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Building Tips and technical articles. => Building techniques => Topic started by: kevin king on February 27, 2021, 04:18:30 PM
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Can some expert please tell me how to attach braided leadout cables to a 4" nylon bellcrank using soft copper tubing? What size soft copper tubing do I need? How big should the hole in the bellcrank be compared the the soft copper tubing that will be going into it?
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Can some expert please tell me how to attach braided leadout cables to a 4" nylon bellcrank using soft copper tubing? What size soft copper tubing do I need? How big should the hole in the bellcrank be compared the the soft copper tubing that will be going into it?
https://stunthanger.com/smf/gettin-all-amp'ed-up!/2016-electric-stunter-build-log/msg430387/#msg430387
Reply #36.
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Thanks Crist. That's a pretty informative thread, packed with good info. I don't have a torch so I guess I will buy one. But first I would like to know if the stuff the LHS carries will work or will it need to be heated up to?.
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The K&S Metals drawn tubing that you can get in the LHS or many of the hardware stores will need to be annealed. Whether you use the copper or the brass. The stuff gets work hardened when they form it. For a lot of applications, that's just what you want. But it makes it hard to bend to a tight radius without collapsing or splitting.
You can easily anneal brass or copper over the kitchen stove, if you have a natural gas cooktop. (Propane is even hotter!) Medium flame and probably less than a minute of holding the tubing at the tip of the flame. Watch copper turn a little glassy and the pull it out to air cool. The hardest part of the whole deal is to remember not to burn your fingers. You might want to take off the grates or whatever they are called so the flame is easy to get to.
No need for an industrial blowtorch rig.
The Divot
PS--What most guys use for lines and leadouts is stranded steel cable. It is not braided. They are just twisted individual wires. The manufacturing process causes them to have a certain twist and are pretensioned to lay against each other. Look closely at a piece and you will see the details. Wire rope and cable terminology is well established--but modelers invented their own lingo which may or may not be very accurate.....
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I do this all the time with a Benz-O-Matic torch. Heat up the brass red hot and let it air cool.
Better to spend $30 on a torch than to get caught using the kitchen stove for a modeling project.
1/16" tubing works for .027" cable. .027" cable will lift 125 pounds per line.
Also note: many hardware stores have the same K&S racks as hobby shops.
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Thanks Crist. That's a pretty informative thread, packed with good info. I don't have a torch so I guess I will buy one. But first I would like to know if the stuff the LHS carries will work or will it need to be heated up to?.
Note that like Crist's pictures, *you need the entire teardrop loop of tubing*, and one improvement I would make to his method would be to wrap the leadouts all the way up to and over the ends of the tubing, so it is one rigid unit, instead of allowing the possibility of deflection between the teardrop and the wrap.
Note that the partial protection "u" loop of tubing is absolutely notorious for the cable failing right at the end of the tubes, you cannot permit flex in that area.
Note that all of this does get heavy and it is critically dependent on workmanship to be acceptable. That's why I don't use bellcranks where the leadouts go through holes any more.
Brett
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Brett, could you show us your bellcrank to leadout set up? As for my self I always use solid leadouts. Never really liked the idea of stranded ones, but I wanted to keep this Vector 40 kit true to its original design.
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Maybe something like this? I now make the bellcranks out of what is called Garolite on the McMaster-Carr site. The nylon works OK but Garolite is strong enough and easier to cut and shape.
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Maybe something like this? I now make the bellcranks out of what is called Garolite on the McMaster-Carr site. The nylon works OK but Garolite is strong enough and easier to cut and shape.
That's how mine are. In mine the teardrop-shaped plastic insert runs on a polished aluminum electronic standoff, through which goes a 4-40 screw with a Nyloc nut, which is then staked in place with JB-weld.
Brett
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Note that like Crist's pictures, *you need the entire teardrop loop of tubing*, and one improvement I would make to his method would be to wrap the leadouts all the way up to and over the ends of the tubing, so it is one rigid unit, instead of allowing the possibility of deflection between the teardrop and the wrap.
Note that the partial protection "u" loop of tubing is absolutely notorious for the cable failing right at the end of the tubes, you cannot permit flex in that area.
Note that all of this does get heavy and it is critically dependent on workmanship to be acceptable. That's why I don't use bellcranks where the leadouts go through holes any more. "
does the loop at the bellcrank tend to straighten out after a pull test or after flying or does it remain as it was built..DOUG