set screws and bell cranks?

[joe]

Hi All,
I'm beginning on a design to build my own pedal steel guitar. I've worked on a bunch of different ones and am now foolish enough to think I can build one too.
One of the things that bothers me is bell cranks. Some types seem prone to loosening or breaking over time. Some are much easier to work on like when you are asked to change a copedant or add something. A bell crank is a simple mechanical device, but there are many engineering choices and decisions that affect success.
I've learned that I think I don't care for set screws on round cross shafts with flats. But maybe I don't know enough about the proper design. I was wondering about clamping the bell crank to a shaft. Clamping to a square shaft ought to work using 2 screws one on each side of the shaft.
The trick may be in making the heads of the screws easily accessible. Things are usually pretty tight by the time you get very many rods in there.
Opinions? Links to discussions of bell cranks?

[Bent]

Joe, set screws on the flat of a round cross shaft works. Myself, I use a pointed set screw on a square shaft. First I machine a 1/32" deep V-groove into the shaft so as to give the set screw some "bite". The parts of the bell crank that slip over the square shaft are 3/16" thick. This gives enough material for tightening up. I tested this in a jig and ended up putting about 60 pounds torque on the bell crank. The crank then started bending - the set screw held tight.

[Bent]

Here's a pic Never use anything smaller than a #8 set screw.

bllcrnk~detail.jpg (71.59 KiB) Viewed 1870 times

[joe]

Hey Bent,
Thanks for the info and especially the pics. I'm curious about the springs used to hold the rods to the bell cranks. Do you have to make them or are they an off the shelf thing from a spring vendor? I've seen them before on other steel guitars.
Joe

[Bent]

Joe, I make them and you won't believe how simple and quick they are to make in a very simple jig. I promised people earlier I would post pics and explanations on how to do them, so stand by...I really gotta get my act together and do it!

[joe]

I'm looking forward to knowing how to wind those springs. Many thanks.
Joe