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Building Tips and technical articles. => Building techniques => Topic started by: Motorman on March 20, 2021, 05:42:57 PM
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What's you favorite way to put "Z" bend wire ends in carbon fiber push rods?
Thanks,
Motorman 8)
Motorman,
haven't used a Z bend in years. All ball links now. The old-school method still works though.
1) Drill a hole in the CF shaft just large enough to let the wire go through about an inch and a quarter from the end of the shaft.
2) Find a dowel that will fit snugly in the shaft, usually you'll have to turn it to Ø. While doing so, create a few radial notches in the dowel to act as glue catchers.
3) Drill a hole down the length of the dowel, and then cut it to a length of about 1" (Some people cut a lengthwise notch to the center. )
4) Slip the wire over the dowel
5) Make a 90° bend in the wire just long enough to fit in the shaft.
6) Cover the inside of the shaft with JB Weld and smear a little on the dowel.
7) Insert the wire and poke the L bend through the hole in the shaft
8)Slide the dowel into the shaft flush with it's end. This locks and aligns everything.
9)Smear JB Weld on the OD of the shaft from the end to just past the hole and wrap with thread or braided fishing line.
I've done them that way for decades and never had a failure, including a spectacular demonstration of entropy when a bellcrank broke on a 60 sized ship. The pushrods were broken but not at the ends.
If you must use Z bends , Z bend pliers are one of modeldom's greatest gifts.
Chuck
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I have used a dowel with a grove cut in to hold the wire about half way in, the wire should have 90 deg bend at the end of the dowel to anchor it, then JB Weld the wire/dowel into the end of the CF tube. I then do a thread wrap around the wire and about 3/4" back over the CF tube. Have not had any failures.
Best, DennisT
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Take your Dremel tool with cut off wheel and cut a slot in the carbon tube wide enough you can slide the L bend into the tube. CA and Kevlar will keep it in place. I've done this on sever carbon tubes not big enough inner dia. to get L bend in. Yes, wrap the end of the tube with Kevlar. D>K
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I would still drill a hole in the shaft, put a bend in the wire to clip into the hole, fill with JB weld and then stuff some balsa in the hole to secure it. Finish it off with some kevlar thread.
Craig
Craig
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Here's what I do
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Here's what I do
I looked at the thumbnails, said "yes, but I'd solder the wire to the music rod" -- then I expanded the picture, and hey! Whada ya know!
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You guys must be talking about arrow shafts. My push rods have 1/8" hole and I'm using .075" wire. I was thinking to put a few kinks in the wire then JB weld it in the tube. This would be just for the bellcrank connection because, I can service the other 3 ball links on a profile fuselage.
Motorman 8)
Yeah, but Euler's equations tell me I need a larger OD. The slenderness ratio is important. Problem with deflecting pushrods is they only seem to deflect when you really need them to be stiff, like the bottom of the hourglass after you overshoot the third turn.
Your plane's control system is not the place to be trying to save a fraction of an ounce. Heck, a lot of modern planes come out too light now anyway.
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I wouldn't even consider using .074" wire, nor a Z bend at the bell crank on any .35 sized model or bigger. May be OK for 1/2A.
Type at you later,
Dan McEntee
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Here's what I do
WOW! That's exactly what I do too. If you cut the Al. tube with a pipe (small) cutter it will fit the wire very well.
Cheers, Jerry
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What do you use to keep it on the suspended bellcrank? 1/8 wire takes some heat to solder, don't want to melt my nice bellcrank or the glue in the tube. What's wrong with a Z bend?
I use 3/32 music wire or push rod wire, depending on the model. I make one 90 degree bend with the vertical section a little longer than necessary, then either use a wheel collar or washer soldered to the wire near the bend. This gives a nice, wide, smooth bearing surface. On the other side of the bell crank, I again use a wheel collar or a washer soldered to the rod/wire. If there is room, I use the wheel collar while doing initial set up and construction so I can remove it easily if necessary. When you are sure of the assembly and movements, mark the location of the wheel collar, take it off, and grind a small flat spot where the set screw will seat, replace the collar and tighten the setscrew. You can set the clearance finer than frogs fur this way. You can then put a dab of thin CA on the set screw to lock it in place, or you can solder the collar in pace at the top. Then trim the rest of the rod/wire to suit. A little dab of the proper type of lubricant, and you are ready to move on.
The problem with Z bends is that you can't get a very tight bend without really stressing the rod/wire. You end up with a lot of slop at that point and a possibility that something can jamb if you get some excess wear On a sport model or something that you just throw together and you can afford a mistake at that pivot, a Z bend can work but like I said, it will be sloppy.
Type at you later,
Dan McEntee
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If you don't want to solder your washers on the suspended bellcrank you can use silicone fuel tubing. It seems to have an infinite life span. I have silicone tubing over 45 years old and it's still like new.
Washer, tubing, washer, bellcrank, washer, tubing, washer.