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Posted by Dave Hinz on March 23, 2006, 12:01 pm
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Building a project out of a piece of 4140 prehard. The local custom
metalcutting shop provided the steel. Problem is, it's magnetic. Not
just a little magnetic, it's "you could use this thing to pick up nails,
small children, and battleships" magnetic. I asked them if they have a
demag ring, they don't (and were surprised but will check their stock...
ok, great, but doesn't help me much at the moment).
So how do I demag this sucker? I know that heat would do it, but I
don't want to mess up my hardening. I know mechanical impact can redue
it, but I don't know if that's one of those "theoretical but not
practical" things, or if it'd work. So, simple question - can I just
smack the (un-machined) end of this sucker with a hammer a bunch of
times and get it down to tolerable, or do I need to find someone with
degaussing apparatus of some sort, or am I SOL? It's annoying, to say
the least, to have every chip re-attach itself to the work, invariably
on the layout lines that I'm trying to see.
Thanks,
Dave Hinz
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Posted by Tim Wescott on March 23, 2006, 12:25 pm
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Dave Hinz wrote:
> Building a project out of a piece of 4140 prehard. The local custom
> metalcutting shop provided the steel. Problem is, it's magnetic. Not
> just a little magnetic, it's "you could use this thing to pick up nails,
> small children, and battleships" magnetic. I asked them if they have a
> demag ring, they don't (and were surprised but will check their stock...
> ok, great, but doesn't help me much at the moment).
>
> So how do I demag this sucker? I know that heat would do it, but I
> don't want to mess up my hardening. I know mechanical impact can redue
> it, but I don't know if that's one of those "theoretical but not
> practical" things, or if it'd work. So, simple question - can I just
> smack the (un-machined) end of this sucker with a hammer a bunch of
> times and get it down to tolerable, or do I need to find someone with
> degaussing apparatus of some sort, or am I SOL? It's annoying, to say
> the least, to have every chip re-attach itself to the work, invariably
> on the layout lines that I'm trying to see.
>
> Thanks,
> Dave Hinz
>
You could wave a magnet in its vicinity.
No kidding -- I have successfully demagnetized screwdrivers with a
strong permanent magnet. Stroke it a few times with one pole, then
reverse the magnet and stroke it a bit further away. Keep doing this
until you're waving the magnet in the air well away from the part.
It _won't_ demagnetize the thing completely, and may not work at all for
complex shapes, but it should make things better.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Posting from Google? See http://cfaj.freeshell.org/google/
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Posted by Dave Hinz on March 23, 2006, 12:37 pm
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> Stroke it a few times with one pole, then
> reverse the magnet and stroke it a bit further away. Keep doing this
> until you're waving the magnet in the air well away from the part.
I'll give that a shot, thanks.
> It _won't_ demagnetize the thing completely, and may not work at all for
> complex shapes, but it should make things better.
Well, right now it's not that complex of a shape, but it will be
shortly. I'll demag it first then.
Thanks
Dave
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Posted by Leo Lichtman on March 23, 2006, 12:44 pm
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"Tim Wescott" wrote: (clip) Stroke it a few times with one pole, then
reverse the magnet and stroke it a bit further away. Keep doing this until
you're waving the magnet in the air well away from the part. (clip)
^^^^^^^^^^^^^^^^
You are, in effect, producing a gradually diminishing AC field. which is
what a degaussing coil does. As you say, it might be only partially
effective, and it would take time. How about wrapping a coil in your steel
bar, and applying a little AC voltage, and then reducing that, with a
Variac? Or look around for an existing coil to use? Lots of mechanical
devices use solenoids to make things move--for example, the automatic locks
on car doors. The important thing is, you need to produce a field that is
as strong as the one in the piece of steel, that reverses a lot of times,
getting gradually weaker and going to zero.
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Posted by Tim Wescott on March 23, 2006, 3:53 pm
Please log in for more thread options Leo Lichtman wrote:
> "Tim Wescott" wrote: (clip) Stroke it a few times with one pole, then
> reverse the magnet and stroke it a bit further away. Keep doing this until
> you're waving the magnet in the air well away from the part. (clip)
> ^^^^^^^^^^^^^^^^
> You are, in effect, producing a gradually diminishing AC field. which is
> what a degaussing coil does. As you say, it might be only partially
> effective, and it would take time. How about wrapping a coil in your steel
> bar, and applying a little AC voltage, and then reducing that, with a
> Variac? Or look around for an existing coil to use? Lots of mechanical
> devices use solenoids to make things move--for example, the automatic locks
> on car doors. The important thing is, you need to produce a field that is
> as strong as the one in the piece of steel, that reverses a lot of times,
> getting gradually weaker and going to zero.
>
>
Yes, it takes time -- but less time than buying or building the right tool.
Were I to do it all the time I'd get or make the right tool.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Posting from Google? See http://cfaj.freeshell.org/google/
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> metalcutting shop provided the steel. Problem is, it's magnetic. Not
> just a little magnetic, it's "you could use this thing to pick up nails,
> small children, and battleships" magnetic. I asked them if they have a
> demag ring, they don't (and were surprised but will check their stock...
> ok, great, but doesn't help me much at the moment).
>
> So how do I demag this sucker? I know that heat would do it, but I
> don't want to mess up my hardening. I know mechanical impact can redue
> it, but I don't know if that's one of those "theoretical but not
> practical" things, or if it'd work. So, simple question - can I just
> smack the (un-machined) end of this sucker with a hammer a bunch of
> times and get it down to tolerable, or do I need to find someone with
> degaussing apparatus of some sort, or am I SOL? It's annoying, to say
> the least, to have every chip re-attach itself to the work, invariably
> on the layout lines that I'm trying to see.
>
> Thanks,
> Dave Hinz
>