z axis loosing steps

[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.

.

[ptjw7uk]

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.
Peter

[irving2008]

Peter,

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

[ptjw7uk]

Direct drive to ball screw moving the whole head.

Peter

[irving2008]

Well ballscrews work both ways because of their efficiency.. so the inertia of the head is driving the motor and overcoming the motor torque. Its not the weight per se (although obviously the inertia is related to the mass of the head) but the overall inertia of the system - head, ballscrew and motor rotor that is the problem.

As a first indication what happens if you program some G-code to move the head down... stop for a while then move it up again... as opposed to changing direction on the fly... does it actually stop on cue, or overrun... if the latter there may be a solution in increasing the deceleration time or reducing the z-speed... which might suggest gearing the motor to the ballscrew to reduce the reflected inertia on the motor...

[ptjw7uk]

Not sure if overrun is a problem but the problem is more apparent if the program I wrote is just run, in step mode the error is small.
I have often wondered if the controller will allow for the steps to be carried out.
All in all I am surprised that this all works as in to get the max power from the steppers you have to step slowly and therefore max moving speed will suffer

Peter

[irving2008]

yes, steppers lose power the faster they go, but this is countered by using higher volts. but z-motion rarely needs high speed, so can afford to gear down and get better results that way

[Robin Hewitt]

Have you tried turning the screw and stalling the motor by hand?

That tells you what you're asking it to do and what it has to offer.

The problem may become instantly apparent :whistling: