Link and pin couplers in 2.5" scale

Discuss park gauge trains and large scale miniature railways having track gauges from 8" to 24" gauge and designed at scales of 2" to the foot or greater - whether modeled for personal use, or purpose built for amusement park operation or private railroading.

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OddDuck
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Link and pin couplers in 2.5" scale

Post by OddDuck »

You know how you can get a song stuck in your head? Same thing happens to me sometimes with an idea, and the only way to get rid of it for me is to run with it, and see if I can make it work.
Got a message from a fella last night looking for link and pin couplers in 2.5" scale. Told him I didn't have anything but I'd look into it. Looked into it. Damn. I could do those, easy peasy.
I guess now I am going to have link and pin couplers in 2.5".
Fast forward to today, here's where I'm at with it. This is going to be the master pattern, I need to cast and adjust 4 copies to make a proper matchplate.
And no, not available yet, and not sure what the price will be.
Oh, in case anyone is wondering, the thin rod poking out of the right side of the shank is a core print that will allow me to embed a 5/16" bolt for the draft spring setup. You can see that on www.cprr.org , which is where I patterned this after. Not an exact copy, but close enough.
Looks like the pic got rotated, the coreprint for the bolt is at the top of the pic.
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IMG_20190901_152516500.jpg
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Glenn Brooks
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Re: Link and pin couplers in 2.5" scale

Post by Glenn Brooks »

Great idea. These look a lot like the link and pin setup used extensively on all the Allied WW1 trench railways. (600mm 24” gauge). BTW the pin on the trench railways were fairly heavily lengths of flat bar, about 2’ long - with elongated eyes on each end. Very stout.

I’d recommend updating the spec for the 5/16” bolt in your prototype to either 3/8” or 7/16” grade 8 material. if you intend this to be the anchor position for the coupler. I have a similar 3/8” draft gear bolt on my 2 1/2” couplers and found the grade 3, 3/8” zinc platted all thread the vendor sold with the coupler, breaks off very easily. The couplers pivot on the frame at this bolt, causing a lot of stress in tight curves, with early metal fatigue. As a result, my 3/8” bolts break easily. So I decided to upgrade to grade 8 attachment points. If that doesn’t work, then I plan to retrofit all my couplers to 7/16” size high strength bolt material. A nuisance, but this point is critical for longevity of the entire train operation.

Also if I remember correctly, the slot in the edge of coupler is cast with a wide opening, allowing the pin to swivel to an acute angle side to side. Very important for short radius track.

Please let us know how your pricing decisions work out. I could see these being a viable alternative to 2 1/2” scale standard ARR couplers.

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

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OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

Thanks for the input, Glenn. I'm going to be casting these with a grade 8 bolt with the head integral to the shaft. I can see allthread breaking easily, the threads probably act as a stress riser right where it doesn't need to be.
I may change the link core to something a little larger, I looked at the coreprint in place and thought it looked a little small. That's an easy fix, though.
Just to feel it out, would , say, $75 a pair be too much? These are going to be a pretty good chunk of bronze when cast.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus
Glenn Brooks
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Re: Link and pin couplers in 2.5" scale

Post by Glenn Brooks »

Odduck,

Glad to see you are doing this. $75 seems more than fair, and bronze would be very nice. You could check around and compare to what ARR 2 1/2” scale couplers are going for - and they are all cast in iron, so far as I know. Good comment about stress riser problem. You are undoubtedly correct. You might even think about going to 1/2” diameter. And they can always be drilled and tapped out latter if need be.

I’d certainly like the link core design to be as robust as possible. Can’t go wrong with even 3” scale size. The various photos I’ve seen show some very robust gear in this design.

Also, I suspect you could find some buyers amongst U.K. loco enthusiasts - particularly Hunslet affectionados. The english kept this style around well after WW1.
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

I think I am going to leave the cast-in bolt version at 5/16", I'd be worried about the strength of the shank being lowered with anything much larger. If someone wants to use a larger bolt I could always just leave it out and the shank could be drilled and tapped.
I do think I will enlarge the link core, there's plenty of room in the head end, I'm going to leave at least a 1/4" wall thickness for strength however.
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Harold_V
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Re: Link and pin couplers in 2.5" scale

Post by Harold_V »

OddDuck wrote: Sun Sep 01, 2019 7:50 pm I'm going to be casting these with a grade 8 bolt with the head integral to the shaft.
Might be a good idea to explore that idea a little closer. In aluminum it might not be too bad of an idea, but the casting temperature of bronze is likely to give some issues with bolt strength. You may start with a grade eight, but that may not be what you have in the end, so the consumer may have a false sense of strength.

H
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OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

I thought of that, Harold. I believe you are probably correct, even in aluminum the heat may be sufficient to change the temper of the bolt. My thoughts on that is it may not be a bad thing. Where that bolt is, and the type of stresses that will be put on it, will require steel that is more flexible and tough than hard. The steel properties that allow hardening to grade 8 will help improve the toughness characteristics even if the temper is reduced to, say, 5 or 6 on a relative scale.
I think as long as I don't shake the casting out too soon, and let it cool slowly it should be fine. Shake it out too quickly and it may cool it too quickly and cause it to be too brittle at that critical junction between the shank and where the bolt sticks out.
Hopefully this makes it clear as mud...
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Glenn Brooks
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Re: Link and pin couplers in 2.5" scale

Post by Glenn Brooks »

Odduck, just for FYI, I measured the shanks on the ARR style couplers I have in my shop. Looks like three different manufacturers. All but one style were nominal 1 1/4” square shanks at the rear end. One or two are 1 1/4” vertical height by 1 1/8” wide- tiny bit rectangular.

Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....
OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

These should have around a 1" square shank when cast. I went off a picture with one legible measurement and extrapolated from that, in a roughly right eyeball measurement kind of way. Pretty close, I think. Proportionally speaking it looks like the picture I based it off.
The copies to make the matchplate are cast, should be able to do a test cast in a few days.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus
Glenn Brooks
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Re: Link and pin couplers in 2.5" scale

Post by Glenn Brooks »

Sounds Great. Interested to see how it comes out...

Glenn
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rkcarguy
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Re: Link and pin couplers in 2.5" scale

Post by rkcarguy »

If you're going to cast in the bolt, use a grade 2. Anything else is going to crystalize from the heat and will be extremely brittle, still might with the grade 2 as well.
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Harold_V
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Re: Link and pin couplers in 2.5" scale

Post by Harold_V »

Heat would soften the bolt, but it's highly unlikely that there'd be a problem with crystallization. In order for the bolt to experience that problem, it would have heated to or beyond the critical temperature (1,550 °F), and then quickly cooled (quenched). That's a highly unlikely condition when casting.

The worst that I would expect would be a softening of the fastener. In that scenario, it would experience an increase in ductility, but at the cost of tensile strength.

H
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