I suppose you mean an arrangement of arms and clamps. This is an old
tool, originally designed for jewellers I believe. Similar tools are
available from several sources. Try Micromark and Model Expo. Walthers
shows "positioners" in its tools section, also.
However, you should be able to whomp one up yourself,
of the sort that hold the car *from the inside*.
Note that this is only useful for "shells" of box cars, locomotives,
hoppers, and the like.
A. Take a stick of balsa or basswood or pine, maybe 8..12" long.
Maybe pine 1x2" (so-called, of course).
Glue a block of foam rubber, such as a cheap kitchen sponge onto each of
two opposite sides. May take some experimenting to figure out how thick
a piece of wood you need based on the thickness of the foam rubber you have.
Come to that, a plain ol' spongey sponge should work well enough,
although it will not be as compressable.
B. Find a pair of toaster tongs -- two long flat blades of wood or metal,
that are joined at one end and separated by a wedge.
Add blocks of foam as above. This version has the advantage that you can
squeeze the blades together (as if gripping a piece of toast)
to make it easier to get the device inside the car,
then let go ones the ends (where the sponges are) are in place.
C. Get a strip of springy metal, and bend it into a U shape.
Proceed as with the toaster-tongs method (B) above.
If you use metal that will deform as well as spring (e.g. brass),
you may find that you have to keep spreading the tongs from time to time.
Perhaps a small coil spring from a local hardware store (or your favourite
uber-hardware-store) will help.
D. Use a couple of lengths of springy wire, bend each one into a U shape,
and stick the ends into a flat piece of wood or Homasote or ceiling tile.
(This is what I do with my N-scale cars, only the wire isn't even that
springy, it's just old solid-copper telephone hookup wire.)
E. You could probably adapt either of the "tongs" methods to work the other
way around, so as to *clamp* a car by the underframe, so that you could
work on other kinds of cars that have no "insides".
Electronics places have various vises for hoolding PC boards. They are low
pressure type vises and can be had with different clamp arrangements.
Personally tho, I prefer to use a large piece of foam which I have cut a
slot in of the right dimensions for HO equipemtn. It is soft and holds
anything without any real problems. You can even hold a boxcar on end if
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