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G98 Why is it necessary?
Posted: Wed Jan 19, 2022 7:04 am
by Black Forest
In watching Marty's video about calibrating the overall turns ration and backlash he stresses to use a G98 before moving the Z axis. Why is/are he/you using the G98? I looked it up but couldn't figure out why it was necessary. I am CNC challenged! I have never been a CNC operator and never played one on TV!
Re: G98 Why is it necessary?
Posted: Wed Jan 19, 2022 8:46 am
by centroidsupport
G98 specifies a feed rate in units per minute rather than in units per revolution of the spindle
Re: G98 Why is it necessary?
Posted: Wed Jan 19, 2022 8:48 am
by Black Forest
OK, I am trying to calibrate a metric mill so that is not necessary for me to use. Thank you.
Re: G98 Why is it necessary?
Posted: Wed Jan 19, 2022 10:28 am
by vw_chuck
It allows you to move your axis without the spindle turning when you don't have an encoder hooked up to the spindle for RPM.
Re: G98 Why is it necessary?
Posted: Wed Jan 19, 2022 11:03 am
by suntravel
G98 for lathe is different from G98 for a mill
Uwe
Re: G98 Why is it necessary?
Posted: Fri Jan 21, 2022 7:17 am
by centroidsupport
Though I should have said "G98 specifies a feed rate in units per minute rather than in units per revolution of the spindle"
I have corrected it.
Re: G98 Why is it necessary?
Posted: Fri Jan 21, 2022 8:34 am
by Black Forest
Got it. Danke!
Re: G98 Why is it necessary?
Posted: Fri Jan 21, 2022 1:16 pm
by cncsnw
A subprogram call is M98, not G98.
G98 on a mill specifies that, after a canned drilling/boring/tapping cycle, Z should return to the initial height it was at before the cycle.
But as has already been established, when doing test moves for axis calibration, backlash measurement, etc. you need G98 on a lathe control. You do not need any equivalent command on a mill control. Not even if you have a spindle encoder on your mill.
Re: G98 Why is it necessary?
Posted: Fri Jan 21, 2022 1:31 pm
by centroidsupport
Thx. Wasn't paying attention at 6am