Re: A little experiment on demagnetization

Interesting post.

It does seem odd that just by moving a magnet it might weaken.
but that is just a total non-edumacated grass roots view.

but, if you can make a magnet out of a needle for your 4th grade
science fair compass, then moving the rotor in the unit might effect
the stator in a similar way.

If that has any bearing in reality, I wonder if the change odccurs
when one removes the rotor, or when one replaces it ?

Regardless, if any of my conjecture has any basis, then your point
that magnetizing when assembled would also be correct. regardless of
my ideas, your point of magnetizing when assembled would be seperate.

I've tested 9 steppers now, and only the NEM23's spin. dern e-bay
junk. anyone have a good source for nema34's that are low in
price ? Since I am moving up from dbl stack 23's, a single stack 34
is all I need.

also, anyone want to play with a few 34's to see if I'm all wet ?


Dave






--- In CAD_CAM_EDM_DRO@yahoogroups.com, "mayfieldtm <mayfiet@i...>"
<mayfiet@i...> wrote:

> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude
> <davemucha@j...>" <davemucha@j...> wrote:
> > Is magnetism lost over time on a
> > shelf ? or in use ? by higher voltage/power ? and disassembly?
>
> More than likely the magnetism is lost over time while
> being used. Magnets DO NOT like heat or vibration.
> Step motors do a lot of vibrating and heating.
> I'm not convinced that slow careful disassembly is
> all that destructive. (some loss not much)
> I'm stating this from a gut feeling fueled with about 10 years
> experience in the magnetic industry, back in the 70's.
>
> The newer fancy magnetic materials are less
> susceptible to heat and vibration.
>
> >"are there any shops/people that re-magnetize?"
>
> Should Be.
> I just took apart a step motor to look at the magnetic circuit.
>
> On the rotor shaft...
> there is a stack of steel laminations,
> then a magnet about 1/8" thick (washer shape),
> another stack of laminations,
> a non magnetic spacer,
> stack of laminations,
> another magnet,
> and a --- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude
> <davemucha@j...>" <davemucha@j...> wrote:
> > Is magnetism lost over time on a
> > shelf ? or in use ? by higher voltage/power ? and disassembly?
>
> More than likely the magnetism is lost over time while being
> used. Magnets DO NOT like heat or vibration.
> Step motors do a lot of vibrating and heating.
> I'm not convinced that slow carfull disassembly is
> all that destructive.
> I'm stating this from a gut feeling fueled with about 10 years
> experience in the magnetic industry, back in the 70's.
> The newer fancy magnetic materials are less susceptible th this.
>
> >"are there any shops/people that re-magnetize?"
>
> Should Be.
> I just took apart a step motor to look at the magnetic circuit.
>
> On the rotor shaft...
> there is a stack of steel laminations,
> then a magnet about 1/8" thick (washer shape),
> another stack of laminations,
> a non magnetic spacer,
> stack of laminations,
> another magnet,
> and a finale stack of laminations,
>
> So... when the rotor is removed...
> it acts like a bar magnet with the North Pole on the
> shaft end and the South Pole on the Bearing end.
>
> This leads me to believe that the motors can be magnetized
> fully assembled.
>
> Place the motor in the Magnetizer with the shaft against
> the South Pole of the Magnetizer and the bearing end of
> the motor against the North Pole of the Magnetizer.
> Even Better... To get that North Pole even closer to the
> rotor, insert the shaft into the hole of a donut shaped
> pole piece.
> Size of which would be...
> OD ~= OD of Stator
> ID = a little larger than shaft size.
> Thickness > Shaft length.
>
> (in truth, North/South orientation is probably
> of little concern)
>
> Look around for shops that make custom magnetic devices.
> Most any city will have one.
> Take a copy of this e-mail and a box of donuts with you.
> I wouldn't think it would cost much if anything.
>
> If the motors are magnetized using the "Discharge" Type
> Magnetizer. I can visualize a heavy coil that the motor
> can fit into about 1.5 to twice as long as the rotor.
>
> Tom M.