ATM Re., JB weld, alternative-

["David Harbour" <scarab@peakonline.com>]

Johnny-
 I have used a product for years that is like JB weld only superior in
several ways. It is called PC-7. A large mass (relatively speaking) can be
molded around (and into) a hardware cloth frame- you can form any shape with
the galvanized hardware cloth- this stuff is a square mesh of galvanized
steel screen, it comes in half inch mesh size, and quarter inch, I think (it
might be a little bit different than those sizes). One can form, for
instance, nicely made little mirror clips out of the stuff by folding up a
little length of hardware cloth, bending the end at the wanted angle, and
then filling it in with PC-7. PC-7 is sandable, and it sets up very dark
grey. One can work with larger masses of it, it will not sag out when it is
setting up. In fact, this is one of its selling points- it says on the can-
"will not sag", etc. The stuff is very strong-m y little mirror clips made
this way can't unbend. I have molded excellent teeth for a sector drive with
PC-7, but have given up on the idea of driving a sector directly with a worm
(threaded rod engaging molded teeth on the rim) now that I have evolved my
design for a rack and pinion sector drive. the drive is nearly complete- a
little angle-aluminum runway lined with 60 grit sandpaper runs under the rim
of a sector that is lined with a permeable lining- the sandpaper grits are
like little gear teeth, sinking in the illustration board lining, and pull
the sector along. The runway ("rack") is of course pulled by a nut held
captive from turning, travelling along a threaded rod. But I digress.

I get my PC-7 at a "True Value" hardware store. I have used it for many
things, it is really more sophisticated than JB weld, and one can form any
kind of shaped thing out of it by making a littel skeleton out of galvanized
hardware store cloth and parging the PC-7 in and around it. It takes four or
five hours to become "relatively stiff", giving you plenty of working time.
Sets up almost completely in 8 hrs or more.

P.S. I have pictures of my new rack and pinion sector drive if anyone would
like for me to send some. I'll be driving the big mount (carrying my 16"
Cass. optics) with it. 140 minute drive, before re-setting the nut.

Clear skies-
Dave