CLICK HERE TO SEE A VIDEO OF MY MACHINE AND WORK:
http://youtu.be/SL1EHI9Wh1U
Rotary Machining: A General Overview
by Randall Newcomb & Bill Schober
Photos courtesy of Jack Jarvis, James McGrew, Jim Van Vegten, Bill Schober
Rotary Machining with Vectric Software
Until recently there was limited software support available for rotary axis work from CNC software vendors. The software that did exist was rather expensive. As a consequence there were few shops that had CNC machines with a rotary axis. Also, a number of shops had purchased a rotary axis (also known as an indexer) but the devices languished unused because they were too difficult to program. It was a "chicken-and-egg" scenario: there were few rotary machines in use because of limited software, and little software development because of so few machines with rotary capabilities.
A small but vocal group encouraged Vectric to move forward with rotary support even though the previewer did not provide the same level of information as standard XYZ axis machining. In December of 2009 Vectric released upgrades to Aspire and VCarve Pro that included support for wrapping X or Y moves around a rotary axis. It was with some trepidation that this feature was included because there would not be a realistic preview of the finished product, which is a hallmark of the Vectric products. Instead the output might be shown as though machined on a flat piece of material and/or as a wireframe cylinder with toolpaths projected onto it.
A small but vocal group encouraged Vectric to move forward with rotary support even though the previewer did not provide the same level of information as standard XYZ axis machining. In December of 2009 Vectric released upgrades to Aspire and VCarve Pro that included support for wrapping X or Y moves around a rotary axis. It was with some trepidation that this feature was included because there would not be a realistic preview of the finished product, which is a hallmark of the Vectric products. Instead the output might be shown as though machined on a flat piece of material and/or as a wireframe cylinder with toolpaths projected onto it.
Major upgrade: ASPIRE v3 & VCarvePro v6
In the fall of 2010 Aspire 3 & VCarve 6 were released and one of the many new features is a realistic wrapped preview!
The above image is an unedited original preview exported directly from Aspire 3.
The new preview feature is great for two reasons; one you can see your work before you cut it, and two the potential client can preview the project before committing. There is nothing worse than cutting and finishing a piece only to find out it's not what they wanted. A picture is worth a thousand words.
Wrapped Models & Rotary Machining
- Draw a fully shaded wrapped model in the 3D view to see how your wrapped design will look.
- Unwrap an imported 3D model to allow it to be machined all the way around using a rotary toolpath.
What It Won't Do
You cannot take a full 3D file and directly toolpath and carve it using the rotary axis machining.
Also, the software does not calculate rotary 4 axis toolpaths for 3D models. It only generates 3 axis toolpaths.
Also, the software does not calculate rotary 4 axis toolpaths for 3D models. It only generates 3 axis toolpaths.
General Indexer Information
This section describes concepts that are applicable to most indexers irrespective of the brand of CNC or of the software used. The descriptions are also applicable no matter whether the indexer is mounted parallel to the X or Y axis.
There are two main sections of this General Information:
Concepts: How designs are translated into actual mechanical movements.
Mechanics: Parts of the indexer and how to mount material for machining.
There are two main sections of this General Information:
Concepts: How designs are translated into actual mechanical movements.
Mechanics: Parts of the indexer and how to mount material for machining.
Concepts
Terminology
Indexer: An indexer (or Rotary Indexing Head) is similar to a lathe in that it allows you to horizontally rotate a part being cut by the router or spindle. It differs from a lathe because it provides precise control of the rotation of the material, whereas a lathe tends to rotate material continuously at a constant speed. With an indexer motion in X, Y, or Z can be coordinated with rotation of the material which allows for spirals, twists, wrapping of text, and even machining of 3D designs on a column.
Lathe: A lathe is a tool which spins a block of material while it is being cut to create an object which has symmetry about an axis of rotation. Typically a lathe is spinning the material at a constant rate independent of motion in the X, Y, or Z planes.
Fourth Axis: Three axis machining usually means motion in the X, Y, and Z planes. A fourth axis frequently refers to adding rotation about the X or Y plane. This tutorial will refer to machining where X or Y movements are translated into rotational movement. This tutorial will not deal with designs where movement is happening simultaneously in all four axes. It will always be assumed that either the X or Y motion is replaced with rotational motion.
Rotary Machining: In this context it means translating movements in the X or Y place to be rotational movements so that a design is wrapped around a column.
Right Hand Rule: Some people find the following description of the right-hand rule helpful in understanding the relationship between XYZ and rotary movement.
Indexer: An indexer (or Rotary Indexing Head) is similar to a lathe in that it allows you to horizontally rotate a part being cut by the router or spindle. It differs from a lathe because it provides precise control of the rotation of the material, whereas a lathe tends to rotate material continuously at a constant speed. With an indexer motion in X, Y, or Z can be coordinated with rotation of the material which allows for spirals, twists, wrapping of text, and even machining of 3D designs on a column.
Lathe: A lathe is a tool which spins a block of material while it is being cut to create an object which has symmetry about an axis of rotation. Typically a lathe is spinning the material at a constant rate independent of motion in the X, Y, or Z planes.
Fourth Axis: Three axis machining usually means motion in the X, Y, and Z planes. A fourth axis frequently refers to adding rotation about the X or Y plane. This tutorial will refer to machining where X or Y movements are translated into rotational movement. This tutorial will not deal with designs where movement is happening simultaneously in all four axes. It will always be assumed that either the X or Y motion is replaced with rotational motion.
Rotary Machining: In this context it means translating movements in the X or Y place to be rotational movements so that a design is wrapped around a column.
Right Hand Rule: Some people find the following description of the right-hand rule helpful in understanding the relationship between XYZ and rotary movement.
Basic Concept 1:
Rotary Machining takes a "flat" or a 2 1/2 D design and wraps it around a column
Rotary 101 The way that rotary support works is to translate moves from the X or Y axis and change them to a move on the rotary axis (usually referred to as the B axis) so the design is wrapped onto a cylinder. This is referred to as "Wrapped Rotary Axis Machining".
Perhaps this is easier to visualize if we take a common cylinder and show it laid out flat and then wrapped into a cylinder. For example:
Rotary 101 The way that rotary support works is to translate moves from the X or Y axis and change them to a move on the rotary axis (usually referred to as the B axis) so the design is wrapped onto a cylinder. This is referred to as "Wrapped Rotary Axis Machining".
Perhaps this is easier to visualize if we take a common cylinder and show it laid out flat and then wrapped into a cylinder. For example:
The following shows how a dish style 3D design is wrapped around a cylinder.
Basic Concept 2:
A spiral is achieved by using a design that is wider than the circumference of the cylinder
Rotary 102: Spirals
Spiral work is essentially wrapping a design around a column more than once. Referring to our visual aid, imagine a design that wraps around the cylinder three times:
In the above example the "ribbon" of material is three times wider than the circumference of the cylinder and one third as tall as the length cylinder.
In the video below, observe how the material spins multiple times to achieve the spiral design.
In the following example I took the Serenity Prayer and wrapped it around a staff. I wonder if this actually makes me a Wrapper or a Wrap artist...
Mechanics
This section identifies common parts of an indexer and describes a method to prepare and load material into an indexer for machining.
Parts of the Indexer
Headstock
Parts of the Indexer
Headstock
The headstock is typically the part that has the motor connected to it. It also has a chuck with jaws that can be adjusted to the size of material. If the material is larger than the chuck then either the material can be cut down on the end, or a mounting plate can be attached to the material. The mounting plate will have a "knob" on it that will fit in the chuck.
Tailstock
The tailstock is a device used to support one end of the material mounted in an indexer. It applies support to the longitudinal rotary axis of a workpiece being machined. A lathe center is mounted in the tailstock and inserted against one end of the workpiece at the center. The tailstock does not move the material, rather it is stationary or turns passively while the workpiece rotates. Once material is mounted in the headstock the tailstock is moved close to the end of the material. It is locked in place then fine adjustments are done with a leadscrew to move it snugly into position. Do not over-tighten as it can split the material.
Indexer Mounting: X or Y?
For subsequent tutorials it will be important to know if your indexer is mounted parallel to the X axis or the Y axis.
Some examples of X mounted indexers:
Some examples of X mounted indexers:
Examples of Y mounted indexers:
Photos coutesy of Jack Jarvis, James McGrew, Jim Van Vegten
Preparing Material and Mounting in the Indexer
Finding the Center of the StockIn order to machine the material efficiently in the indexer the center needs to be located on each end to facilitate mounting in the headstock and tailstock. The most basic way to find the center of the material is to draw a line from one corner to the opposite corner (example: lower left to upper right) and repeat for the other direction (example: upper left to lower right). Where the two lines cross is the center of the material.
Finding the Center of the StockIn order to machine the material efficiently in the indexer the center needs to be located on each end to facilitate mounting in the headstock and tailstock. The most basic way to find the center of the material is to draw a line from one corner to the opposite corner (example: lower left to upper right) and repeat for the other direction (example: upper left to lower right). Where the two lines cross is the center of the material.
There are various center finders on the market which make it faster, easier, and more accurate to find the center of the material. Some are designed to be used with square or round material which can be handy as well. Using a very sharp or fine point pencil greatly increases the accuracy of center finders.
The following photos (courtesy of Jim Van Vegten) show a headstock designed for handling small stock.
Handling Oversize Stock
If the material is too large to fit in the indexer chuck it either needs to be cut down or a piece needs to be attached to the material to adapt it to the indexer chuck. The photos below (courtesy of Jack Jarvis) shows indexing hubs which can be purchased through Legacy Woodworking
If the material is too large to fit in the indexer chuck it either needs to be cut down or a piece needs to be attached to the material to adapt it to the indexer chuck. The photos below (courtesy of Jack Jarvis) shows indexing hubs which can be purchased through Legacy Woodworking
Below is a design for a mounting jig that is used by Scott Cox:
Cutting Down Oversize Material
The information that follows demonstrates how to cut the stock down to size to fit into the indexer chuck. The basic steps are:
Compass Tutorial on YouTube in a new window
The information that follows demonstrates how to cut the stock down to size to fit into the indexer chuck. The basic steps are:
- Mark the center point on each end of the material
- Draw a circle on the end that will go in the indexer chuck
- Saw around the diameter circle
- Use a chisel to remove the excess material
Compass Tutorial on YouTube in a new window
Saw Around the Center
Set the depth of cut on the saw so it stays on the outside of the circle that was drawn with the compass. Cut on all four sides.
Saw Tutorial on YouTube in a new window
Set the depth of cut on the saw so it stays on the outside of the circle that was drawn with the compass. Cut on all four sides.
Saw Tutorial on YouTube in a new window
Chisel Off the Excess Material
Use a chisel to remove the material that was undercut with the saw.
Chisel Tutorial on YouTube in a new window
Use a chisel to remove the material that was undercut with the saw.
Chisel Tutorial on YouTube in a new window
Mounting Material in the Indexer
Mounting Material in the Indexer on YouTube in a new window
Title Text.
Zeroing the Bit
I strongly recommend using the center of the material as the Z-zero point.
The easiest way to do this is to zero off of some known point on the tailstock and adjust your Z height accordingly. On my particular setup the top of the tailstock is exacly 0.750" above the center of the cylinder. When I set Z-zero for rotary work I use the following steps:
I strongly recommend using the center of the material as the Z-zero point.
The easiest way to do this is to zero off of some known point on the tailstock and adjust your Z height accordingly. On my particular setup the top of the tailstock is exacly 0.750" above the center of the cylinder. When I set Z-zero for rotary work I use the following steps:
- Run my Z-zero routine to zero off the top center of the tailstock
- Jog XY to move the bit off to the side of the indexer
- Move the Z down 0.75
- Reset the Z to zero
- Move the Z up to a safe height so it will clear the material
- Move to XY home
Thin Stock Support
by Jack Jarvis
When carving things like balusters, spirals, and other long thin (and some not so thin) parts you need to compensate for the downward and lateral flex exerted on your material from both the tool pushing downward and spinning along with the weakening of the structure when doing something like hollow spirals. The results of these pressures are tragically illustrated here.
by Jack Jarvis
When carving things like balusters, spirals, and other long thin (and some not so thin) parts you need to compensate for the downward and lateral flex exerted on your material from both the tool pushing downward and spinning along with the weakening of the structure when doing something like hollow spirals. The results of these pressures are tragically illustrated here.
Without support
In order to relieve these pressures I tried to figure out what could i use to keep my work from being ruined. After some experimentation with various designs I spotted a pair of old toy rollerskates from my granddaughter that she outgrew. Because they had an adjustment that allowed the rollers to be moved closer together this was perfect for what I was trying to do.
As in the above pictures you may notice that the actual profile cut into the material for the spirals was not very deep and the jig as you see it in will work well.
With support
However if you are doing a design such as the one below you will find that you are cutting away a lot of material and you no longer have support underneath.
To solve that problem I revised the jig so that I had springs inserted under the skate to exert upward pressure to support the stock as material is taken away.
Another design I worked on was a design that ran parallel to the X axis with what looked like two rolling pins. You could also use a couple pieces of PVC pipe.
Another componnent of thin stock support is lateral pressure. The problem when you start cutting into material is that it loses its lateral strength especially when making a hollow spiral.
Another design I worked on was a design that ran parallel to the X axis with what looked like two rolling pins. You could also use a couple pieces of PVC pipe.
Another componnent of thin stock support is lateral pressure. The problem when you start cutting into material is that it loses its lateral strength especially when making a hollow spiral.
Making a Hollow Spiral
by Jack Jarvis
To create a hollow spiral is fairly simple in principle.
- Take a board equal to twice the length of the material you want to end up with.
- Take a core box bit running a half circle down the middle
- Cut it in half
- Join the two halves which form your round empty center after glue up
by Jack Jarvis
To create a hollow spiral is fairly simple in principle.
- Take a board equal to twice the length of the material you want to end up with.
- Take a core box bit running a half circle down the middle
- Cut it in half
- Join the two halves which form your round empty center after glue up
After joining the two halves you need to have internal support when cutting through the material to get to the center.
You need to have a dowel in the center that fits snuggly to support the underside of the spirals when cut.
You are now prepared to make your spiral. Use the appropriate bit with the toolpath or program you use to create your toolpath. This is a 3" rope molding bit from Magnate.net Rope molding bits:
You are now prepared to make your spiral. Use the appropriate bit with the toolpath or program you use to create your toolpath. This is a 3" rope molding bit from Magnate.net Rope molding bits:
www.magnate.net
After you make your spiral toolpath you leave all your settings alone and change your bit to a .25 straight flute bit. The spiral up and downshear bits have a tendancy to grab the sides of the spirals and vibrate the material and can break it.
Take a copy of the original toolpath used to make the 3" spiral and change the cutting depth to 0.10" or 0.15" per pass. Z-zero the bit at the material surface (or a bit above).
After the first pass lower the bit to the depth you just cut (or a hair above) and reZero the Z. Run the toolpath again. Repeat this process while cutting about 0.10" per pass till you cut through and expose the center dowel.
When you expose the center you will end up with a piece that looks like these:
Take a copy of the original toolpath used to make the 3" spiral and change the cutting depth to 0.10" or 0.15" per pass. Z-zero the bit at the material surface (or a bit above).
After the first pass lower the bit to the depth you just cut (or a hair above) and reZero the Z. Run the toolpath again. Repeat this process while cutting about 0.10" per pass till you cut through and expose the center dowel.
When you expose the center you will end up with a piece that looks like these:
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