LNWR Precedent

[NickB]

Sorry Jon,

I thought I'd answered your question but it appears not. Sheesh, anyone got a cure for failing memory? Yes, the loco is also known as a Jumbo, maybe someone can explain why. And it will be in LNWR black.

Back to the tender, and now the sidesheets for the tank. That means rivets, Hundreds and hundreds of them. Luckily Bill Finch (in his book on the Jumbos) has counted them, so we don't have to. But believe me, there are lots and lots of them. Why couldn't the LNWR use flush rivets like certain other companies I could mention?

That immediately settles the question of whether to inset or impress them. Inserted rivets can look very good, but If I went that way it's questionable whether I or the tender would be finished first.

Now I have a rivet punch which I've mentioned previously in this thread but to save you searching, here it is again.



The rivet spacing can be set using anvils of different diameters. I've made a number of them and with care they can give a consistent rivet spacing, but I've found that it is diificult to get an exact spacing. It depends on the shape of the impressed rivet and how you hold the workpiece in relation to the anvil. I wanted an exact spacing to ensure that the horizontal and vertical rows of rivets lined up as they should. Yeah, I know, I'm fussy like that. For that, a template is the answer - a plate with a set of holes through which the rivets are punched.

That was made easier because most of the rivets, wherever they are on the tank, are equispaced. The only exception was some rows that were double spaced. So I decided that a template with a single row of rivet holes would do for everything.



I made sure that all corners of the plate were square and the edges straight so that it could be lined up with the workpiece for bot horizontal and verticals. CNC (or a DRO) makes it possible to drill the holes at exactly the right spacing. And off we go.



Yup, that kept me quiet for quite some time.

I know I regularly moan about Crewe, but one thing they did that makes it easier for the modeller was to overlap the sideplates rather than abut them. Why does that help? Because each corner is a separate plate and there are overlapping plates between each pair of corners fill the sides and end. Without any visible seams or joins, you have to make one plate that wraps around sides and ends and getting two (or more!) bends in the plate exactly the right distance apart for teh corners is a real pain. Been there, done that, still bear the scars.

Of course, square corners are so much easier than round ones. Why weren't they all like that?

So each plate, whether corner, side or end, is separate and can be made oversize then trimmed back to fit. The corner plates are bent around a dowel of suitable size (trial and error to allow for the spring in the material) without worrying about getting it in exactly the right place - just somewhere near.

The plates, by the way, are 0.25 mm nickel silver. That's only slightly thicker than the prototype, and that is important because you can see the thickness at the overlaps.

Four corners done.



Sides and ends added.



At least the assembly was easy!

Nick

 

[Jon Nazareth]

Nick
Brilliant work, as usual. One thing puzzles me though. Why didn’t you use the cross-slide on your lathe for the spacing of the rivets?

Jon

 

[NickB]

Jon,

Unfortuanately the Sherline lathe is too small to take the long plates required for the sides, otherwise it might have worked. I do have a larger lathe and a milling machine and if I'd thought about it hard enough I might have come up with a way to use one or the other of them. But it would have been a fiddle and I didn't think of it at the time.

As it is, I have three ways to space rivets: anvil size, a drilled template, or the lathe. Between them there is a solution to most problems.

Nick

 

[NickB]

Flares seem to have been popular with Victorian engineers. No, not those dubious 60s and 70s fashion items (don't try and kid us that you're too young to remember them, or wear them). I mean those curved bits of metal that they put on the top edges of water tanks, with almost no practical purpose. I mean, if you want to increase the coal capacity, just make the tank bigger.

But we are stuck with them. Tanks with square corners aren't too bad, because you can make the side and end flares overlong then cut and file a nice 45° mitre where they join. But curved corners, they are something else.

In the smaller scales the sides and end parts of the flare are often made as one, curved around the corners, then where the flare has to expand outwards, a set of fingers is cut. When the flare is curved outwards, of course the saw cuts become a set of V-shaped notches at each corner, which have to be filled in with solder, or Milliput. or some combination of the two.

And then the corner must be filed smooth (easy on the outside, not so easy on the inside), and since the filler is softer than the metal it is difficult to prevent a set of facets forming where a smooth curve should be.

At least one kit maker gets round that (no pun intended) by making the corner as a metal casting to which the sides and ends are soldered, then with a bit of care the seams between the various parts can be made inconspicuous. That struck me as a neat idea. Maybe not casting for a one-off model, but machining the flares at the corners.

So now I am making a flare made up of components, straight for the sides and end, and machined 90° turns at each corner.

The corners are still a work in progress, so here are the straight bits. Some experiments with scraps of material to be used for the flares showed me that I needed to bend them around a rod of about 12mm diameter. Which just happens to be the diameter of the bending rolls I made way back when for O gauge. Ah, but they are nowhere near long enough for the flares along the sides of this tender. In principle I could rebuild the tool with longer rollers (an advantage of making your own tools), but under the clamping pressure they would deflect and the bent radius of the material at the centre would be larger than at the ends.

I've had that problem before and got round it by making a single, rigid, roller and manually bending the material around it. The roller has a recess milled along its length and a flat bar screwed in place.



(There, we've got to the photos at last). That keeps it rigid and provides something to hold in the vice. I then clamped the work in place, took another hefty chunk of steel long enough to bend to whole thing in one go, and leaned on it with all my strength and weight (both small in the general scale of things),



And that's the result.



Cutting it to size is a bit tricky, it needs to be firmly clamped to saw a bit at a time.



But finally there are the two sides and one end.



I know I've made myself a hostage to fortune by describing all this without yet having finished corners to show, so if it all goes wrong and you hear large amounts of humble pie being eaten, you know why.

Nick

 

[simond]

I felt flares were a good thing.

The scrawny teenage me had disproportionately large feet*, flares prevented me looking like a cross between Daffy Duck & Max Wall.

* I’ve grown into them since.

 

[timbowales]

"Daffy Duck & Max Wall"
You're really going to sort people out with that reference

 

[Mike W]

A friend who had been a professional builder made his 7mm LNWR tender flares in pairs. The strip was anealed and suaged around the corner of a plate which had been machined to the correct radius and with a groove (I'll try to sketch it out later!). He then slit the U shaped strip up the centre to make a matching pair. Yes, he was building a lot of tenders! I made a pair using his tool but alas didn't inherit the tool from him.

Making them as a pair meant the strip came out straight.

As for the name Jumbo. I suspect the entertainer Barnum was popular at the time, so people had been introduced to his elephant and the next type of engine was known by that name. The Caledonian 0-6-0s were also known as Jumbos and I suspect engines from other railways were too?

Mike

 

[Mikemill]

To form flared corners on tenders I make a negative form in ali. Form the curve then bend the right-angled corner, now anneal the metal, clamp to the ali form and with a ball faced hammer dress into the form.

This will work better with brass as its softer than nickel, but if you keep annealing it should be ok.



Mike

 

[NickB]

Mike x2:

I've tried forming flares in 7mm but was never entirely happy with the results. Maybe I'd have more success in G3 because there is more metal to work with. I wanted to try machining and was probably influenced by the very neat little corner castings that I had seen. Making in pairs is a good idea. I do see what you mean, but as I build one tender every few years, making a special tool is probably not cost-effective.

Nick

PS It's been pointed out to me that photos of Victorian engineers show they were more likely clad in drainies than flares. Don't say you don't know what they are, either.

 

[NickB]

My intention was to CNC mill the inside and outside surfaces of the flare corners. You can't possibly create a toolpath for a 3D shape by hand, you have to use the right software, and there isn't much choice unless you want to spend ££££ on an industrial-strength package. So F360 it was. The trouble is the richness of choice.

F360 offers about a dozen separate cutting strategies, each with up to about 20 knobs you can twiddle to optimise the toolpath. As I'm still climbing a steep learning curve, I spent a lot of time on this. But when to came to cutting metal, the first several attempts ended up something like this.



The problem was that the two surfaces needed very different setups on the mill and they had to be very well aligned with each other because the flare is so thin. In adddition, the outside surface toolpath isn't ideal but was the best I could come up with. It would be much better if the workpiece could be rotated about its axis while cutting. That's 4D milling and I haven't the equipment to do that.

I haven't given up completely and I still think it can be done so at some point I'll come back to it, just for the experience. But at that point I was running short of brass bar of the right size, so I decided to cut and run (not quite literally). Instead of CNC, I decided to turn the outside surface manually on the lathe using a set of cuts of diminishing length (the CAD model was helpful in working them out).



That was cleaned up using files and wet-and-dry, then reversed in the chuck so that I could remove excess material from the inside.



Then on to the CNC mill to cut the inside surface.



Then on to the dividing head to drill holes for the rivets (inserts this time, not impressed) and cut into four segments using the thinnest slitting saw I had.



To finish up, the segments were parted off.



Nick

 

[Jol Wilkinson]

As for the name Jumbo. I suspect the entertainer Barnum was popular at the time, so people had been introduced to his elephant and the next type of engine was known by that name. The Caledonian 0-6-0s were also known as Jumbos and I suspect engines from other railways were too?

Mike

IIRC, according to the Locos Illustrated edition covering LNWR 3 cylinder compounds and the 2-4-0s, the latter were called Jumbos because they were powerful and reliable, something also attributed to elephants.