O scale Harp Switch Stand

Version 1
sectiionActually this is anything BUT a Ver 1 – I went through various different designs but since this is the first one I have had printed I will go with calling it that. In the photo I colored the two halves of the stand green and brown simply so they stand out a bit but both sides is exactly the same with one simply turned 180°. It is designed so they interlock.

On the left is a sectional view. Note the area circled. That is the swivel point for the lever. Pockets for the swivel pin are highlighted in red. The center example shows the stand ‘assembled’ and the right side shows it split.

body3One of the problems I have is visualizing the size of the objects I am working with .. and I am the person doing the darn thing! To help with this .. here’s a view to show the relative (actual) size of the stand. A dime and a figure. This is important as I get comments like .. “Oh. *simply* .. add a clevis-rod” .. this is SMALL .. and once you get out of virtual modeling you have to actually DO it .. make things hinge for example.
Initial Print
SWRenderI am having Shapeways print 10 ea switch stands (or 20 ea halves). This is in WSF – White Strong & Flexible. From that link – this material is produced by sintering Nylon powder with a laser. Basically .. using the laser to melt (sinter) the powder layer by layer. This creates a relatively strong plastic product but it does leave a texture to the surface. IMO .. in O scale it can pass for cast iron. The main thing though, for out purposes is that it SHOULD be strong enough to create a working/reliable switch stand for the layout.
Making it work
Making it work. We can talk about how we may *think* it could be designed .. but actually doing it can be a little harder. Ahh. “Aye, there’st he rub…” .. as the bard said (Hamlet Act 3, scene 1). To that end I will be roping in various individuals to help. Some of them are aware of the task .. some will be caught by surprise. The plan is to pass out the switch stand bodies and see how they might then be made operational.]

4 ea – to myself. I have four places I can use them and then 1 ea to Gary Wise, Andrew Gillette, Shawn Branstetter and Larry Knapp. That leaves two extra for anyone else who wants to join in the fun.

Note: I am *assuming* here that the two halves WILL lock together. I can assume all I want but until I have them in my hand and actually try to fit them together it is all a guess and a hope. Still .. with te assumption that they will fit together ok – I will proceed with some basics for our team.

Dimensions
section_1To start with I sectioned a switch stand vertically through the center so you can see what (hopefully) I am talking about.

For my “Design Team” the two areas of importance are the upper-section where the handle moves and down lower at the pivot area.

Pivot
section_2The two halves of the switch stand creates a pocket. The *plan* is that a small pin is thereby constrained within this pocket and act as a swivel for the handle:

  • Pocket Dia: 1mm/0.040″.
  • Pocket Depth: 0.7mm/0.028″
  • Pin Length: This is the total length possible – 3.1mm/0.122″
  • Pin Shoulder Length: This is the maximum inside distance between the shoulders of the swivel area – 1.7mm/0.067″
  • Bolt Hole: WSF is too coarse to make bolt heads this small so I added a hole where an aftermarket NBW can be inserted – 0.3mm/0.012″
Slot
section_3The top of the switch stand has a slot that the handle moves through. In the real switch stand there was a notch at the end of the slots to lock the handle into .. at least with some of the stands. I didn’t include that in Ver 1 – it may not be necessary with spring loaded switches.

The slot formed by the two halves of the stand is 0.8mm/0.032″.

Connecting Rod
section_4The hole for the connecting rod that connects to the the switch is 0.7mm/0.028″ dia. This pic also shows the mounting holes which are 0.5mm/0.020″ dia. This is about right for a straight pin which I used for mounting my modified caboose ground throw. They hold VERY well when set into a piece of wood and actually act much like steel anchor bolts would.
What next?
Once I get the prints in I will be sending them out for others to experiment with. I thought about making a pivot with a squared shank and insert a piece of .025″ music wire to act as a handle. The end of the wire could fit into a slot in the flattened section of the control rod. A flat handle would swivel easily enough on a 0.040″ pivot pin. How to connect the handle end to the connecting rod is the question. Perhaps something simple? Donno .. Aye .. there’s the rub ..


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