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Calibration/Steps per unit sanity check
« on: October 27, 2015, 06:13:01 PM »
Hello,
This is my first post. I have done a lot of research to get info but still have questions.

I have a plasma machine built and it is working. Speeds are fine but the accuracy seems off. Usually stops short.
It is a rack and pinion drive for the x and y. No reduction, direct drive.
The pinion is metric with a pitch diameter of 20mm and 20 teeth.
Looking at the recommended calcs, I have done the following:

3.14159(pi)x 20= 62.839mm circumference.
200 steps @ x10 setting = 2000 steps total
I want to use inch for the machine so I convert 62.839mm = 2.474inch
Then divide 2000/2.474 = 808.407 steps per inch.

As this is a direct drive it should be simple right? Or have I missed something major?
And would the "Calibration" button be better to use? Haven't seen to many recommending it.
So far the Mach3 program it's self is great. Just need to fine tune it a bit.

Thanks!


Offline ger21

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Re: Calibration/Steps per unit sanity check
« Reply #1 on: October 27, 2015, 08:34:01 PM »
Looks right to me.

I've never used the Calibrate function. My preference is to do the math and adjust as needed.
Gerry

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Offline RICH

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Re: Calibration/Steps per unit sanity check
« Reply #2 on: October 28, 2015, 07:46:15 AM »
Quote
And would the "Calibration" button be better to use?

I recommend that one calculate first and should be correct as noted by Gerry.
The calibration feature does work, is easy to use, to refine actual to calculated value.
Use a  long travel distance, make sure movement is measured accurately,  and remove any backlash prior to using using the calibration feature.

RICH
Re: Calibration/Steps per unit sanity check
« Reply #3 on: October 28, 2015, 09:52:11 AM »
That's great guys. Thanks.

I'm starting to wonder if I'm loosing steps in the travel. I don't have the E-chain hooked up on the x or y yet but I need to be sure there's no friction anywhere obviously. My "cars" are V-groove wheels from Bishop Wiscarver and they did seem to move freely before connecting the pinion gear.
Also, as this is my first machine and I have to deal with random electrical inspections, I chose to use 24vdc @ 13amp power supplies(I was warned by an inspector that they are getting get picky around the 36v mark now). Maybe not enough ommph?

Thanks again for your help. Will let you know how it goes.
Re: Calibration/Steps per unit sanity check
« Reply #4 on: October 30, 2015, 04:52:02 PM »
Ok, back at it again.
Unit works very well and consistent but, I'm an inch out on a 10 inch move- always stops at 9inches. The x and y are doing the same thing.
I've check my setup repeatedly and it's definitely 2000 counts.
At a bit of a loss at this point and would take any suggestions.
Thanks.

Offline RICH

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Re: Calibration/Steps per unit sanity check
« Reply #5 on: October 30, 2015, 06:48:45 PM »
So you use the calibration feature, you say move 10" and it only moves 9", so you input 9" and it calc's the steps per and asks if you want to change them, you say yes
and save settings. When done go out and come back into Mach and things should be correct.

Above from memory and think it's correct,

Is that what you did?

RICH
Re: Calibration/Steps per unit sanity check
« Reply #6 on: October 30, 2015, 10:13:05 PM »
I just did the math and entered that(the number above). It was interesting though. Typed G0 X10 Y10 and both travel 9".
I'll try the calibration next.
Was just wondering if I've missed something.
Ian

Offline RICH

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Re: Calibration/Steps per unit sanity check
« Reply #7 on: October 31, 2015, 06:28:20 AM »
Attach your xml file.

RICH
Re: Calibration/Steps per unit sanity check
« Reply #8 on: November 01, 2015, 02:55:17 PM »
Will do.
But, I think I found the problem. The OD of the pinion in the manual says it should be 22mm. When measured, it reads 20mm.
So the pitch diameter has to be less than 20mm which makes my numbers above wrong.

Ian
Re: Calibration/Steps per unit sanity check
« Reply #9 on: November 02, 2015, 11:49:07 AM »
Yup, just took things apart and found that the pinions are marked "M1-18". So my invoice was wrong.
Lesson learned- CHECK EVERYTHING WHEN RECEIVING.

Learned lots about gears and stepper calibrations though.