Stuart Twin Victoria (Princess Royal) Mill Engine

A lot will depend on how the individual machine bores, I would certainly have to take care to get it parallel and probably opt to do the last few passes with HSS as inserts can tend to get pushed off the surface more though **GT ones will reduce the tendency. Any slight taper can often be honed or lapped out. But as you say between ctrs should give a parallel bore. The longer the bore the more likely it is to taper as you have more of a standard poring bar hanging out the toolpost.

Fabricated cylinders make it a bit easer to know that the end of the bore in the chuck is running true before you start but there are ways to make it easier with castings.

The one I had started to draw up would have been with fabricate dcylinders

basically soldered up from brass and bronze

Bored after soldering and pickling

faces milled

Nice work.

How about with Ramon's PTFE rings? In practical terms is it going to matter about a very slight taper?

I'll probably try the between centres approach, just for the sake of it.

By the way - what is the usual way of aligning and fixing the cylinder if not on the cross slide t-slot bed?

Packing it up from the bed is just fine - holding it to an angle plate or vertical slide allows infinite vertical adjustment but packing of the right height is okay. One thing to really take note of is not over tightening the clamps - not quite so important with cast iron as it is bronze but if you do distort it then the bore will be distorted once the clamps are released. This is one op where that simple slip of paper between the part and clamping surface pays dividends.

If you make yourself an expanding mandrel as has already been suggested you can do both ends of the cylinder as normal facing operations absolutely square to the bore - no fly cutting required. Move that to the mill and you can do all the other ops from the centre line of that mandrel - either still in the lathe chuck if you have a dividing head or as already suggested too bolted to an angle plate or even a piece of steel held vertical in the milling vice.

Doing the bore from the chuck is just as practical but you do run the risk of a taper - not much I grant you and yes you can lap it out but that's more tooling and another op.

If you took a look at the link I posted you will have seen what I mean about a mandrel - once you make these and get used to working with them you will realise just how useful they are. It's much better to make your own. I have a set bought from Arc Euro - they've never been used because they are never quite right size wise.

Any way you are In Jason's good hands so I'll bow out now - too many cooks etc - will end up getting you confused

Good luck with your build - I may be joining you soon

Regards - Ramon

I appreciate your input as I do Jason's - I try to take the bits from both that I'm most comfortable with doing; I know all the advice is sound, any errors arising in the past have been through my own mis-interpretation.

I had planned on using an expanding mandrel in order to find the finished bore axis in the mill - with the centre finder. I may have to reduce the end to a diameter that the finder tip can get to.

I can then offset directly from the axis to setup for the fabricated feet edges, and in the other plane, for the feet and valve pad heights.

Take no offence Doc - but as it is confusing to have several inputs possibly in conflict at times I thought it might be for the best.

I've always advocated 'listen to all' but 'make your own decision from what you've heard' - as you no doubt are aware that applies to plastic modelling as well as ME but too much information can become confusing especially for someone relatively new.

I think I said before we all have differing techniques to achieve an end result - you have to decide which best suits your purpose, your equipment and knowledge.

As said mandrels make for much easier approaches to many machining ops. I can thoroughly recommend you investigate their usefulness

BTW the mandrel should be within the cylinder. Find the centreline of it on the mill before putting the cylinder on it

Regards - Ramon

Quick update - I ordered the main castings yesterday. I've not started on the fabricated base yet becasue I've been distracted with machine fettling (and to be honest I lost interest in that half way through for various reasons), and it's very cold in the garage these days. I'll order the fasteners next month, then that'll be all the main components sorted out.

Well that’s about £300 of Stuart castings:



no going back now...

Been working a bit more on the soleplate CAD. Also spent some time verifying the geometry of the piston stroke/crosshead location/connecting rod etc:



Crank centreline works out spot on the same height as the cylinder axis, and the mid-stroke crosshead position is exactly half way between the guide rail hole centres, so my imperial/metric conversion must have been correct.

Looks like there's a clash with the big end bearing cap if using the original casting dimensions though, so I'll have to extend the sides a bit:



Better to find out now than when assembling it...I do seem to remember someone somewhere mentioning this issue with the connecting rod, and the casting needing a slot filing in it. I thought they meant the rod itself clashed with a soleplate cross brace. I've seen a video online where it looks perilously close, which is why I shortened them, but they must have meant the bearing cap.

Hi Doc G,

The big end will need a groove milled or filed in the end brace unless, as you say, you extend the sides a small amount.

Depends on how you feel about the aesthetics but to have a groove does follow full size practice as many bedplates have 'scallops' cast in for clearance around the rod movement.

'Perilously close' ? - a couple of thou gap is sufficient if there's no play in the moving parts - which is definitely the case on the Waller engine built - 'a miss is as good as a mile' springs to mind there

Regards - Ramon

Funny enough when sketching one out I did do a version with a rounded end to the base casting much like this engine but deleted the drawing a couple of weeks ago which would have given plenty of clearance.

Thanks both.

Ramon - I just looked again at your model and noticed the cut-out. I didn't see it previously, and I don't think you mentioned it before. The P.R. I saw online didn't have the cut-out, but it did have a different bearing cap.

Jason - I'd prefer the non-rounded end TBH. First it's easier to make, and second I'm not sure I like the aesthetics (obviously personal preference).

I'll have a play about and see what it looks like extended. By my reckoning if the end is moved over by c.7 mm, it gives a c. 3 mm clearance on the bearing cap, which probably isn't the end of the world.

Dr G - this project is one you can take 'as far as you like'. The big end can be changed, the end relieved or the sides extended. The choice is yours and will be fine however you do it. A google search should soon find examples of stationary engine connecting rod 'big ends' - there are quite a few to choose from and most would be in keeping.

I don't quite understand though when you refer to the 'bearing cap' ?

Ramon

"Bearing cap" = keep plate on the end of the conrod's split bearing but that would be with marine type big end and PR uses a strap?

If it is a marine type big end then there will also be fixings that stick out further to contend with too.

Edited By JasonB on 17/12/2020 10:28:07

Thanks Jason - always thought of that as bearing 'keep' - for some reason I was thing Doc G was meaning the main bearing hence the confusion - easy for me these days!

I don't think too many mill engines were fitted with marine type big ends were they?

No, a strap with a wedge or a rectangular hole in the end of the rod for the bearing and wedge to close it up would be more typical. The strap can always be made as a dummy if the Doc does not want to do the detailed PR version.

I was using car engine terms when I said bearing cap; I meant half the split block and retaining strap to the right of the drawing here:



Seems a very complicated way of doing things, but I guess it reflects reality.

I'd like to build it like that, as per the plans, although I might go mad and add the lubricator even though it's supposed to be for the reversing engine only. I know...crazy.

Hi Doc, I did mine to print but as you have already seen you need to make allowance for it on the end bar if so. I would imagine it is true to prototype but if not quite in keeping with the period.

You need to lubricate the crank pin even if non reversing. Either a simple type as shown but better (i.e. more realistic) if you do it through the end of the crankpin(s).

If you want to make see through oilers an ideal material for the 'glass' are those crystal clear tubes you get as protectors on artists brushes.

Ramon

Thanks Ramon,

Yes - the one I'd seen that didn't have a cut-out had what I'd describe as a bearing cap, similar to a car engine. I think it's the marine type mentioned by Jason.

The plans show a rotating crankpin oiler, but they imply they're only for show...but that they do in fact sort of work. All a bit confusing actually. I'll go with the plans, and if they work, fine, if not I'll add an additional oiler through the strap.

Doc,

I've just fitted a rotating crankpin oiler to the engine I'm building at present. I sourced some 1mm OD copper tube for other parts but used this as the drip feed to the crankpin pick up. At first I thought that the viscosity of the light oil usually used for lubing running engines was going to be too thick to pass but it was not long before the oiler had emptied - if you are up for it they do work then and do look more in keeping than a oiler on the big end - well worth doing.

I did intend to fit this type of lubricator on my version - I think I even milled a pad to take a pedestal. I found the cups made recently but of course they never got fitted at the time.

Ramon

Ramon, do you have any drawings and/or photos of the oilers you mentioned you’d got working?

Thanks.