Thread: z axis loosing steps
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.
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).
Problem is if you lock the z-axis you wont be able to do engraving!
Yes, but you can check if it moves up and down - it's only for testing.
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.
.John S -
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.
so what should the acceleration be!
I thought more steps was better, obviously not.
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.
.John S -
Got back to my X1 mill and tried JohnS suggestion to reduce the acceleration. Tried a search on the web, not a lot of help so just winged it. Also tried JohnS suggestion about the spaced under the z-axis and it definately showed it losing steps on the up direction.
Thought some more and have now tried a dial gauge, and old one I have had for some time and never found a use for in that it works by pulling up the plunger. So I fixed the plunger rod to a chuck in the z-axis and proceeded to raise and lower the head, could not detect that much change but it did alter over 10 cycles, ie gets lower.
I then thought about the gibs and tried to adjust them, this has made it worse.
I also noticed another strange thing in that if I jog up or down using the slowest jog rate the dial gauge shows the head to move in the same direction for a few steps after I have changed direction?
I have read on the web that some have had problems with the head gibs saying that are difficult to set due the weight of it. I may now have to consider a counter weight system as for what I want the mill for a poor z-axis is next to useless.
How are you driving the Z-axis and what is the drive to the quill motion, a worm and rack or pinion and rack?
Putting in a counterbalance arrangement will aid in supporting the weight of the quill etc, but at the expense of adding more mass to move = lower acceleration for the same motor torque
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