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Eureka! Great Thrumming Material


#1

For many years, now, I have been looking for better ways to clean up
those little tool marks on the inside of piercing work. This week I
found the perfect material: 3M Trizact cloth. For me, this is so
exciting that I need to share it.

I have used the edge of the sawblade and needle files with some
success but these methods still leave something to be desired. (I
seem to have had as much practice using these tools to make nicks as
to remove nicks.)

On page 340 of Dr. Brepohl’s book, Theory and Practice of
Goldsmithing, he describes a process called “Thrumming” where string
is charged with tripoli and drawn through the work. This works fine
if the tool marks are small enough to be abraded away by tripoli.
However, my aging eyes often leave larger saw nicks than the tripoli
will resolve. (Forgive me for blaming my eyes…when I was younger it
was just plain inexperience!)

I have tried various abasive papers and cloths in the past but they
all have failed in one way or another. Narrow strips cut for
thrumming lose their abrasive material too fast or do not conform
well to tight curves or break too easily.

The 3M Trizact is grooved similar to to the grooves in a double cut
file. The abrasive material is charged into the surface of the
grooves. As the grooves wear down, new abrasive material is exposed.
It is strong. flexible and can be cut into narrow strips that are
durable enough to finish thrumming a complex piece of piercing work.
Twenty yard by one inch rolls are available from Rio Grande in grits
from 220 to 1200. (They used to handle it in 3000 grit, I also have a
roll of this.) It is a bit pricey (about $27/roll) to get started but
a roll used for thrumming should last for many years.

I use a utility knife and metal straghtedge to cut narrow strips.
Cut from the back to avoid dulling the blade as fast. I taper the
strips a bit so that the narrow end of the strip can be used for
smaller holes and the wide end for longer edges.

As always avoid breathing the abrasive dust. This material produced
quite a bit of dust when I used it.

Howard Woods
Looking forward to another beautiful day in Eagle Idaho


#2

G’day;

a reasonably cheap material to use for thrumming pierced work is to
place a length of electrical insulation tape close to the edge of a
sheet of wet-'n-dry paper of suitable grit to strengthen it - treat
several grits - then cut strips with a thin sharp blade and straight
edge and use this this for thrumming;. So cheap you can throw it
away when it breaks or loses it’s cut. Another way to use tripoli or
rouge foe this purpose is to rub it on a piece of linen tape

Cheers for now,
John Burgess; @John_Burgess2 of Mapua, Nelson NZ


#3
a reasonably cheap material to use for thrumming pierced work is
to place a length of electrical insulation tape close to the edge
of a sheet of wet-'n-dry paper of suitable grit to strengthen it 

Not quite as cheap, but quicker and I think, perhaps better, is
simply to use the 3M Imperial Microfinishing film. unlike normal wet
dry paper, this stuff is made with a fairly strong polyester film
base. And it’s color coded, so even if you cut very narrow strips and
cannot then read the labelling, the color tells you what grit it is.
I cut thin strips with just a pair of cheap scissors, and use it
mounted in a saw frame. Works great. Doesn’t last all that long, of
course, but lasts long enough to do the job. 3M also makes a tape
product that’s very similar to this, but with two grits, either a
combo of course and medium, or fine and extra fine (whatever those
mean…), in two sections on each single strip. Nice, but since i’ve
already got the sheets of the stuff sitting here, I’ve no need to go
get a bunch of the precut strips…

Peter