New machine bogging down / missing steps

[James123]

Hello there,

I have recently got my machine up and running and im having problems with it bogging down and stalling the steppers.

The problem seems to mainly be on the x axis, though i think i may of missed a few steps on the Y. The X is driven by a 3.1Nm stepper direct drive onto mod 1 rack with 20 tooth pinion, the Y is the same but has 2 motors left and right. I skimmed the bed a few days ago and it seemed to run fine, then i tried cutting some plywood yesterday. The program i ran was quite large and ran for about 2 hours until it obviously bogged down and started to cut where it shouldent of, upon closer inspection it had missed a few steps earlier on in the program.

I made a simpler program today to do each part indivually but it bogged down on the deepest passes on the first part, then it stalled on the next part, i ran the program again and it stalled at the same point (as soon as it had to cut some plywood) i then replaced the cutter and it managed to get through it. I am using 4mm Chinese carbide cutters cutting 12mm birch plywood, 2.2Kw water cooled spindle at 12000 RPM, the passes were 4mm deep with 5mm on the 3rd pass to make sure it cut all the way through. the channels are clogging up as the extraction does not have enough suction to get deep into the channel and there only 4mm, i thought this was the issue and was hoping it would be ok if i switched back to 6mm cutters but then it stalled on a 8mm deep pass that was clean and open as it had a recess next to it.

Im not trying to do hard machining, i used 6mm cutters doing 6mm deep passes with my old machine with a wood router and it cut fine. The new z axis assembly and gantry are heavier than on my old machine, about 55kg now, so i am thinking that running direct with no gearbox may be the issue, but it seems to jog about at 6m/min and not loose steps, (im machine at 2m/min)and it ran the bed skiming program fine, so is it more likely to be down to the cutting?

Im a bit lost with this at the moment so i thought i would put a post up on the forum and see if someone with better understanding could point out whats going wrong.

Many thanks

James

[Blackrat]

The stepper is straight into the pinion with no reduction box ? Is that right ?

[James123]

The stepper is straight into the pinion with no reduction box ? Is that right ?

Yes there is is no reduction, im starting to think this is probably the problem, it seemed ok on my old machine though, but i guess the extra mass combined with hitting a hard bit of plywood could be enough. It occured to me thT the x axis is cutting accross the grain, and the y is cutting down the grain, which might explain why the y axis seems ok.

Cheers

James

[EddyCurrent]

I think you are running the spindle too slow, 16500 to 18000 sounds better, also the depth of cut seems high, and your feedrate is too high.
So I would try this to see how it cuts; speed 18000rpm, depth of cut (with 4mm dia.tool) 2mm, feedrate 800mm/min.
If that works okay you can try to increase the depth of cut and feedrate until it starts to fail.

. . .but i guess the extra mass combined with hitting a hard bit of plywood could be enough. It occured to me thT the x axis is cutting accross the grain, and the y is cutting down the grain, which might explain why the y axis seems ok.

Plywood has grain going at 90 degrees to each other in adjacent layers so there is no 'with' or 'across' the grain.

[James123]

Cheers Eddy, i will try that tomorrow, i used to run at similar feed rates (2-3m/min) with my old machine, when i decreased feedrate it started overheating cutters due to decreasing the chip load, as i had to run the router at full speed to get full torque, so ill start with the numbers you suggested and check the cutter for over heating, im just a bit wary of running too slow feedrate/ too high spindle speed.

TBH i thought i was taking it gently, i used to take 6mm deep passes with a 6mm cutter with a wood router, and this spindle is more powerful... But ill try it shallower. Ive not used 4mm cutters before and yeah 12000 is a bit slow if there smaller then the cutting edge is not moving as fast as a 6mm cutter would, add that to me running too slow and i recon that could cause the problem.

Yeah your right, i do know this i work with birch ply a lot, just my brains a bit scrambled today...it does cut more cleanly on the surface when you cut down the grain though.

Thanks again

James

[EddyCurrent]

Yeah your right, i do know this i work with birch ply a lot, just my brains a bit scrambled today...it does cut more cleanly on the surface when you cut down the grain though.

I just thought, if the depth of cut is the same as the thickness of one plywood layer then yes, there will be a grain direction.