Eccentric crank material

[EOsteam]

I'm about to fabricate the eccentric cranks for my 1.5" 4-8-4 Northern. The plans say to make them out of tool steel but don't suggest a grade of tool steel. Is there a recommended tool steel to use. Are there alternatives? I thought I read somewhere that tool steel when heat treated will warp somewhat. Is that going to be a problem with respect to dimension and precision machining?
Thanks for any guidance you can provide!

Harper

[Steggy]

You didn't say what the bearing material will be in contact with the eccentrics, but assuming it is bronze, you should consider something a little less tough that won't require heat treatment after fabrication. I'd be looking at something such as Stressproof® TGP. StressProof is a specialty steel made from C1144 that has been cold-worked to give it mechanical properties similar to that of medium-carbon, chromium-molybdenum alloys, e.g., 4130, but without the need for post-machining quench-and-temper heat treat—and without the brittleness of tool steels.

Stressproof is of uniform hardness throughout and can be finished to a bearing-quality state with carbide and cutting oil, followed by polishing with crocus and oil. Depending on the size eccentrics you plan to make, you may be able to get the finished size you need in TGP, which requires no further prep for use as a bearing surface.

Using Stressproof, I've made many parts whose bearing surfaces were subjected to P/V ratios well beyond what would be seen in a typical large-scale steam locomotive.

Lastly, only Niagara-LaSalle makes genuine Stressproof. Stressproof starts out as C1144, but C1144 is not Stressproof. Keep that in mind if you decide to go that route so you don't get sold the wrong material.

[LVRR2095]

You didn't say what the bearing material will be in contact with the eccentrics, but assuming it is bronze, you should consider something a little less tough that won't require heat treatment after fabrication. I'd be looking at something such as Stressproof® TGP. StressProof is a specialty steel made from C1144 that has been cold-worked to give it mechanical properties similar to that of medium-carbon, chromium-molybdenum alloys, e.g., 4130, but without the need for post-machining quench-and-temper heat treat—and without the brittleness of tool steels.

Stressproof is of uniform hardness throughout and can be finished to a bearing-quality state with carbide and cutting oil, followed by polishing with crocus and oil. Depending on the size eccentrics you plan to make, you may be able to get the finished size you need in TGP, which requires no further prep for use as a bearing surface.

Using Stressproof, I've made many parts whose bearing surfaces were subjected to P/V ratios well beyond what would be seen in a typical large-scale steam locomotive.

Lastly, only Niagara-LaSalle makes genuine Stressproof. Stressproof starts out as C1144, but C1144 is not Stressproof. Keep that in mind if you decide to go that route so you don't get sold the wrong material.

The original poster said the eccentric cranks for a 4-8-4, so that would have outside valve gear. He is not making an eccentric cam that would contact a strap. One end would be on the crank pin of the driver and the other end connected to an eccentric rod. That rod would then be connected to either the base of the expansion link on Walschaerts or a bell crank on Baker gear.

Keith

[Sandiapaul]

"Lastly, only Niagara-LaSalle makes genuine Stressproof. Stressproof starts out as C1144, but C1144 is not Stressproof. Keep that in mind if you decide to go that route so you don't get sold the wrong material."

I didn't know this...so is there a good source for the "real stuff"?

[Bill Shields]

What's wrong with ground HRS for the crank and something better for the pin?

[cbrew]

there is no reason one can not use A36 flat bar to machine the crank.
Mine are laser cut from a36, and the pins are all 1144 on bronze.
10 years in, no complaints

[k36no4862002]

I have used mild steel with a Delrin bush, 100 hours running a year for 10 years, still nice and tight

[theg8nw]

I too have an LE light Northern, and my eccentric cranks are laser cut from A-36. I do not see any real advantage of using stress proof or tool steels for this part.

[Glenn Brooks]

In the FWIW category, I talked to a local steel supplier recently about Stressproof. Same question as yours, only for a different part. They didn’t carry Stressproof, because they use a different supplier. But said it’s just a trade name. It’s nothing different than 1144 based materials other mills produce. Same specs, standards, and characteristics as the “Stressproof” I was asking about.

[Steggy]

"Lastly, only Niagara-LaSalle makes genuine Stressproof. Stressproof starts out as C1144, but C1144 is not Stressproof. Keep that in mind if you decide to go that route so you don't get sold the wrong material."

I didn't know this...so is there a good source for the "real stuff"?

I'm able to get it from a steel house in our area. I have to buy a “random length” (nominally 12 feet), so what I do is get it in 1" diameter, from which I can make parts as needed. You'd need to call around to find a source in your area. Ryerson may have it. Some on-line metal suppliers list it, but the term “Stressproof” is generically used by them to refer to what is as-rolled C1144, which is not the real McCoy.

[Steggy]

They didn’t carry Stressproof, because they use a different supplier. But said it’s just a trade name. It’s nothing different than 1144 based materials other mills produce. Same specs, standards, and characteristics as the “Stressproof” I was asking about.

They are feeding you some BS, Glenn. The Niagara process is proprietary and the details are a “trade secret”. Other mills are selling a knockoff. I learned this from experience back in my railroading days.

[kapullen]

I would use 1020 hrs.
HRS needs to be skimmed all over but is a good stable material to work with.
If you think you need more strength. Use 1045
Or A36.
I look at it this way, If I have a crash ( likely) what may be the easiest components to replace.
Don't want to make any new crank pins, expansion links, valve rods, brackets...