Motor tuning problems

[rodzilla]

Hay guys i am having some problems getting my motors tuned correctly i am using Mach3 i followed the calculations in the motor tuning section of the setup manual but when i cut anything i am about .010 of i am using 5/8" ball screws with a .2 lead my motors are keling inc 906 ozin motors with 200 steps per rev which by calculations of 200 * 10 for gecko G202 step pulses = 2000 devide that by .2 for the ballscrew pitch = 10000 but when i use those setting my cuts are about .010 off could someone please help with this dilema thank you

[LeeWay]

If you bought the ball screws from Mcmaster Carr or they are Thompson ball screws, the pitch might actually be 13/64".
This is what I have on my router with Gecko's. This is the step setting I use.
9846.153846. It is very close to 10,000, so this may be your problem. Load them in and see if it's not more accurate.

[ataxy]

when you say you are off by 0.01 this is on a distance of what? by that i mean if you cut a 1 inch slot are you off the same as if you would cut a 5 inchs slot

[rodzilla]

I will try this i think i got them from mcmaster i can't remember but i will try those setting. If i cut a 1" slot and a 5" slot they will both be .010 less than 1" and 5" i have cut a few circular pockets all of which were 1" and 1.5 the 1" pockets came out to be .990 diameter and the 1.5 came out to be 1.490 diameter

[ataxy]

humm thats weird cuz if it would be your motor tuning the error would be cummulative
cuz let say your number of step/unit is wrong then
1 would give you 1.01 but two would give you 2.02 and not 2.01

[LeeWay]

Not necessarily.
I have one jig setup that I cut with a setting of 10,000 steps before I realized it was off a bit. Then I calculated the actual steps for these screws on everything else. These parts came out just a shade small. To get a full 1" off between these two step settings, your machine would have to be about 1000 inches long I think. Just guessing there.
Remember these step settings are per inch. The difference is 154/10,000ths of an inch.

Factor in a small amount of backlash on an unpreloaded single nut, and it might be just about what he is coming up with.

[ataxy]

well 154/10000 of an inch is 0.0154 per inch no?

[LeeWay]

Sure! And the accuracy rating on these are .004 per foot. This is still likely to get him closer to what he needs I think. If these are 5/8" screws and he did get them from Mcmaster Carr, the lead is indeed 13/64ths and his step setting should be what I quoted. Any other error is likely coming from somewhere else after that.

[rodzilla]

Hey guys thanks for all of your help. I think i figured out what my problem was i did the automatic steps per calc in Mach 3 settings and i had to do it a few times but now when i move the X,Y,Z axis 1" it actually moves 1" and is repeatable everytime the actual settings are something like 10098.1498 I am using a single ball nut on each axis and i don't see any backlash but i do have the extra ball nuts i just haven't figured out how to implement them for zero backlash setup but i'm not sure if i need them as by the movements in my axis i am not getting any backlash is this possible for a single ballnut setup or am i not doing this right. The way i am checking this is by attaching my calipers to the axis and moving the axis 1" then checking the DRO in Mach and comparing it to what i get on the digital caliper and then moving the axis back to zero then checking what is on the DRO in Mach and checking that against the calipers and everytime i get 1.000" and 0.000 on DRO inmach and Calipers would this be the correct procedure to test for backlash or is there another way?

[LeeWay]

It's kinda difficult to see that actual travel when just using an inch. Like Ataxy mentioned, it may be a cumulative error.
You may want to travel feet and then test. Where you will see backlash is when cutting circles. The axes have to travel back and forth quite a bit swapping directions. It might even be visible to the eye if there is much backlash.
The way I like to test for backlash is to jog an axis using the MDI screen. I tell it to move 5", then back 2" then ahead 3" then back 2" etc, then send it back to zero. Check how far it is from original then. Backlash is only really apparent when the axis changes direction and it can be cumulative and really show if you have a lot of direction changes.
I think the tolerance on Mcmaster Carr of .004" may be an average. It may also be best case scenario. I think mine is pretty close to that, although my tolerances don't need to be that close on my router.

It is odd that you need a step count over 10,000 though.
I don't think this is the correct way to adjust for backlash. Mach 3 has backlash comp where you have to measure exactly what you backlash is and it will make allowances when running the code. Your steps should actually be the number that you work out according to the pitch of the screw and steps of the motor times the 1/10th step for Gecko's.

[rodzilla]

I used the method for backlash compensation when i had the original lead screws in place. I am very new to this so please have patients with me. I thaught that if i machine a circular pocket and then measure the pocket and it is what diameter i was looking for say a 1.5" pocket and it is 1.5" then your machine is fine if there is any deviation of that measurement then your system is not calibrated correctly so am i incorrect in thinking this?

[rodzilla]

O.k. i have been playing around with this thing and it is really driving me crazy. I set the motor tuning to 10000 steps per and moved the axis 5" it actually moved 4.989" according to my digital caliper. So i went to the settings tab on Mach3 and di the steps per calculator and told the x to move 5" it moved 4.989" and Mach recommended what steps per to use so i chose them and moved the x axis 5" and it moved 5" so i changed the setting on the Y axis to the same as the X as they are both using the same ballscrews and motors. Then i cut a circular pocket at 1" the pocket came out to .990 so i cut another at 1.010 and the pocket came out 1.000". So i have established that my machine is off by .010 but i can't seem to figure out how to rectify this so when i cut at say 1" it comes out 1" or i cut at 3" it comes out 3" without making everything .010 larger than normal. I'm not sure if backlash is the problem as if i move the axis 5" it moves 5" and then if i move the axis back to 0 from 5" it moves 0 and both times this reads correct on my calipers. Could someone please help me with this??? I think i am about to lose my mind. I just checked my Ballnuts and they are Thompson ballnuts i got the ballscrews and ballnuts from the same place and i think that was from McMaster Carr