[JestingAngler]

Over traveling on rapids I think. While running image to g-code cutting from left to right and rapiding back. After about 60 passes I notice that the cutter was passing the original x0 by 1/4". At first I thought loosing steps while cutting but I was only feeding at 6ipm, That's where my torque is. I'm now thinking it could be deceleration. Rapid is 60ipm. Using linuxcnc. Although my micro step is set at 1/8. Maybe I am loosing steps. Any help appreciated.

[SCzEngrgGroup]

If your zero point is moving, then you are, pretty much by definition, losing steps, unless there is a mechanical problem, like a slipping shaft coupler.

Regards,
Ray L.

[JestingAngler]

Thanks for the reply. Mechanically all is good, sfu1605 ballscrews and direct drive. I am going to try 1/4 micro stepping, but am worried about choppy feeds with my current setup (0.001" per step). I admit this is my first build, but I don't understand why there isn't any missing at rapid. Which is where the motors have less torque. Why I was thinking possibly over travel.

[arizonavideo]

Drill a zero mark and do a test part and see if you are loosing steps. Its rare to have the computer make mistakes.

[JestingAngler]

Yes, your right. I need to figure out when and how much. My building isn't heated, so I bring the computer and control box inside when not in use through winter. I'll hook it up this weekend and try to better understand what is going on. Thanks

[Fastest1]

Actually I experienced your same feeling a few years ago during some speed testing. However according to the DTI I wasnt losing steps. However watching the carriage move you can clearly see it stopping at different points. Dont know why, nothing was loose and it functioned fine but you can see that it doesnt appear right.
Watch this video and tell me if Y isnt stopping at different points. Odd https://www.youtube.com/watch?v=8CPqGaUcyMc

[JestingAngler]

That is a very impressive machine. If you don't mind my asking, what is the pitch of your lead screw?

[Fastest1]

That is a very impressive machine. If you don't mind my asking, what is the pitch of your lead screw?

If the question was to me, it is running 1605's.

[instructor37]

Over traveling on rapids I think. While running image to g-code cutting from left to right and rapiding back. After about 60 passes I notice that the cutter was passing the original x0 by 1/4". At first I thought loosing steps while cutting but I was only feeding at 6ipm, That's where my torque is. I'm now thinking it could be deceleration. Rapid is 60ipm. Using linuxcnc. Although my micro step is set at 1/8. Maybe I am loosing steps. Any help appreciated.

In Mach 3 you have 2 choices- Exact Stop and Constant Velocity. In Constant Velocity mode the stepper runs full speed up to the stop point, and if you are running fast rapids and have a lot of carriage inertia, the carriage can overpower the stepper and go too far. In Exact stop mode, the stepper speed begins to ramp down before reaching the end of the travel and reduces the inertia of the carriage eliminating the possible over-run.

[SCzEngrgGroup]

In Mach 3 you have 2 choices- Exact Stop and Constant Velocity. In Constant Velocity mode the stepper runs full speed up to the stop point, and if you are running fast rapids and have a lot of carriage inertia, the carriage can overpower the stepper and go too far. In Exact stop mode, the stepper speed begins to ramp down before reaching the end of the travel and reduces the inertia of the carriage eliminating the possible over-run.

And neither will cause the zero point of an axis to shift....

Regards,
Ray L.

[ninefinger]

Check your acceleration values. Try reducing by half and see if that fixes it.
Mike

[JestingAngler]

Reduced acceleration to one full rotation of stepper to max velocity. Also reduced micro stepping from 1/8 to 1/4, and turned my voltage up from 24v to 30v and I'm still losing steps. I'm now convinced that I've got something in step config wizard wrong. I'll do some research on my drivers and double check everything. I'll post my progress. Thanks everyone

[SCzEngrgGroup]

What kind of motors are you using that will operate well on only 30V?? Most decent steppers require anywhere from 50-80V for best operation.... That could very well be your whole problem.

Regards,
Ray L.

[JestingAngler]

The steppers I have are rated 24v-48v 4.2a 566oz-inch bipolar parallel. Nema23 frame but referred as nema24. 8 wire hybrid. Also I am using M542T drivers to power them. Drivers are rated 24v-50v up to 4.5a. 360w power supply 15a

[SCzEngrgGroup]

What is the winding inductance for those motors? That is what determines the optimal voltage.

Regards,
Ray L.

[JestingAngler]

According to the paper work that came with the motors
Dielectric strength 500VAC
4.24a ; phase resistance 0.7ohms ; voltage current/phase (V DC) 2.96; phase inductance (mH) +-20%(1KHz) typical 3.0
Rotor inertia 980gcm sq ; insulation resistance 100Mohm ; 2/4 phase

That's about all the information there is. Also they came from stepperonline. 24HS39-3008D

[SCzEngrgGroup]

OK, so with 3mH winding inductance you should be powering those motors at roughly 55V for optimum performance. At 24V, you were massively under-powering them. At 30V, you're only very slightly better. You should be using at least a 48V/10A supply. Too-low voltage will dramatically reduce operating torque.

Regards,
Ray L.

[ninefinger]

OK, how about some more info. What are you driving? Is it a small mill like a G0704 or is it bigger like the RF45? i.e. How much mass are you moving? You mention 60ipm direct drive and 1605 leadscrews.
If your using LinuxCNC then acceleration values are in machine units per s^2 - what value do you have for the axis in question? I don't want to do the math to figure out "Reduced acceleration to one full rotation of stepper to max velocity" - if you're looking at the bottom of the stepconfig utility is it telling you max velocity is achieved in 0.1968"(5mm)? That should be plenty slow enough...
At this point you are troubleshooting a system and we need to look at all the variables...
As Ray mentions, you are underpowering the steppers. That may be ok as long as you respect that you don't have the power you thought you did. That will mean reduced torque with the resultant reduced acceleration and possibly reduced rapids if torque at velocity is reduced enough. Also, how are they wired - bipolar series or bipolar parallel? What are the settings on the driver - I'm guessing you have it set for max amperage?
Do you have backlash compensation enabled? If so what does it have as values for acceleration / velocity? (you need to be looking in the .ini file for these values - not using the stepconfig utility)

Regards
Mike

[JestingAngler]

The mill is a round column harbor freight mill/drill. Acceleration is set to 2.5 , at the bottom of step config (0.2 to full acceleration) backlash at 0. Motors are wired bipolar parallel. Drivers set at 4.2a. Thanks for all the help. I did order a 48v power supply about a week ago on a hunch. Won't get it till after Christmas though