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The basic principle is a hinge. Like the Stiff records T
shirt said "If It Aint Stiff It Aint Worth A Fuck",
If you try to bend a couple of foot of 16 swg the folder needs
to be pretty stiff. The folder I made last weekend was OK
forming some small 12swg patches for a landy chassis, the
longest patch was 8" long, conveniently that was the
length of the folder.
I have taken a couple of photos, bear in mind this is made
from scrap and fairly quickly, even so it can put neat bends
in sheet quickly and accurately.
Figure 2 should have a piece of metal in it really, this
illustrates the principle, just a hinge. This folder is 1/4
x 2" angle and the clamp is 1/2" x 2". The
clamp piece is a bit that had been used previously as a clamp,
except it had been used near vertically before, the angled
face was bearing down on the sheet. If I had been able to
find some tube to weld to it to mount it like that again I
would of done, it wasn't stiff enough just bolted down.
A basic pan folder is the same as this except it uses loose
fingers instead of the clamp strip. I did a similar thing
with one of my folders the body was built with high sides
and an overhead clamping beam, basically I found a clamp that
was the right length and used a couple of scissor jacks to
clamp it down. I am told in a "proper" pan folder
the clamp looks like segments of angle iron held by a clothes
peg[?] with a clamp pushing them down, well I didn't really
understand either.
The place for material is probably a scrap yard. The folder
body needs to be stiff enough to support the loads from the
other parts, so if they are strong this needs to be. I have
my eye on a piece of 10" deep rsj for the body of my
next folder.
The folder part is much better if it is made from flat stock
with a bit of angle bolted to it, that way you can unbolt
the angle if you need a bend close to another bend and in
the opposite direction, s bend.
The clamp piece needs accurately locating, if you think about
radius of bend and metal thickness you can see what I mean.
In Figure 1 2x6mm socket heads can be seen these are locating
the clamp, the two sets of holes are for 0.083" and 0.061"
sheet. You need to overbend slightly when making a bend, to
get consistant bends stops are very handy. Bolting the clamping
piece down rather than some sort of clamp is fine, you need
to be able to get the clamp out easily when bending a channel.
My hinges are 4 pieces of thickwall tube, I just cut a 2"x1"slot
in the ends of the angle and welded the tubes in. The hinge
pins are some 1/2" socket heads. Each time I make one
of these I make my hinges like this, the centre of the hinges
should be the centre of the sheet bend radius, I haven't put
the centre in the right place on this folder. It would be
far better if the hinges had large diameter pins, an inch
or so, and the position was adjustable so it could be located
perfectly.
I should really go and look at a proper one to see how they
are made, there is nothing worse than redesigning the wheel
only to find they are round not octagonal.
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