Stuart Twin Victoria (Princess Royal) Mill Engine

[JasonBModerator @jasonb]

Ramon, if you say you can't see how the broach will follow the tapered guide what makes it any different to the broach following a parallel guide and not drifting of somehow?

If I tilt the sketch so the exaggerated broach angle is vertical you should be able to see from the drawing that it is cutting a keyway that is parallel to the guide bush, I simply can't see what is different that may cause the broach to move away from the guide

Yes you could tilt the flywheel slightly so the broach is truely vertical but as I said at our sort of sizes the broach is so short the 75mm or so sticking out at the start of teh cut will only be 0.75mm off, thats 0.57degrees so I have not found it needs the work mounting at an angle myself.

Here is a square up against a 6" long parallel in a tapered guide a syou can see it's not far off vertical

As I said the angle in the sketches was exagerated in practice it is very small, this guide bush is 1.5" long and depth of slot varies by 0.35mm, hard to be exact one handed.

Edited By JasonB on 03/09/2022 10:37:08

[Dr_GMJNParticipant @dr_gmjn]

As modelled, would the marginal acute angle where the broach hits the bush tend to push it into the guide slot? So at least in theory, it’s better than a parallel slot?

[Ramon WilsonParticipant @ramonwilson3]

Well actually they can Jason, I have seen that where a broach pulls itself into the workpiece because the broach was not being pushed in truly vertical – when that happens its a bugger to get out sometimes too.

I'm not saying your method doesn't work – you've obviously proved that to yourself for yourself but I'm not convinced from my past use of broaches. Just to be clear – are you pushing the broach right through the workpiece ?

Guys, I'm not being pedantic here but I just don't see, based on my use of push broaches, not just at home, why there is need to go to all these lengths to get a flywheel drive on a shaft, it is after all a pretty basic requirement and to be honest Doc, if you are trying to replicate a full size machine of similar attribute the flywheel would in all probability be staked not keyed – but you'd still need to slot the wheel of course.

From the outset I did say if broaches are not available then slotting is the best (only?) option. A broach is a dedicated piece of kit – not cheap for what it is and can easily be damaged/ broken. A slotting device on your lathe is far more versatile for a relatively short diversion. But that's my take – money and choice being the ever present convention.

[Dr_GMJNParticipant @dr_gmjn]

Ramon, I’m just going on what the plans say would be prototypical – using tapered keys, but with a grub screw rather than a tapered keyway. If it’s fairly easy to make a tapered keyway with a broach to make it reflect reality a bit more…why not try it?

When you say you can’t see the point in going to all these lengths to fit a flywheel to a shaft: so why not just use a grub screw onto a flat in the shaft? The flywheel isn’t under any load in this model, so…where do you stop with simplifications?

Surely embarking on yet another diversion to make a slotting adapter is quite a task. It’s not just cost, it’s time. Today I’ve got a load of stuff I want to do, but by the time I’ve run about after the kids I’ll end up with maybe 2 hours to myself. As I’ve said before, I’ve little interest in making or modifying machinery these days. For the sake of £20-odd I can get a broach and be done with it. If I break it, fine I’ll think again.

[Ramon WilsonParticipant @ramonwilson3]

Well like I said Doc it's down to choice but if there's one thing I do understand it is time – or rather the lack of it so I well appreciate your sentiment but…

When I built my twin Vic, apart from the inlet system, I more or less followed the Stuart drawings. As my knowledge of full size machines grew it was an engine I was never satisfied with – from an aesthetic point of view that is as it certainly worked well enough, but it was always something I wished I'd followed full size practice more and put more into it.

Quite some time after I made it we had someone exhibit a really well modified and very realistic version displayed at the Forncett ME day. I have a feeling it was featured in ME but the builders name escapes me. I'm not an envious person but it reinforced my long held dissatisfaction with mine. In the end I sold it. All the engines I have made since, and no I can't match Jason on quantity, I have tried to simulate where possible the full size – I don't have that same feeling of regret on any of them and most certainly would not part with them

There's been a lot of discussion on this matter so far but no I would not advocate a grub screw drive – a key or more is correct. How it's done is down to individual choice as it's obvious from Jason, Paul and my difference of opinion

I'm not for one minute trying to force you down a path you do not want to take – that decision is yours and yours alone to make for as I have often said 'Listen to all and make your own mind how you want to proceed'.

To modify the topside as previously shown on this thread would, I agree, take time out but unlike myself age is on your side so you would have a new addition to your kit for future use. I do understand your thoughts on spending that time however – it crosses my path everyday – but all being well buying the broach will do the job and you can move on

Very best – R

[Dr_GMJNParticipant @dr_gmjn]

Thanks Ramon. The centre drill arrived I think, but now something else cropped up which leaves me with about an hour to myself today. I may well end up in the garage at 2am; won’t be the first time. It’s peaceful, and I can concentrate, but too many late nights catch up with me quicker than they used to.

Remember this is only my second model. I’m not yet at the stage of being overly critical of details that might not be 100% correct. Not so long ago I was contemplating just getting a Twin Victoria kit and building it ‘OOB’ as it were. The P.R. Version is a big enough step for me from the 10V – maybe even too big a step.

With plastic models I’m like you – every single error taunts me every time I look at a model – even ones that have won a prize. However I have a policy of never going back to correct something once I’ve called it finished. If I did that I would never build anything new.

On a completely different t topic – earlier in this thread my son was helping me with the bed machining, and on other threads making parts for his R/C car. Happy to say he got Level 2 distinctions in his Engineering Design and Engineering Manufacture BTEC exams this summer. Just needs to complete coursework for his final grades. Spending time in the garage figuring machining problems out massively helped with this I think. On more than one occasion he spotted errors in my methods that would have meant a load of re-work (you’re probably not surprised to hear that ha ha).

[Ramon WilsonParticipant @ramonwilson3]

Oh I wish Doc, my days of late nights in the workshop are long over. To think, I used to machine all day then come home again and carry on in my own workshop. For many years it was in the third bedroom! but soon moved into a larger shed. At first I used to rattle around in there – space is pretty limited today for sure.

Yes I do understand it's your second model, my mistake perhaps but I was under the impression you wanted to improve on the PR. I certainly don't think it's too big a step, the 10 was a superb result for a first model and I'm sure this will be no different.

Congratulations to your son for his achievement – looks like he's well on his way to keep tabs on Dad eh? I'm no academic as you know but spent a lot of time machining – for many years nothing short of a passion but its well on the wane now. If I'm lucky I'll get that marine engine finished but I have decided that that will be my last.

 

Regards – R

 

Edited By Ramon Wilson on 03/09/2022 13:29:18

[JasonBModerator @jasonb]

I'm not sure why you say it is not full size practice. Traction engines all tend to have a tapered key to hold the flywheel as do the many open and closed crank type engines and I dare say a few smaller steam engines too The Tidman Organ engine I modelled certainly had single gib head keys for flywheel and pulley on the real thing.. Maybe not right for a big mill engine but the info is now there for other model makers or Doc's future projects

The taper is nothing to do with the drive it is all about lateral location as there is nothing else to stop the flywheel coming off the end of the shaft. The taper being even shallower than say a Morse taper or that of a taper pin grips very well when correctly "fitted"

I think the set of three 1/16, 3/32 & 1/8 broaches I initially bought were good value, as I said more than 50 uses by myself and some leant out to others and no damage or signs of wear. These are just a Chinese set not name brand ones and I have something that I can carry on using for a lot longer

I can see that if you were broaching a much larger keyway there could be an increased risk of bending the broach away from the bush due to larger stick out and the forces needed but with these little broaches only being about 115mm long I've not found it to be an issue on the less than ideal "press" that I use.

Yes I drive the broach all the way through just like you would on a parallel keyway.

I do know of some that stop once the largest tooth just enters and have the key seat on the resulting stepped face of the cut maybe with a bit of filing. Not tried it myself but Graham Corry of Alyn Foundry fame does the engines he builds to order that way with several hundred under his belt many with twin flywheels and I'm told they don't fall off.

I did start making a slotting tool for the lathe, must have been for when I did the Minnie that was back in the 90s when I did not know better but ended up just planning those with the carriage as I did with subsequent models until I got the broaches. It sat in the back of a cupboard for years but recently I put the metal to better use on a model.

[Ramon WilsonParticipant @ramonwilson3]

I think it's time to call it a break Jason don't you think?

Of course there are all sorts of flywheel, and consequently the mounting of too, but we are specifically talking here of a representation of a large double flywheel of several tons on a stationary engine on a shaft supported at either end. 'Horse for Courses' in other words. The flywheel on the Mc'Onie for instance has a tapered key to hold it in situ but not a tapered slot to match. As you rightly say " Maybe not right for a big mill engine"

I'm well aware that the taper is not providing the drive but the key itself – I think by now that it should have been clear that I understand that.

It the situation is as described by Doc he will have a tapered key(s) sitting in a captive slot(s) and have to place the flywheel on the shaft after the key is in place. The tapers will have to match pretty well if the wheel is to stop in the correct place laterally. I'm sorry but I simply can't see that as full size practice.

It's his choice of course, but definitely not the way I would approach the job.

This all began by Doc implying he was going to slot these components using the lathe as a slotting tool. I think I said right at the outset 'unless you have access to broaches' which like you, I happen to have, but many, if not most, don't, then the matter of accurate division on the lathe for two keyways could be an issue.

Try to cut the taper as you suggest by all means – if it works then great – it just isn't the way I was taught to use push though broaches.

Now, I really do think we have exhausted this subject and Doc certainly has enough information to do as he chooses – I think it's time we let Doc get on don't you think

 

Best – R

 

PS The slotting tool I made was a very early tool so that I could do the engraving on a Quorn. Whilst it has had little use in comparison to most accessories made over the years when it has been used it's been quickly realised it was well worth the effort put in to making it – just like the Geo Thomas rolls, little use – godsend when required.

Edited By Ramon Wilson on 03/09/2022 14:32:46

[Martin KyteParticipant @martinkyte99762]

Is there not a reverse taper lurking in the right hand slot of the box. If it is then fitted behind the brach would advance the cut incrementally as the wedge is gradually pushed down. Thats how I thought they worked although I could well be mistaken. The taper on the bush would need to go the other way though.

regards Martin

[Dr_GMJNParticipant @dr_gmjn]

I was going to use the lathe to slot the hubs, and I still might – I don't know. The more things get discussed, the more options there are. For me it's a case of going with the flow and seeing what I think I can do. At one time I was going to make some sealed oilers for the tops of the valve chests, now I think I'll use brass blanking caps (with the number of oilers on this thing, I think there's a danger of it looking like a Christmas tree with candles stuck all over it).

BTW, earlier I mentioned axial pins to locate the crank arms on the shaft – this is what I meant (from the Steam Engine book Jason posted:

[Ramon WilsonParticipant @ramonwilson3]

Hello Martin,

The way a push through broach works is by an increase in height of each tooth from the bottom to the top along it's length. The bush/guide has a parallel slot in so that as the back of the broach moves down in contact the increasing height of each tooth makes subsequent deeper cuts. The depth of cut of one stroke of the broach is the increase from the smallest tooth in initial contact to the largest. The broach is pushed right through the workpiece.

If the slot is not deep enough further depth can be made by introducing shims behind the broach and repeating the process until the required depth (within the limit of the broach) is reached.

As supplied I do not know of guide bushes that feature other than parallel slots – I may be wrong but I don't think so.

Best – R

[JasonBModerator @jasonb]

Doc re the crank pin pin. I've not done one that way but have done a couple with square keys like they show in some of the other illustrations.

Should be easier to do with what you have but may need to be done horizontally in the lathe if you can't get the head height in the lathe. Also easier to get apart than a pin drilled radially into the shaft should the need arrise

Loctite on it's own should do will do so anything else would be for decoration/realisum

Edited By JasonB on 03/09/2022 20:39:09

[Ramon WilsonParticipant @ramonwilson3]

Yes I have a very similar drawing in a book of mine. Nothing wrong with the idea but as mentioned before it's hard to find a full size example in any of the books (of engines) I have. Occasionally the odd one is keyed with a square key but most are simply shrunk on. (there's a great description of how they did that in Arnold Throp's book BTW

If you are using the cast iron cranks from Stuart there may also be the possibility the drill will run off in the softer cast iron so something to be aware of. My moneys on a pin from the major end just through the shaft – as with Jasons thought very easy to drill out if required and very easy to disguise.

Plus one for simply Loctiting the crank pins – I certainly don't bother with tapers – but have the last mil or so a tight interference fit so it tightens up as it presses home

[Dr_GMJNParticipant @dr_gmjn]

Ramon – I think Jason meant the axial pin is easier to remove – presumably you just tap the web off and the pin offers little additional resistance over a press-fit ?

End if the day I’ll see what kind of fit I end up with (as opposed to what I want!).

If it looks like it’s a fit that requires lightly tapping or pressing, I’ll go with Loctite I think – looks cleaner and represents a shrink-fit I guess.

[Paul KempParticipant @paulkemp46892]

Ramon,

If you are interested here is an example of a bush to broach a parallel keyway on coupling for a taper shaft (a lot steeper taper than a taper key). It’s all the same idea though!

Paul.

[Paul LousickParticipant @paullousick59116]

The flywheel on my engine is held by 2 tapered keys, 90 degrees apart.

The taper slot made by making a guide bush with a deeper slot to hold a tapered shim. The flywheel was mounted square on the press and the broach pushed thru at an angle. Take care to back off the pressure on the ram often so the broach is not bent too much and breaks (broach is not aligned with the axis).

A second key slot was machined in the guide bush for aligning the bush with the first slot in the flywheel when the second was made.

(PS. My first attempt at broaching a 3mm wide slot, sheared the drive pin in a light drill press that I was using as a press and is not recommended)

Edited By Paul Lousick on 04/09/2022 01:28:57

[JasonBModerator @jasonb]

Posted by Dr_GMJN on 03/09/2022 23:44:31:

Ramon – I think Jason meant the axial pin is easier to remove – presumably you just tap the web off and the pin offers little additional resistance over a press-fit ?

As you are going for a loctite (or even with a press fit) just heat and pull/drift apart no drilling out needed.

I suppose you could plunge with a small dia milling cutter and it would not have to go full length of the joint so could be kept straight

[Ramon WilsonParticipant @ramonwilson3]

Doc,

The likely hood of you needing to remove the crank(s) in the future is quite remote but I certainly wouldn't go for a fit that you could tap off as that will soon lead to wear when running even if pinned as you want to.

A small cutter could be used as Jason suggests but there is still the potential of dissimilar metals and the cutter going off line. Not definite but possible and if it does then you have a situation that will be difficult to disguise – why go there in the first place especially where, despite the text book diagram, there is little evidence full size.

Loctite will be more than sufficient but I always take a belt and braces approach and put a pin in as mentioned before, easily drilled out – you may recall, I had to do that to mine to change the cranks from 180 to the more norm of 90 – and easily disguised. Your call of course, just my thoughts .

Paul (Kemp). Thanks for the link, that's a beefy key way but as I see it the guide is for cutting a parallel slot on a taper – not cutting a taper in a parallel bore using the broach to achieve it.

 

Paul (Lousick) I don't, nor didn't, doubt your's or Jason's claim, just that to me that's not the way to use a push through broach. As you say you have to constantly relieve the pressure as the broach is pushed off the vertical. To me, though it may, and in your case did, work there is no guarantee the broach stays in contact with the guide – very likely too I agree but not certain.

As I'm sure you are only too aware machining a taper to an exact match has to be perfect, no doubt you can set your flywheel in place where you want it to go and tap the key home from the end of the shaft to locate it in position. As it stands Doc intends to machine two keys that sit in a captive slots and push the flywheel over the keys such that the tapers engage when the flywheel is in the right position.

There may be some leeway in the captive slots but I still stand by my thoughts that this is not the way to go – for a flywheel of this nature.

But then they are only my thoughts

Best everyone – now I'm off for the day to be distracted by my plastic distraction – R

Edited By Ramon Wilson on 04/09/2022 09:23:09

Edited By Ramon Wilson on 04/09/2022 09:25:12

[JasonBModerator @jasonb]

Best not let Ramon see page 304 of the book Doc

[Ramon WilsonParticipant @ramonwilson3]

Ah, then best you share the book together Jason

[Dr_GMJNParticipant @dr_gmjn]

Posted by Ramon Wilson on 04/09/2022 09:22:45:

Doc,

Best everyone – now I'm off for the day to be distracted by my plastic distraction – R

Made a bit of progress on the plastic myself today. Started this thing in November ‘21…















A few errors, but should be correctable.

[Dr_GMJNParticipant @dr_gmjn]

About time there was some progress. Didn’t have much time today after painting plastic, but at least started on the shaft. Cut the new steel to approximately the right length:

Faced and centre drilled:

I used a gauge to hopefully get the same drilling depths in each end, so that I can keep swapping the shaft round between centres and use the same diameter and length settings as I increment down to size. I can check this I guess by clocking each end in turn and seeing if there’s a difference when I’m setting up.

I’ve done a stage drawing for rough machining. I used the slip gauges to get the lengths. A bit tricky to find the end of the shaft each time when re-setting, but it worked to a few thou. I got as far as this today:

This material machines beautifully, completely different from the 080A15. I think with a bit of abrasive finishing it will be spot-on.

[Ramon WilsonParticipant @ramonwilson3]

That's a much better finish eh Doc

Nice work on the Vulcan – do you think we ought to start a 'Plastic Distraction' thread ? There seems to be several on here who are interested.

R

Edited By Ramon Wilson on 04/09/2022 22:17:49

[JasonBModerator @jasonb]

Doc, if there is a difference in hole depths then just set up the stops for the end with the deeper hole at the headstock end. Then when you reverse the work simply slip a spacer in between the stop and whatever it bears against. Probably better to use a feeler gauge rather than a thin gauge block.

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