Offset occurs during cut

I’m having an issue with my x-carve where my the machine seems to slightly offset during the job. I’m working on some wooden sunglasses, and I have a working prototype however this is the only issue. Here’s a picture of a sample piece that shows the offset in detail:

As glasses are symmetrical, each respective measurement should be the same on both sides. What seems to be happening is that when the spindle is done cutting the outer edge and starts to cut the inner edges, it starts slightly to the right of where it should be.

I made the design in Rhino 3d and created my tool paths in Autodesk Fusion 360, and send it out with Universal GCode Sender. I’ve checked my designs and they are perfectly symmetrical.

I’ve re-calibrated my machine about 1000000 times, tightened everything… pretty much rebuilt the thing, but still no luck. I’ve tried slowing down the feedrate of the cut, the surface speed (which I originally thought was the problem), everything.

Any suggestions would be GREATLY appreciated.

You should be cutting the inner edges or holes first, then the outer edge. Looks like your wood is floating after the outer edge is cut. You also need to add a few tabs to keep the parts locked in place.

Thank you for your suggestions!

However, this didn’t work. In fact, rather than wasting more veneer, I’ve been testing the cut on a 1/2" piece of plywood so there’s no risk of the wood moving during the cut. And yet, still the same results.

Youll have to systematically eliminate areas that could be the cause starting with the hold downs on the wood, the order of cut sequence, tabs, etc. maybe try using double sided carpeting tape for now to ensure the wood isnt the issue. if all those check out then look at your carriage for any flex, especially in the spindle. If you can bend the spindle head easily to and fro (x-axis bar) then you’ll need to strengthen.
Also double check your speed/feed rate. Average for me is typically 12,500 at 4-8 inches per sec.

Sounds good. I’m actually already doing a few of these things (mounting tape, stabilizing the spindle, etc). However I haven’t set the machine to cut that slow yet. What is the depth per pass you use at these settings?

And on that note, are there any good references for learning about speed/feed rates vs. depths per pass vs. material types? I can usually only find resources for milling metal, not wood.

My personal preference is to run the first cut shallow. Around .05 to cut through the first layer of ply veneer ( I use mostly Baltic Birch plywood). I also do a first pass on all parts first before running the remaining depth cuts.
I like to run 4 passes per 1/2" of ply minimum. Typically that is one more pass then v-carve defaults to.

I havent tried it yet but I’m planning to run a roundover bevel after the straight cuts are complete to avoid having to router my edges.

As for calculations on f/s there are several out there but I prefer to create my own based on daily usage and results.
One final note. If cutting dense materials like mdf you might consider changing out your bit after the first surface cut to keep it sharp for future jobs, otherwise edge sharpness will diminish quickly and you’ll get a lot of fuzzy edges.

If you’re cutting mostly sunglasses on 1/4" ply see what you can do to the surface to prevent chipping. It looks like you’re using underlayment ply which is cheap wood and have a very thin veneer on the surface that rips really easily. Maybe a spray coat of varnish or sanding sealer to seal in the pores if you are doing volume work otherwise you might get lots of rejects.