Mach3 DRO seems to read differently than actual (Not Missing steps)
I’m running a custom setup, PoKeys 57CNC control board with mach3. When trying to enter g01 commands via MDI, the dro reads innacurately from actual movement. I can do a “g01 z-0.1” and using a digital indicator can confirm it comes within ~0.002” of 0.1” of movement. However, mach3 will read up to 0.06” off of the accurate measurement.
Additionally, if I enter the same command multiple times, mach3 will get closer each time until finally accurate (it might overshoot by 0.04, then after entering again overshoot to -0.03, then on the third time read something like 0.001)
My question is, what might be causing the DRO within mach3 to read differently from what pulses were actually sent? I was under the assumption mach3’s dro got its reading based on these pulses, so it makes no sense to me that it would read innacurately while the machine itself moves accurately
Thus far:
- making changes to exact stop/CV mode makes no difference
- Changing acceleration makes no significant difference (it normally sits at 45 in/s/s. Changing it to 10in/s/s or 80in/s/s didn’t change anything)
- Using g00 vs g01 makes no difference
- Using a slower feed-rate may improve accuracy slightly, but its still off by as much as 0.03” at 6 ipm which is way out of tolerance
- changing my microstepping (both in motor tuning and on my drivers so that it still moves ~1” when told to) makes no difference (currently running at 6400 steps/in)
Re: Mach3 DRO seems to read differently than actual (Not Missing steps)
Mach and pokeys have no idea how far your machine moved. Unless your using closed loop steppers. You need to carefully calibrate each axis. Calibration means it moves an exact distance for a set number of pulses sent.
there are a lot of suggestions how to calibrate in addition to the Mach manual.
Beyond issues with backlash and deflection you shouldn’t see a difference between DRO and actual movement after calibration.
Btw if your drives are set to a low resolution it won’t exactly hit the distance requested.
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Re: Mach3 DRO seems to read differently than actual (Not Missing steps)
What ballscrews are on the machine?.
For instance, If they are C7, Unless they are double nutted you've got no chance tbf.
Single nut are all over place with accuracy.
Next is bearings Standard deep groove bearings make it worse still. These need Angular contact ones.
The rest is as Dean448 said. Learn more about fine calibration techniques.
But, the values you've mentioned leads me to think your machanics are looking a little bit grim.
I have a mill that I've fiddled with on and off. That has gib ways which are set fairly light. The below is what I found.
When I had single nut C7 I found 0.07 to 0.1mm variations (0.003-0.004").
With Double DFU C7 I found no more than 0.07mm variations (0.003").
With a bit/lot of work and patience in packing the DFU I'm now at a maximum variation of 0.04mm (0.0015").
With the DFU packed though, I'm limited with rapid speeds due to tension. 2800mm/min (110ipm).
Thiese values are with AC bearings also fitted to the ends.
Re: Mach3 DRO seems to read differently than actual (Not Missing steps)
Quote:
Originally Posted by
Dean448
Calibration means it moves an exact distance for a set number of pulses sent.
Do you mean calculating my steps/in, or is pulses/distance a different beast entirely?
To clarify, when I tell the machine to move 1", it does (I've verified this with an indicator) which leads me to believe the machine is calibrated. For some reason though, when the machine moves 1" the DRO within mach3 reads something like 0.96". The DRO in mach3 is inaccurate, while the machine itself is moving to within ~0.002" of the commanded distance
Re: Mach3 DRO seems to read differently than actual (Not Missing steps)
Got it. I’ve never heard anything like that. You move it an inch and it moves .960 on the DRO but the machine actually moves an inch. I wonder if it’s worth trying a different version of Mach. Also post the question on the Mach forum.
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Re: Mach3 DRO seems to read differently than actual (Not Missing steps)
Quote:
Originally Posted by
Dean448
Got it. I’ve never heard anything like that. You move it an inch and it moves .960 on the DRO but the machine actually moves an inch. I wonder if it’s worth trying a different version of Mach. Also post the question on the Mach forum.
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I was thinking that too.
I've been rebuilding my electronics and noticed I was using version 043.066. I had a spindle speed difference on dro for ages of around 3%.
I've freshly installed windows and version 043.062 and it's fixed it. (The version that is the final).
I'll be using both mach and uccnc depending on mood. I have the licenses so may as well.
