Weird depth of cut issue

Hey all, I’ve been using my shapeoko pro for about a year and half now, and lately have had some issues with depth of cut.

For this file, the max DOC is 0.08". Using an advanced vcarve my 1/8" endmill hogs out the full 0.08" in a single pass, then my 60° groovee endmill completes the 0.08 in two passes (0.06 then to 0.08). I have attached pictures showing my dilemma. Basically I end up with an unwanted line around the perimeter. It does not appear every time I repeat this cut. It also does it on other files I repeatedly cut, sometimes it is prevalent sometimes it is not at all. I hhave attached a finished piece that does not have this issue, cut from the same file and bits. Has anyone come across this issue? Please help!

Modify the Depth per Pass of the 1/8" endmill so that it makes multiple passes where the last one removes only a small thickness of material, e.g., if cutting to a depth of 0.5" w/ a Depth per Pass of 0.125" and making four full-depth passes, reducing that to 0.124" makes for 5 passes, the last of which removes only 0.004" of material.

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This maybe remedy the issue… However I have other files where my DOC is .125… for those I use multiple passes using the 1/8 and typically end up with the same issue but the results are sporadic from piece to piece. Same file, different results. This is what is perplexing to me.

Also, the line it creates is very crisp and uniform.

Initially I thought it could be a discrepancy between the 1/8 and 60° however where the line appears in the end; it is too far from the edge for that to be the case.
I also thought maybe my plunge rate is too agressive but at 30 for mdf I dont think that is the case, also there is only one initial plunge when I have a single 1/8" pass.

However, to troubleshoot I will try this technique shaving just a little bit on a final pass and report back.

Thanks again Will!:pray:

Another thing to check for is workholding or the stock warping due to internal forces.

Is your 1/8” clearing bit a downcut?

Check out this link:


I thought about this at times, whether my holddowns are relitively even pressured from piece to piece and I believe them to be.

Spoilboard has been resurfaced recently to remove as possibility

As @WillAdams said, internal forces can mess up a dream. I have even had an MDF warp while cutting. The areas supported by thick material don’t warp, whereas the thinner areas do. Moisture content that is hard to control, will get you.

Good luck

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Yes it is! One minute in and I was confident the video would explain the issue.

I typically have done 2 passes with the 1/8 but never an extremely thin second pass. This was a cool video that is right up my alley to understand the engineering as to why the line is created. Invaluable information and a good watch!

Thank you for sharing @CullenS :pray:

I see your problem very clearly. You are making the Buffalo Bulls. That is the problem. Your machine is a fan of another team. :crazy_face:

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No offense here, you are probably right😅

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