tangent hr with sd et pc

Transcription

For more information on stair building please visit my web site :
http://www.stairdesignsoftware.net
COPYRIGHT 2012 by NT Designs.
Copying and distribution of this article is not permitted : page 1/73
Table of Contents
Tangent Hand Railing Using StairDesigner and 3D CADD .................................. 3
An Over View ........................................................................................................................ 3
Starting and Setting up the ProgeCad/Autocad drawing ..................................... 8
Setting up the Template Drawing.......................................................................... 11
Using the Template Drawing ................................................................................. 12
Drawing the Hand Rail Plan ................................................................................... 15
Drawing the Plan of the Prism............................................................................... 17
Draw Centre Line Plan............................................................................................ 18
Drawing the Hand Rail Elevations and Tangent Plane Developments .............. 20
Drawing the elevations of the Side Tangent Plan and Cross Tangent Plane ....................... 20
Elevation of Joint Lines........................................................................................................ 26
Falling Lines Set Up............................................................................................................. 28
First Falling Line.................................................................................................................. 30
Second Falling Line ............................................................................................................. 31
Measuring the Entry Angles................................................................................................. 34
Extruding the Solids............................................................................................... 35
Extrude the 3D Prism ........................................................................................................... 36
Extruding the Centre Line Solid........................................................................................... 37
Extruding Hand Rail Solid ................................................................................................... 37
Drawing the Double Inclined Plane....................................................................... 39
Cutting the Prism to Calculate the Double Inclined Plane................................................... 39
Cleaning Up the Centre Line and Hand Rail......................................................... 49
Centre Line Solid ................................................................................................................. 49
Hand Rail Solid .................................................................................................................... 50
Mark on the Springing Lines................................................................................................ 51
Drawing and Cleaning up the Face Mould Template........................................... 51
Draw 3D Solid Hand Rail ........................................................................................ 54
Drawing the Centre Lines as Polylines ................................................................................ 54
Align the UCS to Draw the Hand Rail Section Perpendicular to the Centre Line............... 55
Draw Hand Rail Section as a Circle..................................................................................... 56
Extrude Circle Along Polyline ............................................................................................. 57
Drawing the Twist Angles From the Solid Cylindrical Rail ................................. 59
Measuring the Twist Angles .................................................................................. 62
Conclusion .............................................................................................................. 67
Building Solid wood Hand Rails.......................................................................................... 67
Round Hand Rails ............................................................................................................... 68
Twisted Laminated Hand Rails ............................................................................................ 70
CNC 5 Axis Programming. .................................................................................................. 73
Tangent Hand Railing Using StairDesigner and 3D CADD
An Over View
One of the most difficult parts of stair building is building a solid continuous curved hand rail,
and the most tricky question is often how to design the rail and mark it up.
I know, and have used 2 methods of marking up a solid hand rail.
These methods traditionally need one to draw up full size plans by hand, and I have made
several stairs this way.
When CAD systems became available in the 1980’s I have found that using 2D CAD made
the drafting much quicker and more accurate and with the event of 3D solid modelling
functions , the efficiency of using CAD for marking out curved parts has again greatly
improved while reducing even more the time necessary to draft up the plans.
The first method I have used back in the 1980’s was the traditional European method that I
have given a rough over view of in this article :
http://stairdesignsoftware.net/how-to-design-curved-strings-and-handrails-usingstairdesigner-and-progecad-3d
Although this method works well for solid strings I find that for precise control of curved
hand rails the English method of tangent hand railing is far superior.
The tangent hand railing system also has a few hidden advantages that have enabled me to
create new techniques that greatly simplify the construction of curved hand rails notably my
system of "twisted round solid rails" and "twisted laminates" that you can see outlined in this
article:
http://stairdesignsoftware.net/different-ways-to-build-curved-stair-parts
One last advantage of the tangent system that is largely unknown and ironical for a system
that is several centauries old and largely forgotten, is that this system is ideal for
programming tool paths on a 5 axis CNC router.
The tangent system produces a 2 dimensional elliptical curve that twists along a 2D path, so
that using the appropriate CAM software, it’s easily to defined a 5 axis tool path from the
ellipse and the twist angles.
The tangent hand railing system is a way of marking out and making a curved piece of wood
that will be used to join 2 inclined stair rails in one continuous movement. This system was
originally defined from principles set down by architect Peter Nicholson in the 18th century
so it's not new high tech.
The important point in the design of a continuous hand rail is that the hand rail moves up in a
continuous and harmonious flow.
The general shape of a stair’s hand rail is defined by the position and shape of the steps, so to
get a perfectly harmoniously flowing hand rail the steps must be arranged in approximately
the right position and the exact shape and position of the hand rail can be determined using
the tangent method.
The elegance of the method for producing perfectly flowing hand rail transitions is due to a
simple fact that is rarely noticed, understood nor expressed.
This fact is that the underlying principle of the system, is the joining of 2 inclined hand rails
with an "elliptical curve" and not a helical curve.
Contrary to common belief the most elegant curve in space to join 2 inclined lines is not the
helical or spiral curve but an elliptical curve.
The reasons behind this are a little to involve to explain in this document but the general idea
and principle of the tangent system are simple.
This system draws a 2 dimensional elliptical curve between the rising angles of 2 inclined
hand rails and allows one to create a 3D solid by sweeping the section of the hand rail along
the curve normal to the ellipse.
This makes it possible to produce a solid where the tope and bottom surfaces are at 90° to the
sides.
This particularity makes tangent hand rail geometry ideal for building curved round rails,
moulded laminated hand rails and the cnc machining of wreathed rails.
Traditional moulded hand rail in walnut I built using the tangent system:
This document is an over view of how to use modern CAD software like AutoCad with 3D
solid modelling to simplify the application of the tangent method for marking up a wreathed
hand rail.
I have based my explanations around the use of AutoCad or ProgeCad's solid modelling
functions but the principles can be used with any 3D CAD system that allows basic 3D
modelling.
As I personally use ProgeCad (much cheaper that Autocad) I'll be explaining commands as
they function in ProgeCad.
These instruction will also be applicable to Autocad as it nearly has exactly the same
command structure, but if you're using another CAD system you'll have to adapt the basic
principles to your system.
Note that although I explain the general CAD command sequences, this document presumes
that you already know how to use AutoCad or Progecad and I don't explain the detailed
functioning of either program.
If you need information on using Autocad please look on the internet where you'll find plenty
of information or download the manuals from my web site.
One last point about using CAD, I use the command sequences that use commands and
tracking tools that work well for me.
If you fell happier drawing construction lines and can get the drawing done another way that
fits you better, don't hesitate to just do it your way.
There's no "better" way to draw the important thing is to understand the principals and get the
job done in the way that suits you and your style of working.
The tangent system has been used for marking out and hand building curved hand rails for
several centauries but as stated above this technique can also be very useful today as a simple
way of defining tool paths for building double curved hand rails on 5 axis CNC.
In this case the use of CAD files for designing the tangent rail and defining tools paths is no
longer optional but becomes an obligation.
This document doesn't give detailed explanations on the principles of tangent geometry and
you should at least have general knowledge of the under lying principles to fully understand
the process written out here.
The basic idea is to use
geometrical construction to get the
shape and sizes of a curved
handrail in an inclined plank or
blank.
To do this, a box is drawn that is
then cut to produce a prism and
inclined plane that symbolizes the
inclination of the piece of wood
that will be used to make and
shape the curved handrail.
The inclined plane gives the size
and shape of the inclined piece of
wood.
The shape of the hand rail on the
inclined plank is called the face
mould, and this is used to shape
the curve of the rail.
For a more detailed description of the tangent method and the underlying principles you can
visit this web site:
http://www.thisiscarpentry.com/2011/11/25/traditional-tangent-handrail/
or /and download this document:
http://stairdesignsoftware.net/downloads/stair%20and%20handrails%20AB%20Emary.pdf
In brief, the basic method I use to draw the hand rail in CAD follows these simple steps:
1) Draw the plan and elevations of the stair and rails. This can come directly from
StairDesigner or another software, or be drafted up by hand.
2) Draw the development along the tangent planes and use this to adjust the overall design of
the hand rails, and measure the angles of the falling lines.
3) Extrude the plan into 3D solids
4) Cut the solids to get the true geometry of the hand rail face moulds and angles.
Note that although when you read through this document, the design process may seem
complex at first, but as with many crafts, once worked through and understood, drafting out
the tangent face moulds with CAD can be fast and fairly simple.
Before starting to read this document I suggest that you look at the video demonstration of the
process on my web site, here is the link:
http://stairdesignsoftware.net/how-to-use-stairdesigner-and-progecad-for-tangent-handrailing
Starting and Setting up the ProgeCad/Autocad drawing
This tutorial has been written to show how to use CAD software for building the wreathed
hand rail on a stair built using the StairDesigner stair building software.
Although the original model comes from StairDesigner you can of course start with any stair
drawn up in a CAD file.
As stated above the actual shape of the stair and hand rail is largely determined by where the
steps are laid out, as theoretically the hand rail follows the step nosing's at +900mm above the
step nosing's.
In practice it's rarely possible to get a perfectly placed hand rail and at the same time have a
perfect harmonious flowing movement, so as with most things in life, stair building is full of
compromise and this is what makes it an art form more than an exact geometrical science.
In real life the exact height of the hand rail can vary by 50 to 80mm without affecting the
safety or the practicability of the stair.
In some cases it's even preferable in a tight turn to purposely place the hand rail at 1000mm
above the step nosing's to avoid a compression effect as the stair rises faster over the narrower
winders in a turning.
In the photo on the left the hand
rail has been purposely raised by
120mm over the turning to
compensate for the compression
effect.
In the drawing below that comes
directly from StairDesigner, the
hand rail is calculated at a
constant 900mm above the
nosing's but due to increased
rising angle around the turning
the hand rail will seem far to low
as one walks around the turning
on the real life stair. In this case,
to compensate I would modify
the lower hand rail by inserting a
curved portion that would
increase the height around the
turning.
Compression effect of the hand rail and steps in a steeply rising turning:
To keep the hand rail height as constant as possible I suggest that you use the 3D modelling of
StairDesigner to optimise the flow of the strings and hand rails as best as possible before
attempting to mark out the tangents.
This is especially useful when intermediary landings interrupt the flow of the stair and the
step nosing's can be adjusted to eliminate as much as possible any bumps in the hand rail
curves.
Take a look at this article to see an example of how this is done:
http://stairdesignsoftware.net/editing-a-curved-string-stair-in-autocad
To use ProgeCad or AutoCad 3D solid modelling to draw the wreathed hand rails it's best to
set up an initial template drawing to make work easier.
While making this tutorial I used the screen configuration that enables me to have all the
necessary commands easily at hand.
If your not familiar with Autocad/ProgeCad commands you might find it easier to configure
your screen like mine.
Here is the configuration I like too use:
For the specific task at hand of drawing the tangent hand rail I suggest creating some standard
layers for organising the drawing, but in your template drawing I also suggest that you include
any other element that you are used to having in your drawings such as text and dimension
styles, line types and colours, etc... In this way you can just open you template, insert your
StairDesigner DXF file or CAD file into the template drawing and everything will always be
set up and ready to go.
Setting up the Template Drawing
To set up a template drawing open a new drawing and do the following.
Open a new drawing
Use the Layer command to create these layers.
Give a different colour to each layer so that you can easily see what layer you are drawing on.
Each layer starts with the letter "t" for tangent so that they show up together in the layer list.
t-cs : cut string plan
t-prism : prism plan and solid
t-cls : centre line plan and solid
t-cl : centre line draw as ellipse
t-clp : centre line drawn as a polyline
t-fl : falling lines
t-hr : handrail face mould
t-hrs : hand rail solid
t-3ds : 3d solid rail
t-ta : twist angles
Add any other set ups such as page set ups, text styles and dimensions styles or items that will
make life easier when you start a new drawing.
Use the Save command to save your template to the hard disk. Use a name such as "tangent
template" so that you know it's the model drawing.
If you want to download the template I use click on the link below:
http://stairdesigner.org/downloads/progecad/tangent%20template.dwg
Note that this is in fact a complete drawing that you can study to see how it's all put together.
To use this as a template just delete all the objects and save under your template name.
Using the Template Drawing
Open the template drawing in ProgeCad.
Open the StairDesigner DXF 2D drawing in another tab.
We are now going to transfer the necessary geometry for building the face moulds used in
tangent hand railing into our working template drawing.
We will be needing the plan and elevation of the hand rail so:
In the StairDesigner drawing, Use the “edit” >copy command,
Copy the polyline of the handrail, to the clip board.
In ProgeCad You can use Copy or Quick Copy it doesn't really make any difference in this
case.
Now go to the Template drawing and use the Edit>Paste command to paste the hand rail into
your template drawing.
To copy the hand rail elevation to your template drawing;
Go back to the StairDesigner drawing,
Use the Edit >copy command,
To copy the elevation view of the handrail and the springing lines (lines where the curved
section starts) , to the clip board.
Go back to the Template Drawing and use the “edit”>paste command to paste the clip board
into the drawing.
For convenience put the hand rail elevation near the plan.
Your Template drawing should now look like this:
Note that you can also copy and paste both plan and elevation in one operation copying all the
elements using edit> copy and then pasting using edit>past to original coordinates.
In this case use the "move" command to place the elevations next to the plan.
To keep the original template drawing safe for another project save the Template drawing
under a new name.
We are now ready to start drawing the tangent hand rails in CADD.
The basic steps that we are going to follow through are:
1) Draw the 2D plans using closed polylines,
2) Extrude the plans into 3D solids,
3) Cut the solids to give the real shape of the face moulds and angles.
Of course you don't have to use my drawing methods to draw the plans but remember that
if you don't use polylines to draw your plan don't forget you must use the "modify polyline"
command to transform the lines into a single closed polyline for extruding into a 3D solid.
Drawing the Hand Rail Plan
The plan of the hand rail is already drawn by StairDesigner and just needs cleaning up.
Here are the steps to follow.
Set the current layer to the hand rail or string layer
To do this click the Set Layer command.
Use the line command to draw the springing lines.
Use the Offset command to draw the joint lines.
Use the Trim command to clean up the hand rail plan.
Use the modify Polyline command to change all the segments into one closed polyline.
Use the "join" option to join all the lines and arcs making up the out line into one continuous
closed polyline.
To keep the drawing layers well organized and tidy it's a good idea to change the hand rail
polyline's layer to th t-hrs layer.
Drawing the Plan of the Prism
At the heart of the tangent system is the notion of a prism that encompasses the curved 3D
rail whose centre line evolves up on it's upper inclined surface.
To draw this prism in CAD we are going to draw the plan using a polyline and then use the
3D solid functions to give it's real 3D volume.
First step lets draw the plan view.
Use the layers command to set current layer to : t-prism
command "rectangle"
snap the "mid point" of the springing lines.
Draw Centre Line Plan
Set current layer t-cls
Use the command polyline
Use the snap "mid point" command and snap the lower springing line.
Draw the first section of the centre line by using snap "end" lower corner of the prism.
Select the "arc" option in the polyline command.
Snap the opposite corner of the prism,
Select the "line" option
Snap the "mid" point of the upper springing line.
Select the "close" option to close the polyline and hit "enter" to exit the command.
You should now have the plan of the hand rail, the centre line drawn and the prism drawn up.
Drawing the Hand Rail Elevations and Tangent Plane
Developments
To get a smooth flowing hand rail we must adjust the elevation of the hand rails to define the
optimal heights and angles of the different sections.
The get a nice smooth flow in the curved section we must develop (un fold) the hand rail
along the 2 tangent planes so that the angles going into and leaving the curved section meet at
the crossing of the 2 tangent planes.
This will enable us to define a single inclined plane on which we can draw an elliptical curve
joining both inclined hand rails.
The straight or single curved portions of the hand rail are adjusted with curved ramp sections
to give the appropriate angles into the curved section.
Drawing the elevations of the Side Tangent Plan and Cross Tangent
Plane
Set the current layer to t-fl
If not already set up it's a good idea to have the elevations near the plan.
To do this use the command "move" and move the hand rail elevation and vertical springing
lines to a clear working space preferably besides the plan
Use the command "trim",
Select vertical springing lines as cutting edges and trim the handrail between the springing
lines.
With the hand rail elevation trimmed, your drawing should look like this:
StairDesigner creates a development of the real hand rail face but for the tangent system we
need the development of the tangent planes.
The development of the tangent planes is slightly longer than the real development.
To get this development we have too modify the distance between the rising rails.
To get the required distances use the command "offset".
The off set distance is the horizontal distance of the prism so to get this distance as the offset
distance when prompted for the offset distance snap the 2 adjacent corners of the prism:
Then off set the left vertical joint lines 2 times to get the width of the 2 tangent planes.
Use the command "move" to put the hand rail elevation in the correct position.
select the lower handrail and the vertical stringing line
snap "end" of vertical springing line
snap to "end" of offset vertical springing line
The drawing should look like this:
Elevation of Joint Lines
Here we are going to draw the elevation of the joints between the rising rails and the curve
wreath.
Using the command "offset"
snap "end" of centre line
snap "end" of straight section of centre line to give the offset distance
Off set the vertical lines of the Side Tangent Plane and the Cross Tangent Plane to give the
vertical joint lines.
Use the “properties drop down list” to change colour of the vertical joint lines to blue or any
other colour so as to distinguish them from the vertical springing lines.
Falling Lines Set Up
We are now going to define in the elevation the slope of the centre of the hand rails.
This operation must be done with care as it will give the overall flow of the hand rail
throughout the stair.
In our example the hand rail is divided into 3 distinct parts:
1) The first rising rail,
2) The curved section between the springing lines,
and the second rail leaving the springing lines.
3) The curved section is divided into 2 parts the Side Tangent Plan and the Cross Tangent
Plane.
To design a smooth global curvature of the hand rail the slope of each section must follow
some simple rules:
1) For the curved section the 2 sloping falling lines must meet at the intersection of the 2
tangent planes
2) The slope of the 1st rising rail at the first springing line must be the same as the slope
of the falling line in the Side Tangent Plane
3) The slope of the 2nd rising rail leaving the curved section must the same as the slope of
the falling line in the cross tangent plane.
As we are always working with the centre lines of the hand rails we will draw the falling lines
as the central axis of the hand rails too. Let's start with the upper falling line's axis .
To draw these falling lines proceed as follows:
To draw a line at the axis of the hand rail use the command "circle"
Snap "mid point between 2 point"
Snap "end" for hand rails at vertical springing line
Entre radius equal to half the hand rail section
First Falling Line
As it's usually better that the hand rails be higher over the turnings it's usually best to draw the
upper hand rail falling line first and then join the lower rail to the appropriate angles.
To do this use the command "construction line"
Snap "centre" circle.
Draw line approximately tangent to the upper curve or so that it's possible to insert a curved
section or ramp to maintain a continuous harmonious flow.
In our example it's possible to not insert a ramp and even though the hand rail height will vary
a bit we can maintain a straight hand rail for the upper section.
Trim the falling line at the middle of the tangent planes.
Use the command "trim" to trim the falling line to the centre springing line.
Second Falling Line
To draw the second falling line, use the command "construction line" again.
Snap "end" of first falling line at the central springing line.
Draw the line approximately tangent to the lower curve or at an angle that allows you to draw
a smoothly sloping curved transition.
Use the command "trim" to trim the second falling line to the centre tangent line
Draw in eventual ramps to adjust the upper and lower handrails to the wreathed entry angles.
Trim falling lines to vertical joint lines and mark the joins of the hand rails at right angles to
each falling line.
Measuring the Entry Angles
To draw the inclined plane in 3D we need to know the exact angles of the falling line within
the curved section.
To measure the exact angles use the command dims "angular".
Click "enter" to dimension the angle by 3 point and dimension the vertical angles of each
falling line using polar tracking for the horizontal.
Extruding the Solids
We are now going to use the solid modelling functions of ProgeCad to calculate and draw the
face mould and angles of the curved rail.
To get a view of the solids as we build them switch the current view to a SE isometric view.
Extrude the 3D Prism
Set current layer to "t-prism"
Use the command "extrude"
Select the polyline representing the plan of the prism and extrude to 2000mm
Extruding the Centre Line Solid
Use the same process to extrude the centre line and the hand rail plan.
Set layer to t-cls
Command "extrude"
Select the polyline representing the centre line in the plan
Extrude to 2000mm
Extruding Hand Rail Solid
Set layer to t-hrs
Command "extrude"
Select the polyline representing the plan of the hand rail
Extrude to 2000mm
Drawing the Double Inclined Plane
To make it easier to draw the real shapes of the double inclined plane and face moulds it's
easier to hide unnecessary screen clutter so switch off the handrail layer t-hrs and just leave
the prism and centre line on screen.
Cutting the Prism to Calculate the Double Inclined Plane
Drawing the lower inclined section/plane
Use the command "UCS" origin
snap lower end of centre line
Use the command "UCS" rotation X
entre the lower falling line angle (positive value : right hand rule)
Use the command solid "section"
Select the 3D solid prism
Select section XY plane
Press "Enter" to select 0,0
ProgeCad should draw a region or surface that cuts the prism along the XY plan and your
drawing should look like this:
Set the UCS back to "world". Use the command "UCS" >"world"
Drawing the upper inclined sections
Use the same process to draw the upper inclined section/plane
Use the command: "UCS" origin.
Snap "end" upper corner of lower inclined plane.
To calculate the upper inclined angle use the command "UCS" rotation Y.
Enter upper falling line angle (negative angle : right hand rule)
Use the command solid "section"
Select 3D solid prism
Enter to select 0,0
Cutting the 3D solids to get the double inclined plane and face mould.
Use the command "UCS" by 3 points.
Using Snap "end" snap the points 1,2,3
The UCS is now aligned to the double inclined plane that has to contain the inclined centre
line of the hand rail i.e., the face mould
We are now going to cut the 3D solids along the double inclined plane.
Use the command solid "slice"
Select "all"
Enter to select 0,0
Specify point at Z=0
We have now finished with the inclined planes so use the command "delete" to erase both
planes (you might only have one to delete as the upper plane is deleted with the "slice"
commmand).
Delete the inclined sections (planes).
Your drawing should now look like this:
If we only display the hand rail solid as a shaded model we should have this:
And only the centre line shaded solid:
Cleaning Up the Centre Line and Hand Rail
We now have the shapes of the hand rail face mould and centre lines projected onto the
double inclined plane as solid sections.
We are now going to eliminate the solids to leave only the geometrical lines necessary for
marking out the hand rails.
Centre Line Solid
To make cleaning up easier isolate the layer cls.
Use the command "explode"
Select solid.
Solid becomes regions.
Use the command "delete".
Delete all vertical planes leaving only the horizontal and double inclined planes.
Use the command "explode" again on plan and inclined regions.
Regions become 2D entities.
Delete cords leaving the centre lines.
Select the double inclined ellipse and lines and change to layer t-cl
Hand Rail Solid
Do the same for the hand rail solid and change the layer of the double inclined plane face
mould to t-hr
Mark on the Springing Lines
Use the prism to draw the springing lines onto the t-hr face mould
command "construction line"
Drawing and Cleaning up the Face Mould Template
To get the real face view of the face mould for printing we have to turn the double inclined
plane parallel to the screen view.
To do this:
Isolate layers, t-hr and t-cl
Use the command "UCS" 3 points
Select points 1,2&3:
The UCS is now aligned with the double inclined plane and the X axis is aligned with the
extreme points of the hand rail face mould.
To align the screen view with the UCS use the command "view" >3d view >plan
view>current UCS
We now need to finish off drawing the face mould.
Use the command "trim"
To trim springing lines.
Draw joints at 90° to tangents and clean up as in the drawing below:
.
Print full size to get the templates for the face moulds.
Draw 3D Solid Hand Rail
A 3D model of a cylindrical hand rail is used to preview the shape of the finished rail and also
provides an easy way of calculating the twist angles.
Because Progecad will not extrude a polyline along an ellipse we a have to redraw the
inclined ellipse as a polyline.
As Autocad can extrude along ellipses this stage can be omitted if you are using Autocad.
Drawing the Centre Lines as Polylines
Draw centre line as a polyline on inclined plane
while leaving the UCS on the double inclined plane.
Set layer to t-clp (centre line polyline).
Use the command "pline".
Snap "end" inclined centre line
Choose polyline option "arc"
Snap "nearest" along the first quarter of the curve then snap to the middle and then "nearest"
and then the "end" of the ellipse.
Choose the polyline option "line"
Snap to the end of centre line.
Turn off the layer t-cl
You should now only display layers t-clp and t-hr
Align the UCS to Draw the Hand Rail Section Perpendicular to the
Centre Line
First align the UCS to the end of the centre line with X pointing in the direction of the centre
line.
Use the command "UCS 3 points" and use the following points:
Now we will rotation the UCS to draw the hand rail section perpendicular to the entre line.
If you haven't already done it, to make visualizing the drawing easier, set an isometric view
of the end of the centre line using the "3D orbit" command.
Use the command "UCS" Y rotate,
Enter 90° as angle of rotation .
Draw Hand Rail Section as a Circle
Set current layer to t-3ds
Command "circle" ( if you haven't changed to an isometric view, you wont see the circle
because its perpendicular to the viewing plane)
Centre 0,0 or snap "end"
Radius : 30 (half the width of hand rail)
You should see the end of the hand rail like this:
Extrude Circle Along Polyline
Command "extrude"
Select the circle
Select option "path"
Select polyline
Once extruded the solid hand rail should look like this:
In the textured version :
In this isometric view you can see how the hand rail solid moves up along the double inclined
plane:
Drawing the Twist Angles From the Solid Cylindrical Rail
We are now going to use the 3D hand rail solid to calculate the twist angles of the rail.
To do this set UCS to world and set to display in an isometric view.
To have a clear workspace display only layers: t-prism, t-pcl(or t-cl if you use Autocad)) and
t-3Ds
Set current layer to t-ta.
Use the command: UCS origin
For the UCS origin snap "end" the upper left corner of prism plan.
The UCS is now in place to calculate the twist angles.
We are going to use the "section" command to generate sections that will give the appropriate
angles.
For the lower twist angle use the command "section"
And select the hand rail solid
Choose to section on YZ plane at 0,0
Then do the same thing to draw the upper twist angle.
Use the command "section"
select hand rail solid
section on ZX plane at 0,0
You should have a drawing like this:
The twist angles are the angles that the vertical plane make with the double inclined plane of
the prism.
To get a clear view of the twist angle planes it’s a good idea to generate the shpae of the hand
rail section on the double inclined plane.
This is very easy to do and will make measuring the angles clearer.
To do this use the "UCS 3 point" command to align the UCS with the double inclined plane.
Then use the "section" command to draw a section through the hand rail solid on the XY
plane.
See the chapter "Cutting the 3D prism to get the double inclined face mould plane" if you
don't remember how to do this.
The following drawing shows an isometric shaded view of the hand rail's double inclined
section in green and the vertical plane in magenta
The twist angles are the angles between these planes on the end joints of the rail.
Here's a view of the twist angles when the hand rail is laid out in the plank that will be used to
cut the rail.
Measuring the Twist Angles
To build the hand rail we need to know the exact twist angles.
To get these angles use the "3D orbit" command to get an isometric view of the end of the
hand rail solid.
You might find it helpful to use a shaded view to clearly see which way round you are
moving the hand rail.
Switch to a wireframe view to continue working.
Use "UCS 3 points" to align UCS with the end of hand rail.
Use dim angle command to dimension the twist angles.
The solid hand rail can be shaded and textured.
To get an idea of the final shape of the entire hand rail it's easy to extrude the circular section
along the lower and upper hand rail centre lines and assemble the entire hand rail in CAD to
preview on the stair's 3D model.
Here's the wreathed rail textured :
This is the rail assembled with the lower and upper rails.
Using the original StairDesigner 3D model I have inserted the tangent hand rail to get a 3D
textured image and verify the general movement and flow of the stair.
Here's another example of a stair rail designed in AutoCad with the tangent system.
Conclusion
The drawings made using this method can be used in several ways according to the
construction method you have chosen for your curved handrails.
Building Solid wood Hand Rails
If you are building solid moulded hand rails you can print out full size the face moulds to give
you the templates to mark up the hand rail blanks for shaping.
To understand how these face moulds are applied to a blank you can take a look at this web
site: http://www.thisiscarpentry.com/2011/11/25/traditional-tangent-handrail/
This traditional moulded wreathed handrail is
made in solid walnut and moves up to a
landing in a graceful half turn sweep.
Round Hand Rails
If you are building a rounded rail you just offset the centre line to give the shape of the 2D
elliptical blank that can be cut and shaped in a flat 2D board. Add the twist angles to each end
that will give the vertical angle for joining the rails to the straight sections.
Here are a few sections with varying twists:
This photo shows a round hand rail built on a
circular cement stair.
The elliptical centre line was also used to
bend the stainless steel tubes that make up the
balustrade.
In this next example I have made 200 meters of rounded hand rail using a cnc router.
The router was used to round of the rail sections and drill the dowel holes at the twist angles .
The hand rails were then assembled to form continuous helical hand rail for a circular cement
stair.
All the wreathed sections are all the same making cnc production fast and efficient.
Twisted Laminated Hand Rails
If you are building using twisted laminates, off set the centre line to give the shape of the
laminates and use the twist angles to build the twist jig.
Here's an example of tangent hand railing applied to a hand rail built for a steel stair. On this
project the laminates are organised to leave a groove on the under side, eliminating any need
for machining.
Here are the laminates are cut to the shape of the face mould with a router .
Note that for these techniques you just off set the centre line and you don't need to develop the
face mould from the hand rail plan, so setting out is even faster .
Twist jig for gluing up twisted laminates.
Gluing up with a twist :
As with the rounded rails all the parts of this helical rail are the same.
Here's the rail partly assembled and showing the groove for capping the metallic hand rail.
CNC 5 Axis Programming.
If you are using a 5 axis cnc to build a moulded wreath use the centre line as a tool path (with
the right off set of course) and program the tool to enter at the first twist angle and leave at the
second twist angle.
Hope this has been of interest to you.
If you have any questions don't hesitate to contact me at :
[email protected]
Happy stair building!
Ness Tillson :
17th May 2012

tangent hr with sd et pc

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