Westlake Publishing Forums

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.

Interesting!

Did the parts need much cleanup?

It will be fun to see how all this turns out.

Russ

I always clean the wax of with this: https://www.amazon.com/Black-Magic-800002222-Bleche-Wite-Cleaner/dp/B005R6LOZM/

I try to sand off any build lines I can get to, and parts that move get the touching faces sanded smooth.  I also dip them in Future floor polish prior to painting to seal them.  FUD is deceptively porous, and RTV does not want to let go if they are raw.  So there's 2 or 3 hours of prep work before molding.

Burl, Sealing the parts by dipping them in Future (now called Pledge Floor Care Finish) is one of those 'Why-didn't-I-think-of-that' tips. Thanks. The couplers look good.

If you had tried to mold a few without, you probably would have thought of it.   I completely destroyed a bolster pattern one time because I thought it was smooth enough without.

First waxes:

Nice!

Finally got all the waxes made up for this one & mailed them to the foundry yesterday:





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





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.

What a Herculean task. -- Russ

I wouldn't contest that it's been a challenge, but I have seen way more intricate projects on this site.  And I am enjoying the design challenges anyway.

I should also add, I had to redesign the striker casting.  If you look at my first photo, you can see the retainer plate is part of it.  After I got the prints in, I realized I could not put the yoke/shank assembly together with it like that.

Fascinating! I'm know of surprised at how many parts it takes to make a coupler.

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.



It was able to successfully rotate 360 degrees:



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.



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:

Most satisfactory. -- Russ