Insulators of glass or pottery have been made for use on telegraph poles since 1844. Later, as technology advanced they were used for telephone lines, electric power lines and other applications. Thousands of different styles of insulators have been made. Most common are those of clear or aqua glass.
This one I found along the side of a railroad. It might have been used for telegraph I suppose. I used this as a guide for making copies in miniature.
|and .. here we go .. converted to a 3D mesh. This is pretty much a copy of the prototype insulator .. which by the way isn’t glass but a plastic – bakelite possibly.|
Here’s a cross-section of the insulator reduced to 1:24. At this size the only problem will be where the metal pin screws into the insulator. The brown was a wooden plug. Now – I have to figure what part of this I can reproduce. The problem here is that the 1:24 insulator is 4.23mm x 3.66mm. This is smaller than the 5x5x5mm minimum for printing in FUD. The human operators have to be able to handle the parts. This means the insulator will have to be mounted on a sprue – so .. what are the constraints?
Constraints – Min unsupported wires – 0.8mm or 1.0mm if bearing weight (like a sprue)
So. Take a look at the insulator. The hole in the wooden plug is 0.65mm dia. The wooden plug itself 1.3mm .. and it would be ‘nice’ to have at least a 0.8mm ‘wire’ to connect to the sprue. It makes sense to me that we would want to connect the sprue to the area of the wooden plug since that will be hidden. Ok .. now .. comes figuring out exactly HOW to do that.
|Connecting to the wire|
We cold ignore that 0.65mm pin hole as far as trying to get it that exact size as we are trying to reproduce this in miniature .. but have to be realistic. It makes sense to me to make that hole a standard size. That converts to about 0.025″ dia. though which is available from K&S (stock No. 500 in a 36″ length). leave the hole 0.065mm dia since that 0.025″ is 0.635mm dia. That’s fine .. but what’s next?
Ok. We have to have a short stud/wire to run from the inside of the insulator down to a sprue so we can reliably print them. The size by the way of the ‘wires’ is sufficiently strong enough the parts can survive the cleaning process after printing.
That cylinder representing the wooden plug .. how thick are the walls? 1.3mm – 0.65mm = 0.65mm. Divide that in half and each wall is 0.325mm .. just above the 0.3mm minimum wall thickness for FUD. So far .. good.
Simplification .. simplification. I merged the wooden plug into the body and then changed dimensions on the body so I have minimum 0.3mm walls and any groove above the 0.1mm minimum detail for FUD. The sprue shown in tan. This SHOULD pass the Shapeways software checks.
The tabs that connect to the bottom of the insulator .. they only need to be 0.3mm wide .. about 4 spaced around should support the insulator well enough but also should be easily snapped off at need.
|The ‘wire’. The upper portion 1.45mm fits up into the insulator body .. the minimum walls 0.3mm .. so everything should again .. pass the software check. I made the body 0.8mm dia to match the 0.8mm wire constraint and 3mm long .. that is only about 1/8″ .. but enough space that the cleaning process get in there.|
|Here, I extruded the wire out and cut away the top so there are only 4 small tabs – each 0.3mm wide. These SHOLD .. AGAIN .. pass the software checks .. and support the insulator body .. AND be small enough they should allow me to twist the wire off the insulator.|
|Finally, putting it all together. The insulator at the top with a hole in the center for a .025″ stud/screw that in turn fits into the pole arm; the ‘wire’ attached to the bottom of the insulator with four .3mm wide tabs that will break off (hopefully) and finally at the bottom a bit of the 1mm sprue.|
|Here is an array of twenty insulators arrayed in four rows of five around a sprue that is 1mm square. There should be plenty of space around the parts for cleaning. It is also important that the parts not be too close together – you can get a ‘welding’ effect if the clearance is isn’t at minimum 0.10mm for FD and 0.05mm for FUD.|
|By putting six copies into a mesh I get 120 ea. This pretty much maxes out the most that can be printed in one mesh as I am near the 60mb file limit. There are ways to reduce the polygon count/file-size. That basically reduces the number of sides of a circle (think of a hexagon bolt as a 6-sided circle) .. and I may try that at some point ..it *probably* wouldn’t make a difference at this size.|