Stuart Twin Victoria (Princess Royal) Mill Engine

I would agree to a degree with Jason here Doc as I didn't take on board that the steps were so shallow.

Even so there is no need to undercut unless something is going to sit firmly against the shoulder in question - money and choice are the keywords but an exposed undercut in a shaft for no practical reason is not going to look right - well not in my book

On the other hand if the shoulder is to locate something then yes an undercut would be needed if the step is minimal.

Though I have quite a few Dickson toolholders I don't have an extended version - just using a longer piece of HSS is enough if the occasion warrants it.

To my mind the tailstock clearance on the top slide is one area where Myford could have made a big improvement to the lathe had they chose to do so. Doesn't the Warco have that Jason?

As an addition to the last post if you take a look at this image again you will see that where there is need for location - Crank web and bearing seats - the radius is reduced to virtually nothing and the mating parts lightly chamfered to accommodate any slight radius in the very corner - no undercuts required.

All other shoulders have a radius - why would there be a need to undercut such and besides it will probably lead to comments such as "What are those undercuts for ?" if you do - horses for course etc

Best - R

Edited By Ramon Wilson on 25/08/2022 11:32:33

Doc's earlier sections through the various parts on the shaft do show them locating against the shoulders though probably only needed for his eccentrics and not the bearings as shown, even then it's debateable if the eccentrics really need it.

EDIT the steps on your crankshaft shown above while I was typing are a lot more than 0.5mm so there is still good location even with internal radius and chamfers of the mating parts. I do a lot of my work with a 0.2mm tip radius insert so apart from threads seldom add an undercut but Doc's tool has a bigger radius

The warco tailstock is not symmetrical when you look from the end unlike the Myford as the vertical part is set towards the rear of the machine so you do get better clearance for the top slide which goes almost under the barrel. I find it's more of a case of clearing the revolving ctr than the tailstock . It could do with a bit more overhang of the casting at the nose as there is a lot further to reach when working on shorter items due to the much wider topslide.

Edited By JasonB on 25/08/2022 11:53:43

Yes I thought that was how the Warco tailstock was relieved, just like on a Colchester 2000 (and many others no doubt)

As you say though the live centre major diameter can be an issue at times. I have a very nice but larger diameter Jones and Shipman that's rarely used due to that situation so my 'turn to' one most of the time is one of those 'Skoda' centres (remember that constant advert in ME ?) bought years ago that still does the business but I recently purchased one of those small diameter ones from Arc - a real asset for sure as it's been well used since.

The only point that actually requires a step for location are the two faces between bearings and that for the crank webs. As you infer it's much better to be able to position the eccentrics from a lining up point of view so allowing that ability is much the better option

Interesting thoughts about bearing location there.

As this is a twin with a crank either end just outside the bearings I would have thought that the large bearing surface between crank arm and bearing flange would be best to locate the shaft from sideways movement.

If the inner step on the shaft were to be used on Doc's model there is very little area for the side of the bearing to run against and could possible wear quicker than if using the whole side of the bearing to locate things.

I suppose that depends on how the bearings are finished off - I don't see this as an issue as you can see the bearing face on the Corliss is just that circle on both sides so the bearing face area is the same either on crank or shaft.

The important thing is that there is clearance on one side or the other so it doesn't matter which side as long as the crankshaft is captive and not allowed to float. Trying to bring both faces on each bearing to a smooth running fit risks the possibility of a tight fit but then the bearing could be tweaked on the faces if so.

This really is a choice thing I guess but I prefer to use the inner faces to keep the shaft in place axially - after all if you don't have a second crank but a pedestal then that's all there is.

As you say Jason, all interesting thoughts throughout a build such as this especially from Doc's perspective

Regards - R

Understood about the need for a bit of end float on the bearings. I've modified the cylindrical lengths to give about 0.25mm float, which can be adjusted to zero by snugging the eccentric against the bearing face, the eccentric subsequently being secured with grub screws (the fitting of which has been previously covered by one of Ramon's posts):



(upper geometry new, lower original).

I think we covered securing the crank webs previously, but my intention is to make them a snug fit on the shaft ends and loctite them on during final assembly. I've seen an axial pin put into the interface of the boss/shaft in some applications, maybe this would be a good mechanical solution to prevent rotation, or maybe there's a better method?

Also increases the bearing annulus area by moving the bearing face from the shaft shoulder to the eccentric:



I'm assuming this is what you meant?

Good Loctite joint should be strong enough, there is plenty of area.

Check your eccentric drawing, there is a small raised boss on the opposite side to the main one

Edited By JasonB on 25/08/2022 16:47:19

Yes, bosses on both sides of the eccentric with blend radii to the disc. Drawing just represents the overall width of the part to get the shaft dimensions about right.

Doc,

I can't think of a single full size crankshaft with an axial pin to prevent the crank moving but there are the odd few that have a tight fitting axial key. As far as I'm aware all full size engines of the size you are replicating would have had the crank shrunk on so a key is unnecessary. Loctite 638 or similar replicates this with ease. The crankpin(s) is just Loctited but I make the last mil or so on the spigot a tight fit in the crank web hole

Apart from one, all the cranks I have made so far then have been Loctited and pinned but with a radial pin going in from the outer diameter of the crank through the shaft and just into the crank opposite. This gives the strongest shear but with only one face to disguise the pin on and a curved one at that - much easier to do that than a flat one if using the likely file and emery paper. The odd one was an attempt at shrinking on but it was well and truly stuck before reaching it's location - never attempted it again.

Crankpins are never pinned but I do make the last mil or so a tight fit as the crankpin reaches its location

That said the shaft and pins are both pinned on this latest one, mainly to assist in reinforcing the shaft as a whole, a 2.5mm pin if my memory serves right. Getting the pin to be invisible is a bit of an art if the crank is a finished item but easy enough if gone about the right way - that can be covered when you get to it. You can just get a hint of it on the upper surface on the right

There's nothing wrong with using the eccentric face as a wear surface just that the eccentric position is then committed.

Just realised I have to go out tonight, I need to get a grip - back later perhaps

R

Edited By Ramon Wilson on 25/08/2022 17:45:20

Re-worked the shaft drawing slightly, to revise the step lengths to give about 0.25mm float for bearing adjustment. I've also removed the undercut from the first steps adjacent to the eccentrics, since they're no longer needed (nothing abutts them). *ETA I guess I could also eliminate the undercuts at the inner ends of the bearing steps, since they no longer abutt the bearing faces. Would just need a decent chamfer or radius on the inside of the bearing bore?

Just thinking, the exposed shaft each side of the flywheel boss - will it look a bit crappy just seeing a thin gap next to the keys on the left? On the right side my intention is to move the pulley over to contact the eccentric, eliminating the gap at that side. Difficult to visualise how it will look in reality. The left end of the keyway extending into the step also looks a bit bodged, but will ultimately be invisible. Just seems it might look like something wasn't machined quite right (see lower image, basically the area between the left end of the key and the eccentric)...any comments on this area?





Ramon, I pinned the fabricated crankshaft on the 10V without much issue. Pins ended up barely visible:

Edited By Dr_GMJN on 26/08/2022 10:02:24

I don't think anyone else looking at the engine will see that slight gap so not worth worrying about

Looks like you've mastered that then Doc

Didn't have much workshop time today, so prepared material for the split main bearings.

Hacksawed the square section brass bar into radius sized pieces (the only size I could get was too small to cut in half and re-solder, so I had to offset the cuts:



Milled them flat, with identical thicknesses:



Tinned and sweated them together:





Them milled the assembly to clean-up the sides:



Centre drilled ready for fitting in the 4-jaw chuck. I did this knowing that the offset from each side to the join was identical, and after checking everything was correct with the edge finder. I thought it would serve as a method of double-checking my centralising of the piece in the 4-jaw; I can centre using the telescopic pointed shaft thing, and also using the dti on opposite faces. Pretty confident it's spot-on though:

One question regarding this: I assume that if this single bar is for both bearings, then I bore all the way through (in order to be able to get the journal lengths fully engaged beyond the crank spigot), periodically checking fit on the shaft? Once parted-off for the first bearing, I'd double-check for fit on the other journal? I assume that the bore will taper slightly, so, assuming both journals are identical diameter, the second bore might need a spring pass or perhaps a few?

You can put the dti on your sprung guide and clock the movement of the ctr hole which is how I usually do it. Back end of the guide wants to be free

Thanks Jason, yes that what I meant. I’m not sure what you mean by back end wants to be free though?

Don't hold it in the tailstock chuck, mine is free to move about as it is supported with a ctr. Though a pointed long length of say 3/16" rod would flex so could be held rigidly.

Hmmm bit of a rubbish day on this, with little to show for a lot of effort. Same old story when turning steel - poor surface finish, plus it’s inconsistent. Also, for the lengths and step sizes I need, my HSS tool is too big and clunky - undercut lengths are huge. It didn’t give a very good finish on the actual shaft material either:



I tried re-grinding it, touching it up on the sander to sharpen it, but I don’t really know what I’m doing. There’s no way I can get an accurate tip radii either, and every modification means re-setting the tool height. I’ve reverted to a GT insert, with finishing with wet and dry paper. It gave the same finish, and also gives much neater undercuts.

I’ve concluded that inserts are the way forward for me since I don’t have the experience to consistently grind HSS, and it’s a difficult skill to learn from a book.

I have at least decided to not have centre holes left in the shaft ends - I’ll face them off in the chuck. On a 9.5mm diameter shaft, centre drillings look far too big to me.

Also realised my drawing is no good, since stepping the shaft has given me a middle section bigger than the stock 1/2” material I got. I could use the 7/16” stock, but as discussed before, it’s slightly undersized, and gives 0.002” runout after centering. It looks pretty thin before skimming it to give no runout. The step sizes also become very small. I’ll probably re-draw it for the 1/2” stuff, but ending at 12.5mm or something.

Currently going to cut a new shaft length, and start again. Any advice on getting a good finish obviously appreciated.

Are you honing the HSS tool after grinding, just a rub in a diamond stone should produce a better cutting edge.

Even with the carbide a small amount of cutting fluid will improve finish

Not sure what size ctr drill you are using but I use a BS-0 which is 1/8" shank and a very small pilot, you only need go in a little way with the 60deg part not full depth

Treat yourself to some 9/16" or 14-15mm bar and get some decent steps, the flywheel hub can take the extra size.

Thanks Jason. I’ll re-draw for 1/2” and treat it as a machining trial.

Im not really sure what you mean by ‘honing’. I’ve got a large ‘oil stone’ for chisels, and some ARC diamond laps, but it seems like whenever I try to clean up a cutting edge, I actually get the angle slightly wrong and end up - probably - dulling the edge. I find it difficult to judge whether the abrasives are actually doing anything, often feels like they’re just skimming across the surface without touching it. The only way I can do it is by trial and error - usually error, and…it just brings me one step closer to packing up the tools and doing something else, when I really want to make progress.