Calibration problem

[johnel1980]

Hello,
I recentrly built a diy cnc and i m having a problem. I set the axis to travel 10 cm so i can set the steps per unit under settings on mach3. Then If i go to mdi and set it to go to 5 cm it stops at 51 mm apx. If i set it to 10 cm it goes to 10 cm. If i set it to 15 cm it goes to 152 apx. Then if i setup the steps per unit again at lets say 15 cm it works fine only at 15cm. Anyone knows whats wrong?

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[skrubol]

Are all of these moves in the same direction? What type of drive do you have (ball screw, acme screw, belt, rack/pinion, other?)

[johnel1980]

Are all of these moves in the same direction? What type of drive do you have (ball screw, acme screw, belt, rack/pinion, other?)

thx for your answer. yes it is in the same direction. when i m trying to set steps per unit on the opposite direction (negative) the motor stalls... i have a rack pinion setup.

[skrubol]

If the motor is stalling in the opposite direction, you should probably figure out that issue first. May be lost steps. You're running steppers I assume?
We'll probably need to know a lot more about your router to give much constructive help though. (dimensions, weight, slide/bearing type, stepper models, drive models, controller, etc.)

[johnel1980]

1.80x1.20 about 250kg i think. i have the nema 34 1600oz stepper motors, with the dq860ma drivers and a cheap 12$ breakout board. My stepper settings are 2.8 Amps half current and 6400 microsteps . I m using mach3 on windows 7 on a very old laptop (pentium).

bboard

steppers



The cnc



Mach settings

[skrubol]

I assume the 6400 is the pulses per rev figure?
I would try increasing the current. I assume those steppers must be rated for a lot more than 2.8A.

[johnel1980]

yes its the pulses. i ll try supplying more current to the motors. do you think the old laptop may be the issue (kernel speed too high)?

[skrubol]

It's certainly a possibility, laptops are definitely not recommended when using the parallel port.
Usually with lost steps, whether due to low current or jitter, the motor will stall. Have you seen any stalling?
Is your rack in good condition? No gaps or anything between sections (if there is more than one section of rack.)
Are all of these issues isolated to one axis?

[johnel1980]

skrubol thx for all the help.

i think the problem was the low amps of the motors. i have less than 0.1 mm accuracy. Fixed but now i have lots of torque on lower speeds and the cnc is shaking because obviously the nema34 1600 oz motors are way too big for me. i ordered the nema 24 and in 5-6 days i ll try to recalibrate. I ll post a video of the "new" cnc maybe

[skrubol]

I would try turning the acceleration down a bit. That should help the shaking assuming it's happening at the start and stop of moves. If not I'd look for something out of balance.
I guess having too high inertia motors might be able to cause that, but I don't know much about inertia matching.