The best grit of the radial bristle discs to use for firescale in
general is the yellow [120 grit, I believe…]. I use the 1" ones in
a stack of three to clean the firescale off of 01 tool steel after
hardening so I can see a clean steel surface during tempering. They
also work well on silver and gold. The yellows are also available in
the 3/4" size.
I have only had bristle loss problems on the very smallest [9/16"],
very softest discs [6 micron and 1 micron, light green and peach].
Even then, I put them through a lot of punishment, and still only lost
about six little bristles. If you are experiencing a huge shedding of
bristles, check to make sure that you have loaded them on the mandrel
with the 3M logo stamp downward, toward the mandrel. The sweep of the
bristles must follow the rotation of the flexshaft so that the sides
of the bristles fall along the surface of the piece. If the discs are
loaded backwards, then the rotation slams the tips of the bristles
down against the surface of the work piece and, yes, you will get a
shower of bristles under those circumstances. If you have loaded a
stack of discs on a mandrel, check to be sure that all of them are
oriented correctly, that you don’t have one in the pack that is
pointing the wrong direction. If you have them loaded correctly, and
you are still having the bristle shedding problem, I would suggest
that you send a message directly to Rick Pihl at 3M. [firstname.lastname@example.org
– he has posted to Orchid often] Tell him exactly how you are using
them and he might want to see the damaged discs, too. These are a new
product, and the guys on the disc team really want to know how the
discs are working out in the real world.
You did not mention what kind of firescale you are trying to remove.
I suspect that you are working with sterling, and if so, the bristle
discs are going to be a real help, but they are not a miracle cure.
The best way to deal with firescale is to keep it from forming by
using Prip’s flux or a thorough coating of paste flux over the entire
piece every single time you heat it. When you get a small region of
staining, especially in a tight area that you can’t reach with
sandpaper or files, then the discs will be a real help. If the piece
is large enough for you to use the 1" discs, start with the brown
[36X], then use the green [50X] and then the yellow.
Hope that helps,