Double sided job problems vcarve

I am trying to do my first double sided job, some simple hold downs. I have it indexed with dowels but the bottom side job doesn’t work right. It seems to jam the z axis carriage and then loses zero.
setup shot

at the end of the milling the recess on the bottom it did this.

went all the way through the side of the board and raked across the spoilboard. Yikes.

this is the toolpath settings

Must admit I am confused by 2 sided machining and don’t want to destroy my machine.

sorry my posts are so haphazard

I’ll admit I’m always a bit confused by the “Zero off the same side” option, but I have a feeling that may be what caused this. For the bottom side, you’re supposed to zero off the wasteboard, for the top side you zero off the top of the material… I think. I usual use zero off the surface and take the check mark out of “zero off same side”.

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Yeah it looks a bit like it returned to a predefined point (maybe your machine zero) at the end of the job, but didn’t lift up high enough…

Can you confirm you zeroed off the correct point? And also check your ‘z safe height’ on the tool path page, put it to at least the material thickness + 1"

I find that having ‘zero off same side’ selected, and having the top of the stock as the zero works well, then when you flip the material you zero off the wasteboard for the second operation.
If you don’t use ‘zero off the same side’ then your material thickness has to be very accurate

good suggestions, the zeroing is probably my problem. Hard to experiment when its seems to go so wrong. Will proceed cautiously. Don’t find the “Zero of the SAME SIDE etc” discussions on youtube very comprehensive in concept. It’s one of those things that is great if one already know how to do it.

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My z zero in the material setup in the tool paths was .96 but should have been 1.75 if I have .75 material right?

I am no expert at all on this, I have only done simple tests to prove the concept so please bear that in mind…

Also I’d get a few bits of pine or plywood and just run the same job or a similar example until you’ve got it sorted out, just to save on wasted material

I’m not sure what ‘z zero’ you’re referring to in your last post, this is the Job setup page I use for double sided job (sorry for the metric… I’m Australian)

And the corresponding material setup page in the toolpaths tab.

There should be no offsets required, or any input of your material thickness other than in the material setup page

so i just tried to zero off the same side and the first side cut all the way through on the first pass and I stopped it. What happened there.

:roll_eyes:I did not set the z zero to the bed when I set “material surface”. Found that very confusing. Kind of gun shy now but will try that on some more material. Just take off the material I guess , set zero to machine bed and then flip and put back on.
For now I just skipped the 2nd side for my hold down project in 3/4 uhmw plastic because I had no trouble on the first side before I flipped.

Feel free to email your part file to me at and I can take a look? I found the 2 sided feature fairly intuitive but I may have just gotten lucky

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Haven’t gotten back to the 2 sided yet. One of the names I have for myself is “upside down and backwards” and I am really good at it. Takes me a while sometimes to get things right.

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