Stuart Twin Victoria (Princess Royal) Mill Engine

[Dr_GMJNParticipant @dr_gmjn]

I got the bolts made today:

I used the end stop and gauges to get everything consistent:

Made a small fixture for getting the heads the same thickness, and the chamfers identical:

And a split fixture for the mill, to get the flat offsets identical:

All seemed to work OK:

After all that, they do assembly very snugly, so I don't thing soldering will be needed for the subsequent machining:

I might add some small 45 degree chamfers to the ends next to the bolts – I think they look a bit clunky as they are now. I was going to make them a semi-cylindrical radius, but the bolts aren't centred on the pads, so that might look a bit odd.

Unfortunately the I don't think there's enough room to make a flanged boss for the eccentric rod, so I'll stick with the rectangular ones as per the article.

[Dr_GMJNParticipant @dr_gmjn]

Still struggling a bit with the straps – a bit of fettling needed tonight, but I think I’m getting there.

The casting flaw I didn’t pay much attention to: it turns out only about 0.3mm needs machining from the o/d, even roughly measuring a Blue-Tack positive impression showed it would definitely still leave a hole:

As suggested, I milled a 3mm hole, but went straight through the flaw and into the I/d. Then turned some similar material (from the spare bearing block) to be a tight fit, then tinned with solder, tapped into position and sweated in place. I misjudged the proximity of the hole to the edge (it now has a very thin wall), but in the end it held:

After filing back, I think it will be fine once finally machined:

[Dr_GMJNParticipant @dr_gmjn]

I guess the reason for the separate central ring is to make machining to a good fit easier, since the eccentric boss can be turned in one pass rather from each side?

Presumably though because of the fitted bolts and lock-nuts, a tight fit can to some extent be compensated for?

[JasonBModerator @jasonb]

At the expense of contact area

[Dr_GMJNParticipant @dr_gmjn]

I’ll hopefully get to making the eccentrics this weekend. I’ll give the parting tool method a go, although judging the right diameter I think I’ll find tricky.

I’m thinking I might turn the outer side of the ridge first, checking fit with half the strap overhanging, then when it’s spot-on, measure and machine the chuck side to the same measurement.

[Dr_GMJNParticipant @dr_gmjn]

I’ll hopefully get to making the eccentrics this weekend. I’ll give the parting tool method a go, although judging the right diameter I think I’ll find tricky.

I’m thinking I might turn the outer side of the ridge first, checking fit with half the strap overhanging, then when it’s spot-on, measure and machine the chuck side to the same measurement.

[Dr_GMJNParticipant @dr_gmjn]

Continued with the straps this morning, marking out for setting up in the 4-jaw chuck:

Zeroed in the chuck:

Bored:

Internal groove turned:

Now for the external milling:

Too cold for comfort in the workshop today, so I’ll start again tomorrow.

[Dr_GMJNParticipant @dr_gmjn]

Made the fixture for milling the outside profile:

The central hole is for a 10mm end mill so I can centre it inthe R/T a bit more easily.

Hopefully the clamp load will be enough to hold it together without bolts.

[Dr_GMJNParticipant @dr_gmjn]

Set the fixture in the R/T:

And milled the outer profiles:

I used my EBay slip gauges, hot-glued together, to support the tail:

They seem ok – one is a bit off around the oiler pad for some reason. I think the pads are too small for an oil pot, so I guess I will need to spot-face them anyway:

I’ll also put chamfers along the square bolt boss edges.

These are a real pain. I’ve been playing catch-up and chasing my tail with various dimensions ever since the first hole went wrong.

[Dr_GMJNParticipant @dr_gmjn]

It’s finished!

Well, this 3D printed version is – it's approximately OO scale:

Jason B kindly gave me the CAD model he's done for his single-cylinder version, and I mirrored it and moved the crankshaft and linkages slightly to form a twin. Then printed a base and wrapped some brick paper around it for a bit of scale.

It's now in place inside a mill building on a work colleague's OO railway (with the flywheel powered by a geared motor and rubber belt).

Edited By Dr_GMJN on 18/04/2023 22:17:19

[JasonBModerator @jasonb]

That looks good Doc, what made you change to the smooth faced flywheel?

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 19/04/2023 10:30:41:

That looks good Doc, what made you change to the smooth faced flywheel?

Thanks Jason,

We ended up making it smooth because the grooves were tiny, and no reasonably sized band would fit. So I turned the grooves off on a mandrel, and formed a recess which both trued the wheel a bit, and made it more suitable for the drive belts that we had..

[Dr_GMJNParticipant @dr_gmjn]

I wasn’t 100% happy with one of the eccentric strap profiles back in March, and I lost a bit of motivation to make another – they had taken a great deal of time and effort (even to get one slightly wrong!). Anyway, three months later I’ve finally made another, which is spot-on. Also added chamfers to the edges to neaten the bosses up. Just need spot-facing and drilling for the oilers, and they will both be done.

Strange how this one took less than a day, the previous ones took a week or more of messing about. Even considering not having to re-make the r/t fixture, I guess that shows the time it takes me to try and figures things out, plus chasing mistakes.

BTW – what oilers you folks put on these? I’m m thinking the plain brass oilers I put on the 10V main bearings might be OK, although presumably on a real engine e they’d be capped? Thanks.

[Dr_GMJNParticipant @dr_gmjn]

Started on the eccentric sheaves. Turned down some mild steel to the locating ring diameter:

Marked out:

Then once machined to a perfect fit on the straps, cut it off and put in the chuck for facing and marking out for the eccentric offset. Padded the chuck jaws with paper to protect the bearing surfaces, and it immediately moved in the chuck, snapping the tool and trashing the part. Strange thing is I almost knew it was going to do that, but did it anyway. Very odd:

Second attempt:

Test fit:

The strap halves just lock onto the eccentric when tight, they need a slight gap between the joint faces:

I think this is right, so they can be adjusted for wear, and that’s why the strap caps have lock-nuts.

I’ll leave the sawing and chucking until tomorrow I think. I need to figure out a method of securely holding in the chuck without damaging them. Maybe an aluminium ring.

[JasonBModerator @jasonb]

Good to see some progress.

Do make sure you have allowed for the slight radius on the tip, it may be a bit tight where the arrow is pointing as that is where I usually need to ease the two corners of the strap's groove

[Dr_GMJNParticipant @dr_gmjn]

Posted by JasonB on 14/06/2023 06:56:22:

Good to see some progress.

Do make sure you have allowed for the slight radius on the tip, it may be a bit tight where the arrow is pointing as that is where I usually need to ease the two corners of the strap's groove

 

Thanks Jason. What I did there was, once everything was to the correct diameter and width, I put the point of the tool in the corner, and fed in and along very slightly to form a tiny undercut, to get rid of any radius.

 

by the way – I re-read your method, using a parting tool to form the diameters. I tried this, but couldn’t get the edge of the tool to cut along its length simultaneously. Moving side-to-side would help, but right next to the raised ring would have been slightly tapered. In the end I used r/h & l/h turning tools, which seemed to work ok.

Edited By Dr_GMJN on 14/06/2023 08:45:24

[JasonBModerator @jasonb]

My small parting tool probably has a "sharper" edge than your insert and also no corner radius on mine which makes it better for sideways use and sneaking up on final diameters.

[Dr_GMJNParticipant @dr_gmjn]

So tonight I spent 6 hours on the new eccentric, only to realise that I’ve made another mistake. I left some excess on the smaller raised eccentric boss length, but then sawed it off and faced it without adding the excess. So I’ve ended up with the right overall width, but the eccentric ring is too far over.

I only realised after setting it up in the R/T to drill the 90 degree grub screw holes:

It was turned, drilled and bored, and was pretty much spot-on. I’ve now used all my mild steel stock, so will have to get some more.

I don’t know whether my concentration is going, or whether there’s something up with me, but I can’t seem to make any progress with anything these days. I seem to be making mistakes at every stage. If I’m honest I’m quite demoralised.

I can only think that because I’m working from both the Stuart Drawing and the Article Drawing, I’ve confused myself. For all other parts, I’ve re-drawn them and converted to metric. I think perhaps doing this lessens the chance of mistakes (for me) because I tend to calculate dimensions I know I’ll need for machining, rather than overall dimensions that need things like offsets calculating.

[Dr_GMJNParticipant @dr_gmjn]

So we go again. I did a drawing, and bought some new steel bar (£3.50!)

And turned the O/Ds to profile, and this time with the correct offsets:

Centered them in the mill:

And centre drilled them offset by 1/8”

Set up in the 4-jaw chuck:

Drilled:

Then bored to a location fit on the crankshaft:

Then fitted into the expanding mandrel and machined the bosses. I used a 0.8mm radius tool, which worked well. The steel gave a much better finish than I got with the 10V eccentric. That steel seemed to tear rather than cut:

Then back over to the mill and set up in the R/T for drilling the 90 degree spaced 7BA grub screw holes:

[Dr_GMJNParticipant @dr_gmjn]

So that’s the eccentric sheaves done apart from trimming the grub screws:

Crankshaft test fitted with the parts I’ve made so far. Still got to cut the grooves in the shaft under the grub screws as per Ramon’s suggestion IIRC:

I might start on the crosshead and slides next, just to do a bit more work at the other end. Any advice, or follow the book/instincts? I think there was some discussion previously about the possibility of the slider rails deforming after machining…

[Dr_GMJNParticipant @dr_gmjn]

All – I'd like to add some stiffening bars and oiler bosses to the crosshead slides. I don't have silver soldering equipment. Could I use soft solder and JB weld for the fillets, or wouldn't that be strong enough?

Thanks.

[JasonBModerator @jasonb]

Depending on what materials you have you could mill down taller stock to leave a central web and then plunge cut to form round pockets to take bosses.

If doing it by adding a web I would go for soft solder as it's a part that is likely to be left bright rather than painted so the soft solder will hardly show and should form it's own fillet. Alternatively add a larger fillet with JBWeld or Milliput and paint just the top "cast" surface leaving the sides and bottom bare metal

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason. I don’t think the bar I’ve got is deep enough to mill to shape. I’ll double-check, but silver soldering should be ok.

[Dr_GMJNParticipant @dr_gmjn]

I thought I do something a bit simpler, so I started on the crosshead slider blocks.

Started by cutting some sections of brass roughly to size:

Then set them up in pairs in the vice and machined five faces in the same setup:

Then drilled and reamed the holes:

Then put in the 4-jaw chuck to turn the bosses:

I left 0.010” on the boss lengths in case they need fettling to fit between the slides.

Done, apart from some minor surface finishing:

I used a 0.8mm radius turning insert to get the fillet. Might be a bit small, but I’m still avoiding grinding tools unless there’s absolutely no other choice.

[Dr_GMJNParticipant @dr_gmjn]

Started on the forked ends for the piston rods. These are made from Mild Steel:

Set them in the mill vice and machined 5 faces to size:

Side milling has always been problematic on my mill. I think it’s a stiffness issue with one or more axis. At one point it dragged the cutter into the vice and took a chunk out of the jaw. Not happy. Strangely, no problem at all with the long faces – quite happily took shallow full depth cuts, but the short ones were hopeless even with incrementing the depth. You can probably see the difference in surface finish.

Then milled the central slot:

Drilled and tapped the 5BA thread:

Then set in the 4-jaw and turned the bosses:

Apart from the shaft holes and locking screw holes, they are done:

They look pretty crude compared with other parts, I’m wondering whether to add some chamfers on the boss annd shoulders, and round off the forked ends. Is there any reason that a real engine wouldn’t have those features?

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