expansion link materials

[hwboivin3]

I'm getting ready to start making expansion links and blocks for a whole bunch of engines. I figure I would get them all done while I'm in the mood. Instead of doing the prototypical block, I'm going to use a round bushing. But, I'm curious as to what materials others have used. I really don't want to heat treat them so what materials hold up the best? Right now I'm thinking of making the link out of 17-4 stainless and ordering a steel bushing from McMaster or making one out of 17-4 or 660 bronze......but I'm pretty much clueless as to which way to go. I don't want the link to wear out.....but also don't want the block wearing out too quickly.

Any advice ?

Thanks

Harry

[Harold_V]

The idea of using 17-4PH in the annealed state isn't wise. The maker suggests it should NOT be put in service without heat treat, although I don't understand the reason why.

Being precipitation hardening, you can easily harden the stuff yourself, assuming you have a small electric heat treat/burnout oven. Condition H900 is good target for hardness. All that is required is to hold the material at the given heat (900° F) for the prescribed period of time, and the job is done. No quench or draw is required.

Harold

[FLtenwheeler]

Hi Harry

Why would you use a round bushing? I have seen them used and they do not last very long. You go from a 1/2" of contact area to a fraction of that on a round bushing.

The ones I have built where steel and then I case harden them. Been going for 25 years with no wear.

Tim

[cbrew]

just food for thought, I have heard of some using a cam follower bearing in place of the link block. at that point, the trick is to find one that will work with in your specs.

I do know of one person that is / was making the link and block with an EDM machine. that may be a route to look at

[Andypullen]

I have made them from 4142PH and A-2.

4142PH is about 35 on the Rockwell C scale. It is tough and abrasion resistant. Not too bad to machine, though. But, if you want to harden it farther, it needs to be annealed first.....ask me how I know that.... A-2 is nice stuff. Decent to machine and it is quite stable dimensionally during heat treat.

I don't think 17-4 can get hard enough. I've machined it in the heat treated condition.

I used a pair of ball bearings in my 0-4-0 originally. The links are annealed A-2. The minimal contact area is a problem. The slots are much looser where the bearing rides. I replaced them with blocks. The links are "on the list" for replacement. I have the A-2 for them and am looking at wire EDM to cut the slots. Heat treat before or after if I go that route.

Andy

[Doug_Edwards]

Harry,

I have made links out of A2 and A6. The A6 heat treats at a lower temp, which is supposed to reduce deformation in the heat treat, but I have had very good results with A2, so the advantage is probably moot for this application, especially with the greater availability of the A2. Another alloy I would not hesitate to use would be S7. I would personally consider D2, but it is a bear to machine compared to the others, although is very abrasion resistant. I have it on hand , otherwise I would buy A2 or S7.

Many Stainless alloys have poor wear characteristics, not sure how the 17-4ph fares on this.

The D2, while being a bear to machine, does not rust as readily as some of the other steel alloys due to the amount of chrome and nickle. Fwiw.

A friend has made links out of O1 and heat treated them with out objectionable deformation, but I personally would chose an air quench steel.

Hardened links and blocks will out last you and much of the loco they are built for!

I like to put bushings in the link where the eccentric rods connect.

Do a search on the board on link materials, as this has been discussed before.

Regards,

Doug

[Bill Shields]

as stated, round blocks are not a good idea...

not only does the block go flat, but it puts 'dings' in the mating surface...especially if you use a cam follower bearing.

In the past, when I made a bunch, I wire cut them out of hardened steel.

Will let you know when the fist set wears out.

all things considered, the cost of the wire work is well worth it.

[Marty_Knox]

I make the links in O-1, and don't harden it. I make the die blocks in 660 bronze, I mill it square a little oversize, then file them to fit.

[Bill Shields]

FILE...ugh.....

this coming from a guy that programs and makes parts to sub-micron tolerances for a living.

OK..I DO occasionally 'paint to fit' when the grinder has been used....giggle...

[NP317]

Round link blocks are a bad solution. You want more contact surface area between the block and the expansion link, to prevent wear.
I recently had a set of expansion links and matching link blocks made for me by Bill Esther, at Elmridge Manufacturing, in Independence, Oregon. http://www.elmridgemfg.com
We used oil-hardening tool steel, 3/8" thick, and he wire-EDM cut them for me. He could have done this with pre-hardened material, too. I then hardened them as required, and they came out with the best fit possible. Quite amazing, actually. The Wire-EDM system is extraordinarily accurate.

[Bill Shields]

wire actually likes HARDENED steel more than soft steel...you get better finish and tolerance

additional advantage is that once hardened and cut, it never moves....

as opposed to hardening afterward sometimes moves a bit....depending on the skill of the oven guy...

of course if you are going to drill and TAP holes you have a problem with pre-hardened...giggle....

[NP317]

Bill:
The oven-heating and oil-quenching process did not cause any distortions in the links.
Perhaps I was lucky?
Also, by using annealed material, I was easily able to drill the required lube oil holes, post wire-cutting.
At any rate, the link sets are now happily operating on my 7.5" gauge 90-ton Mikado project.
~Russ