Hot Wire Cutting Bows.
Here is an easy way to build a very
good, inexpensive bow.
I have had a lot of bows and this has been the best overall.
Here are the parts, they don't have
to be exact.
I used thin oak 7/8" square stock and round stock from "Home
Depot"
It was only about $1.00 for a 4' section. The wire here is for assembly.
You need a spring and a turnbuckle.
The square stock is cut to the
finished length of the bow. The edges
are cut to an inside radius by drilling through the board from each
side with a 1" bit. A pilot hole should be drilled first. The 2 bottom
pieces show the progression to the finished cut.
The round stock is cut to 12"
to 16" depending on the size of the bow.
These bows are 30" and the arms are 14" long. The sides of the
radiused
cut are notched with a file, so the binding wire wont try to slip off center.
The pivot point of the arm is also notched on both sides to prevent slippage.
The pivoting joint is made by
binding the 2 parts together with
thin braided nylon cord. The wrap is started on the cross bar and
tightly wrapped around the pivot twice, then it is wrapped around itself
on the bar to take up slack and hold the cross bar in compression so it
wont split down the grain. The tension wire on top is fed through a hole,
Then wrapped completely around the arm and twisted around itself.
The cutting wire (below right) is wrapped around a drywall screw that has had
it's head broken off. The feed wire is bound to the end of the arm.
The cutting wire is twisted around that binding to make contact.
The cutting wire is .024 SS fishing leader.
Here is the finished bow all
tightened up and ready to go. The rear end will
be suspended by a string from the ceiling, so it can clear the foam block.
Some other Bows.
These are the bows I used for left and right wing panels.
They have a tension
adjustment and adjustable trailing
bars. These required heavy drop bars
and had a spring loaded "lift" line from above to reduce the weight on
the templates. This system works very well and has repeatable results.
I cut more than 1000 airplanes on this set of bows. They are 1/2" conduit
with wood dowel ends as insulators. The middle bar is all thread and the tension
can be adjusted with wing nuts at the ends. Not as simple as the wood bows.
This is a "Parallel Arm"
cutting machine that I designed for cutting my
small "Noseeum" wing cores. The amount of sweep can be adjusted by
increasing or decreasing the amount of space between the arms at the
outboard end. There is a long spring running across the arms and it causes
the bows to travel forward, there are no weights with this system.