a way to use 4 axis on rotary

Topics related to wrapped rotary machining in Aspire or VCarve Pro
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richard@cnc
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a way to use 4 axis on rotary

Post by richard@cnc »

hi Guys
I would like to make a polygon with the rotation axis
To do this, you would have to be able to address all 4 axes because otherwise it would be rather inefficient with a drawn fillet to take the rotation into account for a flat surface
I have done it once before and have turned the axle by hand, but this is very time consuming for larger quantities

Is there an additional program to control all axes in one step?

regards Richard

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rscrawford
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Re: a way to use 4 axis on rotary

Post by rscrawford »

I would just edit your G-code and add the rotation and copy and paste the 'pocket' tool path that cuts each face for each rotation until you are done.
Russell Crawford
http://www.cherryleaf-rustle.com

richard@cnc
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Re: a way to use 4 axis on rotary

Post by richard@cnc »

I'll try it out on the next project......

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Re: a way to use 4 axis on rotary

Post by 4DThinker »

Using Aspire or Vcarve there is no way to directly control all 4 axes in the same file. To make a polygon though you can use the moulding toolpath and a little drafting to come up with a vector path for the moulding toolpath to follow. I've posted an octagonal shape in another thread here. In this post below is a 5-sided polygon extrusion cut from a 1.5" dowel. Basically start with a circle the diameter of your blank, then draw the polygon shape you want made inside the circle. The distance between the center of each flat face of the polygon and the circle is how deep a curve needs to be that gets stretched across the material block. You are essentially unfolding the circle perimeter with the polygon faces remaining the same distance from the circle. All vectors used in the Aspire file attached. Version 9.519.
5-sided moulding.jpg
4D
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5-sided rotary moulding.crv3d
(119 KiB) Downloaded 22 times

gregk
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Re: a way to use 4 axis on rotary

Post by gregk »

Since Aspire v9.5 there is a built-in vector unwrapper. This tool can be used in connection with moulding toolpath or two-rail sweep. When using this tool is no need to draw a circle. Just draw a desired polygon and select 'Vector Unwrapper'.
The tool will display a circle with the same diameter as the job. Once polygon is positioned in the middle, it can be easily resized to fit the circle (holding shift while resizing is recommended). The click 'Apply' and the tool will create a curve.
This curve can be used directly with the moulding toolpath.

Greg K

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Re: a way to use 4 axis on rotary

Post by 4DThinker »

Thanks for point out the vector unwrapping tool, gregk. I hadn't noticed that before. I used it to duplicate what I did in my previous post and found a few significant differences in the results.
First is that the moulding result has slight concave curves in the faces that the original vector polygon did not have.
Secondly the created curves aren't curves but rather a bunch of closely spaced vectors with legs that aren't needed for the moulding toolpath. . Yes I know the legs are easily deleted and the lines can be turned into simpler arcs.
Thirdly the result also looks to be making a shape that isn't centered in the stock.
Again my file is from Aspire 9.519.
Vector unwrapped sample.jpg
4D
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vector unwrapped 4D.crv3d
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gregk
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Re: a way to use 4 axis on rotary

Post by gregk »

4DThinker wrote:Thanks for point out the vector unwrapping tool, gregk. I hadn't noticed that before. I used it to duplicate what I did in my previous post and found a few significant differences in the results.
First is that the moulding result has slight concave curves in the faces that the original vector polygon did not have.
This is most likely an issue of numerical accuracy. And I can also see this slight concavity with your vectors
4DThinker wrote: Secondly the created curves aren't curves but rather a bunch of closely spaced vectors with legs that aren't needed for the moulding toolpath. . Yes I know the legs are easily deleted and the lines can be turned into simpler arcs.
4D
You can try ticking 'Simplify unwrapped vectors' option (or use Curve Fit afterwards as this gives more control). However, as far as moulding toolpath is concerned, this doesn't really matter as the toolpath will polygonise those curves internally.
I wouldn't remove the legs, as they help to ensure that the toolpath is positioned accurately in z. If that distance is adjusted, the result will be a polygon with rounded sides.
Of course if the material have the exact same diameter as the polygon and the gap above toolpath is set to 0, the results will be accurate. But if you decide to make this polygon slightly smaller, then with legs you can just need to ensure that gap below toolpath is 0.
Without legs you will need to be more careful with positioning the toolpath.

I hope that this makes sense.

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Re: a way to use 4 axis on rotary

Post by 4DThinker »

The tiny arc in my first 5-sided example is easily corrected by changing the height of my curve row that made the extrusion. Mathematically the faces should be flat but the slight curve may be due to the shape of the ball nose bit and it's approach to the face as the angle changes.
With the legs left on of the unwrapping tool vectors an error is generated that prevents the moulding tool from finishing. "Cut Depth Exceeds Thickness!".
The generated vectors rise up in the middle and in theory should be a flat row. Another flaw in the calculation which is what results in an off-center cut.

The unwrapping tool may produce better unwrapped results with different shapes, but as is I wouldn't trust it to create accurate vectors for the moulding toolpath on simple flat faced polygons.

4D

gregk
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Re: a way to use 4 axis on rotary

Post by gregk »

Keep in mind that the unwrapper tool allows you to pick the centre of the polygon, so you can create 'off centre' polygons if you want:
Using center of vector's bounding box - results in profile being slightly off-centre
Incorrect.png
Using the actual center of the shape
Correct.png
This tool was specifically developed with simple polygons in mind. And I can trust its results since I spend quite some time developing this and other rotary features :)
But I understand that if you did the math yourself and understand the whole process, you may feel more comfortable with your solution rather than some black box.

In any case, thanks for you contribution into wrapped rotary machining!

Greg K

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Re: a way to use 4 axis on rotary

Post by 4DThinker »

Yep. I should spend more time with a new (to me) feature before drawing a conclusion about its usefulness. That centering option I didn't notice since I started with a circle the diameter of my blank. I've been challenging this tool with all sorts of shapes since I last posted and have found it does a good job most of the time once I've centered the shape using that option. From triangles to ellipses to bumpy mutations all seemed to work unless the result would have undercuts if done on a rotary axis. Polygons with an odd number of sides don't automatically get centered even if they "look" centered in the circles I've drawn them in. The slight curve in what should be flat faces is so small when cut that it sands flat easily.

As always Aspire continues to amaze me with the great drafting tools and features. I often use the measure tool to help students calculate spacing for kerf cuts in plywood they want to bend, and many cases where precision dimensions are needed on complex shapes. My students have other drafting software that "should" be able to help them come up with the same answers, but are usually impressed with how direct/simple/obvious the features are in Aspire that gets them the answers they need.

4D

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