Identifying and eliminating software generated chatter marks

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Identifying and eliminating software generated chatter marks

Postby Rcnewcomb » Sat Sep 05, 2009 7:28 am

Summary:
Get in the habit if creating a component that is the same size as your material. The component can have a thickness of 0.

Details:
Identifying and eliminating software generated chatter marks:
James Booth and Mark have talked about this in the past, but I thought I'd remind others of the steps to identify and eliminate software generated chatter marks.

Imagine that you are creating a plaque that has an oval dish as part of the design. For example:
Image

While doing the design I ran into an issue with software generated chatter on the border. Brian reminded me of the cure. I recall that James mentions this in his training videos.

So here is a refresher for those like me who have forgotten the cause and the cure of software generated chatter marks. I'll show the problem as well as the solution.

How to Create the Problem
1. Create a new project that is 24x18x1.25
2. Draw an ellipse 18x9 and center it in the project
3. Choose the "Create Shapes from Vectors" tool
4. Choose a Dome shape with an angle of -85°, Scale to Exact Height of 1"
Image
5. Make this into a component and close the Create Shape tool
6. Switch to the toolpaths tab
7. Select Create Finish Toolpath (the ellipse should still be selected)
8. Calculate a toolpath with a 0.25" ballnose at 8% stepover, raster strategy
9. Preview the toolpath
10. Zoom into the top of the ellipse and note the "chatter" marks.
Image

So what is causing the "chatter" to appear near the edge of the 3D machining boundary? Brian described the problem this way: Some of the near to edge points on the dish are below zero, as there are no points outside the dish, the tool can go a little lower at these points. A 'transparent' point is limited in height to the base of the material, so in effect you have a sharp vertical wall outside your dish. To cure the problem just model a plane for the material surface to subtract the dish from - this will ensure that the tool forms a clean edge at the material surface.

Allow me to paraphrase:
Imagine the router bit is like an ancient mariner sailing the known 3D world that was
defined by the ellipse. Beyond the ellipse is an area labeled "Here there be dragons".
Image
If the router bit sails too close to the edge it may fall off of the edge of the 3D world. The chatter is caused because the router bit isn't sure where to move since it has fallen off of the 3D world.

The Solution
The solution is to create a 3D plane that extends beyond the edge of the ellipse dish being carved. For example:
1) When creating a new project the first thing to do is create a rectangle the same size as the project.
2) With the rectangle selected choose the "Create Shapes from Vectors" tool
3) Choose the flat profile with a base height of 0.0
Image
4) Click Add
5) Make this into a component and close the Create Shape tool

Now create the ellipse and the dish component. This time when you generate the 3D toolpath you will not see the chatter marks that were visible before.
Image
- Randall Newcomb
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Re: Identifying and eliminating software generated chatter marks

Postby Tony Mac » Sat Sep 05, 2009 12:42 pm

Top tip and excellent explanation Randall.

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Re: Identifying and eliminating software generated chatter marks

Postby Phil » Sat Sep 05, 2009 1:21 pm

Rabdall,

thanks for taking the time to put the explanation together and post it.

Phil
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Re: Identifying and eliminating software generated chatter m

Postby tmerrill » Sat Sep 05, 2009 1:46 pm

Randall,

A most excellent post!

Your answer is very complete and stands on it's own. It will be a great post to reference people to when this question pops up again in the future, as we know it will. Thanks for the time and effort.


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Re: Identifying and eliminating software generated chatter marks

Postby Burchtree » Sat Sep 05, 2009 4:40 pm

Randall
Very well done. Now what we need is a place to keep top tips accessible.
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Re: Identifying and eliminating software generated chatter marks

Postby moto633 » Sat Sep 05, 2009 5:41 pm

Here there be Dragons :lol:
That is awsome!!
Great tip
Thanks!,
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Re: Identifying and eliminating software generated chatter marks

Postby GripUs » Sun Sep 06, 2009 2:21 am

Hey Gang,
You might check this out to see how to make nice clean sides. I think he may have some left but you would probably want to hurry.

Joe
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Re: Identifying and eliminating software generated chatter marks

Postby Greolt » Sun Sep 06, 2009 2:54 am

Yeah great stuff Randall. Thanks for taking the time to do a well set out tutorial.

I have not encountered this missing edges thing and I am not sure why I have not.

I just place the dished model. Put a vector around it to constrain the 3D toolpath and generate a toolpath.

I know that is not enough, but not sure why I have not seen the problem that always pops up on the forum and you are addressing.

Thanks again, Greg
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Re: Identifying and eliminating software generated chatter marks

Postby Joe Bloggs » Tue Sep 08, 2009 2:43 am

I guess I do not understand one part, which vector do you use to define you toolpaths? A large rectangular vector, or the oval vector that created the dish?
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Re: Identifying and eliminating software generated chatter marks

Postby tmerrill » Tue Sep 08, 2009 9:44 am

Joe,

It depends on whether you want to include the entire top in your toolpaths or just the dish. Whatever vector you have selected when you calculate your rough/finish toolpaths will become the outer border.

In most cases, to get the best edge quality you would select the vector you want to use as your boundary, use the Offset Selected Vectors Tool to extend that out by at least the radius of the bit you want to use, then use this new vector as your machining boundary.

Tim
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Re: Identifying and eliminating software generated chatter marks

Postby Rcnewcomb » Tue Sep 08, 2009 2:38 pm

which vector do you use to define you toolpaths? A large rectangular vector, or the oval vector that created the dish?
In this particular example it was the oval.
- Randall Newcomb
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Re: Identifying and eliminating software generated chatter marks

Postby Joe Bloggs » Wed Sep 09, 2009 3:25 am

so the large rectangular vector you made and set to zero and made as a shape then a component did absolutely nothing except lay the dish component inside the large rectangular component?
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Re: Identifying and eliminating software generated chatter marks

Postby Rcnewcomb » Wed Sep 09, 2009 3:44 am

did absolutely nothing
Well, it did keep the bit from falling off the edge of the 3D world <wink> :mrgreen:
- Randall Newcomb
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Re: Identifying and eliminating software generated chatter marks

Postby dr_when » Mon Nov 16, 2009 8:43 pm

Just curious why James Booth's demo when toolpathing the oval did not have "chatter" marks? In this demo the oval is not sitting on any plane as such. Or am I missing something?
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Re: Identifying and eliminating software generated chatter marks

Postby Rcnewcomb » Mon Nov 16, 2009 9:25 pm

Just curious why James Booth's demo when toolpathing the oval did not have "chatter" marks?
James talked about this at the users group. The short answer is that the software chatter doesn't ALWAYS show up. Adding the additional component that is larger than the 3D carved area takes care of it if/when it does show up.
- Randall Newcomb
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