Z-axis problems (backlash/lost steps? Im new to this)

[Moesian]

Hi everyone,

Ive recently bought a taig mill that ive converted to cnc. Ive finally got round to cutting some parts on the machine, however ive run in to a problem thats concerning me. Im peck drilling some holes in 6mm aluminium, it works fine for the first couple of holes, but after a while the z-axis zero point seems to get progressivly higher. Also after running the sam g-code a few times this holes first made seemed to become slightly elongated along the y-axis, is this perhaps a related problem?. Im using a xylotex board, mach 2 and the 1/4inch 180ncm shaft steppers from arc euro trade.

www.arceurotrade.co.uk

If you've got any ideas on whats causing this, your suggestions would be much appreciated.

Thanks alot,

Roland

[tintruder]

Sounds like it's missing steps for sure:

Let's say the controller sends 1000 pulses "down" to move an inch.
Because of the missed steps, it only goes down .993" (equal to 993 pulses) then raises up 1000 pulses. Every time this happens, the resting Z position will be physically higher.

Sounds like you have a Y Axis issue too.

Depending upon your stepper drivers, you have a few options:

1. lower your feed rates and any rapid rates.
2. choose a different microstepping multiplier
3. adjust stepper drive to raise current to motors (if it is set too low)
4. check power supply for adequate voltage/current capacity
5. be sure the mill itself is clean, smooth moving, lubricated properly and gibs adjusted properly.
6. On the Z, be sure any "balance" issues like counterweights or gas struts are installed properly to make head motion as neutral as possible.
7. replace motors; http://www.kelinginc.net/ has really good prices on steppers. If you are using NEMA23 motors, he has a 425oz-in model for $54 (300oz-in if unipolar wired) that is probably stronger than what you have now.

Hope that helps...

Tom

[cartertool]

If it isn't the electronics, then it's an issue with adjusting the gibs, tramming, etc.
See here for some tips on mechanical alignment and adjustment:
http://www.cartertools.com/millset2.html