Gunmetal or bms?

[AndrewP]

Getting to crossheads and motion plates on Rob Roy and I have a choice of gunmetal castings (which I have) or bms and hack 'em out.
I'm sure many will have a preference but can we arrive at a concensus for which gives the best finished job?
My first thought is that a gm crosshead is going to look a bit strange.

Cheers, Andy

[baggo]

Hi Andy,

My personal preference for crossheads is mild steel with the slide bar grooves case hardened and running on gauge plate slide bars. It's probably no more trouble to machine a crosshead from the solid than to machine a casting. The awkward bit can be turning the boss for the piston rod but I use a very narrow pointed tool to get in.

I made some new steel crossheads for my brothers Rob Roy as the original gunmetal ones had been very poorly machined by the original builder.

The Simplex crossheads are steel fabrications with a centre piece that fits between the slidebars and separate front and back plates which makes it easier to machine the recess for the connecting rod little end.

John

[dscott]

What I did with my Hunslet's and Gemma, was to machine some mild steel from the back which was two simple boring opperations to make the spaces for the connecting rods, drill the center for the pin. next mill out in a y or v section to join the two together. Mill a wide slot down the center so that the connecting rod will fit once the cover has been milled and silver soldered over the top, cut out any fancy bits, turn the bit in the middles polish and fit thin sheet phosphor bronze folded up slippers, replace every 20 years.
if you have been over eager in the milling!!! fit two sets of slippers, and replace every 40 years!!!

David.

[ron]

Andrew
I made Simplex crossheads using Blackgates gunmetal castings for the centre and MS for the side plates, if you search in the Simplex picture section you'll find a photo of them. I used MS for the slide bars and M High's lazer cut motion brackets, I was warned off using cast motion brackets, again pics in the same place.
Ron

[teakfreak]

I had a pair of gunmetal motion brackets for Simplex, but found that they bent as I was trying to machine the first one, even with very light cuts. I ended up fabricating them from plate and angle, still have one untouched casting if anybody is in need of one!