[TheForge] bar twisters

[RIES NIEMI]

Ed- Dave's twister applies pressure thru the large spring which pushes the
pipe clamp carriage away from the motor.
However, I am not at all sure that it is necessary at all to apply such
pressure. 

I have the ferrari of storebought twisters- A Hebo, and it does superlative
twisting with no pulling action whatsoever. In fact, when you think about
it, the piece should actually get shorter as it is twisted. My hebo has dies
that are just loose enough to allow the piece to contract as it is twisted.
Most material will not contract a noticeable amount unless you are really
twisting it a lot. 
The hebo has about a 5hp 3ph motor, with fiendish german gear reduction, so
the torque is extreme. It will twist 1 1/2" square cold as tight as you
want, and a big problem with hot twisting is overtwisting to the point where
the metal just comes apart, like playdoh.
I was working on a piece of 1" square recently, with lots and lots of
reverse twists, and I would twist a section, then put it in the forge and
get the next bit hot, cooling with water the parts I didnt want to twist. I
over twisted it, at about the point when the twists were about 1/16" apart,
and the 1" square parted like tearing a hot chocolate chip cookie. If the
twister was exerting a pulling force on the bar, this sort of hot parting
would take place sooner.

ries