Stuart Twin Victoria (Princess Royal) Mill Engine

Take a cut at say 1.2mm from stock top and then measure how high that side is compared to the other and lower your tool by the difference. Probably would have been better to do upto the edge of the cross head guide pad and not the narrow cut the other side then no blending needed, if you have the movement with the second setup I'd set it to just skim upto the edge of those pads

At the end of the day you are replicating a casting and some deviation is desirable and helps make it look like a casting rather than painted barstock. Look at this shot of where I machined off the unused bearing pad on the Victoria I did recently, one end is about 5 thou above the surrounding cast surface the other a similar amount below and thats over 2" distance.

All blends in fine with a bit of Dremel, file and Emery work

Thanks Jason.

Yes, the initial idea was to do as you suggested and machine up to one side of the right hand pad. I changed my mind because I wanted all four pads exactly the same length, and was using the DRO datumed on the left inner edge of the bed. If I'd have only machined one side, any error in the bed length would have thrown out the DRO reading when re-datumed at the other end after swapping the part on the bed. OK it seems less than 0.5mm, but I didn't want to take any chances - my mill bed and all my accurate measuring equipment can't accommodate these part lengths in one go.

I suppose I could have machined to the scribed lines, but I went down the track of getting pad widths perfect rather than simplifying bed height match. Anyway, it'll be fine once sanded.

I did notice in the article that it was suggested to relieve the centre and end undersides of the bed, to guarantee the pads contact. Is that what you're checking with the feeler gauge in the picture? I thought of finishing everything, then just flatting the middle and ends with abrasive paper just to give a fraction of clearance. At present they're flat all over.

The bed had been part machined when I got it and the bottom possibly just filed which meant it rocked on the mill table so I shimmed it up with feeler gauges so that the clamps would not distort the bed and subsequently machined the tops of all the pads and the bottom flat.

Back on this one after a week in deepest West Wales...

After finishing all the pads (needed four setups), and drilling and tapping all the holes, I set up for skimming the pads:



I took a 0.1 mm cut, again using four setups, but with the z-axis locked:






All flat and parallel:






Then began filing radii on all the upper edges:



Now ready for some Milliput in the internal corners:



Hopefully after cleaning with detergent, it will stick...

I've not had problems with the Milliput staying put. Just test any etch primers on a bit first as I did have one that affected the surface.

Same here - it should be OK I think, although in the past I've only really used it on plastic.

Made a start by squidging some Milliput into the appropriate corners:





Then drawing the ball-ended tools along the bead:



Then cleaning up the excess with a scraper and painting along the edges with a wet brush to feather the edges:



So far so good, but still plenty to do:

Finished the Milliputing of the radii, flatting the excess and feathering off any rough edges, then abraded all over with Scotchbrite:



Immediately after Scotchbriting, sprayed with etch primer, and then skimmed the mating faces back to bare metal with #800 wet and dry:







A few bits need some very minor further filling, but they can wait I until final painting on completion.

They’ve taken a lot longer than I thought to make, but I’ve learned some stuff on the way and overall I’m very happy with them. IMO they look much more refined than the Stuart originals - with the plinth around the bases, the throttle bell crank boss, and the top pads are now specific for the modified Princess Royal components. I suppose you could argue that the surface finish is too good for a casting, then again the bed for the 10V is very smooth, and I spent some time flatting that a bit before painting.

Anyway thanks to Jason and Ramon for the idea, and the advice along the way. At last some results after a long build thread with no actual building!

Next job: cylinder feet I think.

A really excellent result after a great deal of thought going in to their manufacture. They certainly look convincing from here.

Great job Doc G

Ramon

Thanks Ramon, much appreciated.

Yes, some thought and planning, perhaps too much for what they are, yet still some mistakes (to learn from)!

Anyway - the result is what counts, I hope everything fits! Cheers.

A good indicator to how well the rest of the engine should turn out.

If you do feel you want a bit more texture then spraying with low pressure or an old can of primer can give a slightly more lumpy finish or I have even stippled primer on in the past. You can also run the edge of a slow running grinding bit or burr in a Dremel against the surfaces.

However let's not forget the scale of this engine which is a lot smaller than the original 1/5th scale of Victoria so any texture left from casting will be next to nothing. Think of it like abrasive paper, the original may have had a 60g texture at about 1/18th scale yours will be more like 1000g

Edited By JasonB on 11/06/2021 07:21:09

Thanks Jason. Yes I thought of spraying Mr. Surfacer (a filler primer for models) at low pressure from a distance, or even getting a spatter cap for the airbrush. I’ll experiment with that when the time comes to finally paint it.

Hoping to make a start on the cylinders today - at least cleaning them up ready for attaching their feet.

The article says use 1/2” x 1/2” steel for them, which I’ve bought. Unfortunately, while I got more than enough for four lengths, I effectively need six, because I want to try using the three strips soldered together method for boring the arcs.

Any ideas how to get around this, or just buy more steel?

Thanks.

You don't need a full strip in the middle so short bits will do or anything that could be cut to 1/2" long.

Don't forget to poke some fuse wire down the cast steam passages as they are often still full of core sand and you don't want to go spreading that over your machines

Thanks Jason. I’m not sure if I’ve misunderstood the concept - the image in the article is just a blur.

I assume the strips are arranged like this:



and you bore the assembly until it’s like this:



and you’re suggesting something like this, which will have intermittent cuts?



With either of these it seems like there’s only a small amount of material to withstand the clamp force from the Chuck? Is it likely to be an issue?

Thanks.

That's it. The intermittant cut should not be an issue and if you had the "spacers" a little closer together in your sketch then the final cuts will be constant.

A loose packer at either end will spread the load rather than push against the central soldered in packers, infacct arranged that way you could use superglue rather than solder as then it is only a case of stopping the bits sliding about when initially clamping.

Great - thanks Jason.

Clearly a nice model coming along. Might I make a suggestion; when building my Victoria recently, I made the cylinder supports from 1" BMS angle. The web is deep enough to allow marking of the centre of the 1/2" radius and the other web allows holding in the 4-jaw for machining out the curve. Afterwards it is sawn away, filed and drilled to form the mounting feet. Simple and saves quite a bit of milling away of surplus material.

Incidentally, as with the OP, the bed of my engine is fabricated from aluminium flat, helped along with epoxy filler, but of more plain appearance without a flanged lower edge.

Thanks Clive - looks like a very nice model.

The feet an mine are different - they fit underneath. They are made from machined 1/2" x 1/2" steel, profiled to fit the cylinder, and screwed into it with JB Weld as a gap filler. They are meant to look like cast-in features once complete.

So on to the cylinders - I needed to clean them up to get an idea of the diameter to machine into the modified feet blocks.

I actually have three - one was damaged when I got it; looked like whatever was used to separate it from its runner might have cut into the valve face:



There isn’t much machining allowance on there, so I sent a photo to Stuart Models who immediately sent another (excellent service). The intention is to use the damaged one for a machining test run, so I bodged some JB Weld into the cuts:



I cleaned the other two up, initially with a wire brush:



and removed the drain cock pads with a file, in preparation for fitting the feet:



But then I noticed quite a bit of scaling on the surface, which wouldn’t come off:



The file just skated off it, so I resorted to a grinding bit in the Dremel:



Which seemed to do the trick, but there’s still a lot to remove. It’s worse on one casting than the other two. I wonder if putting them in the fire made it worse. I’m thinking of trying to remove it from the cylinder bore as well, before machining. I now understand What all the fuss is about regarding casting skins, and them ruining tools. There was none on the 10V.

Also began poking the steam ports with wire to remove any residual mould sand - again, one was much worse than the other:



So current status is two are about 50% fettled, still waiting for the JB weld to set on the other:



BTW the nominal diameter seems to be about 33.5mm, so I’ll machine the feet to 34 and hope for the best; the JB Weld should make up the rest.

This all took longer than I thought, so the feet will have to wait for a few more days...

Apologies, I hadn't twigged that your proposed feet were integral with the cylinder. I was going by my "single". Should've looked at the diagrams more closely,.

In fact, from looking at Google images, are both types of foot used for the twin?