CC - 'Stock to Leave' on 3D finishing passes

I find on softwoods like cedar, that I often get very small but still noticeable tearout when running the 3D finishing pass.

To help with this, I have been running two passes, one at 15 deg and one at 0 deg. The first one is my ‘rough’ finishing pass (removing almost all the stock remaining after the actual 3D rough pass), and the second is my real finishing pass. Because of the tearout, I have found that lowering my Z very slightly for the last pass (on the order of 0.1mm) greatly improves the finish.

Rather than faffing around with my Z, I would like to be able to specify ‘Stock to Leave’ on the first finishing pass, just like on the rough pass.

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A work-around for this would be to define a second-pass roughing tool which has a Depth per Pass greater than the stock thickness — after the normal 3D Roughing toolpath, create a second with this tool which should then cut in a single pass, but should leave the desired uncut thickness.

Will, that only cuts the bottom level. i.e. the deepest areas of the 3D surface.
In this case, it only cut the level at the bottom of stock, and didn’t cut any of the 3D model

That should only happen if the stock thickness and model thickness differ by less than the stock to leave.

If that’s not the case, upload the file.

OK, here’s a simple example

He’s talking about removing the peaks (Red) to get closer to the finished surface but still leave some stock. Kinda like a semi-rough or semi-finish operation.

This is 1.75 tall, 0.75 base, 1.0 curved contour
If I copy the rough operation, change the stock to leave to something smaller, and set the DOC on the tool to 2", it cuts nothing. If I set the DOC to 1", it only cuts the top of the flat (Blue).
If I set it 0.5", it cuts one pass 0.5 deep, then the top of the flat area only.

File too big. But you can duplicate this in a few minutes.

Ideally, what he wants is a new toolpath type, “Semi-Rough” that would do a contour on each level instead of a pocket. Then you could set the depth of cut smaller, still have “Stock to Leave”, and not waste time cutting air. (Z-level profile in NX)

What he’s asking for would be more like a semi-finish, that just adds some stock to leave to a finish pass. You could run this with a larger stepover, but still remove the steps from the roughing pass.

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I think for my purposes, what you described as ‘semi-finish’ works better than the ‘semi-rough’. I don’t think that the ‘semi-rough’ followed by the finish pass would minimize the tearout I’ve been getting.

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Tear out on softer woods is hard to fix.
Case in point, the Halloween boxes that are the fade. I was breaking off fine details. I solved it with soaking the Cedar in Linseed oil for a while. There were still problems, but it reduced my issues. If soft wood is dry, it is going to tear out or feather.

Good Luck

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Rough path for reference…

Here’s a semi rough


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And here’s a semi finish with the same stock & stepover

image
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Both get the stock down close to the finished surface.

For giggles, here’s a mixed cut that uses the semi-rough (Z-level) for steep areas, and the semi-finish (zig-zag) for non-steep

image

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Another possible workaround…

The problem with just adjusting the Z is it just moves the toolpath straight up, which leaves your finish stock on the flatter areas, but not on the steep areas.
To get an even amount of stock everywhere, you could program the path with a slightly larger tool, increasing the tool radius by the amount of stock you want to leave. So in this case if you’re using a 1/8" ball and want to leave 0.1mm (0.004"), increase the tool from 0.125" to 0.133".
So you program with the 0.133", and actually cut with the 0.125"
When you set your Z for this tool, you need to set Z zero 0.004 above the zero height.
Coincidentally, the thickness of a standard piece of paper is 0.004" :wink:

image

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