Rectangular cotter holes

[Russ Hanscom]

RRs are not always know for the simple approach, why have a round cotter hole when it is so much more challenging to have rectangular ones. A hundred plus years ago, some party in authority at the D&RG narrow gauge had the strange idea to use rectangular cotters. Not sure if any other RR did this, I have not seen any elsewhere. Between the journal box covers, brake shoe pins and brake rigging, there are at least 24 such pins on a typical D&RG vintage freight car.

Pretty sure EDM s were not popular 100 years ago, so it had to be a bunch of cheap apprentices making the holes. Anyway after looking at some of the original pins, I was confident it was a hot punching approach. I conjured up a punch and die set and the first run was 5/8” dia pins. Next batch is ¾” dia. Fortunately all pin sizes use the same size cotter. Die was showing a bit of drag after the 10th pin so I was thinking may have to alloy face it, or redress after every 10 pins. Then after cleaning the die, enlarging the waste hole, and applying a bit of never-seize every four or five pins, it popped out another 20 with no problem.

Success, Really happy when the press came down and there were no unexpected crunching sounds. We try to stay authentic at the museum and this was a good exercise.

These pins hold the journal box covers, next set was the ¾ ones holding the brake shoes, and then finally a bunch of 1” ones for the brake rigging. Original pin is across the bottom. Old and new cotters on the left side.

[tornitore45]

A rectangular cotter pin with the aspect ratio shown has great strength against axial pull out of the clevis pin, yet it may be built as an hairpin with a head to keep if from falling through and made springy to stay put while easy to be compressed by hand.
Flexible in one direction and strong on the perpendicular.
No round cotter can do that.

[makinsmoke]

Congratulations for doing the hard work, to make them like they came from the shops.

Saving old technology for the future.

Kudos.

[Rwilliams]

Nice work on recreation of the rectangular holes for the hairpin cotters. Never an easy task in full size.

Long ago I saw an unfinished model live steamer in 1.5 scale that had some incredible craftsmanship up until the original builder passed on. One of the most stunning achievements was scale hairpin cotters and the rectangular holes in some 3/16 diameter round pins. The finish inside the rectangular holes was very smooth as well as both entry and exit of what ever tool was used to create the holes. I would have suspected EDM, but with the age of the model construction, EDM was still years away. We looked real hard at the rectangular holes and never did figure out what secret the deceased builder used to create the ultimate in hairpin cotter detail. The age of the model was from the middle 1950's to perhaps as late as 1960.

Still wonder to this day how the builder worked his rectangular hole magic.

[Comstock-Friend]

All the locomotive journal boxes of that period that I have seen have rectangular cotter holes (V&T and on the Glenbrook).

Here is the Central Pacific built V&T #18 'Dayton'. Note the lead truck swing links bars...

John Friend

[Russ Hanscom]

So there are other users.

One way to get smooth entry and exit holes would be to start with a rod one size larger then turn down the outside after punching the hole.; but not necessary for common freight equipment.

[John Hasler]

You could hone away the tool marks from the punch before turning the pin down.

[Rwilliams]

Forgot to mention that in working on a 1922 Baldwin steamer recently, I found use of hairpin cotters. We removed the pilot truck grease cellars for cleaning and inspection. Two long 1/2 inch diameter pins secured the grease cellars. Security was provided by hairpin cotters in perfect formed rectangular slots. They really knew what they were doing a hundred years ago.

[little giant]

You can make rectangular slots with a shaper attachment on a Bridgeport with a square tool bit or a square file on a filing machine starting out in a hole.

[Russ Hanscom]

True, and I have a shaper, but for more than a few, the punch is better for this application. The HSS punch leaves a good finish in the slot, and I can make one every two minutes once organized; and I need 50+. If they were too pretty, they would not be authentic.