Where did I go wrong?

Trying to make a mold, cutting into this Renshape 460 competitor called Precision Board - it’s pretty cool stuff, by the way, and mills beautifully - I’ve got the 48lbs per square inch board. You can control whether your mill produces dust or chips, just by tweaking the speed vs feed.

The roughing went very well, using a .25" bit I got from Harvey Tools. A bit noisy, but I assumed it was due to the slightly lower RPM and Higher Feed rate I chose, in order to produce more chips than dust.

Switched bits, to a 1/16" long-reach end mill from Harvey Tools - 952062. It seemed like it was working well. I watched it do a few Finishing passes on the mold walls, and happily went outside to do lawn things, at which point the Nomad proceeded to eat the workpiece, as you can see in the photo.

Note that I measured the distance between where it was creating the shapes and where it was meant to, and it was getting increasingly off as it went along. Does this indicate anything?

Where did I go wrong? Speeds/Feeds too high? There were a bunch of larger shavings in there when I stopped it, is it possible that the toolpath caused it to not fully destroy all the material in one of the channels, and it got hung up on a large chip or something? Is there a way to make MeshCAM create toolpaths that wipe out all the material in a cavity, instead of just cutting the outlines?

Any thoughts will be appreciated!

Note that it was not a case of the Collet hitting the side of the mold - I learned that lesson already, it’s why I was using that long-reach cutter.


Tool Definition:

Waterline Toolpath, which looks correct:

My guess would be that your stock moved during the cut - or - your long reach bit deflected too much and caused the nomad to skip a step, which threw off the zero and caused a problem from that point on.

I say this b/c I’ve been having problems cutting with a .250" cutter - it’s long and sticks out of the spindal ~2", even when I bottom it out in the collet. For no apparent reason, during my cuts with the 1/4" cutter it skips a step and ruins the job. I was thinking of getting a 1/4" cutter that has a shorter shank, so I can stick it further up in the collet.

Can you include a picture of your tool? Does it have a tapered shank?

Also, can you include a view of your tool-paths? You may have had a rapid move that went through your stock, if your actual stock and your representation of the stock in MeshCAM weren’t well aligned. After a rapid crash it could be off by a substantial margin…