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Re: Jerky movement
Posted: Fri Jul 25, 2025 3:29 pm
by cnckeith
Farnsbarns wrote: ↑Fri Jul 25, 2025 7:23 am
Hi all,
I'm new here, and new to CNC, and new to any type of milling. Cue lots of broken cutters, etc, I'm sure.
I converted an old Bridgeport mill to CNC using Acorn and Centroid CNC12. I created some models in fusion. I created tool paths with advice from a few people and today I have made my first basic part (just an odd shaped block with some holes). I have done the first 2 operations which are clearing from top, flipping the stock, re-probing and clearing the bottom. It has gone very well. The part is within the desired tolerance with a reasonable finish despite very little dialling in.
However, I notice that the mill movement is slightly jerky, feeding a little bit, stopping, feeding again in ~0.5 second pulses. If I do a dry run with no stock the jerking stops.
I am using very cautious feed rates and step overs at the moment (100-200mm/min and 1.2mm step over with 5mm step downs. The stock is ally and I'm using a 12mm 3 flute cutter.
My acceleration was set to 0.5, tried 0.3 and it was worse. 0.6 seems about the same and if I try to set it any slower Centroid CNC says this is atypical and suggests I don't.
Can anyone offer any advice or insight?
Thanks in advance.
please post the g code you are running.
Re: Jerky movement
Posted: Fri Jul 25, 2025 3:30 pm
by cnckeith
what steps per rev to you have the stepper drives themselves set to? need lots of photos and more info to help you!
Re: Jerky movement
Posted: Fri Jul 25, 2025 3:47 pm
by Farnsbarns
Each axis has a 6A 60v DC power supply. The motor controllers are CL86T...
https://www.stepperonline.co.uk/closed- ... VuuIj7-eR4
And these are the stepper motors.
https://www.stepperonline.co.uk/p-serie ... k-120.html
I'm all but certain power isn't the issue. My brother's setup is almost identical but with a 4th axis. And weirdly, all on the same circuit in a unit which is divided up with some plywood walls, but it's all the same power and the same setup.
I'll do a copy pasta of the G code, probably be tomorrow now, I've had a beer. I'm leaning towards that being the issue. I'm not new to modeling but milling tool paths are a little bit new to me.
It also occurs to me the pulsing is quite subtle. It may be happening with no load but not be perceivable.
If I get that far with no solution I'll make a video of what's happening. That'll tell a lot more than me describing it.
Re: Jerky movement
Posted: Fri Jul 25, 2025 3:50 pm
by cnckeith
attached the file, not a copy paste.
what steps per rev. do you have the drive dip switches set to?
if you have the motor wiring with a phase flip it would act like your descriptions as well.
Re: Jerky movement
Posted: Fri Jul 25, 2025 3:53 pm
by cnckeith
thanks for the photos. you have the cl86t's wired wrong.
follow this schematic.
https://www.centroidcnc.com/dealersuppo ... 207.r1.pdf
Re: Jerky movement
Posted: Sat Jul 26, 2025 6:17 am
by Farnsbarns
What are you seeing that's wrong? If it's the three alarms in series instead of in parallel, that's deliberate. I was advised to do that and I know of 3 other machines built that way that aren't moving with this pulsing.
If there's something other than alarm channels I'm missing it, could you elaborate?
Re: Jerky movement
Posted: Sat Jul 26, 2025 6:50 am
by avp
Those drives need to be wired to the DB25 connector. Your photo shows them wired to the headers on the board.
Re: Jerky movement
Posted: Sat Jul 26, 2025 8:19 am
by suntravel
Yep, wire to DB25 and use shielded cable with the shield on one end to common GND
Uwe
Re: Jerky movement
Posted: Sat Jul 26, 2025 3:00 pm
by cnckeith
Farnsbarns wrote: ↑Sat Jul 26, 2025 6:17 am
What are you seeing that's wrong? If it's the three alarms in series instead of in parallel, that's deliberate. I was advised to do that and I know of 3 other machines built that way that aren't moving with this pulsing.
If there's something other than alarm channels I'm missing it, could you elaborate?
please look at the schematic i attached.
Re: Jerky movement
Posted: Mon Jul 28, 2025 5:00 am
by Farnsbarns
Thanks for all the suggestions. I'd forgotten that we'd gone for the 24v configuration for the motors (actually built this last October) but that's within the spec for all components and 2 machines previously built identically don't suffer the same problem.