I drilled and filed my first set of expansion links … they're still in the Maisie 30+ years later but due for replacement. I then used the swinging arm technique to great effect but now have the luxury of a rotary table. I found that light cuts with a new cutter was the key and I'm sure you will be well pleased with the outcome.

N

Surely, if the die blocks were round then they would rotate? Not slide friction wise like square ones.

Clive

Not sure about that? Assume Stephenson's valve gear with a mid point suspension. The valve rod can only move linearly. If the expansion link is not set so the dieblock is at the centre it moves in a slight arc. So there is some small amount of sliding of the dieblock. I think that the sliding moment reverses as the expansion link reverses, so a round dieblock may just oscillate rather than continuously rotate. Or it may just slide depending on forces and lubrication.

In fullsize at least, the forces in a valve rod (with slide valves) can be significant, hundreds of pounds, depending upon steam chest pressure and slide valve lubrication.

Andrew

Hello Peter,

For more years than I can remember, I've used gsuge plate in it's normal state for the links with cast Iron die blocks. The load on the slide valve is high as Andrew has pointed out, but the load on the valve isn't that extreme as the exhaust port, being open to atmosphere must be taken ito consideration in any calculation and often the steam chest pressure will rarely match the boiler pressure due to internal losses and wire drawing. I've yet to meet many who will drive a locomotive with a fully open regulator, controlling the progress of the locomotive on the reverser.

Fear nought, a mild steel link with a bronze die block will probably see you out!

Use cast iron for your axle boxes, with cast iron there will be very little wear. Put an oil way throuth the end of the axles to a cross drilling where the axle box runs and you'll always push any dirt out, almost essential with the trailing set in the area of the ash pan.

Regards,

Bob

The surface of laser cut parts is like a very fine abrasive stick. If you get expansion links laser cut you'll need to polish up the inner curved surfaces with a diamond file or similar. Ordinary files no good. Water jet cutting should be OK, not sure about wire erosion, perhaps a metalurgist out there can advise.

Several people in out club have had success with PTFE die blocks, the loaded stuff, not the white virgin. I machined mine to size and shape, but I've heard of others just making a rectangle, bludgeoning it into the slot and waiting for a few days, seems it creeps very quickly and takes on the shape of the slot. Seemed a bit brutal to me.

Hello Duncan,

I think Model Engineers Laser use a water jet cutting system for their links when using gauge plate.

A good friend had his 4" Foster traction engine link and die block wire eroded in gauge plate, the fit and finish is superb, not a cheap exercise though.

Well done Ivattlms pointing out that round die blocks just slide, old LBSC pointed that out in one of his articles back in the 50's and as someone has already said it would only provide a point loading on the link.

Regards

Bob