I love PC-7. Another thing that can be done along these same lines
which can get very thin and light, although of limited strength is
making a sort of "tortilla". One nice thing about pc-7 is that it WON'T
stick to polyethylene (saran wrap, etc.) What I have done is to lay out
a sheet of plastic wrap, a layer of lightweight hobby fiberglass, a
small blob of pc-7 and another layer of plastic wrap. Then take a
rolling pin and roll it out very thin like a tortilla, and you now have
a flexible sheet which can be wrapped around a form. When the pc-7
cures, remove the now hard shell from the form and peel away the plastic
wrap. The result will be a thin hard and shiny shell, suitable for
housings, robotics etc. Groovy, huh?
This has limited strength but I think it all depends on the thinckness
and the type of mesh used. Using steel mesh and more thickness would of
course result in something stronger. You can also extend pc-7 by mixing
sand with it. Gives an interesting effect and can also be used as an
abrasive thingee.
Cheers,
Pc-7 of 9.
David Harbour wrote:
>
> 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