Securing metal wire to carbon tube pushrods.

[Brian Sweeting 1]

I'm wanting to make up some lightweight pushrods for my Min-Bee glider so have just got a length of 2mmOD x 1mmID carbon tube.

 

I already have 0.5mmOD metal wire for the servo and hinge links but am wondering about the best method of securing the wire inside the carbon tube.  Apart from putting some minute crimps in the wire end it a basically a straight round wire in round tube connection.

 

Would a CA glue be good enough or should I go for an 2 pack epoxy joint.

 

Any advice is welcomed, thanks.

Brian.

[Geoff S]

I usually use 3mm carbon tube with a 2mm hole in which I epoxy 2mm threaded rod but perhaps that's too big for you?  In your case, I'd hesitate to try and glue any metal wire less than 1mm in diameter. The 0.5mm is too small IMO.  One way you could try is to pack the tube with balsa to make the wire a tight fit and either use epoxy or cyano though I'd go for the epoxy.

 

Geoff

[Martin Harris - Moderator]

Perhaps try bending the end of the wire back on itself and back again to form a triangular bundle to insert into the carbon tube which would take up most of the excessive clearance and give a larger gluing area for a wipe of epoxy?

 

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(without the spaces)

 

Alternatively, how about a 0.5mm hole in the flank of the tube, form an L shape on the end of the wire which goes into the hole and bind the wire to the outside of the carbon rod with glue soaked thread whipping.

[Brian Sweeting 1]

Martin, I like the idea of tripling up the wire with epoxy, well worth a try.

 

Your second suggestion is my current method but using a balsa pushrod, I do cheat a little by using shrink tube instead of thread whipping though.

 

Geoff S, I appreciate your comment on the small diameters in use and the packing idea is something I hadn't thought of.

 

Thank you both.

[Engine Doctor]

Don't use epoxy with cf tubing. It can often go soft when mixed in small amounts likely to be mixed for these jobs. Thick cyano is much better as it sets solid then bind with some thread to stop tube splitting then run cyano into the thread.

[PatMc]

I've used kevlar thread like this & medium cyano. Just double the about 1cm of the wire back on itself before whipping with the thread. You won't be able to remove the wire from the carbon even if you want to once the CA has gone off.  

 

PS I've used this method for single wheel U/C strut on indoor models.

Edited June 25, 2021 by PatMc

[Andy Gates]

CF rod, thin wire?

 

In the past I have used heatshrink to hold the wire in place then run thin CA down the side of the wire. Not broken on yet BUT I only use this on park fly type models.

 

When I have "retired" the plane to the recyclers (dust bin) I have had to slice the heatshrink away to give me any chance of removing the rod.

[Paul De Tourtoulon]

You can always do it the other way around, your wire in an "L" up the inside and jammed in with a drip of cyano on a round slither of balsa.

[Martin McIntosh]

JB Weld will hold (roughened or threaded) wire to carbon very well but would be an overkill with 1mm i/d on a micro model where heatshrink, plus maybe a bit of ca should be fine. On more normal 2 or 3mm holes I prime with 3M 05917 polyolefin which will allow you to ca or JB almost anything to anything else.

[Brian Sweeting 1]

Thank you all for your thoughts and ideas.

 

I have gone with the heatshrink with a flow of CA down the wire which seems to have acheived a solid fix.  Time will tell but as the model weighs in at 125g I don't think things will be too heavily stressed.

Edited June 27, 2021 by Brian Sweeting 1
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