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routercnc
28-12-2015, 10:59 AM
I have analogue drives (DQ860MA) and when switching on there is a thud from the steppers depending on how far they are away from a whole step and the ballscrew rotate slightly. Normally this is fine as I home the machine etc. but on a recent job I was surfacing a part and had to stop part way through. I wanted to keep the Z height exactly where I left off so I attached a DTI to the Z axis switched on (which moved the needle slightly) and then I jogged it back to zero.
Out of interest is there any way of knowing before switching off how far the stepper is from a whole step? I know some drivers have the feature of remembering which micro step they are in but is there any other way of knowing using the drivers I have now?

Clive S
28-12-2015, 11:42 AM
I would have thought that if you saved the fixture in Mach as you was shutting down then on restart homed the machine it would be correct.

JAZZCNC
28-12-2015, 12:30 PM
Nope without the phase feature of the drive then it's not something easily done. Thou if you use the Enable of the drives then some times it can help or remove the twitch.!

Best way is like clive suggests. Either save the Work offsets or write the Z axis position down and return to it after homing. It wouldn't be hard to knock up a on screen button to save the Z axis current location and another to return to it if required. Personally I'd write it down then use the MDI if need an exact location.

routercnc
28-12-2015, 01:07 PM
Good info thank you - confirmed my suspicions
On this occasion I was trying to get the most accurate position so used the DTI to be extra sure!
I do normally write down the machine coordinates of the work origin as I've never got the save fixture on mach3 exit to work. Maybe I'm doing it wrong but when I switch mach3 on again the numbers in the DRO appear random.
So I home the machine, MDI to the previous coordinates then zero the DROs.

JAZZCNC
28-12-2015, 01:16 PM
The numbers will appear random until you have homed. Then when you push go to Zero it will go back to XYZ Zero offset in work coordinates or if you type in the exact coordinate you finished at in mdi it will go there.

Maybe your misunderstanding the Work Offset.? It doesn't save the exact location you turned the machine off at. It only saves the Work Zero offfset in relation to Machine coordinates. This is why you must home first. Then you can go to Work Zero offset or any location you type relative to Work Zero.

routercnc
28-12-2015, 02:36 PM
Just tried it and it works! I was expecting it to pick up where I left off it doesn't work like that - homing and mdi to zero and I'm back. Part of my problem was that I often don't home the machine especially for small jobs

Clive S
28-12-2015, 03:08 PM
Part of my problem was that I often don't home the machine especially for small jobsIt takes less than a minute to home and whatever if you don't. its a no brainer !!

JAZZCNC
28-12-2015, 03:09 PM
Just tried it and it works! I was expecting it to pick up where I left off it doesn't work like that - homing and mdi to zero and I'm back. Part of my problem was that I often don't home the machine especially for small jobs

It's a good habbit to get used to homing the machine when first turned on. Most industrial machines won't do anything until the machine is referenced home.

If you did want to save the location at shut down then it wouldnt be too hard to knock a script up which did this. Then have button to take you back after homing or even include it in the Homing script. (thou not good idea.!)