got a strange problem with my lathe

[jasminder]

friends,
i just replaced a stepper driver to bipolar and after running my machine, i found that the machine is loosing steps. the strange thing is that in every cycle run of a part program, the machine is loosing 0.005 in. i checked with a dro that the x was not reaching its 0 after a part was made. I again checked the dro and after the second part was finished, the x has lost 10 thou.
i don't see any striking signs on the workpiece that makes sure that the tool is not crashing into the workpiece.

the worst thing about the problem is that the turning tool is missing steps but the parting tool at the opposite side of the workpiece is not ( i think that the parting tool faces max force while cutting towards chuck and hence it should miss some steps in case my steppers are under-powered) i am currently using gang tooling with a turning tool in the x++ direction and parting tool in the x-- direction.

i will check the motor couplings and screws for any play ( but could they miss just 5thou everytime?)
i have turned a lot of parts on the lathe but the problem persists after replacing a driver but it was not of my x. it was for my turret so it has nothing to do with it. I checked the x with a dro but there is no error in movement while jogging in the mdi mode.

many thanks for any advice in advance,
jasminder singh

[doorknob]

Unfortunately I do not have any suggestions related to your problem.

I wonder, however, whether you might have a photograph that you could post that shows how your gang tooling is arranged.

I am interested in possibly modifying my mini lathe to handle gang tooling, but I have not seen many examples of it in operation.

[jasminder]

Unfortunately I do not have any suggestions related to your problem.

I wonder, however, whether you might have a photograph that you could post that shows how your gang tooling is arranged.

I am interested in possibly modifying my mini lathe to handle gang tooling, but I have not seen many examples of it in operation.

hi doorknob,
i have a very good turret on the lathe now but i have a video on youtube here [nomedia="http://www.youtube.com/watch?v=5C66pCB6u6k"]YouTube - home made cnc lathe[/nomedia]
when there wasn't a turret.
see the other video with the turret also on my channel.
the problem with my lathe was a bad parallel port cable. now it is fine.

jasminder singh

[jhowelb]

My cnc converted lathe was "losing" steps on every pass. A .5" cut would become .495 on the next pass, then .490 and so on making a stair step.

This was the case even if it was "cutting air" and by switching cables the problem would move from the Z to the Y axis and back.

I replaced the Gecko 203V with another identical unit and the problem vanished. The problematic Gecko performed flawlessly in another application.......go figure!

[doorknob]

hi doorknob,
i have a very good turret on the lathe now but i have a video on youtube here
when there wasn't a turret.
see the other video with the turret also on my channel.
the problem with my lathe was a bad parallel port cable. now it is fine.

jasminder singh

jasminder, thanks for the link, your videos are quite interesting.

Do you have a thread on cnczone that describes your turret?

Does it lock into place via a detent, or is there a magnetic brake or other method of holding each tool in a fixed position? Do you use a solenoid or air piston or some other mechanism to push and retract the turret in order to rotate it or lock it into place?

[jasminder]

jasminder, thanks for the link, your videos are quite interesting.

Do you have a thread on cnczone that describes your turret?

Does it lock into place via a detent, or is there a magnetic brake or other method of holding each tool in a fixed position? Do you use a solenoid or air piston or some other mechanism to push and retract the turret in order to rotate it or lock it into place?

dear doorknob,
the design was taken from guldberg's build here on cnczone. here is a video on youtube what i used to learn the mechanism.
[nomedia="http://www.youtube.com/watch?v=o-9J4KsXYwU"]YouTube - CNC Turret[/nomedia]
it uses helical couplings or taperered face gears called in some countries and a pneumatic (air) piston to unlock the toolplate then a stepper rotates it and piston goes deactive to lock it back with a spring. it is sooooo easy. (may be cuz i have already build it) if you can take help from a cnc then it will be more easy.

jasminder singh

[jasminder]

My cnc converted lathe was "losing" steps on every pass. A .5" cut would become .495 on the next pass, then .490 and so on making a stair step.

This was the case even if it was "cutting air" and by switching cables the problem would move from the Z to the Y axis and back.

I replaced the Gecko 203V with another identical unit and the problem vanished. The problematic Gecko performed flawlessly in another application.......go figure!

thanks for the help,
same thing happens here. the motors and wires were swapped but the problem moves to the z now. Gotta replace the driver now and see the result.
btw any video of you lathe running?
i love to see other machines running (i learned a lot from the youtube cnc videos)

jasminder singh