Now I've been back 24 hours and mowed the lawn I had a go at drawing the various boiler plates. I am finding that LBSC's text and his drawings do not always speak the same language! 1. Is a Combustion Chamber Throatplate the same as a Firebox Front Plate? There are no other drawings so they must be..... 2. It says 'To make the Combustion Chamber Throatplate, use the same former as used for the Doorplate' . The side sweeps and the base width may be similar but the top of the doorplate is a full half inch narrower than the Combustion Chamber Throatplate. Not a potentially good fit I would say. What do I do now? 3. The drawing states 'The Backhead uses the same curves as the Throat Plate'. However, the backhead curves on the drawing look nothing like the curves on the throatplate! Was someone being lazy? In addition, the greater accuracy of Autocad arcs makes the original representations look decidedly 'iffy'.
Has anyone made the LBSC Brit boiler themselves? My instincts are to make all as consistent as possible, but my precision engineering approach has got me in trouble a couple of times already....... JB
G'Day JB, I don't have any experience with LBSC's Brit. but if his Virginia is any indication, I understand your problem. I used Autocad the redraw/design the boiler and found quite a few anomalies including substantial interference between the firebox and the frame. I would stick with Autocad and your instincts and make things look "right". Autocad was very useful in producing DXF files for use on the local joiners CNC router on which he cut the formers for the plates, worked a treat. He also cut some templates that I used to drill holes in the backhead. Autocad was also useful for checking the backhead stay layout to ensure that it complied with our boiler code. Nothing wrong with precision. Good Luck
I agree with Arch, draw it out in CAD and 'adjust' if necessary as there does seem to be a few 'discrepancies' in the dimensions. LBSC admitted himself that he was 'no draughtsman' so the drawings of the 'curves' on the plates may only be an approximation.
You will have to look at the plain butt joints between the two throatplates and the barrel and combustion chamber which may give your boiler inspector a coronary nowadays He/she will probably expect either a proper flanged joint or at least a reinforcing strip to increase the area of the joint.
I am not familiar with Brit , I suggest to look at full size drawing just to ensure if the fire box is parallel both sideways and top surface ,some boilers are not and if they are not then the curves will not be the same ,just a thought. The combustion chamber is a part/extension of the front fire box plate , just a humble advice ,ensure 100% good joints in the combustion chamber as if there is a leak ,it is NOT easy to fix .A lot of people built such boilers for models without combustion camber for that reason .Not putting it in will of-course reduce the heating surface and therefore efficiency , it is a compromise ( I am not suggesting to do that , personal choice ) .
I am finding that LBSC's text and his drawings do not always speak the same language! 1. Is a Combustion Chamber Throatplate the same as a Firebox Front Plate? JB
JB I think the answer to this is 'Yes'. My LBSC 'V4' words do not always follow the music. As you can see from the photo of my words he refers to it as being the 'front plate of the firebox'. The bottom part of course forming the combustion chamber throatplate.
Thanks to Chris, Baggo, Shawki and Arch, I now have a better idea of what I am doing. The throat plate will require a flange at its lower half where the boiler barrel should sit flush, but that shouldn't present a problem. I now have paper templates of all the formers, and whilst away money grubbing this month I will spend quality time in the hotel room drawing up sections of the boiler, just to be sure, to be sure. It might, I say MIGHT, keep me out of the bar....... JB
Well, I've started my first loco boiler. I thought I'd start with something relatively easy, so I chose the firebox and combustion chamber! Question is, how accurate does the end shape have to be? I couldn't quite manage the tight radii represented on the CAD template, but it looks alright to me, and will leave a fair amount of space around the superheater (sorry, steam drier) tubes.
I'm also a bit concerned about the overlap joint: it looks very untidy and the tube plate will be less than a perfect fit. Is it OK to file off the surplus to blend the curve after brazing ? I don't want to upset our Club inspector with my first offering! ! Next job: the taper barrel! JB
Does the tubeplate flange overlap the outside of the combustion chamber? Pretty important joint that one, as it's not easily accessible later in the build. Thanks for uploading the photos, as I'm nearing starting on my boiler soon. These photos are already giving me 'food for thought!' I haven't tackled a combustion chamber boiler before. It's good to see you diving in at the deep end, but I know you like a challenge!
Hi Chris. Yes, it is a 'coffee tin lid' fit on the outside, so I want as smooth a fit as possible, hence the question about filing the overlap. Glad the photos are a help. Good luck with yours, I'm finding this is great fun as I haven't bashed any tin since 1964! JB
Hi Jb in my limited knowledge of boiler making i would be inclined to offset one edge of the joint by the thickness of the copper to bring the edges flush, rather than trying to file it flush as this might weaken the joint considerably. Did you use a former to shape the curves as I would have thought that the radii you have on the template should be achieveable on the copper. I cheated on the boiler for the Stirling and bought one from Western steam, I would strongly recommend them to anyone. The only effort I put into building the boiler was 2 phone calls and a nice pleasantdrive to Burnham on Sea. Looking forward to seeing your future boiler progress. Mike
Hi Mike. No former I'm afraid, just solid bars sticking out of the vice as needed! I take your point about the offset joint though. I thought about doing a butt strip to give me a smooth joint but this would deviate from the 'Established Design' principle, and I will have to talk to our local expert before I do this. By the way, 13g copper is pretty heavy stuff to bash! Regarding Western Steam, I know they are good, but when you are a poor old pensioner the going rate for a Brit boiler is just about my annual marina fee....... JB
JB. I think the important thing with that important joint is - The face of the combustion chamber is FLAT. Then the 'coco tin lid' will be soldered between flange and curve surface and also the flat faces of the plate and the flat edge of the combustion chamber. The space between flange and combustion chamber curve surface will 'fill' slightly with silver solder where they are not in very close contact.
LNER B1 - Runs but needs platework finishing. Simplex - well run and looks it. Simplex Nail - backup runner. LNER V4 - in the making. It's never ending. Still good fun though.
Hi JB Are there any stays to support the combustion chamber top flat surface ? Or are there any Galloway tubes to do that ? As I mentioned before ensure these and front tubes are 100% leak proof . Access to these is very difficult if not impossible when boiler is complete. Many years ago I know of one that leaked from one or two tubes if my memory is right . The repair scheme involved cutting a hole in the barrel to get access to fix the problem then fixing the barrel , then a hydrostatic test .I am not discouraging you but just to let you know what to do here. Take care & good luck.
We had experience some years ago of a club Heilan Lassie which wore out three boilers over many years of intensive use. A recurring problem seemed to be leaks at the combustion chamber tube plate. I always thought that the combustion chamber was 'nodding' with the continuous expansion and contraction, causing the tube joints to crack. It had Galloway tubes, so the top sheet was supported, but I have wondered if it would not be worthwhile to extend the centre firebox crown stay along the length of the combustion chamber to give it some added stiffness. Some perforations may be necessary to aid circulation.
Can i suggest putting a joggle in one plate of the lap joint, this will give a better fit for the 'tin lid' tubeplate. Alternatively, use a coppersmiths or dovetail joint, but I suppose this is going away from the published design, so perhaps better not.
Thanks for all the advice, most welcome. I had another look at the words and music and it does mention 'the option' of filing the overlap, so I left a decent lap, put a number of rivets in, and soldered it up using a 3x1mm strip laid on the joint. You can see that the solder has travelled right through the 3/8 wide joint, and I was able to file the lap to shape. I'm quite pleased with the result 'cos it doesn't look like 'Brighton Rock' as LBSC used to say!
I didn't have any steel to hand for the flange plate, but I do have some inch thick Iroko hardwood, and that was pressed into service. At that thickness it doesn't deflect (much) when it is clouted! Three anneals later I had a tube plate cap. I have eased the end of the combustion chamber a little, and the cap just goes on nicely with a light tap. Seems to sit square as well! On reflection the radius on the edge of the former ended up a bit larger than I liked, because the hardwood 'gave' just a little where steel wouldn't. I will make the other flange plates to reflect this. I wonder if the rest of it will go as well......
It had Galloway tubes, so the top sheet was supported, but I have wondered if it would not be worthwhile to extend the centre firebox crown stay along the length of the combustion chamber to give it some added stiffness. Some perforations may be necessary to aid circulation.
I did consider suggesting that myself. Paul Wiese, who designed the 2½" gauge Flying Scotsman described in ME some years ago did just that on the boiler for that. Apparently his local club had another 'Lassie' which had the crown of the combustion chamber sag after a period of use, hence the extended centre stay on the Scotsman boiler, just to be on the safe side.
The crown of the Brit combustion chamber is virtually flat so a bit of additional support may not be amiss.
I have just placed the tapered boiler shell on the chassis, 'just for fun', to await my return in the Autumn when the silver soldering starts in earnest. I'm just starting to realise how big this loco is and what a job I've taken on! The thing is HUGE: the top of the boiler is nearly a foot off the bench! A 3 1/2"? Looks more like a small 5 inch to me! Oh well, if I couldn't take a joke I shouldn't have joined the club! Encouragement on a postcard please to Bateau INKA, Port Ariane, Lattes, France......... JB