"Jim Wilkins" wrote in message news
"Bob La Londe" wrote in message
news
I don't care for using magnets in molds. For the most part its
unnecessary. Once you get a feel for the mold it gets to be pretty easy to
slide a hook or a keeper into its slot. Even if you have to wear glasses
like I have had to for the last decade.

Sometimes though the only way to get a piece of hardware to stay in place
is with a magnet. This leads me to why I felt the need to post this. I
learned recently that rare earth magnets have a failing. Above a certain
temperature they loose their magnetism and that temperature is much lower
than you might think. A little higher and they lose their magnetism
permanently. These temps are below the melting temperature of lead. Now
a mold rarely gets as hot as lead. Even if you set it on top of the lead
pot to preheat, but it does get pretty hot. Hot enough that you have to
wear gloves to handle it safely. Maybe closer than you might like to
degmagnetizing temperature of the magnet.

I didn't research other magnets as I like the strong holding force of even
tiny rare earth (neodymium) magnets for these problematic applications. I
discovered that for a little more money there were higher heat rated rare
earth magnets. I check a couple sources. MSC didn't have any in a size I
wanted. McMaster had one size that was useful. K&J had them much cheaper
than McMaster, but they were further away and only shipped UPS. I ordered
from both McMaster and K&J Magnetics.

I actually had two molds that I couldn't come up with any other solution
for. The first was done with the McMaster magnets and like other magnets
I have ordered they were a little under their specified dimensions. They
also did not seem to have a hard coating like most rare earth mags I have
bought in the past. I just glued them in place with JB weld. The K&J
magnets came in a few days later, and I miced them. I took measurements
on 2 or 3 out of each pack. They were all within 0.0005" of target
diameter, and about the same for target length. They also had the nice
shiny nickel coating I am used to seeing. I machined tapered holes (.001
over at the top to .001 under at the bottom) to press the magnets into and
they fit perfectly. I expect if you rapped the mold sharply on the bench
you could knock them free, but neodymium magnets are pretty fragile. I
didn't want to break them when pressing them in.

Another thing learned. I hope it helps somebody else.

If you were desperate enough you could run a piece of steel out the
side and slip a solenoid coil over it.
-jsw

*** My first reaction was literally to laugh out loud, but of course you are
right. I had this visualization of some poor tackle maker wondering why his
jig mold looked like a miniature Russian EMP generator and why in the heck
he would have to plug it in to the wall. LOL.