Couplers, revisted

[Burl]

Ray's post on changing scales inspired me.  He wanted to go bigger, and that certainly has it's challenges.  I, however, decided to try going smaller.

I wanted to see how small I could make a working coupler.  Trip pin, knuckle, draft gear and all.  At first, I was going to simulate the draft gear action with a spring... but then I thought: why not make the draft gear too?

I have been experimenting with using a cat whisker to trigger the trip pin.  Unfortunately, they are very easy to lose, and my cat isn't very happy with me right now.

More photos here: http://burlrice.com/couplers/

And before anyone asks, here's my scale:

[Bill Gill]

Hi Burl, Welcome to the forums. Nice work, but you'l have to knuckle down about  a couple things if you want to be taken seriously
How about a few words how you did it.

[finescalerr]

We need to change the name of this place to The Comedy Forum! -- Russ

[Burl]

When I first started making my own couplers, I was having a pattern made by Shapeways in brass.  I was sending these to a foundry, where it was duplicated in the investment casting process.  After a while, when I looked at how much I was ordering from the foundry, I realized it would be cheaper for me to do the wax injecting myself.  I have several years experience in resin casting, so the transition was pretty smooth.  I bought my own wax injector, a couple different flavors of wax, and started experimenting with platinum based RTV (all the Tin-cure RTVs I had any experience with were too soft).  It didn't take long before I was successful.



My first iteration of this coupler included the centersill as a cast piece:



After running a few, I could see it wasn't cost effective.  I was looking at $10-$12 for each centersill.  I also intended to attach the bottom plate with screws.  I was not thrilled with the idea of drilling and tapping all those tiny holes, but I couldn't think of anything better.  I also did not have a good answer for replicating the draft gear mechanism.

Then the light bulb came on: photoetch.  It would require soldering, but I figured I could silver solder the front & rear draft lugs, and the striker plate.  Then I could assemble the whole thing and solder the bottom plate on with a lower temp (silver-bearing) solder.  It worked acceptably, but I can see after making one up, I need to tweak the fit of some things.  Its hard to calculate exactly how the photoetched parts will bend, and a few thousands of an inch makes a difference.  And the price came way down - like $2 each.

In my next revision, the striker plate and the front draft lugs will be once piece.  They are designed to lock into the centersill when its folded, so no need for a clamping mechanism for soldering.  I'm also going to try using .032" rivets to hold the bottom plate in place for soldering.  Will post more photos as I progress.

[Ray Dunakin]

Stunning quality!

[finescalerr]

And clever. -- Russ

[Lawton Maner]

Jewel like work.  The humor of the illustration of the scale you work in will make you fit in well with this group. 

[Burl]

I have decided to rework my trip pin, and see if I can make it operable.  My first revision required the pin to be manually pushed up from beneath.  If this revision succeeds, it will be operable by a cut lever.

Here's a 3d rendering:



And here are the patterns ready for molding:

[Burl]

I got distracted last week with some unexpected dental work, but have gotten back to wax casting.  Here's the latest batch about to be sent off to the foundry:

[Bill Gill]

These will be exciting to see assembled!
If this works well are these couplers you are considering offering for sale?

[finescalerr]

Those turned out beautifully. -- Russ

[Burl]

Bill: If it works, AND I can keep the price reasonable, yes.