Type-F rotary couplers in 1:29

Burl Rice

Burl Rice

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rotary_pattern.jpg


I spent probably 2-3 weeks drawing this in Sketchup. Finally got to where I was satisfied I understood how everything was supposed to work & ordered my prints from Shapeways. They came in this morning. There are painted gloss black to make them easier to mold.

This is a departure from my past approaches. Before, I tried to figure out how to make the shank rotate separately from the head. This time, I am attempting to model a prototypical draft gear & yoke.
 
Finally got all the waxes made up for this one & mailed them to the foundry yesterday:

rotary_wax2.jpg


I would have been finished a week ago, but this particular piece turned out to be more difficult than I had imagined:

rotary_wax3.jpg


I re-made the mold at least 5 times. I kept getting air bubbles in the spring pocket. My first attempts were to cast it without the openings. I planned to carved them out later. However, the RTV is so thick, I never could get it to flow completely into the cavity. Even after I opened up the pattern, I still had trouble getting it to go in. In my last attempt, I vacuumed the RTV (a second time) after I poured the mold. Still, I had a couple small air bubbles, but I could cut those out of the casting. I am currently pouring yet another mold, which has been vacuumed, and is now curing in my pressure pot at 60 PSI.
 
Interesting. Are you planning a rotary coal dumper ?
 
Not exactly. The prototype I model (Nashville & Eastern) runs two types of cars that use rotary couplers. Both are used in scrap metal service. This is more of a bucket-list, see-if-I-can-do-it, project for me.
 
Made some progress on assembly today. Definitely the most complicated thing I have built in a while. Took me 3 hours to put one together. Hopefully the next one will go together faster. I think I counted 14 individual pieces, not counting springs.

rotary_top.jpg


It was able to successfully rotate 360 degrees:

rotary_top_rotated.jpg


I'm still experimenting to find the proper strength for the draft gear springs. It still seems a little stiff. I may try phosphor-bronze wire, instead of music wire.

rotary_bottom.jpg


The trip pin is actuated by a lever on the bottom (this is what the cut bar will press on the finished model). It has an internal spring to keep the pin down when the coupler is upside down. I used an HO scale Kadee knuckle spring for this. In this photo, you can see open vs. closed:

rotary_knuckle_detail.jpg
 
I hooked them up to a rotisserie and shot some video. First time I think I've tried something like this, so it may be a little rough.


rotary_coupler.gif
 
These are awesome!

I presume you have mainly left the 'out of the mould' finish? - Think you said cast in brass?
Other than not covered in grease, and muck, these could be full-size.

How do you get a finish like that?
More importantly, how robust is the finish? - Does it wear easily??
 
After everything is assembled, I clean them with a 2:1 mixture of distilled white vinegar and hydrogen peroxide. The solution is warmed up in the microwave to make it work faster. This gets all the dirt & flux off, and helps the blackening to take. It also speeds up the oxidization process, and turns the brass a deep brownish/green.

After they're rinsed in cold water, I apply a chemical blackening agent (Birchwood Casey Brass Black).

Chemical blackening won't affect the soldered areas, so I apply a light coat of Krylon Camo Brown spray paint.

You can see in the video some areas where the finish has worn off & raw brass is visible. Since these are my "proof of concept" pieces, I have been carrying them around quite a bit. I assume in normal model railroad operation, they wouldn't get tumbled as much. I also suspect the raw brass will oxidize over time.
 
I should also add: it helps to shoot photos out doors, under natural sunlight. If I shot the same couplers indoors, the finish wouldn't show the same amount of depth.
 
Thanks for the extra information..

The investment it time and materials you have put into this is impressive.
 
PhilP said:
Thanks for the extra information..

The investment it time and materials you have put into this is impressive.
Click to expand...

It's surprising what can be achieved when you 'knuckle' down to it....

David
 
I had some time to work on the yoke drawing for the non-rotary end. This will eliminate a couple steps of assembly.


rotary_coupler10.jpg
 
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