[TheForge] Fly Press

[Don Sinclaire]

Michael Horgan:
I used a 1-1/4 inch screw and nut that I picked up at a scrap yard, not
aware that it was a 2-start screw.  It looks like 4 TPI initially, but
because it is a 2-start screw, the threads are at a steeper angle, and the
screw advances 1/2 inch per turn.  This worked out OK but the diameter is a
bit small and I will have to be careful that I don't damage the screw.

If I use a 2-inch screw, it should really have a much coarser thread so that
it still goes down fast enough- it should almost free-wheel down on its own
in order to have a good "feel" and not bind when it bottoms out. I don't
think it is possible to turn a screw like this on a lathe, since it would
advance so fast that you would have to be careful not to run the tool into
the chuck.  Check the other posting regarding the use of a screw from a gate
valve.  Probably not a good choice, but I have not rulled it out yet.

I would like to try a 2-inch 4TPI Acme screw, but the bolt supply shop here
wants $105 for a 3-foot length, and the nut is $40.  And that is at
wholesale.  If you can find those parts at the scrap yard at 15 cents a
pound, it would be worth a try.  At worst you would have a pretty good arbor
press.