Crank axles for split axles

[Steph Dale]

Well, that's the idea anyway!

I've had a couple of inquiries about how to make an electrically split crank axle and so thought it was probably time to put my money where my mouth is.

So here's an approach to making an insulated crank axle for a Slater's axle/wheel set using Laurie Griffin components. It's going to be a bit of a blow by blow account so may take me a little while to get to the end of the description, I hope you'll bear with me.

So to start. We'll come to the components and ideas in a moment, but first I feel I should say that if this is either your first crank axle or you first go at split axles it probably shouldn't be! It will help enormously if you've done a few of each before you start trying to combine the two.

We'll start with the crank axle this evening and worry about the insulation a little later.

Pics shortly!

Steph

 

[Rob Pulham]

I am sitting comfortably Steph

 

[adrian]

Likewise - I'll be watching this as it's something I want to try.

 

[Dikitriki]

Yup, me too, popcorn standing by.

 

[Steph Dale]

Hi Rob, Adrian, Richard,

Ahem, sorry about the slight delay. I started typing and them realised I needed to resize the pics...! Can't get the bloomin' staff...

Right; here's a pair of cranks, eccentrics and an axle. The crank on the left has been slightly re-shaped and then dressed with a 10" second-cut file on all external surfaces, the one on the right shows the shape as it comes out of the packet. The connecting rods have been test fitted to the cranks too, the crankpins being run over with a needle file and emery paper. Check the wheel/axle fit as it's easiest to do any fiddling that's required now. In this instance the crank axle is for a LSWR G6, and seems to apply equally to all Adams locos in terms of style/outline.


After both cranks have been re-shaped and dressed all components are given a good polish with 150grit wet/dry paper, used wet. All parts are then rinsed and can then have a counter-sink run round all the holes to ensure they're free from burrs. They can now be considered clean enough for soldering, so are checked for fit. The main issue at the moment is whether the pin joining the eccentrics needs shortening; the holes in the cranks which it engages in will need drilling out (0.85mm to give an easy fit). Of course, if you're modelling the SECR or other left-handed railway you may have a little more to do at this stage.


And then the wheels are fitted. This picture shows my trick for aligning the inside cranks with the cranks in the wheels. The screws can be adjusted back and forth to get the cranks/eccentrics central on the axle too. Of course this technique won't work for 3-cylinder locos, Lord Nelsons or one or two other types. You can also see that the width of the cranks/eccentrics will fit in the frames of a finescale loco without any major problem. Incidentally, the crankpins are 10BA screws, not the weedy 12BA jobbies supplied by Slater's. I can show you a trick for tapping the crankpin bushes to take the 10BA screws later if y'like...


Next job is to clamp up a crank in a toolmaker's clamp. If you clamp the cranks this way you'll be able to drill or otherwise fiddle them without causing any distortion. This is particularly the case as assembly progresses and axles get cut a little later on.


The full set up for drilling the cranks is like this, with the clamp held securely in a bench vise. The aim is to drill (0.5mm) straight down through the inside web of the crank, as deep as you feel comfortable with. This is important - doing the insulation might get a little complicated if you pin the outer web at this stage.


And on to the second one. A length of 0.45mm wire is used as a pin to secure the first crank.


All done. Although not obvious the second crank is also pinned in place - by the drill that broke off in the hole. No real bother as it'll all be soldered in a mo...


Steph

 

[Eastsidepilot]

Hi Rob, Adrian, Richard,




....................- by the drill that broke off in the hole. .........


Steph

Yeah, tell me about it.......I got two T shirts and a badge.... and I bet you had to wait to buy another drill as there we'rnt one in the box.
Nice work though Steph

Col.

 

[Steph Dale]

Soldering up the axle is pretty straightforward.

Here's the wee beastie assembled and ready to go, all nice and shiny.

And here's the gear I use. The torch is propane, and I typically use it with a black plumber's soldering mat. The solder is CPL 183/188 (can't remember!), and the little bottle contains Baker's No.3, which is great for jobs like this. As you can see I happily do the soldering on the top of the stove. Your domestic authorities may not be quite so liberal, but it does go to show that you don't need a fully fitted-out workshop.


So the drill is to slosh some of the Baker's fluid flux over the workpiece. Use the lighter's flame to light the torch. Gently and evenly heat the workpiece and carefully alternate solder and flame until the solder has run through the job. You won't need to get any colour in to the work to successfully solder at 180-250 degrees and if you do it'll only anneal the brass/nickel-silver components which won't be a great idea. Let the work cool down naturally, don't be tempted to quench it; you want a nice relaxed piece for the next stage(s); there will be a number of opportunities for any stresses in the materials to come out which might cause distortion. If you think you overheated the part then put it on a south facing windowsill in the sunlight for a couple of weeks, the thermal cycling will toughen the materials again.


It's not quite so pretty now, but it possible to see that solder has successfully wicked into all four crank webs and is even emerging between the eccentrics. There are variations on this particular theme of course and many of those techniques have been covered on the forum before.

Right, clean up time. That may well be it for this evening, more will follow shortly.

Steph

 

[Dog Star]

... I can show you a trick for tapping the crankpin bushes to take the 10BA screws later if y'like...

Yep, I like.

Waiting and watching.

 

[Steph Dale]

Last post for this evening, two little jobs;

First up, the crank axle has been cleaned up in preparation for the application of the insulation; more on that in a day or two. After scraping off the solder a thorough scrubbing in Bar-Keeper's Friend resulted in this, note that the cranks haven't been cut:


One other little job was to shorten the axle screws. In this instance I went for making them the thickness of the wheel, so here's (from left to right); a shortened screw hiding in a wheel, a shortened screw on its own, an original screw, the 6BA split nut that's used for holding and de-burring the screws as they're shortened.I now need to leave the crank axle to dry off after its recent wash so tune in next time as we start to work in the insulation.

And yes, Graham, I'll weave in to a thread somewhere how to easily tap Slater's crankpin bushes.

Steph

 

[Overseer]

I don't want to derail the thread, but I am curious about the alignment of the inside cranks with the wheel cranks. All the inside cylinder locos I have looked at in any detail are pre 1900 and from memory they have the inside cranks at 180 degrees to the outside cranks, the theory being they balanced each other. Did the usual practice change later or did different designers have differing views on how to do things?

As an example, a 1880s Kitson design 0-6-0 with 4'6" wheels -

 

[Dikitriki]

I wondered that, and then assumed that when the wheels were finally assembled, they were put on at 180 degrees to the set up position. All Steph is doing is is accurately setting the cranks with respect to lead and the square axle end.

........I think

Richard

 

[Steph Dale]

Overseer,

Derail away! Actually there are a good few locos that have inside and outside cranks in alignment, it is referred to as a Stroudley type crank-axle. He argued that it made it easier to work out the balancing of the wheels and motion so resulted in smoother running locos. Fairly obviously, Stroudley locos were so-fitted, as were a number of inside-cylinder GWR locos. I assume there were others and the Stroudley influence on the Scottish school of loco design means there might be some there, but Dugald Drummond at least didn't use this approach, or didn't by the time he got on to the LSWR.

But in this instance, Richard has the correct explanation for what you see here. The thread I did on WT a while ago on my GWR 2251 raised the same issue, in that case the Stroudley crank axle was correct and photographic evidence available; although it did surprise some people!

Steph

 

[Overseer]

Steph

I should have remembered about Stroudley's axles. My model of Highland Railway 'Balnain' doesn't have a crank axle, presumably Stroudley designed it with his type but there is no GA surviving and the combination of all over tank and disc wheels make it impossible to see what it had in photos. The Terriers certainly did. Not sure how much direct influence Stroudley had on Scottish locomotive development, David Jones, his successor on the Highland borrowed his cab design but little else, being a firm believer in outside cylinders.

 

[JimG]

I assume there were others and the Stroudley influence on the Scottish school of loco design means there might be some there, but Dugald Drummond at least didn't use this approach, or didn't by the time he got on to the LSWR.

Steph,

I've just checked some Caledonian locomotive GA drawings I have, of Drummond, Lambie and MacIntosh designs and the inside cranks are 180 degrees to the outside cranks. I suspect that Drummond had a stronger influence on Scottish locomotive design than Stroudley, with his work at the North British then his work at the Caledonian which was carried on and developed by Smellie, Lambie and MacIntosh.

Jim.

 

[Rob Pulham]

Cracking stuff Steph

 

[adrian]

Thanks for posting - the information will be useful.

Just a couple of questions though!

First how did you clean up the main crank journals, are they just dressed with a file or did you manage to machine them? If dressed with a file how happy are you that they are circular or is it just not that critical?

Second question is regarding soldering up the main crank and eccentrics. Having built a couple of small steamers in the past I would have gone for silver-soldering the main crank, so would this be overkill for dummy motion?

 

[Dog Star]

First how did you clean up the main crank journals, are they just dressed with a file or did you manage to machine them? If dressed with a file how happy are you that they are circular or is it just not that critical?

Good question... to which may I add:-

What keeps each eccentric strap in correct alignment relative to the corresponding sheave?
What clearances are you providing for the big end and straps?

Or do those considerations not matter for (dummy) working motion?

thank you, Graham

 

[adrian]

Good question... to which may I add:-
What keeps each eccentric strap in correct alignment relative to the corresponding sheave?

I was wondering about that but careful inspection of the first photo in the thread reveals what I think is the answer. I hope I'm not stealing Steph's thunder but in the first photo there is a pin through the eccentric sheaves which appears to locate into the side of the crank web, there is a little pin hole top right from the hole for the axle.

 

[Steph Dale]

First how did you clean up the main crank journals, are they just dressed with a file or did you manage to machine them? If dressed with a file how happy are you that they are circular or is it just not that critical?

Second question is regarding soldering up the main crank and eccentrics. Having built a couple of small steamers in the past I would have gone for silver-soldering the main crank, so would this be overkill for dummy motion?

Adrian,
1. It's not actually that critical, I just dressed these with a file, taking more care to remove lumps and bumps that worrying about them being truely circular.
2. In the past I've used Loctite 638, silver solder and soft solder. All have their advantages and disadvantages. The problem with silver soldering is that the materials can anneal, which is a problem when the cranks are only nickel-silver, the bronze cranks Laurie used to do would be fine to silver solder, but yes it's a bit over kill for cosmetic motion.

What keeps each eccentric strap in correct alignment relative to the corresponding sheave?

What clearances are you providing for the big end and straps?

Or do those considerations not matter for (dummy) working motion?

Graham,
Eccentric straps are aligned on the sheave purely by the fact that they're trapped against the adjacent sheave or crank.
Clearances on the big end straps are just whether the parts fit and run smoothly.
So, in short, it's not that critical.

I was wondering about that but careful inspection of the first photo in the thread reveals what I think is the answer. I hope I'm not stealing Steph's thunder but in the first photo there is a pin through the eccentric sheaves which appears to locate into the side of the crank web, there is a little pin hole top right from the hole for the axle.

Well, that takes care of the alignment and phasing of the eccentrics, but the fit of the parts that run on them needs a bit of fiddling.

I hope to come back to some of this as the crank axle is installed on the chassis and the valve gear built up around it. You might get a flavour from the 2251 thread I had...

Happy to take and/or answer questions here, but might not have suitable examples/illustrations just at the moment.

Steph

 

[Eastsidepilot]

I was wondering about that but careful inspection of the first photo in the thread reveals what I think is the answer. I hope I'm not stealing Steph's thunder but in the first photo there is a pin through the eccentric sheaves which appears to locate into the side of the crank web, there is a little pin hole top right from the hole for the axle.

The same way as Laurie Griffin's, the eccentrics don't have to be soldered as the pin just takes them round for the ride as it were.
Col.