LNWR Precedent

[Nick]

Specially for Mike Williams (post #39) 

[MikeWilliams]

Thank you Nick, I will sleep easier tonight knowing you have done that!

Now be honest, having mentioned it (my big mouth!), had you not done that, then it would have bugged you every time you looked at the engine?  A bit like Geoff Pember's 7mm version 40 years ago.  He found that he had the wrong crank leading.  Nobody else knew or could see it, but he knew and couldn't live with it until he'd made a new axle!
 
Mike

[Nick]

Mike,

You're quite right (of course). When you first mentioned it, it went on the To Do list. I'm very grateful to people who point out to me things like that, because I find that it's very easy to overlook details.

Nick

[Nick]

Not much time in the workshop recently, what with other things (not just the G3S Newsletter) getting in the way. However, I've recently been continuing the bodywork with the rear splashers, which have a curved corner and then merge with the firebox.



The tape is holding it temporarily in position. I'm not ready to solder it up, but I have to check the fit to the firebox and the fit of other cab parts to it. If you are hoping I can reveal some clever CAD-based method to make the curve where it meets the firebox, I'm going to disappoint you. The trouble is that anything I make that is folded or curved never comes out exactly to the drawing, and that applies here to both the splasher and the firebox. In CAD I can define the curved end of the splasher to the n'th decimal place, but in metal it never quite fits. Instead it required patient cutting and filing by hand until the gap is small enough to be able to solder it up – in fact, the traditional way.

The other problem was the arm rest on the top of the splasher. For some unaccountable reason I persuaded myself to solder the splasher side to an oversize piece of material and cut it to the correct profile. Not clever. It is really difficult to get the saw in close and still control it, so it goes wandering. After messing up the first two attempts, I did the sensible thing which was to cut it out first then solder it. The cutting was done on the milling machine with a rotary table to make the round end where the handrail fits, and after that it just needed the top edges rounding and polishing.



Nick

[753]

Nick
One way I have found to tackle boilers and firebox to fit over splashers is to make dummies. Draw out the development in CAD print it and use the print as a template to cut out the shape in styrene, then offer up to the splashers and note where adjustments may be needed, and repeat the exercise until you have a good fit.
However, there is always a bit of fettling needed.
Mike

[Nick]

I was peering under the footplate for some reason or other, and realised that the low angle could give an unusual and striking photograph. Since the sun was shining I took it out into the garden to make best use of the natural light. I don't have a garden railway, it is just perched on a suitable timber.

Both sets of splashers are done. A few details to add to the footplate then on with the cab.

Nick

[Nick]

The cab structure is mostly complete. The roof is the only outstanding part and that will be removable in order to access the interior and backhead. Like all platework, it is sawing, filing and soldering and there isn't much more to be said about it. People have asked about the sharp corners. The trick is to make one side very slightly (fraction of a millimetre) over-length, run a fillet of solder into the inside corner so formed, and file the excess away.





Now that the nights are drawing in I'm less enthusiatic about heading to the workshop in the evening, so I've been drawing the backhead fittings. I haven't drawn all the pipework because that will be done using copper or brass wire, bent and cut to fit. The fittings will mostly be 3D printed in nylon or, where the finish is brass, cast from 3D printed masters. The casting is a lot more expensive, but fortunately the LNWR didn't go in for "bling" as much as some railways and were happy to paint rather than polish a lot of parts.



Nick

[Nick]

Santa (cleverly disguised as a delivery driver) came early this year. Let's see what is in the stocking ...

First up, brass castings of several backhead fittings.





These were done by the hybrid process: a wax pattern was made by 3D printing from my solid model, and that was used to make an investment casting in brass. It saves me having to make a pattern, and the casting quality is quite good enough and needs little in the way of finishing from me. I put all the parts on a sprue. Because of the nature of the casting process, that made a big difference to the cost over casting each part separately. However, the per-unit cost of casting is quite high for one-offs and to take advantage of the price breaks I had four sets made. That's one for this project, one for a future project still in the thinking about stage, and, er, two extra. Maybe there is someone out there also building an LNWR prototype?

Next a collection of parts 3D printed in SLS nylon.



Hmm, a bit of a mixed bag here. The little fittings - fixing brackets, elbows, tees - are nice. The reverser is okay but missing the handle on the outer rim of the handwheel (a bit of wire will fix that). Close up, the finish is a bit rough but I can smooth that down.



The steam turret is supposed to have three handwheels.



The centre one is broken and the smaller outer wheels just haven't come out. Clearly the spokes are too thin for the printing process. In the past suppliers have warned about this sort of thing when I submit the file, but I guess they didn't do that check this time. I will take it up with them, but most likely I won't get anything more than a refund on these parts. Apart from the handwheels they are okay, so either I'll get the handwheels cast in brass and end up with a lot of extra ones, or I'll have to machine up the few I need. I will think about that over the turkey and pud.

The injector controls also have handwheels. In one case here one wheel is broken, but the other is okay and there are enough spare for what I want. When ordering 3D prints of small components, I often get considerably more than I have asked for at no extra charge. Mavbe that's how their automated process works. Whatever, more and more surplus fittings are accumulating in my workshop drawers.



In the meantime I have also been machining some fittings that for various reasons weren't feasible or economic to print, or I just fancied making them the traditional ways. Here are the spectacle frames, gauges, whistles and safety loops. And there are more to come.



In the detailing phase, I spend some time going over the drawings and photos, making a list of all the parts to do. That way things don't get forgotten, but it also gives me a sense of achievement as I tick each one off the list as I do it.

Nick

[MikeWilliams]

Just magnificent.  Reminds me of when a company "Hobbyhorse Developments" started out in 7mm many years ago.

"Maybe there is someone out there also building an LNWR prototype?"  I don't know of one (seriously!), but hope the parts will be available not just to current builders but well into the future, somehow.

Mike

[John Candy]

NOTE : A discussion revolving around availability of parts is continued at
http://g3forum.org.uk/index.php?topic=3122.msg19622;topicseen#msg19622

John Candy

[Nick]

I've started adding parts to the backhead.



This is where the photos of the cab interior of the preserved loco are really helpful because with all the pipework it becomes a 3D jigsaw so I am starting at the back and working forward. Once I've populated the backhead as far as possible, it goes into the cab and then the fun really starts.

Nick

[Nick]

I blame Bill Finch. If he hadn't published a book full of dimensioned sketches of the preserved loco, there are details I would never know existed, let alone model. And if I didn't get so distracted, it would be nearer finished. So, on the side of the cab we now have the staff carrier and the boiler certificate holder. Who knew?



Nick

[Nick]

I wasn't happy with the print of the steam turret and I was prepared to replace the handwheels, but discovered that I'd made a mistake in the solid model so decided to do the whole thing again. This time I thickened up the spokes and lever arms in the hope of makng the print more reliable, and I got the print made elsewhere by an individual recommended to me by Mike Palmer (thanks, Mike).



It's done in a softer plastic but it carries no load so that should not matter. The quality is pretty good, though the spokes, particularly on the smaller wheels, now look a bit heavy. I will try to improve the appearance with a bit of gentle scraping with a sharp knife.

Nick

[Nick]

First it was freezing cold, and now half an alphabet of storms have blown over, so I've left the workshop for the time being and have been working in my warm office on the solid model of the tender. It isn't and won't be a complete model. I have concentrated on those parts that I plan to get made and omitted a lot that I know I'll be making myself.



Most of the work has gone into the chassis. Almost everything you can see here will be made by laser cutting (the flat parts) or 3D printing (springs and axleboxes).



Another concern was fitting everything together, particularly around the water scoop where it and its actuator, the brake rods and their actuator, and the axlebox keepers all get a bit close. At the same time, I've tried to work out how it can all be assembled and disassembled. I had to leave off a couple of minor details, which I hope are inconspicuous, because it was just too difficult to fit them in. I'll leave it to the LNWR experts to see if they can spot what they are.



Nick

[Nick]

Yay! The cab and backhead are finished at last. There were so many details to do, everything had to be done in the right order and painted as we go because there is no hope of painting them afterwards. (There's still some painting of the more accessible parts to be done). The pipework is a real cat's cradle and I bet it drove the Crewe fitters as nuts as it did me. Most of the pipes had to be made two or three times before I got them right. They are mostly copper but some are brass where I didn't have copper wire of the right diameter.





I'm still not entirely pleased with the steam fountain. The handwheels and levers look somewhat coarse. As previously discussed, that is because I was pushing the limits of the printing process. In the end I decided to put up with it because, when I put the cab roof on I realised that it wasn't as obvious as it is in the photos. But if I were doing it again, I would get a casting made. Not only for the sake of appearance, but also because I could then solder all the pipes to it. As it is, they had to be glued, and plastic doesn't take well to being glued to metal. When I made the solid model I included holes for the various pipes sized so that the pipes were a good push fit. The inherent elasticity of the plastic allows that and it is probably that more than the adhesive that is holding them in place. Some of them are so wedged in place between other bits that they won't move anyway.

Nick