Stuart Twin Victoria (Princess Royal) Mill Engine

[JasonB]

On JasonB Said:

Going back to the handwheel suggestion. Put your alignment pin in the flywheel that is in the chuck, slip on the previously turned one and touch the tool on the rim and zero the handwheel. Now you know the setting to turn the second handwheel to.

It’s times like these that my 300mm digi calliper comes out of the draw.

Yes, another option. I’d already forgotten about the spigot.

[Dr_GMJNParticipant @dr_gmjn]

OK, so I’ve used three measuring methods – just out of interest to see the relative accuracies:

1) A strip of card wrapped around the smaller wheel, and its length (circumference) measured with a tape measure, then wrapped around the larger wheel and the difference measured with verniers:

2) Measuring the chord length and its offest from the circumference using verniers:

3) Height gauge:

 

Assuming the height gauge is the datum (as the most accurate method) Anyone fancy a bank holiday guess at the maximum and minimum deviation from this – on radius, in terms of thou – between the chord and tape methods?

I’m going to use Jason’s spigot method as a double-check on the height gauge readings, and hopefully get it done this afternoon.

Thanks all.

 

[JasonBModerator @jasonb]

I thought you wanted to do the measuring with the second one still in the lathe, if so height gauge method may be tricky.

 

If off the lathe then stand the two side by side and measure the height difference with depth gauge or the back of your callipers.

But as you have a height gauge then just clamp a flat plate to the bottom and you effectively have a vernier calliper.

[Dr_GMJNParticipant @dr_gmjn]

I did want to keep it on the lathe, but as mentioned I then thought that I really want to bore the hub and face the mating parts of the rim/hub in one setup, to reduce the chance of them being out of true. I’d machined the outer face first (as per the article method I think), which I suppose was a mistake.

So with both wheels off the lathe, I’ve now just measured them directly with the height gauge, and will take off the measured difference once the second wheel has been re-set.

I tried the other two methods out of interest to see how accurate (or inaccurate) they would have been.

 

[Dr_GMJNParticipant @dr_gmjn]

Mounted the second wheel and machined it to the o/d of the first:

Counterbored the hub – I hope this doesn’t interfere with the broching process too much:

Here are the two wheels:

One middle boss is wider than the other, but I suppose this will not be visible once joined and filled. There is still metal-on in terms of overall outer circumference face width, and overall hub length, which I will re-size on the faceplate after joining.

And fitted to the spigot:

I managed to get both small bores to zero difference according to my gauge and verniers, but unfortunately, despite the spigot being a decent fit in both, I can still wobble the wheels against each other very slightly. I could re-make another shaft to be a tight fit, but am slightly concerned it might lock iteslf in place after clamping the wheels together. I suppose I could make it in brass and that might be easier to drift out?

Next job is to drill the peripheral holes for the clamping screws, and then do a bit more clean-up of the cast areas before finally bringing them together. Didn’t quite get them joined this holiday, but still some progress.

 

By the way, the difference in radius between the card tape, vernier-measured chord, and height gauge (datum) was +/- 0.001″. Maybe it was luck, but I found that pretty incredible especially with the card tape.

[Dr_GMJNParticipant @dr_gmjn]

Thinking out loud again:

For the final facing operations (after joining), and machining the recess for the barring ring, if I did make a tap-fit brass spigot, turned between centres, could I machine the whole assembly between centres, using a drive dog through the spokes?

Seems like it would save a lot of setup time, and be more accurate than setting and re-setting on a faceplate for each operation?

Thanks.

[JasonBModerator @jasonb]

I’ve never got a good finish doing flywheels mounted like that as the lack of support at the rim causes fine chatter marks Probably won’t be rigid enough for rope grooves either.

I prefer to machine the rim OD, one side and do the bore all in one setting which keeps things true then the other side of the rim is a simple facing job.

[Dr_GMJNParticipant @dr_gmjn]

Yes, I forgot about the most important thing – the bore, which needs opening from about 11mm to 14mm.

Re. Bonding the halves, I think JB weld for the hub, and Araldite for the rim – I’m concerned that JB weld on the rim might leave a black line, which, I think in theory would end up on top of the middle peak of the rope grooves. So it would presumably be quite visible. I guess I could JB Weld where the inner spoke blocks are, but from memory it’s quite grainy and might hold the rim apart slightly. Could relieve them a bit, but is it worth the effort?

[JasonBModerator @jasonb]

Unless you ar eonly using one of the two tubes your JBW should be grey and quite close to the colour of cast iron. Applied very thinly it should not show anymore than the amber of Araldite.

I’d much rather machine across the JBW than Araldite which is always a bit soft even after setting and I’m sure that if Tubal Cain had it available 40yrs ago then he would have used it.

[Dr_GMJNParticipant @dr_gmjn]

OK, JB Weld it is.

Bit more progress last night – I measured from the shaft o/d to the inside of the machined rim, and subtracted half the head diameter of an M4 caphead (M3 didn’t look robust enough to me):

Then turned over and marked each square pad to make sure I could drill and tap it. It was very close, but it’s just about do-able.

Then centre marked them:

Drilled to 4mm, and countersunk the mating face holes:

Then turned over, and counterbored with a 6mm end mill. I turned down the M4 caphead head diameters from 7mm to just under 6mm, because even at 6mm, somehow the end mill grazed the machined rim (doesn’t matter too much I guess because that part will be machined away for the barring ring insert):

Plenty of thread protruding – next job is to align the wheels on the spigot, then drill and tap the other side. I’ll make blind holes to save filling – that side will be untouched apart from clean-up and a slight recess machined under the rim.

So after drilling and tapping I’ll do a final clean-up of the cast surfaces – the pads will need matching becasue some have a prominent step.

I may also grind a small chamfer along all mating edges (apart from the outer edges to be machined) as a sort of JB Weld-prep. May help with disguising the joint line.

[Dr_GMJNParticipant @dr_gmjn]

Made a jig to align the spokes, and then, with the spigot fitted and a slip gauge under the rim, marked through the counterbored holes onto the second flywheel with a drill:

Then centre-punched & drilled:

Countersunk slightly:

and tapped M4:

All fitted together nicely (dry):

I then put the assembly in the lathe between centres, and checked runout.

Radial runout on both wheels was a couple of thou, but axial runout was 0.018″, and gave a visible wobble.

From this I assume the two wheels are not co-axial – this seemed to be confirmed when I could feel a slight step at the join line on one side, but smooth on the opposite side.

This may not be surprising since despite re-machining the spigot to give a better fit, I can still very slightly rock the two wheels against each other. I don’t think I can get the spigot a tight fit on both wheels due to the bores being very slightly different. I tried a dodgy method of centre-punching around th espigot to get a tigher fit, but obviously that didn’t work too well.

I suppose I can try to correct this by feel on the step of the rim to get them more co-axial, but it’s a bit hit-and-miss- especially when I finally assemble with JB Weld.

Anyway, it is what it is (which isn’t a disaster by any means), I will just have to get it as good as I can I guess.

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