After finding plans for a home built bending
brake on vansairforce.org
here,
I wanted to give it a try. I picked up the steel from a scrap metal
place for $37 ($0.25/lbs).
The rusty angle iron was laying around in the dirt and was quite
a bit stronger than in the plans. Fortunately, because I believe anything
less strong wouldn't have been stiff enough (my bending brake is a bit
longer than the one in the plans).
It took a while to remove the rust with a sand blaster and an angle
grinder. What a chore.
In deviation to the plans I added another end plate to the apron to
simplify the built of the hinges (see pictures). At first I planned
to screw this extra plate to the first plate (which is welded against
the apron). But I didn't have the right tap so I welded it all together.
That was a mistake, because the hinges weren't positioned optimally
(see below).
It was surprisingly easy to shape the bending edge with the angle grinder.
The radius is 0.25" and I wrap a aluminum sheets around the edge
to increase the desired bending radius, if needed.
I ended up having to correct a few things on my brake before it produced
acceptable results. The main problem with my bending brake was the alignment
and position of the hinges in relation the axis of the bending edge.
Tips:
- It is not easy to position the hinges. When you weld the end plates
make sure the apron stays parallel to the fixed beam even when rotated
up. Measure the width of the gap with a drill bit. Does the width
of the gap stays constant during the entire rotation?
- Use a long rod as hinge axis and stick it through both hinges. The
rod ensures the hinges are in one line and helps position them relative
to the bending edge. See the first picture.
- My bending brake would not rotate far enough. The spring back requires
you to rotate it way beyond 90°. My hinges blocked further rotation
and I had to remove material, which wasn't easy on the assembled brake.
- Don't position the pivot line too high above the bending axis. The
higher it is the more the apron will move away from the bending axis
and the less pressure it will put on the sheet metal. The pivot axis
on my bending brake was too high. I didn't want to re-weld the hinges
and mounted a 0.04" aluminum plate on the horizontal surfaces.
That worked well.
- Move the apron as close to the fixed beam as possible. There really
doesn't need to be a gap when the brake is "open". Since
the gap will widen when you rotate the apron you may end up with a
too large gap while closing the brake.
- Use a very strong handle. Mine is a 0.1" pipe and is already
badly bent and even cracked. The forces to bend a 50" 0.063"
2024-T3 are incredible high!
- The ribs of beam No. 2 (the fixed beam) in the plans don't allow
enough room to bend a 2x2 C channel. I had to pretty much grind them
away (see picture).
- Test your brake with C channels. Measure the width of your channel
at the ends and then in the middle. Does it stay constant? Chances
are that the width in the middle is greater than at the ends. At first
my brake produced unacceptable differences for that width. It turned
out that the pivot line was too high. After reducing the distance
between the bending axis and the pivot axis the width of C channels
was only little wider in the middle. The apron is now forming the
sheet metal closer around the bending edge because of the reduced
gap between the two beams of the bending brake.
- Verify that the beams you bought are straight. Mine were not.
- Bend beam No. 2 (the upper fixed beam) so that it has a bow that
points downward. With this you can apply pressure on the sheet metal
in the middle of the bending brake by fastening the screws at the
ends of the brake. A 12 ton bottle jack works very well to bend the
beams. I found two parallel beams under our house. Before I found
out about these I considered going to an unused rail way and use the
parallel tracks. You will need two fixed parallel beams that are quite
a bit stronger than the beams of your bending brake.
- Consider leaving the brake unpolished and mount an aluminum plate
onto the surfaces that are in contact with the sheet metal that you
bend.
- I think the maximal length of such a bending brake is pretty much
what I have built: 50". The plans point this out too, but only
after building it I also believe it.
Good luck building your brake!
Holger
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The parts after cutting, removing the rust and polishing the areas that
would touch the aluminum. Ready to be welded. The long rod through both
hinges helps position the end plates and hinges.
Bending the beam with a bottle jack under our house.
Bending the beam with a bottle jack under our house.
Finished assembled
The apron swiveled up.
Is it 90°?
Bending a C channel. This is a 4" wide channel. You can image a
2" wide will hit the ribs of beam No. 2 while overbending it for
spring-back. The next picture shows the changed rib shape because of
this problem. Also, here the extra plate for the hinge is visible.
The cut-out ribs of beam No. 2.
The blue lines mark the edges of the bending radius and the red line
is the center of the radius. I position the sheet metal so that the
red mark is in one line with the bending edge of beam No. 2 (when I
look down from vertically above it).
View from below. The apron is rotated up. You see the gap between the
apron and the bending edge. If that gap is too wide the bending radius
will not be precise. |
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