um values - could someone explain please

[NickWL]

Could someone tell me - in very few words - what an 'um' value is and why I should need to know about them.
Please...

[NickWL]

I can only assume that the silent response means I don't really need to know about them (since - I suspect - no one else does either!)

[Stephen6309]

It's basically the steps the motor needs to move the head a specific distance (like a millimeter).

[Greolt]

The AWC608 and other sister programs from China, use the distance travelled per step in micrometers. (um)

This is the "step value"

Most other step and direction motion controls I have seen use "steps per unit" as the step value. eg, 600 steps per mm

And so it can be at first a little confusing for those coming to these controllers from other CNC experience.

[NickWL]

Aaaah! Now I get it! Many thanks all.
Well - sort of, anyway.
'Distance' is an odd concept when dealing with rotation so I'm going to guess that it refers to belt travel. I suppose it's not that important as long as I know that jiggling it will affect the distance travelled by the business end.
It also explains why I'm having trouble with scaling.
Oh, isn't learning new stuff SUCH FUN!!!!

[Greolt]

'Distance' is an odd concept when dealing with rotation so I'm going to guess that it refers to belt travel.

It is not how much the motor rotates but rather how far the axis moves.

Yes I know how far the axis moves is dependent on how much the motor rotates, but we need to think, "how much does the axis move per step"

That axis may derive its movement from the motors rotation via ballscrew, belt, rack & pinion, etc.

Unless of course we mean a rotary axis. But that is a whole new subject on its own.

[NickWL]

Thanks for that.
However, I'm finding that no matter what I do to the um value there is no change in the length of a 'printed' line. My 100mm line ALWAYS comes out at 98.5mm.
Frustrating! I'd kill for a copy of a .cf5 file from someone who has got a DSP'd K40 running smoothly (that is a great big HINT!!)

[Greolt]

However, I'm finding that no matter what I do to the um value there is no change in the length of a 'printed' line. My 100mm line ALWAYS comes out at 98.5mm.

Read, then change um value and Save, then Reset.

Then re download the 100m line and try again.

Try a very large um value. Say twice what it should be. Then see if you get a different result.

That will at least demonstrate that changes are having an effect.

[NickWL]

changed x-um from 9 to 20, saved, OK'd and reset.
My 100mm line is STILL only 98.5mm long.
What am I missing?

[Greolt]

Did you "read" again to see if the um value change registered?

I have no other explanation than that you must have missed a step. ☺

[NickWL]

Still waiting to try these solutions - blew my ammeter (don't know how) - it doesn't stop me firing the laser but without a readout I don't want to risk damaging the already fragile K40 tube.
Patience is a virtue....
(but not easy!)