Stuart No. 4 crosshead

[smfr]

Hi folks

Newbie here, but I'm getting into machining casting kits (Stuart, PM Research etc) so you'll probably see more of me.

I obtained a Stuart No. 4 casting kit on eBay, with a photocopy of the plans (dated 1953). I've no idea if the kit matches the date of the plans; I suspect it's more recent.

What confuses me is the crosshead/piston rod. The plans show the crosshead and piston rod as what looks like a single part (part 20), possibly turned from a casting. However, my kit didn't include a casting for this, and http://www.stuartmodels.com/part_cat.cfm?cat=18 doesn't list one. Also confusing is that http://www.stuartmodels.com/inprod_det.cfm/section/casting/mod_id/65 lists the crosshead as a gunmetal casting.

If I were to make the crosshead from stock, I guess I'd want to thread the end of the piston rod, and use a lock nut there too? It looks like that locknut might have to be recessed into the crosshead though.

Also, if I were to make the crosshead from bar stock, what would the best material be? It's going to be sliding against the cast iron of the standard.

Thanks
Simon

 

[Mainer]

Cast iron works well against a variety of surfaces, including cast iron, one of the few metal that makes a good bearing surface with itself. It's pretty much up to you.

There are about a gazillion kinds of brass. One of the most common, 360 brass, is not that great as a bearing material in general, but you probably aren't going to be running this engine a lot so using brass for appearance would be fine. There may be other brass alloys that are better.

Bearing bronze, so called, might be the best thing. Be sure you get solid, not the oilite type.

Or steel would work. Up to you.

 

[steamer]

If your making the crosshead seperate from the piston rod, I would go with 660 bearing bronze. Cuts nice and works well. Finish the OD of the crosshead using the piston rod as an arbor ( just the last OD cut) That way it is dead concentric with the rod and it won't bind.

Make the piston rod from 303SS and you will not have any rust issues...of course if you only run on air this is not really a problem.

Dave