cncrp truncation makes for drift?

[digitalcoleman]

Hello all. I have been running my cncrp 4848 10 hours a day for about a month now, giving it a good run thru. I recently switched from a smoothStepper to a parallel cable because of buffer issues with the smoothstepper causing long 4 hour jobs to cut out several times.
At any rate I have noticed recently that over a current 6000 inch long pattern I am cutting I am getting a drift on my y axis by about a 1/4 inch. At the end I do a cutout of the full design and have had to adjust that cutout to account for the 1/4. I also note that when I setup the next sheet, nearly every time I am recalibrating the Y axis by .22"
None of this seemed to be happening until I started using the parallel cable, but it may have been a fluke I didnt notice. I was looking at the steps/inch calculation provided by cncrp:

MACH Settings for R&P:
The R&P system is based on a pinion with a 1" pitch circle. The total linear distance traveled per revolution of the pinion is thus 3.14159". With the Nema 34 R&P 2:1 reduction, this means that the distance traveled per motor revolution is 3.14159 / 2, or 1.5708". If you have a stepper with 200 steps per revolution, this means you have 200 / 1.5708" = 127.324 steps per inch, or 0.007854" per step. With 10x microstepping (like in the G201x or G203V), you would have 1273.2 steps per inch, or 0.0007854" per step.

and wondered if the truncation of 1237.2 as opposed to 1237.24 could be causing the drift issue?
Does anyone have any other suggestions? The X axis seems to be staying much more calibrated....

[louieatienza]

You seem to be losing steps. Have you tried lowering your rapids or acceleration a little to see if it helps?

[digitalcoleman]

Hmm. No i have not, I figured with Nema 34 and ppl talking about crazy rapids on this machine, it wasnt much of an issue. you mean the rack and pinion might be jumping track? I think my rapids are set at 500 with acceleration at 12 or so. I could also tighten the spring on the y axis rack and pinion tension, as it is looser than the ones on the x axis.
Thanks for the tip...

[freecncplans]

I would tighten the springs more and double check the pinion set screws. I had one come loose and it was only slipping in one direction. It wasn't by much and it seemed to accumulate over time. I would check mechanical first.

If it was the steps per inch setting, it would come back to the same place every time at the zero wouldn't it? I believe it is something else.

I would swap the x motor and wiring with the y axis if mechanical and wiring seems to be good and connected good. If that doesn't fix it, try changing the x and y axis outputs and wiring. That should confirm a computer issue.

Sean

[freecncplans]

I run rapids at 2,000 and accel at 50. You should not be losing steps per inch at those settings.

I tightened the springs on my machine about tight as they can go. We cut 1/2" birch ply all day long and occasionally 3/4" birch ply, oak and pine and no issues so far.

Check to make sure you don't have power cables running along the motor wires. Could be interference as well.

Sean

[digitalcoleman]

Sean, I will look at the set screw for sure. I do have the A/C cord for the router running thru my cable management with the rest of the cables, but they all seemed to be well shielded...

Thanks for the tips, have to dig in and do some more fine tuning.
Chrid