[TheForge] Upsetting the middle of a bar

[Bruce Freeman]

The following is either "book larnin'" or else something I picked up
from a demonstration or a video - I just don't remember.  But I haven't
tried it myself.

First, the physics:  If you tie a steel cable tightly between a heavy,
movable object and an immovable object, then push sideways on the middle
of the cable, the heavy object can be moved with ease.  The reason is
that the relatively small force exerted sideways on the cable is
translated into a large tension on the cable that can move the heavy
object.  It's rather like leverage, but different.  If you've never
played with this, try it with small objects and you'll be convinced...

This upsetting technique is sort of the inverse of the above technique
- a sideways force is put on a slightly bent bar to exert high
compression force along the length of the bar.  Drop a couple of drift
pins in your acorn table, separated by a little more than the length of
the ballaster bar.  Against one of the pins, put a (sideways) "stack" of
"shims" to reduce the distance between the pins to something a little
less than the length of the ballaster bar.  

Heat the ballaster bar to yellow in the center (preferably with a
torch, but heating on a forge and selectively cooling should work too).
Bend the bar slightly at the hot spot, place it between the two
pins/shims with the bend up, and press (or hammer) the bar down.  Repeat
this step, adding shims, until the desired upset is obtained.

Bruce
NJ

>>> irony at epowerc.net 10/27/2004 10:40:29 PM >>>
Y'all:
I have a stair and a parapet railing to make with about 60 balusters,
each having a long leaf forge welded near the middle of each bar.  My
stock is 5/8 square.  I am looking for a simple way to upset each bar
for the weld and am not having much luck.  I have used my coal forge
with a fairly narrow fire on some and on others, a rosebud to make the
heated area shorter.  I have been using a 2-1/2" depression in a swage
block as a base and either a 4# hand hammer or a special tool for my
air
chisel that is a cup about 3" deep.  Either way the process seems far
too slow.  If I use the air chisel and keep the rosebud on the stock
constantly at almost a welding heat it barely upsets the metal even
after 5 heat/upset/straighten distortion cycles.  Using the hand
hammer
seems to be the fastest way, but even that way it still takes 5 heats
or
so.  Is there something basic I'm not seeing here?

 Stephen McGehee
 Publisher of
 Irony, the sketchbook of an apprentice blacksmith
 P. O. Box 9822  Pine Bluff, AR 71611
 irony at epowerc.net 
 (870) 540-0142
 (479) 643-3299 (farm)
 You can see a sample of IRONY magazine here:

  http://lametalsmiths.org/news/page4.htm  )


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