Stuart Twin Victoria (Princess Royal) Mill Engine

Hi guys,

Following Jason post on another thread on the subject of broaching a slot.....

I broach my flywheels to match the angle of the gib head keys, plain milled slot in the shafts and not had one fall off yet out of about 25 done that way. No grub screws used either. Before getting some broaches I planed my keyways with the lathe moving the carriage in and out with a 1thou cut per pass, tilt the flywheel in the chuck or pack on the faceplate to get the seat angle.

and Paul's comment earlier...

Now, you’re talking, you could even go the extra mile and taper the bottom of the bush slot for a “proper” tapered key

I'd appreciate it if you could explain how you do that using a push through broach in parallel bore with a parallel guide.

Despite making my comment above on possibly tapering the slot (in the guide), I got my broaches out today and tried to envisage how the broach would act with the part tilted. I guess I'm being clouded by something or missing something completely but I simply can't see how that would work in practice let alone effectively and accurately.

On my slotting head, should I want to induce a taper in the keyway (and I have to say I haven't felt need so far), then it's a simple matter of setting the slotting head to the angle required.

I'd be interested to hear how you both go about it

Best - R

Edited By Ramon Wilson on 02/09/2022 21:58:18

Edited By Ramon Wilson on 02/09/2022 21:58:47

Ramon,

it is simple. Flywheel remains flat and perpendicular as any conventional operation ie parallel in all directions to the plane of the press ram. The way you get the taper in the keyway which is not on the sides of the keyway, these are parallel in all circumstances, the taper, as mentioned is only on the head of the keyway. To get that taper which as Jason points out is very small anyway either 1:96 imperial or 1:100 metric when you cut the slot in the guide bush to carry the broach you pack the dividing method (rotary table, plain dividing head etc) or if you are lucky enough to have a universal dividing head you can tilt it. If the total length of your bush is say an inch and we are working to the metric standard you need 10 thou of inclination across the length of the bush. Mill your slot in the normal way. Place your bush in the hole large end up preferably and broach. The taper in the base of the bush slot is what guides the cut of the broach and automatically you will have the required taper in your keyway. Use your shims behind the broach in the normal way to get the required depth. The very small angle of the broach to vertical caused by the guide will not cause the broach any distress at all.

I am afraid I am not CAD literate but I am sure Jason in the blink of an eye can produce a sketch that illustrates if this text is not clear.

Machine your key to the same angle on its TOP face and as long as you drive it in from the right side you will get a uniform contact over the length of the key and no tilting force to wobble ur wheel. If you drive it in too hard it won’t be coming out in a hurry!

Paul.

As an aside and not relevant to this conversation as Doc doesn’t have a shaper I believe I have also made a replacement clapper box for my hand shaper with a guide arbor that allows setting of a hole for a keyway of whatever size I desire to grind the tool to either parallel or at any angle I wish! That is a similar approach to Jason’s method of packing the work piece - you can do that with a single point tool but not with a broach. I don’t think in any of my posts I have suggested a parallel bush and tilting the wheel to use a broach and I don’t think Jason did either?

Paul.

I must be missing some fundamental issue, because I can’t see any problem with the concept of milling the guide slot in the bush at an angle to the axis of the bush, and this giving a tapered keyway in the hub.

If the broach goes right through the hub, you get a keyway depth proportional to the highest tooth whether it’s at zero degrees or 30 degrees. All that changes is that the entry and exit depths from the hub are different, giving a taper relative to the bore axis.

A guide slot parallel to the bush axis gives a keyway parallel to the hub axis, so what stops an angled guide slot giving an angled keyway in the bush?

Its something I’d like to try in some scrap, and if I can do it, I’ll use tapered keyways and keys in the flywheel. If I mess it up, I'll JB Weld everything into submission.

You are not missing anything doc, it's exactly as Paul explains. As I said with the very shallow taper the size broaches we are talking about will only lean by about 0.75mm do I don't bother to tilt the flywheel. The only time I have tilted the work is when doing much steeper angles as you might find on a tapered timing gear or flywheel bore that has a woodruff key

The broach is driven as Paul says which allows it to go right through just like doing a parallel keyway and can be driven from either side but I find it better to have it doing the deepest part at the top.

Better than draw it, I'll take a couple of close ups of one of the taper bushes from this lot, most of those loose custom made ones are for tapered keys

Edited By JasonB on 03/09/2022 07:13:05

In the mean time for Paul and the Doc I have drawn it up with exaggerated taper so it's easy to see. Broach just has a few equal height teeth but enough to give the idea as it's only the last tooth that really matters.

Section with broach in place,

Section with broach removed you can clearly see the tapered slot in the bush and the broach will cut parallel to that and therefore give a taper to the keyway in the hub

This will give what is shown in Machenery's Handbook of matching tapered surfaces to key and hub keyway

If you have a slotting attachment for a lathe then that can be mounted at an angle to do the same, if a slotting attachment for mill or doing it on a shaper then the work needs to be tilted so the cut is at an angle to the works central axis.

Well, I've read that through and I'm still not convinced by your sketch Jason or your description Paul

Forgive me for being thick but if the broach is pushed through as it is designed to do then the wide end of the broach is doing the final cutting and sizing the depth of the slot on each stroke. Cutting a taper in the guide slot is not a guarantee that the broach will follow, besides although diagrammatical, you have the broach tilted.

Paul , I'm well aware that the key is not tapered on the sides - how on earth could you broach anything if it was.

With regards to shaping I've already said that from the very beginning, and in my last post, the axis of travel defines whatever taper you desire - it's basic and easy to do by shaping on the lathe if you have the means to alter the angle of travel

This extension to the Bentley crankshaft required a key to be absolutely accurate to ensure concentricity. The picture is rather dark but you can make out the slot inside the mating taper

This shows it in place, the hole is where the tool bit ran out to clear the swarf. The tapered area between the two parts roughly in the centre is also tapered with a key though it cant be seen. The key slot is at the same taper

The mating part is slotted at the same matching angle but the drive is off the side of the key not the taper itself

So on that note "you broach how you want to" - I'll stick to what I know.

Paul, I'll rephrase that remark , "I'm well aware that the key is not tapered on the sides" - brain fade on my part I was seeing this different to how you obviously meant.

To make a matching key tapered on the sides if you did however would require some pretty sophisticated machining of the key.

Obviously theres a big difference in being able to shape/slot the keyway than to broaching - but I'm not convinced on achieving a guaranteed taper with the latter as shown.

Machining matching tapers at any time on anything is not the easiest to achieve though not impossible but it brings me back to my early thought - make the key parallel such that it is slightly higher that required and then file a very slow taper on the top face until it just nips up as it drives home

On that note, this is taking far to much time from my plastic distraction so I'll bow out now

Good luck with it Doc however you do it

R

Thanks all.

Work on the shaft is on hold because my centre drill is stuck somewhere due to the Royal Mail strike…

Jason - your CAD is how I imagined it would work. Is there any benefit to tapering the bush slot the other way to help keep the broach in contact - as Ramon mentioned - or do the cutting forces make this irrelevant?

Edited By Dr_GMJN on 03/09/2022 09:59:58

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

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?

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.

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.

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

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).

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

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.

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

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

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: