Gem Mercontrol PTFE tube

[John CutlerParticipant]

I am having great difficulty with threading the wire Gem provide, through their PTFE flexible tubing.

I have learned to cut the tube with a craft knife rather than scissors. But I still drill out the end (0.45mm) to get access for the wire. Forcing the wire through is the main issue. It seems cutting or (inadvertently through gripping) crimping or kinking the tube dooms the wire to clogging or digging through the tube. It is possible the wire has sharp leading edges which need rounding/chamfering off, but I do not have the equipment/expertise/eyesight to do that.

Even getting the Gem wire of 0.48mm diameter through a few inches of tube results in a stiffness that makes me believe this system will not work efficiently over the 85cms curving run needed. I tried adding Vaseline to the wire but this just means gripping the wire to feed into the tube becomes messy if not impossible. The wire supplied is just too thick for the PTFE.

Plan B is to use a thinner wire. I tried guitar wire gauge 16 (0.4mm dia) but this gave me the same problem.
I have read a recommendation to use 0.3mm steel so have ordered some gauge 12 (0.3mm?) guitar wire to try out.
Will that be strong enough?

I have got some much thicker model aircraft control cable which uses nylon (2mm dia) in tube. This functions superbly and smoothly but is awkward to affix either end. Is there any supplier of similar nylon cable in a much smaller diameter? I am surprised no-one seems to promote or sell this sort of system for model railway use. Some model railway products seem stuck in 1950/60s technology.

Annoyingly I only need this control cable solution for one awkward (and stiff-bladed) turnout. I seem to be spending disproportionate time and money on it!

Any ideas will be welcome (Plan C?).
(Not servos; I do use them elsewhere. And definitely not solenoid motors; my experience is that their force is destructive)

Thanks
John Cutler

[John CutlerParticipant]

Plan B using guitar wire gauge 14 (0.35mm dia) works well! No Vaseline needed!

I also bought some new Gem wire. This seems slightly thinner at 0.46mm diameter than my previous purchase from a few years ago but is still far too tight a fit in the PTFE tube. So this is filed in the spares (=junk!) box.

John Cutler

[Ray BydeParticipant]

Have you tried using thick walled, small bore copper tubing instead of the PTFE tube? This is what used to be supplied with Mercontrol point control system. I’m not 100% surre if this is still available as I bought mine several years ago, but I have used it with 0.5 mm piano wire and it works quite well. As long as the wire is passed through the copper tube before you try to curve it, it will go round quite tight curves.
RayByde

[Author]

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