Axes not moving correct distance 7i96 KL-5056-E

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02 Dec 2019 00:32 #151715 by LinfieldGarage
Hello All,
I have been stalling on trying to fix this for a few months now while I get the rest of my 50x50 plasma table finished. The issue is that although the machine functions correctly in most ways, the axes do not move the exact prescribed distance. I am using the Plasmac interface with a PREEMPT RT kernel now, but this problem existed from day 1 when using an older version of LinuxCNC.

I am using a Mesa 7i96 board, KL 5056-E drives, open loop steppers, rack and pinion drives (same on X and Y). The math tells me that my steps per inch should be:
(8 micro steps * 200 steps per rev *3 gear reduction) / (1in pitch diameter * pi) = 1,527,88745 steps per inch.

I am not sure if I should put that number directly into my ini file as the STEP_SCALE (I really forget how I got it to be this close ;)
My drive jumpers are all correct.
ini file attached.

When I use a dial indicator and do some move tests, I get the following:
G0 (rapid) X0 X1 = 1.030 inches
G1 f20 = 1.026
G1 f40 = 1.028
G1 f60 = 1.029
G1 f80 = 1.030

I get similar results on the Y axis but they are not quite as far off. The faster the travel, the worse my result.

Is this an acceleration problem? I used some basic numbers for my ini file based on google and forum searches. Can anyone with a similar setup please post your settings and/or ini files?

Thanks in advance,
Jamie

File Attachment:

File Name: bigblue.ini
File Size:11 KB
Attachments:

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02 Dec 2019 00:36 - 02 Dec 2019 01:07 #151716 by Leon82
I'm starting to think the label is wrong on mine. But as far as scale,

Do you have a 5mm ball screw and have set it to 3/16?

Never mind you have a rack and pinion.

You can use an indicator and precision blocks to fine tune the scale.

Under tools there is a calibration menu which will save to the ini while running CNC

Also, be sure to "load the screw" when you check. Otherwise you will have backlash and slack adding or subtracting to your values.
Last edit: 02 Dec 2019 01:07 by Leon82.

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02 Dec 2019 01:02 #151717 by Leon82
I emailed him for the recommended timings for the 5056e and he sent me

Step Time 1200
Step Space 1200
Direction Hold 5000
Direction Setup 5000

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02 Dec 2019 01:25 #151718 by LinfieldGarage
Thanks for the tips Leon82.

I remember starting with those default numbers a while back. When I use them today, but leave the STEP_SCALE at 1377, the machine moves painfully slow. I assume the right combination of numbers exists but I don't know exactly how to find it.

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02 Dec 2019 01:28 #151719 by Leon82
There are 4 velocities to increase if you want to speed it up . Along with the display max velocity

Axis and joint.

Plus the step gen and another I don't remember off the top of my head

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02 Dec 2019 20:47 #151773 by Leon82
4800 pulses should get you 3.14 inches based on the circumference of your gear

Divide than by your reduction and it's about 1.046.

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03 Dec 2019 01:10 #151803 by andypugh
I think that 1527.88745 is the correct step scale.

Are you sure that the gear has a 1" pitch diameter? (eg, 20 teeth on a 20DP)

It does look like your machine might be over-shooting. You can try lower acceleration to see if that makes any difference.

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