Building Tips and technical articles. > Building techniques
Bellcrank post.
Perry Rose:
I've always used 1/8 music wire for the post and the hole in the bushing is larger causing some slop. The other day I was looking for some 1/8 wire and came across a piece of wire from a political sign support. It's a perfect fit. I know it's not as stiff as the music wire but trying to bend a 2 1/2 inch piece by hand isn't possible.
Jim Svitko:
What are you using for the bushing? 1/8 music wire or 1/8 A2 steel rod fits very well into a bushing made from 5/32 brass tube. Of course, there is some slop, but not enough to be concerned about.
Kim Doherty:
--- Quote from: Perry Rose on April 19, 2021, 01:06:35 PM ---I've always used 1/8 music wire for the post and the hole in the bushing is larger causing some slop. The other day I was looking for some 1/8 wire and came across a piece of wire from a political sign support. It's a perfect fit. I know it's not as stiff as the music wire but trying to bend a 2 1/2 inch piece by hand isn't possible.
--- End quote ---
Perry,
Go get your bathroom scale and two small blocks of wood. Suspend the piece of wire (cut to length) between the blocks and use another piece of wood the same thickness as the portion of the bellcrank that will bear against the wire and push on the wire in the middle until you see 40 pounds. You will never reach this value while still flying. If the wire has not bent you are good to go.
Kim
Brent Williams:
I doubt the metal from a political sign is very good for our needs. I would suspect it is soft and flexible.
A high speed steel 1/8" drill blank is very strong, very smooth and polished. Much nicer than rough music wire.
1/8" x 2.75" = $1.91 https://www.grainger.com/product/VERMONT-GAGE-High-Speed-Steel-Jobber-Drill-403H63
The phenolic material is tough and fairly self lubricating. An additional brass bushing for the post seems a bit redundant, imho.
This bellcrank example is from Crist Rigotti. Simple and effective.
Avaiojet:
--- Quote from: Perry Rose on April 19, 2021, 01:06:35 PM ---I've always used 1/8 music wire for the post and the hole in the bushing is larger causing some slop. The other day I was looking for some 1/8 wire and came across a piece of wire from a political sign support. It's a perfect fit. I know it's not as stiff as the music wire but trying to bend a 2 1/2 inch piece by hand isn't possible.
--- End quote ---
That's inexpensive wire and it's not tempered. I wouldn't use it.
Unless the sign industry has changed?
Why not sleeve the post and drill out the bell crank? This will remove slop but not ware.
Once the lines are tight, the slop isn't felt, or is it?
Why are you bending a 2.5" piece of wire? Heat will do this and a good vice. I bend 90's all the time with mu wire bender?
Do you have a wire bender?
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