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

100% correct. It is in fact mpossible to magnitize the rotor already in
place, so they must be done outside and then asm'd.

At 11:27 AM 2/4/03 +0000, you wrote:

>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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>>
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>>
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>>
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>>bill
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>>
>>
>>
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>
>Regards,
>Tony
>
>
>
>Addresses:
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>
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timg@...

>Moderator: pentam@... indigo_red@... [Moderators]
>URL to this group: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO
>
>OFF Topic POSTS: General Machining
>If you wish to post on unlimited OT subjects goto:

aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.

>http://www.metalworking.com/news_servers.html
>
>http://groups.yahoo.com/group/jobshophomeshop I consider this to be a

sister site to the CCED group, as many of the same members are there, for
OT subjects, that are not allowed on the CCED list.

>
>NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.

DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........

>bill
>List Mom
>List Owner
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
>
>

Regards, Hoyt McKagen


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