Setting up stepper motor drivers

[croy]

Hi, i need some help/advice on setting up stepper drives, Currently trying to CNC my lathe i have a 14mm dia x 4mm pitch ballscrew for the leadscrew and a 8mm dia x 2mm pitch for the cross slide.

i have a Nema 23 on the leadscrew and a nema 17 on the cross-slide. these are driven MSD542's powered by a 50V DC 10A power supply.

I have setup the micro drivers to 8 microsteps, Is this possible too much? as the motors sound rough.

Some background ( i had the drives etc working on the old 8 TPI leadscrew) so there is no problemas with power motors or drivers..

Thanks
Roy

[John S]

Roy,
Have you tried any other settings ?
How are you connecting the motors to the screws ? Oldhams or lovejaw type couplings ?

[JAZZCNC]

50V supply on 50V drive is bad idea.! . . . your in danger of back emf frying them on de-acceleration. On a lathe it probably won't be a massive issue because it wont be de-accelerating from high feeds but @50V your on the edge.!!

First I would double, triple check all your wiring, esp the motors phase connections.

Check your amps are not set too high on drive, then like john says try other settings.

What model motors are they.?
How have you got the motors wired.? Parallel or series or unipolar.

[croy]

I think it is just my settings. as the only thing that changed was to replace the myford leadscrew with a ballscrew.

coupled with a belt 20 tooth on the motor and 40 tooth on the screw.




50V supply on 50V drive is bad idea.! . . . your in danger of back emf frying them on de-acceleration. On a lathe it probably won't be a massive issue because it wont be de-accelerating from high feeds but @50V your on the edge.!!

First I would double, triple check all your wiring, esp the motors phase connections.

Check your amps are not set too high on drive, then like john says try other settings.

What model motors are they.?
How have you got the motors wired.? Parallel or series or unipolar.

[croy]

Thanks John,

i been fiddling with the settings in MACH since the screw changed from 8TPI to 4mm pitch. so i am guessing this is the area of problem.


PS, assembling the PCB this afternoon to test. will keep you posted.


Roy,
Have you tried any other settings ?
How are you connecting the motors to the screws ? Oldhams or lovejaw type couplings ?

[John S]

Try different velocity and acceleration settings in Mach

[JAZZCNC]

I think it is just my settings. as the only thing that changed was to replace the myford leadscrew with a ballscrew.

coupled with a belt 20 tooth on the motor and 40 tooth on the screw.

Please dont take this wrong way but you have changed the steps per to take into account the gearing.?

[croy]

Hi No i dont think i have.

Dont worry i am not offended just grateful for the help

[JAZZCNC]

Hi No i dont think i have.

Dont worry i am not offended just grateful for the help

Well there's your problem then.

If 1600 micro steps and 4mm pitch with 20T on motor and 40T screw then try 800 in steps per. So formule (micro steps/pitch) * (screw pulley/motor pulley)

[croy]

Thanks, i am going to finish watching the rugby, then i'll give it another try.


Well there's your problem then.

If 1600 micro steps and 4mm pitch with 20T on motor and 40T screw then try 800 in steps per. So formule (micro steps/pitch) * (screw pulley/motor pulley)

[JAZZCNC]

Thanks, i am going to finish watching the rugby, then i'll give it another try.

Erm ye Should I really be helping a welsh man after kicking our arse's yesterday. .:joker:

[croy]

I'm not Welsh, I'm South African. but i did support the Welsh yesterday.

and I'm still grateful for your help.

[JAZZCNC]

I'm not Welsh, I'm South African. but i did support the Welsh yesterday.

and I'm still grateful for your help.

It's ok I'd much prefer to sit watch that lion on your avitar than rubgy or football.!!. . . . Now motoX or any motosports then thats different story.!

[croy]

Hi Jazzcnc, going on the figures you worked out would i then be correct in surmising that my potential accuracy for turning can be 0.005mm

Accuracy = Pitch/Steps per


Well there's your problem then.

If 1600 micro steps and 4mm pitch with 20T on motor and 40T screw then try 800 in steps per. So formule (micro steps/pitch) * (screw pulley/motor pulley)

[croy]

It's ok I'd much prefer to sit watch that lion on your avitar than rubgy or football.!!. . . . Now motoX or any motosports then thats different story.!

This screw still sounds very rough when it is running. any thoughts on Acceleration and Velocity

[JAZZCNC]

This screw still sounds very rough when it is running. any thoughts on Acceleration and Velocity

What settings are you set to at the minute.? both Acc and velocity please give micro steps drives set to as well.

[croy]

Hi,


Mach3 settings
Steps per is 800, velocity 200, acceleration 74

PM542 Controller settings
microstep 8 which is 1600 usetps/rev
4.2 Amps


What settings are you set to at the minute.? both Acc and velocity please give micro steps drives set to as well.

[JAZZCNC]

Have you tried upping both as 200 & 74 is very low.!! When you say they are rough sounding in what way do you mean.? could you take a video.

What Nm size motors.? how are they wired, Bi-polar parallel or series.? Are you absolutely sure you have wired the phase's correct.?

[JohnHaine]

Hi, it would be really interesting to know how you have fitted the leadscrew please? I have CNC'd my S7 with ordinary screws but accuracy isn't great and I want to fit ballscrews. The Z axis looks a bit of a challenge and it would be good to know how someone else has done it.

Thanks,

John.

[irving2008]

John,

The z-axis on a lathe is always a challenge. Have a look at this thread http://www.mycncuk.com/forums/lathe-build-logs/4497-micro-lathe-zero-backlash%2A-conversion.html to see one approach that should work on any lathe...

[croy]

Hi, it would be really interesting to know how you have fitted the leadscrew please? I have CNC'd my S7 with ordinary screws but accuracy isn't great and I want to fit ballscrews. The Z axis looks a bit of a challenge and it would be good to know how someone else has done it.

Thanks,

John.

Hi John,

I bought C2 ground ballscrews, to replace leadscrew and cross slide, on ebay , then made a backing plate, that replaces the rack, to hold the ballscrew brackets.

I have since sold the lathe but the new owner did not want the CNC kit so if you are interested i have the ballscrews for both X & Z axis as well as the brackets to fit. the only thing still to do is to make the Ballnut carrier for the saddle.
regards Roy

[JohnHaine]

Hello Roy,

That could be interesting! I am thinking of fitting the leadscrew in the normal location and making a replacement apron (really just a bracket) to carry the nut. What pattern nut do you have please? Problem with my approach is that because the L/S is slightly recessed into a kind of channel in the bed there doesn't seem to be much room for a flanged nut and I would have to use the type that has a threaded spigot. And how much would you want?

Regards, John.

[croy]

Hello Roy,

That could be interesting! I am thinking of fitting the leadscrew in the normal location and making a replacement apron (really just a bracket) to carry the nut. What pattern nut do you have please? Problem with my approach is that because the L/S is slightly recessed into a kind of channel in the bed there doesn't seem to be much room for a flanged nut and I would have to use the type that has a threaded spigot. And how much would you want?

Regards, John.

Hi John,

The nut is flanged but my intension was to do away with the apron and only have a nut "carrier".
I spent over £800 on the two ballscrews, the gears belts and motors and the extension for the topslide and brackets.
Make an offer if you are interested.

Regards
Roy roy(at)rsmail.me.uk

[JohnHaine]

Hello Roy,

From your description, I guess that the Z-axis ballscrew isn't full length (since the rack only goes as far as the bed gap)? Do you have any photos showing the ballscrew fitted so I can get an idea please?

John.

[croy]

Hi John,
No i do not have any photos as i sold the lathe. the ballscrew dos end at the gap but as the nut carrier should be fitted to the righthand side of the saddel, you will get full bed travel.

if you want to chat call me on 077 3420 6952.
Regards
Roy

[JohnHaine]

Hi Roy, just spent some time thinking and looking at the lathe and I think one of the problems with the shortened leadscrew is that it's difficult to protect it against swarf? I'm inclined to go for a full-length screw and make up telescopic covers for it - for that you need a reasonable amount of space at each end to telescope the tubes together. I have a screw that should do the cross slide with a little bit of careful shaving off the cross slide to clear the nut flange (I may buy a spare s/h slide to butcher rather than risk the existing one on the lathe!). Thanks for the offer anyway and the useful chat.