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General Mach Discussion / G2/G3 Inaccuracies, yet linear moves are dead-on.

« on: October 04, 2021, 11:06:07 PM »

Backlash is the first culprit to suspect when you attempt to mill 1" diameter circles and get slight ovals instead! 

however.... I've tested linear moves under load - cutting Positive and Negative direction and those are Dead On Accurate.  Even setting a dial indicator at the start of an X0 and Z-0.125 to X20 the back to X0 at Z-.25 cut or (y20 back to Y0) and the dial indicator shows the spindle returning to exactly the same spot within .001 or .003 at max. Good accuracy for my machine!   

But... whenever my Fusion 360-genearated G-code models use G2 or G3 commands, I get about .01 short of what the position of the arc end should be.   This appears to compound.  Meaning, cut a 1" circuit and you'll get an oval off by .01 in one direction (the X is short in both "semi circle mills).  Mill a 4 inch circle and the inaccuracy is now .04 off in the X plane. 

Can this be a SW issue?  (Fusion 360 Cam to Mach 3 driving a UC300eth attached to a CNC4PC C76 controller with Nema 34 Chinese motors/drivers.)

I've mathematically checked the fusion G-code. it's right.  That code is making arcs and circles with the correct ending location (on paper anyway)

How would I approach calibrating this type of "software backlash" and measuring it?

THanks!

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General Mach Discussion / All was fine, then Huanyang spindle started fluctuating in RPM. Cant find cause

« on: September 15, 2021, 11:23:40 PM »

There was an old post with someone saying they had the Exact symptom I have, but there was no solution.  I was working normally yesterday, but then when I ran the next job, I heard the spindle RPM fluctuating (pulsating) about +/- 400RPM swing according to the digital readout on the inverter.  ..about 1 cycle per second of audible change in RPM swing.

Setup:
Mach 3.  UCETH300 with CNC4PC C76 board.   2.2KW Huanyang spindle (110V) connected as per spec between the inverter and C76 board.

Arturo @ CNC4PC says he's never seen this issue before.  I discovered the 0-10V analog outputs on the C76 board dropped from what used to be a working 0-10v swing to 0-4.2V  AND  The Spindle started pulsating RPM.    Even though the voltage is not what it used to be when it was working, it does seem stable on my analog and digital meters. - so why the pulsating all of a sudden?

Tried a backup install of Mach3, same issue.  Arturo suggested trying Mach4 in demo to see if the voltage/pulsating persisted, but I spent 2 hours trying to figure out why M4 wouldn't come out of E-stop, so I haven't completed that test yet.

Anyone have a similar issue?   It seems to point to a hardware issue on the CNC4PC C76 BOB, but with the voltage "wrong but stable" I can't figure out why the spindle RPM isn't stable.   When run manually (J1 jumper to VR and PD001=0 and PC070=1) the spindle works perfectly and steady from the inverter panel controls.

Lastly, and most oddly, I'm also not witnessing the voltage to S<rpm> commands reversed.  S100 is commanding the 4.2V now, and S24000 is getting me 0V.  Linear in between.  This is causing the spindle to spin SLOW at S24000 commands and FAST at say, S100 commands.    All this just happened out of the blue and I can't figure out why.