Hi,
I am working on my first 3D milling wood piece. The 3D model is a concave fruit bowl, with multiple concave parts to it.
I'm using a stepcraft 840 machine, with a MM-1000 spindle.
The first settings I used were:
8mm, 3-flute bit
30% stepover
Pass depth 4mm
12000 RPM
15mm/sec feed rate
10mm/sec plunge rate
machine allowance 0.5mm
ramp plunge 5mm
The program settings were a 'roughing pass' for the 8mm, and I also have a path for a smoothing with a 3mm bit.
Once the job started, at first it went well, but then I noticed it was a bit jumpy as some spots, so I thought to raise the RPM.
I raised it to 16000.
The I thought it might be good to lower the feed rate, so I lowered it in UCCNC to 60%, which makes it 9mm/sec.
But at this point, the bit was strangely waaaay too deep in the wood, kind of double the depth it should have been.
Then quite quickly the whole piece jumped, I think because the wood touched the shank of the 8mm bit, because it was too deep in the thin cut it made in the wood.
The questions are:
1) Are the feeds and speeds I set wrong?
2) After this fatal error, I would take out the 8mm bit from the spindle by hand.. so I think the collet is broken... how can I check and make sure if that's the case?
3) How is it possible that the spindle went down to a Z of more than 4mm, if the pass was set to 4mm? (the first few cm of top-surface were cut to 4mm, but then it went down further without completing a first pass).
4) There was literally a hole straight through the spot where it jumped. Only by chance it didn't go through the entire 38mm. It's not supposed to go any deeper than 20mm into the material, more or less, according to the file.
I would really appreciate any help and insight to prevent this from happening again...
Thanks!