Wire in tube point operation: Z bend

[philsandy]

I have built points for a TT120 layout and plan to operate them by wire in tube method using slide switches.

Did a search on here and some advise using a Z bend rather than Omega wire. My question is does the Z bend have to be made from sprung wire or can the Z be made DIY, by bending it into the actuating wire, which will be 0.8mm dia. piano wire.

Also where is the best position for the Z bend, close to to point tie bar or at the slide switch, or does it not make any difference?

Edited October 3, 2023 by philsandy
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[34theletterbetweenB&D]

Always as close as practical to the point tie bar; the principle is to have as little friction as possible by direct drive to the wire in tube run from the actuating location.

[DCB]

I wouldn't use a Z bend. The Omega loop gives a straight  pull or push and has no real stress raiser kinks.   The Z bend has two stress raisers in its sharp bends which will likely encourage it to snap off at the bend.  It also risks putting side thrust onto the mechanism.  Wire in tube works best with dead straight runs, if your runs are dead straight whether the omega is at the point end or switch is a bit irrelevant, it obviously looks best at the switch end.   0.8mm means nothing to me but I use piano wire for handrails, so best of luck making piano wire into an Omega Loop and a Z is probably going to snap when you are making it.  A couple of coil springs at the switch end would be my go to.      

[Darwinian]

I have used a Z bend in the drive to my point tiebars (00 handbuilt track) from Fulgurex point motors. Simply bent into piano wire although I think mine is nearer 0.5mm. I bend it so that the drive in and drive out are opposite one another. Also try to keep the bends to each side equal. So more like two Vs linked together.

They absorb the overthrow of the motors and keep light pressure on the thrown tiebars. No problem with failures so far.

[philsandy]

1 hour ago, Darwinian said:

I have used a Z bend in the drive to my point tiebars (00 handbuilt track) from Fulgurex point motors. Simply bent into piano wire although I think mine is nearer 0.5mm. I bend it so that the drive in and drive out are opposite one another. Also try to keep the bends to each side equal. So more like two Vs linked together.

They absorb the overthrow of the motors and keep light pressure on the thrown tiebars. No problem with failures so far.

 

Thanks for your reply.

Drive in and out opposite one another, does this mean the straight lengths of the wire on either side of the Z are in line with each other?

[Darwinian]

Yes. 

 

[JeremyC]

To reduce the chance of the wire breaking at the corners I would suggest you form the bends with round nosed pliers so they're more of a curve than a sharp bend.