Motor choice

[IanT]

https://www.watdon.co.uk/acatalog/insect-pins-accessories.html

IanT

[Nick]

Chris,

Yes, I see the problem! Mine are indeed old stock, so old that I have no idea where they came from. I can find all-metal pins with heads that appear to be about the right shape at waldon.co.uk and at spentex.co.uk. It's difficult to be sure from the web site photos, but they are cheap enough to be worth a punt (IMO).

Nick

[Chris_P]

I have just received the pins ordered via IanT's link. The nickel plated brass sounded ideal and they are nicely shaped with a heads of approximately 1.5 mm diameter and around 0.8 mm height. Inevitably there is a degree of variation of about + or - 0.1 mm in these dimensions as I suspect their intended users don't need great accuracy. 

I'll leave the experts to debate whether this is a scale size for whatever they are modelling.

[Nick]

You know those projects where everything that can go wrong, does go wrong? You think three times, measure twice, cut once and still put the hole in the wrong place? This turned out to be one of those. I expected the rear beam to be no more than a plate across the back ends of the frames with a slot for the drawbar, but when I examined the drawings and photos it was apparent that the ejectors, feedwater pipes and cab steps were all hung off the beam and provisions for them were necessary.

With hindsight I probably made it over-complicated, and that may have been the root of the problem. I broke my rule of making things with the fewest number of parts. I see now that with a bit more machining I could have reduced the parts count by half with fewer opportunities for things not to fit and have to be re-made.

Still, it is done now and the rear ends of the running plates are secured. Next up will be the aforementioned bits and pieces. The ejectors look to be a particular challenge.

Nick

[Nick]

I had Shapeways 3D print the injectors in brass from my solid model. That was a lot easier than machining, and the photo shows them as received. Actually the layering looks a lot worse in the photo than in reality (to my eye, at least). It depends very much on how the light catches them. A little polish on the visible surfaces brought them up really well. I should have thought to include a scale in the photo - they are about 20 mm end to end.

I thought the cost at about £30 the pair was reasonable and competitive with casting for such a small number. Dimensionally they are dead accurate, no messing about with drilling out holes for the pipework. And they had to be brass because the prototype was unpainted, and nothing looks like brass so much as, well, brass.

I will be back to Shapeways for more fittings. Unlike plastics, I don't think we will be 3D printing metals at home any time soon. Apart from the cost of the machine, it requires a high power laser, high temperatures, coolant supply and goodness knows what else. Not something to run in the spare bedroom.

Nick

[AshleyW]

richard toplis did some injectors, as fitted to my J39, not sure how much he'd charge but could be another source.

[Nick]

Some more fittings, 3D printed in brass. For the one with the three handwheels, the handwheels and stems were too thin to be printed (I'm learning the limitations of the process as I go on), so I had the body printed, turned the handwheels and soldered them in place.

By the way, does anyone know what it is for? I can identify most fittings but that one has defeated me. It is attached to the side of the smokebox and presumably communicates with the smokebox interior - otherwise why put it there? There are two narrow pipes that disappear behind the smokebox, but unfortunately none of my photos show where they go. Just curious.

Nick





 

[John Candy]

Very nicely made!
It is a lubricator, most likely feeding the cylinders via the steam chest. It is a common fitting on many early LSWR locos (e.g. Beattie 0298 class 2-4-0 well tanks, the Adams 0415 4-4-2 tanks and 0395 class 0-6-0.... to mention just a few) as well as other locos from other companies (e.g. the LNWR Coal Tank).
Regards,
John.

[Nick]

I haven't posted any photos for some time. The bodywork has taken quite a long time because of the way the splashers, firebox, boiler and cab front all intersect each other in complicated shapes, all in the best traditions of Victorian railway engineering.

Clever me thought that because I had made a CAD model of the loco, I could use that to develop the curved surfaces on to plane ones, cut out the parts, bend them up and everything would fit together nicely. In theory, yes, but in practice, any time you curve and assemble metal sheets, they are not going to be exactly as the drawing unless you do the curves precisely with specially prepared press and forming tools. For a one-off, that wasn't a good use of my time. My curving wasn't at all bad, but the curve only needs to be fractionally in the wrong place or slightly the wrong radius and things don't fit together as they should.

So I resorted to the traditional cut-and-try, offering up each part, marking out as best I could material to be sawn and filed away, and just kept going until eventually things fitted together well enough for assembly.





Holding everything together with squares, packing. clamps and sticky tape to ensure it was straight (where it should be) and square, I tacked it, and then moved the assembly to a cradle for soldering up. Moving it away from the chassis means keeping the chassis clear of the flux and filings that can get everywhere and do no good.





All done then? Err, no. The join between the splashers and the firebox was strengthened with angle iron bent to shape (that must have kept the Nine Elms blacksmiths busy), and then there is decorative brass beading along the top edges of the splashers. I didn't try to make the angles in one piece. The two parts of the angle were cut separately, soldered in place, and any remaining gaps were small enough to fill with solder.





There are more photos at http://www.nickbaines.me.uk/T3.html. Till next time.

Nick

[John Candy]

All looking very neat and tidy .... definitely been worth the effort.

John.

[IanT]

Really nice work Nick - very well done.

Regards,

IanT

[753]

Nick

After going through the same exercise and on reflection I think I would make a sacrificial boiler tube, do all the fitting and then un roll it and wrap it around the real boiler and mark out. There would still be some fettling but should cut down the amount of work.

Your loco body is looking excellent, keep up the good work.

Mike

[Nick]

Mike,

I think I did something not totally dissimilar to that. Here's an example where I wrapped a sheet of tracing paper around the boilerand marked the splasher outline with a very sharp pencil. That then gave me a template to cut to. I used that method a few times on different surfaces, both to get the component shapes and also the shapes of the overlaid angles.



Maybe the ideal would be to CNC mill the splashers on each side from solid as a single part, and the firebox from solid as another part. That way one could get all the bends and curves exactly to drawing and the parts should fit together nicely. The boiler is a plain cylinder and could stay as a fabrication. Large enough chunks of brass would be horrendously expensive at today's prices, maybe I'd have to use aluminium instead and ask John Candy to weld it up for me. No, I'm not entirely serious. How one's thoughts wander during lockdown ...

Nick

[MikeWilliams]

I think Nick that the result you have achieved on the model has proved that your method works well.  In real life these things didn't always fit perfectly.  I have seen engines in the '60s with gouges out of their frames where the wheels have been rubbing.  When making a tender I crawled all over a preserved example at the NRM to check how the plates lapped inside the horseshoe tank, only to find that it was so badly bashed about from use and the joins obscured by 1/4in of paint, rust and dirt that I still wasn't sure.  Your model is superb.

Mike
 

[Nick]

I machined the chimney, dome and safety valve cover. As always, the tricky bit was the flare where it seats on the boiler. I've done a lot of these in O gauge so I had the procedures and tooling pretty well sorted out, but in the larger scale there is a lot more material to remove. G3 is nearly twice the size of O gauge, so eight times as much (in case you are interested).

If I ever do any more of them, it will be by CNC or 3DP.

Nick