LNWR Precedent

[Nick]

The brakes are between the driving wheels, with a single actuating lever. This appears to be common for 4-coupled LNWR locos of this era, and it is a characteristic feature. The parts are the usual mixture of laser cut, 3D printed and fabricated.



Of course the assembly hides much of it. At least I didn't have to model all the linkage behind that cover.



This is the brake cylinder located beneath the cab and the various actuating bits and bobs. Notice the pull rod - as an experiment I had it 3D printed.



The eyes are fine, but the rod itself looks rather coarse and is not straight. The material is sufficiently elastic that it won't straighten of itself so I might have to tension it when I assemble it enough to pull it straight. If that doesn't work I will replace it with a metal rod and reuse the ends if possible.

Nick

[Nick]

I didn't like the pull rod, but I did manage to cut off the forked ends and drill them for a steel rod so it was not wasted. This is a trial assembly. Hats off to Crewe, it is an ingenious mechanism that pulls the engine and tender brakes all from the one cylinder. I won't try to replicate that completely, even in a non-working form.

Nick

[Nick]

Thinking ahead, I shall need a number of brass fittings in the cab. For the T3 I had similar fittings 3D printed in brass and was very pleased with the results. However, this process has become a lot more expensive and that's made me think about alternatives. Mike Williams suggested I have several sets cast and take advantage of the economies of scale, because the same fittings were used in different classes of loco. But at my rate of building I doubt that I will last long enough to make it worth doing.

I wondered about metallic paint on 3D print in a plastic material. It is a long time since I last used such paint and maybe it was worth another try. The motion plate printed in PA-11 MJF that I had rejected as too flexible was now spare and served as a test piece. The paint is Humbrol #54.

The left hand half of the plate in the photo is out of the tin. For comparison and because your screen will probably render colours differently from mine, I included a couple of scrap pieces of brass, one newly polished and the other somewhat tarnished. The paint colour is much too red, more like bronze than brass. The right hand half is the brass paint with a bit of yellow added. That brings the shade closer to the tarnished piece but also loses some of the metallic lustre. I think that's because the brass paint is actually tiny flakes of brass in a clear paint medium, and adding a non-metallic colour has the effect of diluting them.

So I'm really not sure at present. Fine-tuning the mix will probably get the shade more accurate but I'm not hopeful about getting that lovely polished brass finish this way.

Nick

[Nick]

The ash hopper under the smokebox is fairly unique to LNWR locos as far as I know. Photos don't make it clear, but by peering underneath the preserved Hardwicke I managed to make out what it looked like, and I think this is a fair representation. The cylinder drain cocks were based on commercial handrail knobs, since they were a spherical shape and about the right size. It saved me a tricky machining job.



The last details are the drain cock linkage, the pipe to the crosshead pump, and the oilers to the leading wheel axleboxes. And that completes the model below the footplate (I think). Next up will be the smokebox.



Nick

[IanT]

Stunning attention to detail Nick, it really shows what is possible in Gauge '3'.

Thank you for sharing this.

Regards,

IanT

[753]

Model engineering at it's finest, a joy to behold.

Mike

[Nick]

Some more experiments with colour. I realised that the base colour might make a difference, so on the LHS of this test piece I first painted an opaque layer of yellow then covered it with out-of-the-tin "brass" paint. It's about the same shade as the sample of brass and yellow mixed, but with a bit more metallic lustre.

It was also suggested to me that I try gold paint, and that is what you can see on the RHS. It's not very brassy, and not very gold either for that matter. I also tried a sample on a plain white background to see if it made a difference, but not really.

So I still haven't found a way to make plastic look like brass.

Nick

[Nick]

Back to the loco. Most electrically powered locos, as far as I know, are built using a separate chassis and body, the body removing to get at the works. That's not going to work here because of the way the leading wheel spring is attached. The hangers are bolted to the frames to take the load, but the front hanger has to pierce the smokebox wrapper.



That means if you bolt the hangers to the frames, you can't get the smokebox off, but with the smokebox and boiler in place it is all but impossible to remove the spring. Incidentaly, on the real thing lead sheet was forced into the space between the hanger and the wrapper to preserve the smokebox vacuum. It all sounds like a bit of a bodge. Couldn't they come up with a better idea? Clearly, DFMA (Design for Manufacture and Assembly) hadn't been invented in Victorian times.

My answer is to attach the smokebox permanently to the frames. The boiler is part of the body assembly, and bayonets into the back of the smokebox. To remove the body, release the screws which will be under the cab, slide the body backwards about a millimetre, and lift it off vertically. It will work because there are only two external pipes connecting the boiler and the smokebox and it's easy enough to release them for dismantling.

The smokebox skeleton is a straight forward bit of sawing, filing, and turning.



Thw wrapper has two rows of rivets at front and rear. I decided to press them rather than add them separately and solder them, partly because I couldn't find any rivets of the right size, but mainly because I didn't fancy drilling so many tiny holes.

When I made my rivetting tool, many years ago, I designed it so that it could be clamped to the bed of my Sherline lathe. The work is clamped to the cross slide and moving the saddle and cross slide gives nice uniform rows of rivets in both directions. Here is the first row



and here is the second row, positioned by cranking the x-axis the correct amount and maintaining the same spacing on the cross slide.



I prefer doing it that way than relying on the anvil diameter to space the rivets. It works better for me but I know that the late, great Beeson and Reynalds both used the anvil edges, and who am I to argue?

Nick 

[Nick]

I hope no-one is expecting an easy way to form the reverse curves in the wrapper so that it fits the skeleton, because I'm going to disappoint you. I used rolling bars and bending bars, did it a bit at a time, kept trying it against the skeleton - and it still didn't fit perfectly. But I managed to persuade it into place by holding it on the skeleton with a collection of clamps before soldering it up. It was not perfect but the solder fills up any remaining gaps.

But before that, it was necessary to add the dummy boltheads at the lower edge of the wrapper. The missing one is where the spring hanger will go.



I cut the wrapper slightly over width so that I had an edge on the outside to solder to (much easier than soldering inside), then filed it back flush to give nice sharp corners.





The black bits are 3D prints of the chimney, door, and the blower pipe elbow in SLS nylon. I had them done in black rather than the default white so that if anything got scratched it would not show badly. Unfortunately it makes it difficult to photograph to show the detail to advantage, but take my word for it that the surface finish and the detail are excellent. I was particularly impressed by the consistently thin base of the chimney (it used to take me several hours to file these up in brass and I never got it that consistent) and the detail of the door wheel and handle.

These prints are a step up from the last set of comparable prints that I had done a couple of years ago. It just shows how quickly 3D printing technology continues to evolve.

Nick

[MikeWilliams]

Quite superb Nick, as ever.  You might want to check the bolts on that excellent chimney base because I THINK the centre bolt on Jumbos also held the petticoat pipe in place and had a lock nut.

Mike

[Nick]

Mike,

The preserved Hardwcke has a locknut on the LHS only. But there is also a photo of that same loco in LMS days with a locknut on the RHS - whether in addition to or instead of the LHS isn't clear. Photos of other members of the class show both with and without but of course show only one side.

But your point is well made. I'll have to decide whether to get a new print done, or add a tiny nut with a drop of adhesive. To which side depends on the name and number I finally choose.

Nick

[Nick]

Next up, the footplates. Yes, there are two of them, LH and RH. Oh dear, more curves to form where the tops go up and over the coupling rods. After an abortive attempt to make them in one piece, I decided to make them in three pieces and join them. Here is a reverse curve being formed around suitable blocks (diameter chosen by experiment on pieces of scrap).



Then soldered to the footplate side.



You can never have too many clamps.



All done and cleaned up. Unlike Ernie Wise's hairpiece, you can see the joins (just) but they will disappear under a coat of paint.



When I encounter things like this I always wonder how it was done on the prototype. Did they somehow shape it all in one piece, or make it in sections? There is no evidence of joins in any of the photos that I have. I'll have to examine Hardwicke again next time I get the chance of a visit to Shildon.

Nick

[IanT]

Lovely work Nick!

Regards,

IanT

[MikeWilliams]

I see you have the rear corner of the footplates just right.  The curves there are very important, which many people don't realise until they come to do the lining!  But you clearly know that because it is superb.

Mike

[Nick]

Thanks Ian and Mike. I always try to collect as many photos of the prototype as I can, so that I can understand and get right details like the rear corners. Glad you spotted it!

The firebox is the usual wrapper around a skeleton, and the boiler is simply a rolled cylinder.



Then I did a trial assembly to make sure everything fits. The dome, safety valves and backhead are 3D prints.



Here's the backhead in detail. It took quite a long time to draw because of the complexity, but it was worth the effort. I'm sure I saved myself a lot of time. Actually I had to carve bits off the bottom to get it to fit. It was just a bit too tight due to the stackup of tolerances (a posh way of saying that I got the boiler just slightly too long). In future I will try to allow for things like that when drawing them. Incidentally, there is some wierd camera lens distortion in that photo - the boiler fittings are actually in a line.



Another interference point is that the boiler makes contact with the leading drivers because the G3 back to back dimension is smaller than scale. I'll have to cut out a clearance for that, which won't be visible behind the splashers.

Nick