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 think you are correct, Harold. That's my expectation, that the temper of the bolt will be changed. I don't think there is enough thermal mass in the shank to cause recrystallization. That would require the steel to be over red hot, I doubt it's going to get anywhere close to that. I suppose if I were really concerned the entire coupler could be brought up to a temperature to allow hardening and re-tempering the bolt, but that would be overkill and unnecessary, I think.
"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 »

I am curious, why do you plan to cast the bolt in place, Rather than drill and tap a hole and screw in a threaded piece? Also, Will a casting hold the bolt properly?

thanks
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 »

I'm going to embed the head end of the bolt, not the thread end. The main force is going to be direct tension on the bolt, the head embedded should be substantially stronger than just threads. Also, the end user will just have to slide on the keepers and spring for the draft gear, add a nut or locknut, and install. Ease of use, one less thing for the builder to mess with. The big drawback to this is if the bolt does break (eventually, my personal opinion is that they will last a long time) it will be a PITA to drill and tap for a new one.
I'm going to offer the option to leave the bolt out, for those that want a larger diameter.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus
OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

For grins and giggles I looked up the proof load for a grade 8 5/16" coarse thread bolt, it's 6300 lbs. Even in the bigger scales, that's a good sized train. Granted, that's a static load, with no side motion, but should be more than sufficient, with a safety factor.
"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 »

I've welded a lot of bolts into parts (machinist and fabricator for 10 years prior to back injury), and learned the hard way that most of them were easily broken off with a mild tap with a hammer. All of the weld studs, threaded studs, etc that are "shot" or welded onto parts are mild steel (grade-2 equal).

https://www.portlandbolt.com/technical/ ... hor-bolts/
OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

Tell ya what, I'll do some destructive testing when I cast the first one to test the theory. I think they should be okay, there will be no change of state to the bolt, only the metal being cast around it. The sand that the bolt shank will be set in when the mold is made should serve as a heat sink to help slow down the cooling process. If it cools slowly it should normalize rather than turn brittle.
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OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

Success! They turned out pretty good. Test cast complete, I will be doing a bending test on the embedded bolt to test wether or not the strength of the bolt was changed drastically. One of them is a 5/16" bolt, the other one is a 3/8".
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IMG_20190907_174406130.jpg
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OddDuck
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Re: Link and pin couplers in 2.5" scale

Post by OddDuck »

And here's the video:
https://youtu.be/H5KwY-7gK04
It was as I suspected, it bent rather than snapped. I didn't even bother to try the 3/8" one.
"If you took the bones out they wouldn't be crunchy!" -Monty Python's Flying Circus
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Harold_V
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Re: Link and pin couplers in 2.5" scale

Post by Harold_V »

I'm not surprised. Without rapid cooling (quenching), there's no reason for the bolt to do anything more than it did. Even shaking out the mold earlier wouldn't be a problem, not so long as the material from which it was cast had solidified and was no longer at red heat. Common sense tells us that you should not open a mold too early when the metal may be hot short.

H
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Glenn Brooks
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Re: Link and pin couplers in 2.5" scale

Post by Glenn Brooks »

Hi Odduck,

Good to see your test castings came out so nice. And very glad to see you did a video bending test on the cast draft gear attachment pin. Looks like casting the pins in place will work well.

I do have concerns over the small size you propose for this pin. Regarding safety and longevity of operation, I would really encourage you to specify a minimum size range of 3/8” to 1/2” draw bar pin for all 2 1/2” scale equipment - forgoing the 5/16” size rod tested in your video. I mention this as a both safety and long term operating issue.

My concern is 2 1/2” train weights and small park guage operating conditions will subject this pin attachment point to many thousands of individual side loading stresses during routine operation. And this pin will also be subject to additional strong torsional bending stresses during derailments, (and backing up events).

In short, this draft gear pin is the most important connection point in the entire consist, and should be of the strongest possible design.

In this regard here are a couple of data points that support this upgrade.

- bolt manufacturers say that side loads reduce breaking strength of ASME bolt strengths by around 60%. Hence a 5/16” bolt rated at 8000PSI will have an estimated side loading working capacity of around 4800 PSI. Not much of a safety factor even for 1.6” scale operations.

- Max gross (loaded) weight loads for a typical 8’ to 12’ long, 2 1/2” scale rail car can exceed 4000#/car, (500 # per wheel rail loading) and can routinely carry 3500 pound capacity. Hence a 5 car consist, having a gross load capacity would approach 20,000 pound total load. This suggests the need for a 1/2” diameter pin connection.

- finally, as an ancillary note, my Ottaway (12” gauge, 2 1/2” scale steam, 1950 era steam locomotive amusement park equipment) uses a 1/2” link and pin draw bar connection between each car. Hence Ottaway cars use a 1/2” diameter hardened bolt, rather than 5/16” or even 3/8”.

Iam offering this note from personal experience. Last year I purchased several 2 1/2” couplers from a very well known live steam vendor and they promptly broke due to installed, undersized draft gear bolts. (Less than a dozen runs on my track).

Typically I expect an undercarriage component will last 30 or 40 years with occasional use, not just three days. As this is perhaps the most important connection point in the train consist, I just haven’t been able to recognize value in undersizing such an inexpensive component at the most critical attachment point in the coupler gear.

Anyway, I very much appreciate you developing this unique and nifty addition to the Hobby’s parts inventory! Thanks for considering my comments.

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

Post by OddDuck »

Glenn, I concur, after doing that test I'm not going to use 5/16" bolts, the cast in ones will be 3/8". if someone wants 1/2", they will need to get the no-bolt option and drill and tap it themselves. My concern with using 1/2" is that may be enough thermal mass to cause a short pour, and there won't be much wall thickness for strength even if the casting filled all the way. I would have to modify the bolt by cutting off the head. The shank is 1" square, roughly speaking.
And thank you for the comments, it helps to have experienced voices add their two cents in a constructive manner.
"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 hear you have decided to go up one size to 3/8”. I think it will be a very positive upgrade. Let me know when you are ready to make a production run. I would like to order a couple of units for an upcoming WWI trench railway car and tender build.

Cheers,
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....
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