Stepper Motor Question

One more question. Will a gear motor also freewheel? I know that some won't with the worm gear drive.. There will be times that hand movement will be better. If it can't this can be overcome by letting one cogged pulley slip when needed.

"Billy G"
 
Bill Gruby said:
So you are saying I need this driver instead?

http://www.ebay.com/itm/Linistepper...787?pt=LH_DefaultDomain_0&hash=item43baf98ddb

"Billy G"
Click to expand...

No, you can use the KL-3040, and will probably get better performance with motor hooked up bipolar.

Just saying that you could also have used the linistepper.

Unfortunately, folks sometimes label motors as "unipolar" or "bipolar", when this is really describing the drive, and the hookup..

As I mentioned, an 8-wire motor will work with either unipolar or bipolar drives, So will a 6-wire motor. A 4-wire motor will only work with a bipolar drive.
 
A gear motor won't freewheel (well, worm drives won't, a regular gear reduction drive _will_ with a lot of effort). Easy solution is to slip the belt, or to add a dog clutch.

MrPete had a video where he did this on this on an atlas I believe. He used an industrial controller and motor out of an old welding wire feeder. IIRC, he just had a V belt pulley on his lead screw, and removed the belt when he wasn't using the power feed. This was for the longitudinal feed of course, but no reason you couldn't do it for the cross slide if you can get access to the screw.

Here's the video [video=youtube_share;3DlPDr4f6xQ]http://youtu.be/3DlPDr4f6xQ[/video]

If you go the DC route, that speed controller TomG posted looks like a great deal.
 
Hi Bill,

I'm not sure if you mean freewheel as in overtravel after you shut off, or backdrive. It's true that the stepper motor will just stop and hold. A gearmotor, especially one with a high reduction ration (like the ones given as examples), will generally stop very quickly. You can stop it even quicker if you wire your motor switch such that the (+) and (-) leads are shorted when you turn it off.

Whether a motor will or will not backdrive is another matter. Generally speaking, a worm drive gearbox will not backdrive, but you can under certain circumstances - usually causing undue wear to the worm gear (the gear that's normally driven by the worm).

A non-worm gear box can be backdriven, but you have to satisfy some requirements first. All motors (even so-called cogless motors) have some detent torque. In addition, there is static friction (AKA stiction) and kinetic friction (AKA running friction) to consider. Assuming the gearhead is 100% efficient (which they never are), the torque required to backdrive a gearmotor is the gear ratio times the sum of the restraining torques (stiction + detent for a stopped motor). There are a few more contributors, but those described above are the major players.

All that theory being what it is, I've been presuming all along that you're simply planning to drive your existing leadscrew with a stepper or gearmotor. If this is the case, no worries. It's difficult to backdrive a leadscrew alone. Adding the gearmotor to it, menas you have to overcome the backdrive torque of the leadscrew PLUS the backdrive torque of the gearmotor. If you have a ballscrew, the situation is a bit different, but you still have to overcome the backdrive torque of the gearmotor.

All in all, I strongly believe things will all work out fine with a gearmotor -especially if you use one with a large reduction ratio.

If you end up using a stepper, you have one more thing to consider. Steppers have significant unpowered detent torque which you'd need to overcome when using the cross slide manually. The best bet, in both the gearmotor and stepper case, would be to have some method of disengaging the motor from the leadscrew for manual operation. Say a mechanical or solenoid operated tooth clutch or particle clutch or one of your own design.

John
 
By freewheel I mean the motor must be able to be disengaged so I can adjust manually for OD cutting and bore cutting. I only want the auto mode to face cut.

"Billy G"
 
Bill,

In my experience, back driving gearmotors is generally a bad idea, it's not only cumbersome, it's also hard on the gear train. I would drive the feed through a dog clutch. Then the clutch could be disengaged for manual feed or re-engaged for power. Make the dog clutch with lots of teeth to make it easier to engage, or better yet, use a toothed clutch. They are easy to engag and will probably handle more than enough torque for your application.

Tom
 
Just found this vid via a link from CNC Zone http://www.cnczone.com/forums/gener...1-home_made_cross_slide_power_feed_small.html

He's got the motor and drive box mounted to the carriage, and then just uses a rubber belt to drive the dials directly. Pull the belt off to disengage.

[video=youtube;08fmpfDY0I4]http://www.youtube.com/watch?v=08fmpfDY0I4[/video]

His looks like maybe a 9x20. What type of machine is yours Bill?
 
DMS;

That is a Jet 9X20 same as mine. Gonna look close at that one. Tom, Dog Clutch is also a good idea. John, we're missin a little closer. :lmao:

"Billy G"
 
Last edited by a moderator:
Yup, that'll generate enough torque to twist your arm off.
 
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