Stuart Twin Victoria (Princess Royal) Mill Engine

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason.

Whats the method for holding the fork and shaft in a vice? I can’t figure it out!

I assume the taper pin axis is going vertically through the shaft/fork interface?

[JasonBModerator @jasonb]

Face where the piston rod goes in against the fixed jaw. Bit of aluminium backing against the pin and moving jaw. That will hold the two together, rest crosshead on parallels.

For something like that which is just to stop rotation you can either go through on ctr line of the pin or offset so the pin just nicks the shaft which is what I did with the part above

[Dr_GMJNParticipant @dr_gmjn]

OK thanks Jason.

The ends of the bosses were turned in the lathe with the forks held in the 4-jaw, so they should be parallel enough.

Re. The stepped drill method. I’ve got drills in 0.1mm increments, but I’m guessing the diameters I’ll need are much closer than that.

Any recommendations for drills?

Also, large diameter first, then small?

[JasonBModerator @jasonb]

No, 0.1mm will do just pick the nearest and drill to appropriate depth, you are just aiming to take out a bit more material so the reamer does not have to do all the work. Doormer A002.

Smallest right through then open up to the required depth with the next drill.

[Dr_GMJNParticipant @dr_gmjn]

OK so a quick measurement suggests I can use 2 drills – just about.

Is it best to hand ream the hole to size?

[JasonBModerator @jasonb]

Yes use the reamer by hand and go very carefully.

[Dr_GMJNParticipant @dr_gmjn]

I had a go at the drilling and reaming today – as outlined above.

Spotted the forks:

Drilled, 1.4mm first for 4mm, then 1.3mm through:

Then reamed:

The reaming was very slow. It was as if the reamer wasn’t very sharp. There were some shavings, but I thought it would be easier.

This is how they assemble:

The pins tap in tightly, but the shafts rattle. I think this is a consequence of loading the shafts towards the hole during reaming. Once they are released, any slight play in the shaft/fork causes the cross-pin to be a slack fit in that area.

I’ve tried reaming them again ‘loose’ in the hand, in an attempt to offset the pin taper outwards, and also just reaming the forks in an attempt to take up the play. It’s worked on one, but not yet on the other. I’m running out of diameter to tap the taper pins in without them becoming flush with the upper fork surface.

Anyway, at least no drills snapped in blind holes. Here they are assembled to the sliders. I will cut the rods to length once test-assembled to the slide bars.

[Dr_GMJNParticipant @dr_gmjn]

I might do the crosshead bars next, then I can test assemble the blocks and forks etc, and get everything machined to size.

I think I bought this square bar for them:

Seems like the right width:

I thought that I’d machine a stiffener profile as below:

So the upper bar would be milled to two triangular stiffeners, then a boss hole plunge milled. I’d then turn a boss to fit, and soft solder in place. Then add some Milliut radii and that would be about it.

I’m thinking that flatting the sliding surfaces on a surface plate with wet & dry would get them flat enough?

Comments welcome as always.

[JasonBModerator @jasonb]

That’s more or less what I have done a couple of times, but wanting to leave them bright did not use the Milliput. Check for flatness after machining as you are taking most of the material off one sid eof teh bright bar, or normalise it first

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason.

How do I normalise the bar? Heat it up and let it cool in air?

I want to paint the upper ‘cast’ bits of the bars, but leave the long edge faces and ends bright.

Any comments on how to take up the play in the taper pin reaming? Am I on the right lines by reaming without the rod in place?

 

Thanks.

[JasonBModerator @jasonb]

Heat to bright red approx 875deg C and hold it there, on 1/4″ sq 3-4mins should do and then allow to cool as slowly as possible. As it is supposed to be BBQ season you could heat with the blowtorch and then put in the the BBQ or ashes from a fire and let them cool over a few hours.

To Take up the slack ream the croshed without the pin provided you can get deeper without the head going below the surface. It is really only rotation you are looking to stop so that the brasses rotate on the pin rather than the pin rotate in the crosshead.

 

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason. Presumably the 1/4 taper pins are measured at the wide end, so getting longer ones wouldn’t be possible in case I need to open them up more that head diameter?

Id assumed they were for stopping lateral movement, since there’s nothing else stopping the pins from falling out of the brass blocks.

[WearyParticipant @weary]

Yes, imperial taper-pin’s diameter measured at the ‘top’-end; i.e. largest diameter.

Note: Metric taper-pin’s diameter measured at the ‘bottom’-end; i.e. smallest diameter.

So, as you are using 1/16″ taper pins (I think),  an option for you might be to ‘go up’ to long 1.5mm metric taper-pins if you are really concerned about your fit and re-ream in the light of your experience.  Get long pins, i.e. 16 or 18mm & cut them down as appropriate.  You will of course need a metric reamer for this approach.

Phil

[JasonBModerator @jasonb]

Or you could turn yourself a couple of pins at the imperial 1:48 taper and make them longer than standard so you get a larger dia at the thick end.

[Dr_GMJNParticipant @dr_gmjn]

<p style=”text-align: left;”>Thanks all. I’ll try again with the ones I’ve got. There is some variation in the depth they push-in.</p>
Im assuming 0.5mm – 1mm protrusion would look OK?

[Dr_GMJNParticipant @dr_gmjn]

I’ve struggled to find smokeless fuel for the fire to do the heat treatment of the crosshead bars, so I decided to have a go at the valve rods and ends.

Turning some stainless was straightforward:

But as with the 10V, the adjusment thread was problematic because the split die, even when fully opened, wouldn’t pass over the reduced diameter part of the rod. I had to turn it down more than I’d like, to be able to thread it, but I think it’s still just about a good enough fit in the valve chest hole to be OK.

I hope that the tapped thread in the brass valve plate will be a good fit on the thread, but I get the impression it will be very loose.

Then on to the rod ends. Simple turning, threading and chamfering, and got a good fit on the rods:

I thought I’d be clever and make a flanged, split fixture for them to mill the ends. I thought once the flats were milled, I could re-position in the vice (on the side of the jaws) and drill the 2.4mm hole, and the flange would ensure it was all perpendicular:

Unfortunately, it slipped, and one is ruined:

Mght try the rotary table next time, but might not have enough clearance for the milling/drilling head.

Then the valve sliders. The ones I bought from Stuart Models don’t look much like the ones in the plans:

I think they are die cast.

Obviously I can’t machine them to the drawings, but the recess seems to be the right size, so I might just flat the base and lap it to the valve faces on the cylinders. Not sure if anything needs to be machined at all on them tbh.

[JasonBModerator @jasonb]

On a small part like the rod ends I try and do most of the work while they are still attached to the rest of the bar as you have plenty to grip, or work them on either end of a shorter length and cut in half after milling. If you have a square collet block, that would have been ideal as you can index them around for milling and then drilling the hole. Failing that a block with a grub screw that bears on the bar beyond the bit you want will do the job.

The valves are hot pressed brass. The only sizes that really matter are the 0.657″ and the central 0.375″ The fact these two dims are given as decimals indicates they are more important than the fractional ones.

That many burrs also suggests your cutter is getting a bit blunt.

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason.

I might make both ends again – I think there’s enough material.

I’ve heard a lot about collet blocks over the months looking at these forums, I’ll look at getting one.

I already got some new milling cutters, but thought I could get away with it for one more job.

[Dr_GMJNParticipant @dr_gmjn]

Found the last bag of smokeless fuel in the area this afternoon. Currently roasting in the living room. Hopefully this will be hot enough to heat treat the bars? Photo is pretty accurate colour – orange. I’ll leave them in there until morning.

[Dr_GMJNParticipant @dr_gmjn]

This morning I removed to bars from the fire, but they were scaled. I milled off the scale to the minimum I could, but this has left them undersized, so I guess they are scrap.

Maybe they got too hot.

[JasonBModerator @jasonb]

Acid dip or good old drawfiling would have taken less off.

Top and bottom were likely to be machined anyway, how much too narrow are they going to end up? Is there enough to set them slightly to one side, if a few thou I doubt it will be noticable.

[Dr_GMJNParticipant @dr_gmjn]

Thanks Jason.

So I’d assumed for my drawings that the 1/4″ square would be 0.25″ (6.35 mm), so I’d drawn the bars to be 6.33 mm on height (so I could allow for some flatting), and 6.35 wide to match the crosshead blocks. However, once all the rust/crud was wire brushed off (the original un-heat treated bar), they are in reality 0.248″ (6.29 mm square). So before I even start, I couldn’t hit the dimensions I’d drawn.

Once the scale is removed from the heat treated bars, they’re down to 6.12 mm, and that’s with some scale remaining, so not really near a finish suitable for a sliding fit.

I decided to go ahead and machine one from un-treated bar, mainly just to do something (and to get my inevitable machining mistakes out of the way).

3D printed a jig for the slopes:

Milled the central pocket OK (1 mm hole first):

Fairly happy with the form of them, although a few machining things to change for the next ones:

And of course as expected they are bowed:

It’s 0.003″ – 0.004″

I’m wondering if it’s even worth heat treating them?

1) I might be able to 3-point bend them in a vice to get that bow out.

or

2) Shell-mill the face (I can get a very good finish with that).

Both followed by flatting on the surface plate with abrasives/oil for final finishing.

I’m assuming that final soldering of the oiler bosses won’t make much difference to the bow, but I guess I could fit them first, then flat them.

Seems easier that heat-treating and removing scale, and then having undersized parts?

[JasonBModerator @jasonb]

I don’t see why you can’t reduce the height of the webs slightly which would allow what you have to be used. Width will depend on if you have any fitting allowance on the slippers.

Usual to buy black bar a bit larger  or normalise oversize bright and then machine to finish size

[Dr_GMJNParticipant @dr_gmjn]

Height isn’t much of an issue, but they’re already a bit too narrow.

The reason I re-made the crosshead forks was to get the overall width right.

So I’m already slightly beyond the limit on width, any more adjustment will mean moving the slide bars in, away from the centre of the bed pads (which I wanted to avoid).

I terms of height, aren’t I better off machining out the 0.003” bow anyway? still be better than using the treated bars even without all the scale removed, because they are already 0.007” undersized?

 

 

[JasonBModerator @jasonb]

If you have the material then flattening may be easier for you. As I said make sure they are flat OR normalise.

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