Re: [CAD_CAM_EDM_DRO] Question to Mariss about demagnetion was Re: Torque when usin

I think that there are a lot of "old wives tales" surrounding the supposed
dangers of removing stepper motor end caps. I have done this with several
different motors, with no detectable change in their performance. I think
it unlikely that the rotor/stator would come to harm during this procedure
unless you handled it very roughly.

Obviously, it is a smart move to take sensible precautions (don't work next
to your mill while flycutting a piece of cast iron, for example), but
nothing more than you would take when dismantling/assembling any other
precision device, and bearing in mind that magnets will naturally attract
any stray ferromagnetic particles.

Most recently, I removed the end cap from a 200 oz-in size 23 motor to
change it from 6-wire to 4-wire configuration; perfectly possible to do
with care, and the patient definitely survived. Whether it was a worthwhile
thing to do is a completely separate question of course - the jury is still
out on that!

Regards,
Tony

At 11:06 04/02/2003 +0000, you wrote:

> > This has been discussed many times on the list, and one of the
>opinions that
> > came up was, once you remove either endcap, there is nothing
>supporting the
> > rotor, which will be pulled sideways onto the magnet, chipping
>pieces off in
> > the process.
>
>
>
>The magnets are alnico which are not the absolute worst far as
>chipping. The magnets in these hybrid motors are encased between the
>silicon steel laminations (very low carbon, and soft), so there is
>much greater risk of distorting the small pole features than there is
>chipping the magnets (very small chance there). Removing the end caps
>without damaging the rotor is no serious challenge for your average
>butter fingers. What seems to be very difficult is putting it back
>together without managing to include metal filing from some other
>source. So clean and inspect all tools and materials used in the job
>before commencing work and operate in a very clean area. Next to a
>milling machine will not cut it. No pun. Obviously, it would be
>foolish to attempt rotating the shaft or reciprocating it very much
>once it lack bearing support.
>
>
>
> The little pieces will be impossible to remove with the rotor
> > still in the motor and difficult to do with it removed. They will
>then cause
> > the motor to jam up as the pieces wedge between the magnets and
>rotor. The
> > magnets are very brittle, and they use special jigs at the factory
>to keep
> > that from happening.
> >
> > That said, if you have a motor with bad bearings, and it's no good
>as it is,
> > give it a try. What have you got to lose. I once had a PacSci Nema
>34 motor
> > with a bent shaft, I took the rotor out, whacked the bent shaft with
>a
> > hammer about 100 times until I got it fairly straight, and put it
>all back
> > together. Seemed to work ok for me after it went back together. I
>was going
> > to toss it away anyhow, so I gave it a try.
>
>If you manage a locked rotor due to foreign material you are probably
>finished, buy a new motor. Also, bent shafts can not be tolerated on
>account of the extremely tight and uniform gaps required in any
>variation of a reluctance motors. Whacking, in all my practice, is a
>means that could hardly be used for re-lignment. Bent shafts are
>another reason common as demagnetization that these things wind up in
>the hands of surplus dealers.
>
>
>
> It may have lost some torque in
> > the process I suppose, but I used that motor until I upgraded to
>servos.
> >
> > Bill
> >
> > ps For sale, 1 PacSci Nema 34 stepper motor with a slightly bent
>shaft :)
> >
> >
> > > Thanks for your very helpful comments Mariss.
> > > I dont see major mechanical problem dismantling a stepper without
>removing
> > the rotor. The small ballraces used won't need heaps of pressure to
>slip
> > them off a shaft.
> > >
> > > Its really just a matter of making a simple puller and a simple
>clamp
> > system that will allow an end housing to be slipped off a shaft
>without
> > displacing the rotor.
> > >
> > > I agree making up loose pole pieces to slip the rotor into to
>maintain a
> > magnetic circuit would be an engineering exercize not worth
>considering.
> > >
> > > In the US its certainly worthwhile just getting new motors rather
>than
> > mess around but here in Australia steppers are not cheap or easy to
>find and
> > international mail at about $25 or far worse Fedex at about $95 for
>goodies
> > about 6lb weight can mean ebay might be impractical sometimes.
>(especially
> > if the vendor dislikes mail)
> > >
> > > Again, thank you Mariss, forwarned is forearmed.
> > >
> > > Bob
> > >
>
>
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Regards,
Tony