Buck Jumping on Mass

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Will L
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Re: Buck Jumping on Mass

Postby Will L » Thu Jul 30, 2020 1:18 pm



Just reacting to a proliferation of red underlined words Keith. As a champion misspelled I'm very sensitive to such things.

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Will L
Posts: 1818
Joined: Sun Jul 20, 2008 3:54 pm

Buck Jumping on Mass - The Build Phase

Postby Will L » Sun Aug 09, 2020 1:15 pm

Part 21 – Fitting Boiler to Body

When I decided that I wanted the boilers to be removable, my going in position was to assume I would need to bolt them down in two places, From under the footplate into the smokebox/smokebox saddle, and from within the cab into firebox end of the boiler. I have successfully used this approach before in the J10 which starred in my early posting on the use of CSBs. The J10 had a white metal footplate which was pretty flexible and needed the boiler to keep the overall ensemble rigid, but, for these little brass built tank locos, the footplate and cab assembly was already pretty rigid.

As I worked on them, I discovered that the tank top plates that butt up to/overlap the boiler actually do a good job of keeping the boiler where it is meant to be. As a result I decided to omit the bolt at the firebox end and just provide a ledge on the cab spectacle plate on which the firebox end of the boiler could sit.

Both kits were designed so the smokebox was positioned by a slot in the footplate which mated with a tab at the bottom of the smokebox front plate. The rest of the saddle needs to be finished off flat and square so it sits on the footplate with no gaps. I was going to use a 12BA bolt run up from under the footplate through the saddle into the boiler. Given that the sandboxes sit on the footplate and hide the meeting with the saddle sides, the joints where I needed to be most careful about visible gaps were, between the front of the smokebox and the footplate, and between the fire box end of the boiler and the spectacle plate.

The J69

I did this one first and started by trying to sort out the smokebox saddle end of things, and as often happens the best laid plans don’t survive the first engagement with the enemy. Using the tab on the smokebox front to locate it on the footplate wasn’t going to work. The slot was obstructed, partly by the captive chassis fixing nut, and partly by the pad constructed under the front of the footplate to space it from the chassis (which we discussed in Part 9 - The body is a foot... plate). It was also true that the footplate in this area was distinctly thin and fragile. It was a single sheet of 10 thou brass half etched in this area from underneath. I was clearly going to need to reinforce it as tightening up the bolt would have distorted it out of shape.

An oblong of 20 thou scrap etch, which would fit within the underside of the saddle, was soldered to the top of the footplate where the back of the saddle would locate against it. A hole, tapping size for 12BA, was drilled centrally through this and the footplate. Having filed back the front edge of the captive nut to allow it, the slot in the footplate was filled and a thin metal strip formed into an up-stand that would fit just inside the front of the saddle. A little judicious use of a file ensured the open underside of the saddle fitted snugly around these two. The drilled hole was extended upward into the boiler tube. In the boiler it was tapped 12BA and the original hole was then opened out to 12BA clearance. The result, while not very pretty internally, did locate the smokebox saddle firmly and accurately on the foot plate.

Buck J69 boiler fix.jpg
Buck J69 boiler fix.jpg (60.59 KiB) Viewed 130 times


When bolted down, the boiler ran back level and at the right height just under the edge of the tank top sheets, but it was between 10 and 15 thou short of the Spectacle Plate. The instructions did warn that accumulated bending and fitting errors were inclined to give this result. There was an easy fix, a piece of 15 thou scrap etch was soldered flat across the end of the remaining boiler tube at the fire box end. Once the excess metal is filed away you are left with the boiler extended by the required amount. Now when the boiler was bolted down it was a snug fit against the spectacle plate.

I provided a lip on the cab front for the boiler to sit on. This was made from more scrap etch filed to the profile of the inside of the boiler tube. With the boiler tube bolted in place, I carefully soldered the lip to the spectacle plate so it was tight against the tube while, ensuring the boiler was being held snugly against the tank top plates and hence at the right height.

I then made the interesting discovery that, when I assembled boiler to body they went together with a satisfying click. The boiler was held firmly in place even without the bolt.

The J65

On this one, the slot in the footplate was available to take the tab on the smoke box front. When this was engaged the saddle sat neatly on the footplate and didn’t need any further alignment. The reinforcement for the bolt was still required. It was attached below the footplate this time, ensuring it was clear of the frames. As before the bolt hole was drilled through the reinforcement and into the boiler tube and tapped to suit a 12BA bolt. The boiler again fitted snugly against the tank top plates and again came up about 10 thou short of the spectacle plate, so the tube was extended as before.

A pleasant surprise

By now I had begun to realise just how snugly these boilers were fitting in place, and that given the snug fit against the tank top plates that the lip on the spectacle plate may well be unnecessary. Certainly true on the J65, which without it still goes together with a satisfying click, and reliably stays assembled and handleable without the smokebox bolt. Since then I’ve completely given up bolting on the boilers while I’m still working on them. Once you have fitted the chimney (coming soon), you can happily pick up either one by it and be sure they won’t fall apart. I will put the bolt in on final assembly, for security of mind yes, but also it has developed a further use as a way of securing in place a slug of lead in the boiler/smokebox area. The pictures show my removable boilers do fit well leaving no unsightly gaps. Neither is bolted together in these pictures. On the J69 (left) you can just see how the boiler has been extended.

Buck Gaps.jpg
Buck Gaps.jpg (88.19 KiB) Viewed 130 times


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