O scale Telephone/Telegraph Pole Insulator Evolution

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Real World Insulator

I stole borrowed this from my friend Gary Wise. It is a common example of a telegraph pole insulator. This one is made to slip through a hole in a cross-arm, secured with the nut. There was also a large lag screw version which let it be attached elsewhere such as the top of a pole.

Here you can see the size compared to my hand. I suppose the black plastic could be Bakelite – being an early plastic, in fact the world’s first synthetic plastic in 1907 – but .. I doubt it is anything more than a fairly modern plastic.

Looking at the underside we can see that there was a wooden piece with threads. The rod you see in the first picture was bolted to the cross-arm and the insulator screwed down over it

The wooden piece was itself screwed into the insulator.

 

Version 1

This was my first attempt. The sprues are huge .. but you are limited in that Shapeways has a minimum wire dia for FUD (a wire being a shape that has a length that is 1-1/2 times it’s diameter). This means that .6mm is the minimum dia. I put the insulators on a central sprue. In hindsight while this worked it meant that you could only paint to rows at a time. Still .. they worked.

They came out pretty good overall. I didn’t like the big honking sprue as I said. Cutting off most of the sprue and inserting into a cross-arm worked and you mostly can’t see the oversize pin but what I wanted was an insulator that could fit over a wire. The problem being these little O scale insulators need to be sprued in some fashion.

 

Version 2-ish

I call this Version 2-ish because there were several versions .. I supposed should have been called Version 2a, Version 2b and so on. I was attempting to create a way for the insulator body to snap off of the sprue – leaving a hole for a wire pin. To do this I tried four smaller sprues at the top of the longer sprue. The picture is actually from my 1:24 version but the principal is the same.

Let’s call this Version 2a – arranged around a central sprue. The rendering shows pretty well the little ‘break-off’ tab idea.

and this one Version 2b. Here I changed the arrangement to vertically off of a base. The idea being it would be much better for painting.

In any case .. it didn’t work. It printed but those little tabs and narrow spacing etc. all fused together. Oh well. You gotta try.

 

Version 3

Next I wondered if I could rotate the insulator 180° and attach the top to the sprue leaving the bottom with the opening clear. There would be a scar where the insulator detached from the sprue but at this scale it might just be fine. Wanting to keep any such scaring to a minimum I made the little connecting sprue 0.4mm dia. I returned to a central main sprue since the insulators would be detached before painting.

It almost worked. Shapeways tried printing them and failed. The photo was from Shapeways. The model actually passed the software checks but failed during processing, breaking off where they attached to the main sprue. What I ultimately wanted .. but not while still being processed. Darn it.

So. What next? I considered increasing the size of the connecting-sprue from the current (and breaking) 0.4mm to 0.6mm .. but the problem is that now this sprue is starting to approach the dia at the top of the insulator. This seems to me to be a blind alley – heck I don’t know that increasing the sprue that much will even help. So .. to Version 4 ..

 

Version 4

I went back to attaching to the base of the insulator. What if I made a fairly large connecting-sprue as shown. The 0.38mm/0.15″ hole passes completely through. This size hole would let the insulator sit on a 0.015″ wire pin. I like this because the pin would be near to the full-scale 1/2″ dimension. I am pretty sure I can get a 0.38mm/0.015″ hole printed – not so much a 0.25mm/0.010″ hole. The 1mm O.D. is enough to give us 0.31mm walls – which is a slight padding to the 0.3mm minimum wall thickness for FUD/FXD. The idea is that you take a X-Acto knife and slice the insulator off of the sprue at the base of the insulator. I suspect the knife needs to be sharp as a dull knife might collapse the pin hole.

I arrayed 10 ea with a 0.5mm sprue connecting them together. I did a test-upload to Shapeways and it passed the checks.

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