A Pair of Stuarts

[smfr]

Bet you didn't know there was a water-cooled version of the Stuart Twin Launch  :



I sent this picture to Stuart Models, and they send me a new casting, no questions asked, even though this original casting set is probably from the 1970s or 1980s.

Anyway, here are some other shots of the two cylinder castings:





I think its was around this time, while waiting for the replacement casting from Stuart, that this pair got put to one side, and other hobbies took over for a while. We'll pick up more recent work soon!

[tghs]

fun to watch ,my compound kit had very bad HP cylinder rings,, I emailed ST a photo, within minutes they replied to see if I needed anything else as long they sending the rings

[Kim]

Hi Simon!
Great to hear from you!  Looking forward to watching the continuation of your build! 
Kim

[smfr]

Fast forward to December 2020, and we have the new casting from Stuart cleaned up, and it's looking much better than the holey one:



Now I can find the center line, and mark them both up:





and then drill for the supporting columns:



It's good to have these holes be accurate, so they are handy as a reference line for later operations. For example, the setup to mill the sides of each end:





I then used a roughing end mill to clean up the bore of the new casting:



and remove some excess material from the valve faces:

[smfr]

Now it's time to bore the bores! I made some gauges, and used an end mill shank for the 3/4" (later I would find an end mill with a very precise 1" shank in the drawer which I could have used for the Twin 1" cylinders). The 1.001" gauge is 0.998" on the other end.



To ensure that the bores are perpendicular to the base of the casting, on my little mill table that I don't really trust, I bolted some bits of Al to the table and skimmed the tops to the same height:



Then I could clamp the cylinder blocks down onto those for the boring operation:



The gauges were useful, backed up by a telescoping bore gauge:



Big ol' counter sink to put a chamfer on:



The Twin bores ended up on size, with a decent finish, and maybe a thou left for honing.

The large bore of the Compound also turned out well:



The smaller bore didn't go quite so well; things went slightly wonky because I didn't snug up the quill of the mill, so it ended up a couple of thou oversize and could still use a bit of cleanup with a hone. Will a 0.753"-ish bore be OK with the supplied cast iron piston rings?

[smfr]

Columns! All 10 of them. Rather than use the stock supplied with the kits, I used 1/4" precision ground stainless rod:



I did experiment with putting a fishbelly on a test rod which I think would look nice, but the rear three columns need a spot to hold the valve slide support piece, so shaping those would get a little more tricky.

[Jasonb]

Good to see you back on these.

[tghs]

you should be fine on the HP bore,, test fit the rings in the bore mine were tight..

[john mills]

the gap on the rings when  in the bore would be slightly larger try them in the bore and see what it is  will still work
John

[fumopuc]

Hi Simon,
good to see you back in business.

[Michael S.]

Hello Simon,
I used the cast iron piston rings on my compound.
That worked well. The compound first ran a lot with compressed air. I later tested it with steam. The machine ran much better then. Then she was suddenly stuck!
This was not due to the piston rings but to the failure of the displacement oiler.
The steam pressure during the test was 6 bar and the steam temperature was therefore too high.
So it is better to use an oil pump.

Michael