New machine bogging down / missing steps

[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.

[James123]

I ran it today and cut a few more parts at 18000rpm, 1500mm/m feed rate and 2mm deep passes and it didnt miss any steps, ill finish it off tomorrow at 3mm deep and see how it does. It might just be that the plywood is really hard due to the cold, its not been much above 0 degress in my workshop for about a week now.

[EddyCurrent]

Sounds good, maybe you should invest in a wood burner, this is the one I use and it's great; http://tecnikstoves.co.uk/8-kilowatt-stoves

[JAZZCNC]

Give us some more info on system like motor wiring parallel or serial, voltage, micro stepping etc drives are running at to get better idea of system.

But still your going to want a ratio applying as 20t pulley direct drive means 63mm pitch which is way too high really and torque low so any stiction will have an affect which is why your bogging down. (2m/min shouldn't be a problem in plywood)
If you use 3:1 ratio you'll triple the torque and put the motors in an rpm range there more happy running and still get decent rapid speeds, well in excess of 10M/min.

[James123]

Ive cut more pieces today and had lots more missed steps on the x axis, i then realized the pinion was completely free on the x axis. The pinions are held with 2 M3 grub screws, one tightens onto the flat part of the stepper shaft. I have ordered some M3 cap head screws so i can get more tension into it, with the little grub screws i couldn't get that much tension into it as it was bending and twisting the hex key, i think this is the issue as it would also explain the small amount of missed steps i am getting with the Y axis, theirs 2 motors on the Y so if one came loose it would still be driven by the other.

Thanks Jazzcnc, The steppers are all wired in parallel, the supply voltage is 36V and i think i left it on 1/16th micro stepping in the end, Its not very smooth though you can really hear it when it accelerates and decelerates, I think im going to go for some reduction, ive been looking at the pulleys on CNC4YOU and i could get 3.333/1 ratio with a 15 tooth on the motor and a 50 tooth on a shaft to my 20 tooth pinion. What do people use for a shaft? Will M8 threaded rod work or should i go for some 8mm aluminum rod and tap one end to mount it onto a bearing? I think it should be possable to modify what ive already done and add in some reduction, ill try and work it out and do some drawings.

Yeah those stoves look great Eddycurrent , youve got me trying to think of ways to get a flu through my plastic roof... the problem is with my workshop is its got very little to hold the heat in, I think im just going to have to live with it for this winter at least.

Thanks again for your help guys!

James