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.

Moderators: Glenn Brooks, Harold_V

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Topics may include: antique park gauge train restoration, preservation, and history; building new grand scale equipment from scratch; large scale miniature railway construction, maintenance, and safe operation; fallen flags; track, gauge, and equipment standards; grand scale vendor offerings; and, compiling an on-line motive power roster.
OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

I'll be casting this week, hopefully have a dozen or so sets ready to go by the end of the week. I'll keep you posted.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus
rkcarguy
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Re: Link and pin couplers in 2.5" scale

Post by rkcarguy »

Good to see, interesting that the grade 8 bolt appears to have softened and bends without snapping off. Its a big unknown with casting due to the rate of cooling what is going to happen. Honestly I would let the end user drill and tap their own hole and install the bolt, because of "Litigious America", but that is just me.
It is also an unknown with the rolling weight of our trains how much actual force is imparted on the couplers as I assume it isn't the same as dangling the entire train in the air by it's coupler. I'd expect it's only a small fraction of the rolling weight exerted, but shock forces of coupling and taking up slack are going to be the main concern plus derailments...and what you WANT to have happen in a derailment...IE the couplers are the weak point and intended to break, or have everything very strong but risk bending/twisting damage to your frames....
Glenn, that's strange you broke so many couplers. Possible that your turn radii made the coupler bind in the box? I struggled with the choice of tapping my shanks for rear mounted bolts with springs on both sides or using vertical through bolts as pivot points with everything pretty much solid, and went for the latter. I figure it gets the threads out of the "shear plane", places the pivot point closer to the end of the coupler box allowing more swing in the coupler(can accommodate tighter turns) and I will then use a custom sprung "shock absorber draw bar" between my locomotive and riding car so I have some give.
Glenn Brooks
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Re: Link and pin couplers in 2.5" scale

Post by Glenn Brooks »

Ryan, interesting points. yep, I indeed have one or two short radius turns - atypical for many Park gauge layouts. Correction, not all my couplers failed- just the one with undersized pins. Iam sure binding in the curve contributed to the problem, however I don’t have room for wider curvature, so the Engineering has to be adequate... the biggest factor was undersized and low grade allthread. Nothing wrong with dropping a vertical pin down thru the coupler shank- for freight cars. However It does make for a more jarring ride for passengers, without spring loading. Hence Iam happy to see these new coupler styles will be produced with the more robust draft gear shanks.

One more thing I’ve been thinking about, and I don’t know the answer. one should consider also foot pounds of energy working on this attachment pin - not just the static weight on the draw bar. As in force applied laterally to the coupler attachment point due to (speed down the track) x (car weight)x (turning moment).

If I see any signs of trouble with my upgraded 3/8” coupler pins this fall, I plan to redrill and tap for 7/16”, 1/2” if possible, on all my couplers. Just more work to add to the list...

Glenn
Moderator - Grand Scale Forum

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....
rkcarguy
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Joined: Tue Aug 22, 2017 10:33 am
Location: Wa State

Re: Link and pin couplers in 2.5" scale

Post by rkcarguy »

Glenn Brooks wrote: Mon Sep 09, 2019 3:27 pm One more thing I’ve been thinking about, and I don’t know the answer. one should consider also foot pounds of energy working on this attachment pin - not just the static weight on the draw bar. As in force applied laterally to the coupler attachment point due to (speed down the track) x (car weight)x (turning moment).
Glenn

I've found nothing for figuring out such forces, as applies to train weight, speed, grade, etc. All I know is I've worked some of the math on the gas hydraulic setups used in some model "diesels" and it equates to about 160ft/lb's of torque at the wheels, and that seems to be enough torque to pull quite an weighty train before wheel slip or running out of power occurs. I think BDD was saying 8,000#'s gross for his up a 1.8% grade and it was pushing max pressure on the hydraulics at that point so one might say 40ft/lbs per each ton? Shock loading is a whole different animal though.

I figure with my grades in the 2.5-3.5% range I may have make concessions on cargo limits when the track is wet, but I know no other way than to simply start pilling on the weight and try it, when I'm up and running.

I have seen a couple designs where slots are milled in the coupler shank, and then a square bar sleeve was inserted for the coupler pin to pass through with springs on both sides. At the weight and grades I'm moving, I dismissed this as I don't think I can get enough spring in there to do anything without significantly weakening the coupler shank.
Glenn Brooks
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Joined: Mon Nov 10, 2014 1:39 pm
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Re: Link and pin couplers in 2.5" scale

Post by Glenn Brooks »

Well, one thing in your favor, is that the general design limits of 2 1/2” scale have been well tested and refined over the years. Literally, since Heywords first estate gauge railway back in 1890s in England. So you are already working well within the envelope so to speak. But, yep, it does get complicated. I am hoping others on the list may be able to add to the discussion, also. I know there are quite a few structural and mechanical engineers on Chaski, but unsure if they follow the Grand Scale threads.

FWIW, so far, I am quite happy with the traditional live steam design of putting two small springs over the coupler pin and bolting up the middle (between the springs) to the frame.this has worked very well for me. So long as the diameter and tensile strength of the pin are adequate, this is a very simple approach and seems to work extremely well for the modest loads we all carry. e.g. >4000 pound range/car.
Moderator - Grand Scale Forum

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
Posts: 434
Joined: Fri Dec 16, 2011 1:00 am
Location: Somewhere south of Mt. Katahdin
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

And the pile starts to grow... Seven pair cast so far, more to come. I will let everyone know when I am ready to take orders.
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"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus
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