So I bought another mag chuck for my little Sanford Surface grinder.

(The chuck I bought initially does not have the holding power I'm hoping
for)

Problem is, this chuck is about 50 years old, and has been sitting
unused for about 30.

Needless to say, the grease inside it has gotten THICK and HARD and so
engaging the magnet is HARD WORK.

Now, the chuck comes apart quite easily (once the lead is fished out of
the heads of the allen screws).

I removed the bottom plate. I was a bit concerned about demagnetization and
whatnot, but the chuck was not useful as is, so why not.

It's basically five major pieces,

.. a pair of end plates (angle brackets, really)
.. the top
.. the bottom ( a single piece of flat steel 4" x 8" x 3/4") and
.. what I assume is a magnet, because it's what you rotate to "turn it on".

The "magnet" looks like nothing more than a 1.5" diameter round shaft covered
in old grease.

So, I can just dump the whole thing into a tank of solvent for a week, hope
the grease dissolves, hope I get all the solvent out and then hope I can get
fresh grease into all the places it needs to go.

Or I can remove four more allen screws, disassemble it completely and
clean it properly.

Here's the question. If I disassemble it completely, am I likely to
demagnetize something somehow ?


Thanks for any insight.


Alan


--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta

According to Alan Rothenbush :

So I bought another mag chuck for my little Sanford Surface grinder.

[ ... ]

Needless to say, the grease inside it has gotten THICK and HARD and so
engaging the magnet is HARD WORK.

[ ... ]

It's basically five major pieces,

. a pair of end plates (angle brackets, really)
. the top
. the bottom ( a single piece of flat steel 4" x 8" x 3/4") and
. what I assume is a magnet, because it's what you rotate to "turn it on".

The "magnet" looks like nothing more than a 1.5" diameter round shaft covered
in old grease.

So, I can just dump the whole thing into a tank of solvent for a week, hope
the grease dissolves, hope I get all the solvent out and then hope I can get
fresh grease into all the places it needs to go.

Or I can remove four more allen screws, disassemble it completely and
clean it properly.

Here's the question. If I disassemble it completely, am I likely to
demagnetize something somehow ?

To disassemble it, you need some way of replacing the magnetic
circuit around the permanent magnet. And I don't know whether this is
really possible. Some PM chucks were polarized by an external magnetic
pulse applied through the pole pieces after assembly. Disassembling it
risks serious weakening of the field strength, leaving you with *two*
chucks which are too weak.

I would either try the solvent approach, or perhaps the heat
one, as long as you don't go too high in temperature, as that, too, can
degauss the permanent magnet.

Of course, if you had a service in town which could re-polarize
your chuck, disassembly would be the way to go.

Good Luck,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Fri, 17 Feb 2006 04:33:16 +0000 (UTC), Alan Rothenbush
wrote:


So I bought another mag chuck for my little Sanford Surface grinder.

(The chuck I bought initially does not have the holding power I'm hoping
for)

Problem is, this chuck is about 50 years old, and has been sitting
unused for about 30.

Needless to say, the grease inside it has gotten THICK and HARD and so
engaging the magnet is HARD WORK.

Now, the chuck comes apart quite easily (once the lead is fished out of
the heads of the allen screws).

I removed the bottom plate. I was a bit concerned about demagnetization and
whatnot, but the chuck was not useful as is, so why not.

It's basically five major pieces,

. a pair of end plates (angle brackets, really)
. the top
. the bottom ( a single piece of flat steel 4" x 8" x 3/4") and
. what I assume is a magnet, because it's what you rotate to "turn it on".

The "magnet" looks like nothing more than a 1.5" diameter round shaft covered
in old grease.

So, I can just dump the whole thing into a tank of solvent for a week, hope
the grease dissolves, hope I get all the solvent out and then hope I can get
fresh grease into all the places it needs to go.

Or I can remove four more allen screws, disassemble it completely and
clean it properly.

Here's the question. If I disassemble it completely, am I likely to
demagnetize something somehow ?


Thanks for any insight.


Alan

In a 50 year old magnetic chuck the magnet will certainly
be of the Alnico family. These need to be magnetised in the fully
assemmbled state with special rigs. In all normal use magnets do
not wear out but they must NEVER be removed from contact with the
pole piece assembly.

If it's showing poor holding power it's either not fully
mechanically switched 'On'or the working surface is not properly
flat and needs regrinding.

In disassembly it's safe to remove any non magnetic item or
any iron item that's easily removable by unassisted hand force

Eclipse magnetic chucks use SAE140 gear oil for lubrication.

Jim.

Alan Rothenbush wrote:
(The chuck I bought initially does not have the holding power I'm hoping
for)

Any chance you could replace the magnet(s) with rare earth magnet(s)?
See the Lee Valley site for some shapes and sizes. These are MUCH more
resistant to demagnetization and are damn powerfull.

Ted

On 2006-02-17, Ted Edwards wrote:
Any chance you could replace the magnet(s) with rare earth magnet(s)?
See the Lee Valley site for some shapes and sizes. These are MUCH more
resistant to demagnetization and are damn powerfull.

It's surely occurred to me !

But from other coversations I've had, this may not be so wise a solution.

If I'm really serious, the plan might be to send it away to someone who
actually knows what they're doing ! G


Here's what prompted all of this. It occurred to me that it might be nice
to use the little SG to sharpen my woodworking chisels. I've got a fair
collection, and all are dull .. at best. I'm not real proud about the dings
in some of them, said dings looking distinctly like they were used as cold
chisels and not wood chisels.

G

I could either build a pair of jigs to hold the chisels at the appropriate
angles OR I could use my adjustable magnetic block.

It's the same one as is shown at

http://www.travers.com

in their online catalog page 636, and is their part number 57-062-120

This unit has ..OK.. holding power when oriented so that the pole pieces
match the pole pieces of the mag chuck. However, when oriented at 90 degrees
to the chuck (which is the more convenient orientation), it has virtually no
holding power at all (not entirely unexpected, I suppose).

I think I'll just build the jigs and be done with it.


Alan

--
Alan Rothenbush | The Spartans do not ask the number of the
Academic Computing Services | enemy, only where they are.
Simon Fraser University |
Burnaby, B.C., Canada | Agix of Sparta

On Fri, 17 Feb 2006 19:55:21 GMT, Ted Edwards
wrote:

Alan Rothenbush wrote:
(The chuck I bought initially does not have the holding power I'm hoping
for)

Any chance you could replace the magnet(s) with rare earth magnet(s)?
See the Lee Valley site for some shapes and sizes. These are MUCH more
resistant to demagnetization and are damn powerfull.

Ted

I think those are poled wrong, Ted. The Lee Valley magnets are poled
axially while I think the magnet in a mag chuck is poled crosswise.

On Fri, 17 Feb 2006 04:33:16 +0000 (UTC), Alan Rothenbush
wrote:



Here's the question. If I disassemble it completely, am I likely to
demagnetize something somehow ?

Yes. A chuck that old will surely have an alnico magnet. If you
remove the magnet you will lose some magnetism that can only be
recovered by re-poling the whole works after reassembly.

" In all normal use magnets do not wear out but they must NEVER be
removed from contact with the pole piece assembly. "

I have taken apart stepper motors and "lost the magnetism"...where does
it go? Why does it go?

TMT

On 17 Feb 2006 22:16:18 -0800, "Too_Many_Tools"
wrote:

" In all normal use magnets do not wear out but they must NEVER be
removed from contact with the pole piece assembly. "

I have taken apart stepper motors and "lost the magnetism"...where does
it go? Why does it go?

TMT


Not easy to answer this one simply. The following may help
(or perhaps leave you more comprehensively puzzled!).

Magnetisation of ferrous materials follows a hysteresis
curve. This means that as you apply increasing magnetising force
(ampere turns in a surrounding coil) flux density will steadily
increase until limited by magnetic saturation.

If the magnetising force is then steadily decreased the flux
density does not decrease along the same curve as when it was
increasing but lags behind it retaining more flux than would be
produced by the magnetising force when in the increasing
direction.

When the magnetising force has reached zero, because of
this lag, some flux density remains. The amount that is left
depends on the type of ferrous material - a very small amount for
tranformer iron - a large amount for permanent magnet material.

It also depends on the total magnetic circuit reluctance. In
practical terms this almost wholly arises from the reluctance of
the effective air gap that separates the N and S poles of the
sample.

If this reluctance is small, a lot of flux density is
retained. This the case of a permanent magnet assembly magnetised
after final assembly with the airgap reducing pole pieces in
place. If this airgap is now increased, flux density reduces as
the magnet moves further down the decreasing limb of the
hysteresis curve.

If the original much smaller air gap is restored the
flux density returns on a recoil loop which lies between the
increasing and decreasing magnetisation curves. The shape of this
recoil loop depends on the type of magnet material. With the
older tungsten/iron and Alnico steels only partial recovery
occurs and there can be a substantial loss in performance.
Ferrite and rare earth magnets have a more favourably shqaped
recoil loop and can recover almost completely after being exposed
to an excessive air gap.

Jim