z axis loosing steps

[ptjw7uk]

Hi All
Got back to playing with my cnc mill. Tried to do some engraving but as the engraving proceeds accross the x axis the cutting depth gets greater so I assume the z axis is loosing steps.
How is one supposed to test for this, I think I should try a dial gauge.

Peter

[tribbles]

That sounds to me like the surface isn't parallel to the X-axis. Does the cutting depth get less when moving the other way around (just an obvious thing to check!)

You could also try locking the Z-axis somehow (so it won't move).

[ptjw7uk]

Problem is if you lock the z-axis you wont be able to do engraving!

peter

[tribbles]

Yes, but you can check if it moves up and down - it's only for testing.

[John S]

Reduce the acceleration what is happening is that the Z axis is losing steps on the way up so when it lowers it goes deeper into the work.

May pay to also reduce the microstepping as more steps, less torque.


.

[Robin Hewitt]

There is a difference between up and down.

Up can be the start of two consecutive G0's with a 180 degree turn in the middle.

A sort of worst case scenario for losing steps if you're accelerations aren't quite up to scratch.

[ptjw7uk]

so what should the acceleration be!
I thought more steps was better, obviously not.

Peter

[John S]

Unfortunately no one can tell you as it's all machine dependant.

You need to alter the settings and try it under power.

Replace the tool for something with a flat end [ reverse the cutter ? ] and then get something like a 1/2" roller or just a piece of short scrap.
Put that under the 'cutter' and zero onto it. Remove roller and move head up and down a few times and see if the roller will roll back under when it's in the down position.
This will give you a bit of leeway for it to move without clouting into any work.

.

[Owen.gray]

sorry to say but most reliable answer to this prob is to get a bigger stepping mottor for that axis

[irving2008]

which is what Peter did. however bigger motor isnt always the solution to losing steps... could just have been too high an acceleration rate, or he could have supported the motor with a spring or pulley/mass system to balance up and down movements