
IN NORMAL DUTY ON A1-1/2 X 8" SPINDLE
.900
1.400
LOGAN POWER-KRAFT 10" LATHE
WELDED BACKING PLATE COMPONENTS
BREAK OR DEBURR
EDGES UNLESS OTHERWISE SPECIFIED
A
A
STEEL, 1 REQ'D
BACKING PLATE DISK
STEEL, 1 REQ'D
BACKING PLATE COLLAR
Section B-B
M
M
EDITED BY
MIKE REHMUS
DO NOT SCALE
© 2012 BY
ELMWOOD
PUBLISHING, INC.
DRAWN BY
2
3RD
ANGLE PROJ.
Mike Rehmus
PROJECT
DWG # 2 OF
Logan Actuator
DESIGNED BY
Logan Lathe Backing Plate
PROJECT
ONLY NECESSARY FOR ARC WELDING - MIG, TIG OR STICK
DO NOT GROOVE FOR BRAZING BUT DO ALLOW ABOUT 0.002"
FOR THE BRAZE TO FLOW
DIMENSIONS ARE FOR A 5" CHUCK
ADJUST YOUR DIMENSIONS
ACCORDINGLY
COLLAR BORE FOR 75% THREAD
CONSULT REFERENCE FOR BORE
DEPENDING ON LENGTH OF THREAD
ENGAGEMENT VS THREAD MAJOR DIAMETER
AND COLLAR MATERIAL.
M
90
B
B
BACKING PLATE ASSEMBLY