New machine bogging down / missing steps

[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

[mike os]

Although I have limited CNC, I am generally considered fairly expert when it comes to wood...., my thoughts on the above

rule of thumb for cutting wood... depth of cut never greater than cutter diameter, to a maximum of shaft diameter... so 4mm = max 4mm cut, for say 10mm with 1/4(6mm) shank = 1/4 etc.... obviously this is a catch all and can be pushed, but with this you will generally not break tooling, burn material or blunt tooling with rubbing, damage collets, and allows for better chip clearance.... although at less than 6mm this will often be an issue with cuts more than 2x dia. and up to 1/2" at more than 3x dia deep

cutting speed is crucial with small cutters, at 4mm I would be running nearer 30000rmp and adjust depth and feed to suit... ie shallow & fast

[Blackrat]

ooer ... i cut 10-12mm with a 6mm bit , maybe i should lighten up a bit :D

[EddyCurrent]

cutting speed is crucial with small cutters, at 4mm I would be running nearer 30000rmp and adjust depth and feed to suit... ie shallow & fast

You'll probably pay a premium for a decent size spindle to run at this speed, mine can run at 24k but it was quite a bit more expensive than the 18k model.

[mike os]

24k is not bad tbh... more in reference to running at 12k.. :-)