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Stuart Twin Victoria (Princess Royal) Mill Engine

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Ramon Wilson24/09/2021 17:34:28
1194 forum posts
296 photos

Hi again Doc, just checked through my PM's and yes you did share in the PTFE yarn. It's excellent material so you should have no issues fitting it

Dr_GMJN24/09/2021 17:42:19
1225 forum posts

Thanks Ramon, yes this is the stuff:

So about 0.005” protrusion on diameter ( if I can figure out the nominal thickness)?

And 0.003-4” piston undersized to bore diameter. Presumably the bore needs finishing to be very smooth / polished?

Also, I’ve been marking out the cylinder valve faces for milling to size. All looks fine apart from on one cylinder (on the left below):

The cylinder longitudinal midpoint is out w.r.t. the central valve port, by about 0.5mm. Presumably I can adjust the mid point of the slide valve to compensate with no ill effects?

The valve pads will be machined to the upper and lower scribed lines, giving equal flat areas on all 4 ends.


Ramon Wilson25/09/2021 08:11:21
1194 forum posts
296 photos

Doc, if the machining inside the bore is as reasonable off the tool as you said then you shouldn't need to hone or lap the surface as such other than with some wet and dry paper.

If you turn a piece of wood or ally to about 30 - 40 thou down on bore size about as long as a cylinder and wrap some 400 wet and dry around it that will out smooth the surface more that well enough. Drill it through to hold it on a handle of some kind and cut a slot along it deep enough to slot one edge of the wet and dry into then wrap round so that the motion tightens the abrasive not unwraps it.

Re the valve ports - this is what I meant about cast in ones from Stuart. You may be able to accommodate the error with the valve position but if you want to be absolutely certain of identical positions then as previously said you have to fit an insert with correctly machined porting. Not difficult to do and a bit late in the stage of thing but still achievable if you desire to go down that road.

Steve Withnell26/09/2021 09:13:15
843 forum posts
222 photos
Posted by Dr_GMJN on 19/09/2021 07:47:40:

Talking of valve chest covers, I want to put an oiler in the middle, so am planning on leaving a circular raised face in the milled centre. I was looking at this engine last weekend:

And noticed it had an oiler on the cover as well:

It seems to have two taps, perhaps so you can oil during running. Are these available for models?

I think a single tap with a screw cap might look neater, but just wondered.

Where is the best supplier for fittings like these?


That oiler is a 'shapely lady' I think. For my single cyclinder victoria I made my own, which isn't too difficult. Im not an expert, but I don't think the one in the photo is big enough.

I copied mine from this engine - for scale the screws are 12BA. This link takes you to how I made the lubricator for my Victoria.

Shapely Lady


Dr_GMJN26/09/2021 21:30:23
1225 forum posts

Thanks both.

Ramon - I think I’ll see how it goes before committing to making inserts. I don’t think it’s that far out, but I guess if it turns out to be a problem, it’s removing cast iron rather than adding it. The cylinders are OK, but I think they still need a bit of finishing in the bores, mainly to get rid of the slight discolouration half way down one of them, and also to make sure the JB Weld filler in the screw holes is truly flush.

Steve - thanks for the info about the oilers. I think on mine they will just be simple brass cups with lids, so I can drop oil in occasionally, rather than the reservoir type you describe.

Dr_GMJN26/09/2021 22:15:06
1225 forum posts

I had a go at the cylinder covers this afternoon. I’ve read the article method loads of times, but still couldn’t make head or tail of the descriptions: It says machine the plain cover spigot first, to a good fit to the cylinder, the reason being that it centralises the packing…but there isn’t any packing on that cover.

It then says make the spigot on the gland cover ends (the ones with the packing) a slack fit. It also says to machine the spigot diameter after facing, to ensure concentricity. Surely concentricity doesn’t depend on the face being true, plus if it’s slack, why is it important?

I was left wondering why in those cases bother with either spigot at all since one has nothing to centre, and the other is a slack fit anyway.

In the end I just went with what seemed logical. I assume when the article was written, the covers didn’t come with cast tails on the back, so I used those to mount in the chuck. I first faced the gland bosses, centre drilled them as best I could on the mill after marking with the verniers, and set up true in the 4 jaw. Then turned the bolt faces and re-faced the gland bosses to the correct depths:

Then drilled the piston rod and packing holes:

The 10V piston hole was reamed, but it says not to bother for this one. Which seems logical since it’s the piston and cross head that seem to define the rod position. Adding a third fit seems pointless, especially when the packing will centralise the rod. Anyway, that got me here:

Then sawed off the tails:

Made a mandrel as per the article:

Set up with a dti (both were within 0.002” O/D and 0.001” on the face, so I thought that was ok:

And turned the inside spigots and the flanges to thickness. I made the spigots a good fit to the cylinders. I can slacken them off if I need to I suppose:

Then finished the spigot faces in the 3 jaw:

I guess there was better way to do it than this, but it seemed to work ok:

Dr_GMJN26/09/2021 22:16:59
1225 forum posts

The castings where right on the edge of being big enough for the stated dimensions, in fact there are still a couple of pinholes on one of the gasket faces. The brass extrusion I bought was never going to be big enough to make the glands:

Got plenty spare…

I’ve got some brass bar, so I’ll try to make them from that:

Lessons learned: I should have bored the packing holes rather than drilled them - my smallest boring bar will just fit. Oh well, I think they will be ok.

Next job is to make a mounting block for them for the R/T vice, and get them milled as per the valve blocks. I might put some JB Weld around the bosses - they look very close to being undersized despite everything being pretty central.

Dr_GMJN26/09/2021 22:40:20
1225 forum posts

In other news, went to the Kelham Island museum this morning (it’s only 30 minutes from home). Parked next to a double flywheel similar to the one on the Twin Victoria. Never seen one before, it looks like it was part of some electrical machine judging by the circumferential details:

A few other engines:

And things in glass cases (always good):

And of course the 12,000hp River Don engine:

Bought myself a poster for the workshop:

Unfortunately it wasn’t running today due to a boiler issue. I’m always amazed it can go from full forward speed to full reverse speed in 2 seconds, without shutting the throttles. It’s one of those things where you can feel the power just by standing near to it when it’s working. Same awesomeness as a Typhoon display, or being on the pit wall at Silverstone when the old 3.5 litre V10 F1 cars were current.

Other random stuff:

Sheffield Simplex:

Cavity magnetron (with Sheffield made magnet!):

Anyway, a great museum, and it’s free (of course made a donation though).

Dr_GMJN04/10/2021 18:46:04
1225 forum posts

The back cylinder caps are domed, and this was a challenge. I took the advice I understood from the other thread (on machining domes believe it or not), and drew out the profile in CAD, then machined from a bar of cast iron:

I set the tool parallel to the bed:

And using more CAD:

Roughed the domes out:

Then using co-ordinates, approximated the profile:

Then using a combination of a dremel, files and abrasive paper:

Smoothed to shape:

Parted off using the home made rear post from earlier this year (worked great):

Then made a spacer ring and reversed in the chuck to turn and mill the inside details:

Took a few goes, but eventually I got a decent result:

The domes are primed; they’ll be painted blue eventually. I checked the height offsets with the height gauge, and they were identical to within half a thou believe it or not.

JasonB04/10/2021 18:51:06
21435 forum posts
2448 photos
1 articles

They look the partsmiley

Dr_GMJN04/10/2021 21:16:24
1225 forum posts
Posted by JasonB on 04/10/2021 18:51:06:

They look the partsmiley

Yep - really pleased with how they look, and fun to make as well. Thanks for the advice on the other thread.

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