Bonding Nylon Snake into Steel Socket

Hi,

I have a standard nylon snake inner which I wish to bond into a socket of a custom made steel fork end. The socket i/d is approx 0.005" larger than the nylon o/d. This can be increased if necessary. The steel does not lend itself to compressing to effect a grip.

The snakes are to control rudder & elevator of a radio assisted "Junior 60".

Does anyone know of a readily obtainable material which will reliably bond this joint?

Regards, Peter Gain.

H'mmm...if I understand you Peter this is a bit like the sort of "threaded end" you might solder onto a piece of wire but you want to glue it to the exposed end of a nylon snake.....

I would feel a bit uncomfortable with this as you are then relying on a glue joint. Nylon is not an easy material to glue at the best of times & as I understand it the inner rods are often coated with PTFE to make them slide through the outers with less stiction...... PTFE is almost impossible to glue....

When I use snakes they are usually terminated by a short length of M2 studding that then screws into a clevis....could you perhaps modify your steel fork so it has an internal M2 thread & could screw onto an M2 thread like a clevis?

Use a 'solder extender' or 'closed loop extender' from SLEC ( see website ) if you cannot use just an M2 ' threaded insert' into the snake. Then solder onto the fitting. But much better to use proven commercial fititngs throughout!

The easy way to insert these studding threaded ends into a snake is to get a spare ( or old ) metal clevis and spin it onto the studding then put another M2 bolt or studding or threaded part into the other end.  When tightened by hand this will lock the clevis on and allow the studding to self tap into the snake.  Bend the old clevis arms out to get a decent hand grip ( dont reuse after! ) Afterwards unscrew the locking bolt then the clevis will come off the studding without unscrewing it from the snake.

Note that some American snakes may use non metric threads which are very slightly different and make a slightly sloppy fit.

Edited By kc on 03/08/2012 13:09:30

Edited By kc on 03/08/2012 13:16:53

Edited By kc on 03/08/2012 13:29:46

doesnt sound a great idea,  unless you can crimp the thing that the nylon is going into,  can you not just closed loop both surfaces, easy enough

Edited By Alan Cantwell on 03/08/2012 15:21:05

wrap the nylon inner with one layer of cotton or fine thread tightly and push your clevis on using epoxy as an adhesive . it works .

Nice on Myron, belt and braces job.

OK so the difference is 5 thou? Well I agree with the others - you'd be better adding a proper M2 termination. But if for some reason you cant you this then abrade the snake end to provide a textured surface. Note, "abrade" not slash to bits! You just want a clean, slightly roughened, surface. If you are at all unsure then abrade inside the socket as well. Then expoxy the two together. With a good keying of the surfaces and only a 5 thou gap the expoxy will be plenty strong enough and it simplier than the cotton packing.

BEB

I don't think epoxy will make a good joint. If you must consider this then make a test joint from a scrap piece of snake and test to destruction. Either BEB etc will be proven right or I will be right!

I still favour an M2 threaded end ( or studding ) soldered into the clevis, maybe sleeved with brass tube to make a close fit. Why take chances?

Hi,

Thanks for your replies. I think some respondents did not understand the problem. However, I will take your collective advice on board & for this model ("Junior 60" revert to commercial fittings. Next time I will plan ahead (no small radii bends) & use metal control rods then I can silver solder all the joints.

Regards,

Peter Gain.

Hi,

This to BEB.

Why did that silly blob appear after Junior 60? I certainly did not type it.

Peter Gain.

Hi Peter, maybe I can explain about the silly blob.

It's called a smiley or an emoticon. We can add them by using the smiley button above the posting box.

But we can also add them by typing a few punctuation marks next to each other, which is what I'm guessing you did?

I'll try a ; next to a ) at the end of this line and see what we get.

Maybe a picture or two would help our understanding Peter...

Peter is the snake one of the small ones with a yellow tube outer and a solid white nylon inner?

If so I have sucessfully screwed these into a female thread, probably M2. This is pretty secure and could be backed up with some epoxy.

Hi,

To BEB.

Please advise as to how one up-loads photos to this forum. Also preferred format, jpeg, TIFF, or other? Size? Resolution?

Regards,

Peter Gain.

Hi Peter

To see how to load pictures go to the main index page here

Then find "The Site Platform" and then "2012 Forum How to's"

There's tutorials there for a number of different forum techniques.

Hi,

Thanks to all who replied. As suggested, I decided to carry out some tests. The results are as follows.

The test.

Object. To determine the breaking strain of various mechanical joints between a 0”.080 (80 “thou&rdquo dia nylon snake inner rod & it’s end fittings. All proprietary items ie. fittings & snakes were purchased from the LMR. Workshop made fittings were produced by the author. This size of snake is suitable for small to medium size model a/c not subject to violent aerobatics. Specifically a “Keil Kraft” “Junior 60” powered by a home workshop built 6cc spark engine.

Equipment. A Record 4” bench vice, and an angler’s spring balance graduated 0 – 22 Kg. See photo.

Method. The blank end of the nylon inner was gripped in the bench vice. The opposite end ie. the fitting, was attached to the angler’s spring balance. A horizontal force was applied to the handle of the spring balance. Readings of the point at which the joint failed were recorded. In some cases where a high loading occurred the reading was noted & the load removed before rupture. The vertical component was ignored, as it will be very small in relation the horizontal one.

Results.

1) Nylon inner, no joint. A load of 18Kg. was recorded. The nylon did not rupture.

2) Nylon factory crimped into proprietary clevis fitting. The nylon pulled out of the socket at a loading of 11Kg.

3) Workshop made joint with nylon glued into a steel socket using cyano. No crimping. Joint failed at less that 0.5Kg.

4) Nylon crimped into workshop made steel socket. A reading of 15Kg was recorded. The joint did not fail.

5) As test No.5. A reading of 17Kg was recorded. The joint did not fail.

6) Threaded joint. The nearest thread to 0.080 dia. is M2. As a M2 die was not available, the nylon was threaded 8 BA. (8 BA is 0.087dia with a core dia of 0.066). The steel socket was tapped 8 BA. The joint failed at 18Kg. As would be expected the failure occurred at the thread root, at the point where the thread runs out.

7) As a comparison, a 16mm wide plastic hinge was tested. (Ie., the type of hinge likely to be employed with this size of snake). One side of the hinge was gripped in the vice; the other side was attached to the spring balance using a tool-maker’s clamp. The hinge failed at 19KKg. As would be expected it failed across the thinnest section.

Conclusion. With the exception of the “glued only” joint, all other joints far exceeded the expected loads that would be applied in service. The loads noted were such that airframe structural failure would occur well before these figures were reached. It was therefore considered that the above tests are valid for the above size of model. The threaded joint gave the neatest result.

Caveat. An accredited test laboratory would test very many samples, not just one of each type. However, as the loads achieved were so far in excess of airframe integrity it was concluded that the tests are valid.

Peter Gain.

Hi,

Apologies for the stupid blob. I typed in Word then pasted into the thread, thinking that this would inhibit the confounded thing. There must surely be a way to beat it.

Also, not sure why two pics appeared.

Regards,

Peter Gain.

As a pro - I'll give you an "Alpha-" for that lab report Peter.

The minus is because you didn't test epoxy. CA would never hold a joint like this - its mechnical strength in bulk is very poor. But I still feel that, approriately keyed, a well cured epoxy joint would support a fair load.

BEB

PS The "blob" appeared becuase the html interpreter used here sees certain combinations of characters as shorthand graphics - and example is a colon followed by a close bracket - ie

Great tests Peter, I'm pleasantly surprised at some of them, particularly the threaded one. I'm pleased with that one though 'cos I use it.

Of course what you need now is a mechanincal rig to do repeated pushes and pulls to see which resists stress fracture the best. (Only joking).

Well done

Chris

A well presented and methodical piece of testing Peter. very interesting