[apt403]

Howdy all,

Have a 5x10 Pro router at work. Centroid controller (Acorn) with NEMA 34 ClearPath servos. Been having an interesting time trying to get the turns ratio dialed in.

Started from the information on the website:

PRO Rack and Pinion Drive, NEMA 34 | Avid CNC

pi/3.2 gear reduction = .9817" of linear travel per motor revolution. Centroid's software (CNC12) is setup in turns/inch of travel. Reciprocal of .9817"/rev = ~1.01864. That's what I used as my starting point, ~1.01874 turns of the motor shaft per inch of linear travel.

That number results in incorrectly sized pockets, however, so I indicated in a couple 246 blocks on the table with a test indicator and started adjusting the turns ratio until touching off on both sides of the block resulted in correct figures.

Here's the strange part - It's not consistent.

I setup a 10" stack with the 246 blocks (6" side butted up against the 4" side of another block), zero'd out a test indicator on one side of the stack, then zero'd again on the other side of the stack. Adjusting the turns ratio from 1.01874 to 1.02562 results in 10" being 10", however that's the only distance that's correct. Below is an error map:

6": 6.026"
10": 10.000"
13": 12.977"
16": 15.951"

I'm not sure what to make of this. There's definitely some inconsistency in the rack (moving the 246 blocks around the table causes a lot of variance), but the above numbers are all from the same localized area - I can't imagine the rack is that inconsistent over less than 2ft. And the same general sort of error repeats itself anywhere on the table.

There's negligible backlash relative to the numbers above, belt is tight as is the spring that pulls the pinion gear against the rack. ClearPath's smoothing algorithm is set to a minimum value (also tried turning it off completely, no noticeable change.)

Appreciate it,

- Apt

[Richmaple]

Are you sure your clearpath aren't missing step signals from the acorn here and there? I just set up an avid benchtop pro with acorn and clearpaths too and until I bridged the - and + of the step pins as per the tecnic instructions, I was missing steps.

Plug in the USB cable into your motors and make sure the counts they're reporting are the right number from your acorn.

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[Richmaple]

Also is this a new install of centroid? Make sure your ballscrew compensation is set to 0! It's settable at various positions which would explain the inconsistency you're seeing.

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[bphillip2]

Setting the steps to 6400 seems to solve the issue. We had the cnc12 and the motors set the same steps. The documentation says higher or lower steps than the actual encoder is fine, but in our case produced unexpected results. No lost steps, just Inconsistent Linear Motion.

Also is this a new install of centroid? Make sure your ballscrew compensation is set to 0! It's settable at various positions which would explain the inconsistency you're seeing.

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