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LNWR Precedent

Started by Nick, Aug 26 2022 20:21

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Just fabulous.  Faultless.  What an incredible advert for our scale.



Nick I thought I recognized this loco from another place. Wow wonderful work.



The loco has now gone to the paint shop, where it will be for some time because painting isn't my favourite task and I'll happily take any excuse to do something else. The present excuse is that bits for the tender have arrived and are just asking to be worked on.

The wheels, as before, have 3D printed nylon centres. Previously, I made the tyres for the loco wheels from some large diameter steel bar. This time I got blanks laser cut in steel. It actually worked out roughly the same price (large diameter bar isn't cheap) and should be quicker to cut because there is much less material to bore out from the centre.

Carrying wheels.png

So why so many wheels? Well, I decided to get enough parts for two tenders. The LNWR must have built lots of these tenders because I've seen photos of them trundling around behind many different classes - so I have options for future (undefined) projects. I might even build two because it's usually quicker to build together rather than one after another. I also needed a new wheelset for the loco to replace the existing one that has the wrong number of spokes (oops), and I added a few more just because. Actually I think I got a price break on either the centres or the blanks. It's worth seeing where this cuts in when placing an order.

Along with the tyres, I ordered the steel parts for the tender frames. Again there's enough for two tenders. When I get bored of turning tyres I can start assembling this lot.

Tender frames.png



Two tenders!  I can't wait to see what the second engine might be.  If its a goods engine you'll be wanting plenty of LNWR wagons  ;)



Haha! Actually I do quite like the Crewe 0-8-0s, particularly the ones that had to have a kink in the valve rod to avoid the front axle, but I might want to negotiate a discount for quantity on wagons.

Now, where were we? Oh yes, tyres. Warning: this post is about turning tyres, so if you have no interest at all in lathe work, you may decide it is not for you. Feel free to move on.

And if you're one of those annoying people with a toolroom quality lathe and a zillion years' experience, this post certainly isn't for you. I'm not in your league. I'm one of those people who thought it would be fun to have a lathe and went on from there.

The first task is to reduce the blank to thickness and bore out the ID to the correct size. My chuck was only just big enough, but it did hold them securely. I used a headstock backstop so that each blank goes in the same position, and a carriage stop to avoid running into it with the boring bar. All the tyres were done using this setup before moving on.

The lesson here was the layer of hardened material that is formed by the heat of the laser at the cut edges. Reminiscent of the skin on the sand casting beloved by model engineers of a certain generation. Not tool steel hard, it does cut, but takes it out on the tool.

I was expecting that, but I was surprised how deep it was - up to 0.8mm in my case. It dulled the edge of an HSS tool very quickly. Yes, I'm still in the 20th century for lathe tools but I mostly use HSS tools because so much of the turning that I do requires a special tool form to be ground and it's a lot easier in HSS.

That was certainly true until I discovered that the awkward bits could be 3D printed.

Anyway, I switched to a carbide insert boring bar which did a much better job of cutting. The only tool I had available is much longer than I needed so it vibrates a bit and the quality of the finish is not great. But I will be gluing the centre in place, and a slightly rough finish (this isn't an argument for a ploughed field finish) means a greater surface area in contact with the glue which is all to the good.


Once the ID is correct the tyres go on this fixture. Where the tyre is mounted it is turned in situ to a good running fit on the tyre ID. Then it never leaves the chuck until the whole batch is done to ensure that the tyres are concentric.


Each tyre is clamped in position, and the first task is to reduce the OD to the diameter over the flange. Again there is a layer of hardened material to get rid of and I used a carbide insert tool for this. Incidentally, when I ordered the tyre blanks from the cutting firm, I did add enough margin on both ID and OD  - just. Phew.


Now to form the profile. Lock the saddle and set the top slide over at 3 deg to give the correct taper on the tyre. The tool is moved exclusively by the top and cross slides in this operation. The leading edge of the tool is set at the correct angle for the flange. Then cut to final diameter plus a very small margin (say, 0.05 mm or a couple of thou in old money).


Now for the controversial bit! I get the final shape using a form tool (from Mark Wood). I like it because the final profile is entirely consistent. Lock everything that can be locked on the lathe, use a very slow speed and feed the tool in slowly. If you do it right and keep the final cut very fine, it doesn't chatter.

People have told me they can get just as good a finish with conventional tooling and the form tool isn't worth the cost. I just checked and I see that the cost is almost double what I paid about eight years ago, so you might think twice about it. Anyway, I've done about 40 tyres in G3 so far so it's beginning to pay for itself.


We're still not quite finished. The surface needs some attention with a fine file (I know, sacrilege) and wet-and-dry paper. Then it is finally done.


Rinse and repeat twenty times. A pile of finished tyres is gradually building.


That's it. There are lots of instructions on the web about how to turn wheels from castings, but I decided to set out how I did it from laser cut blanks, which isn't quite the same. If you stayed the course, thanks for your company.



Stepping back to the engine for a moment, I've finished painting the chassis. Quite easy due to the monchrome tendencies of the LNWR. The eagle-eyed will notice that the front wheels now have the correct number of spokes.

Chassis painted_1.png

Back to the tender, I now have enough wheelsets for two six-wheel tenders. And a few spare wheels in the drawer just in case.

Tender wheelsets.png

This is a trial assembly of the frames, all set up ready for soldering.

Tender frame assy.png



The next job is the hornguides. I need a couple of dozen of them, so some organisation is called for, because I'd drive myself nuts if I had to mark out and cut each one individually. What we need is a jig, or several jigs. Spoiler alert! This is the end product.


The first question is, what are the important dimensions and features? The holes here have to align with the holes in the frame to pass the rivets through, and the hornguide must be a right angle for the axlebox to move as it should. Sounds obvious, but the answer tells us how to proceed. Get those things right and the parts will fit and do what they have to do. I can allow a bit of leeway elsewhere. Not so much as to be screaming obvious, just not to be quite so careful about.

The right angle is ensured by starting with some milled (not rolled) angle of the correct dimension. The photos below shows one such clamped in a jig for drilling the holes. That way I have only to set out the holes once. The jig is also the exact width so that after drilling I can use it to cut and file the angle to length without having to measure.

The angles are LH and RH, so the jig is reversible - do one half the angles, turn it over and do the other half.



And here are the two sets.


One of the outer corners is radiused. I filed a quarter circle on a scrap of material of the right size, clamped it to each angle in turn and used it as a filing jig. But forgot to take a photograph - sorry.

Next up is the base which is soldered in place. Here is the soldering jig which is just a few pieces of scrap wood. It holds each angle against a strip of material that has the correct width and is much too long in order to make it easy to hold. After soldering, the base is cut and filed to size. The soldering jig has LH and RH sides, too.


Finally, there is a hole to drill and tap in the base for the stud that will eventually hold the keeper in place. Another drilling jig is called for in which the angle can be clamped for drilling. Tapping is then done by hand.



And there they all are, lined up and ready for riveting to the frame. Yes, there are two tenders' worth. It's a lot more time-effective to set up and do them all now, rather than half now and half at some later date.




The keepers are assemblies of plates which are bolted to the hornguides and rods between them. This is the drilling jig for the plates, two holes for the hornguide studs, and one hole at one or both ends (depending on whether it is an outside or centre axle).


And here are all the parts for one assembly, ready for soldering.


Once soldered, the ends of the plates had to be filed to a smooth transition to the connecting rods. There's no easy way to do this. Coarse then fine half-round needle files, followed by coarse then file wet and dry, and keep inspecting it from all angles to spot and get rid of the humps and dips.




Not much progress recently, what with the G3 Society Annual Show and then the Newsletter, and as I write this the sun is shining (at last) which doubtless will mean a summons from the Head Gardener. In between whiles, here are the tender buffers.

The heads and stocks are fairly straight forward turnings. Here are the stocks rough turned:

Tender buffer stocks.png

and fine turned and polished.

Tender buffer 1.png

Drilling holes for the rivets, using the rotary table to get an even pattern. That drill is 0.8mm diameter and I decided that the hole is far too deep, so I drilled most of the way using a larger drill and left a couple of millimetres to break through. The rivets turned out to be a good push fit and would probably have held themselves in place, but I added some epoxy to make sure.

Tender buffer 2.png

Here is the assembly. The stock is drilled deep enough to accommodate the head and the spring compressed, and then continued at a clearance diameter for the screw. The back face is counterbored quite deeply so that the head of the screw remains in the hole when the spring is fully compressed. That way the buffer is fully self-contained.

Tender buffer 3.png