Roger Froud | 04/11/2013 17:05:38 |
27 forum posts 14 photos | I just picked up on this thread because I can see that there's an error on the plans and couldn't see what was meant by the drawing bearing the title 'CROSS SECTION AT FIREBOX TUBEPLATE. Clearly there should be two thicknesses of copper showing on the drawing because you should be able to see the edge of the tubeplate flanges. From the discussion above it seems clear that the flange should be shown between the firebox wrapper and the boiler tubes, that's why the tubes are a little close to the flange. My instinct is to very slightly move the wrapper away from the small tubes where they are too close, say by one millimeter. I would imagine it to be very difficult to guarantee a good joint is the tubes are pressing against the inside of the flange. The large tubes look fine, as does the bottom row of small tubes. |
Roger Froud | 06/11/2013 09:42:42 |
27 forum posts 14 photos | Posted by DMB on 12/03/2013 22:39:50:
fizzy, beware, if you make a Speedy boiler. One of the members @ my club was building one and showed us all a small problem. He said there was insufficient clearance between the undersides of the bottom row of flues and the throatplate flange. He had filed small scallops of metal from the flange to accomodate those boiler tubes. Obviously, I do not know if he had followed the drawing exactly, as he said he had or if he made a small error of which he was unaware or if drawing was at fault. All I`m saying is just be aware and check very carefully. Godd luck. John
Unfortunately the drawing leaves you guessing as to the position of the tubes, there are no dimensions to tie it down. There's also an error on the section view because it doesn't show the edge of the firebox tubeplate flange. I think that's why some builders could be caught out. The geometry of the curves where the firebox wrapper comes close to the tubes isn't defined either so there's no need for the flange to be too close.
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Roger Froud | 06/11/2013 10:05:58 |
27 forum posts 14 photos | Posted by DMB on 12/03/2013 22:39:50:
fizzy, beware, if you make a Speedy boiler. One of the members @ my club was building one and showed us all a small problem. He said there was insufficient clearance between the undersides of the bottom row of flues and the throatplate flange. He had filed small scallops of metal from the flange to accomodate those boiler tubes. Obviously, I do not know if he had followed the drawing exactly, as he said he had or if he made a small error of which he was unaware or if drawing was at fault. All I`m saying is just be aware and check very carefully. Godd luck. John
Unfortunately the drawing leaves you guessing as to the precise position of the tubes, there are no dimensions to tie it down. There's also an error on the section view because it doesn't show the edge of the firebox tubeplate flange. I think that's why some builders could be caught out. The geometry of the curves where the firebox wrapper comes close to the tubes isn't defined either so there's no need for the flange to be too close.
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DMB | 06/11/2013 10:20:37 |
1585 forum posts 1 photos | Roger, The WDSME member I was referring to, was I believe, making his first loco. I think his job was a "chippy." I dont think a Speedy boiler is a beginners but he seemed to have done some nice work. I would think that a boiler like this with tubes so close to the "outer skin" calls for the essential use of only pre-treated water to prevent furring-up with chalky deposits. This could build up very quickly in a really hard water area like Sussex south coast - Worthing/Brighton. Prevention is very much better than attempted cure for this problem. Back to prev., he used a round file to put a couple of small scallops in the flange. I am not aware of any other probs. with this boiler and I believe he died before completing the engine and I dont know what happened to it so cannot comment further on success of test or running performance. Can only say its a shame LBSC apparently left black holes like you mention and very often in valve gears of a number of his designs. He did however say that his published VG designs left out a small detail so he always had an ace up his sleeve. John |
Roger Froud | 06/11/2013 10:33:50 |
27 forum posts 14 photos | I hear what you say and take it all on board. I'm lucky in that I can build the computer model and look at it from every angle, tweaking things where they look a bit close. It's tempting to move the outer two of the bottom row of small flues slightly. in fact, it might make sense to very slightly bunch up the diagonal row of small flues towards the centre of the crown. I'm sure an extra millimeter could clearance between that tube and the barrel diameter could be achieved without compromising anything else. |
Speedy Builder5 | 06/11/2013 16:01:53 |
2878 forum posts 248 photos | Hi Roger, that's the problem of using millimeters !!! I used fractions and although it is close, the tubes do fit in using the measurements as given for the Firebox Tubeplate and dimension from 'Curleys' book. He states on page 31 (Smokebox Tubeplate) , that the centre line of the bottom tubes should be 5/8" from the outside of the TP flange. After that, the other dimensions are as sht 5. You may note from my photo that the outer bottom tube holes have 'grazed' the flange - It is close. Bob |
Roger Froud | 06/11/2013 17:10:06 |
27 forum posts 14 photos | You've lost me there Bob, I convert everything to within a micron so it's the same dimension. It really is about time we finally changed to metric, I was a teenager when we went over to it, and I'm sure it puts a lot of young people off the hobby. Most of them don't know what an inch is, and why should they? I see where you've had to file away the flange on the bottom outside flues, just like my computer model shows. I don't see that as a big problem, it's just not ideal. I'll take a look at the dimension I've ended up with and compare that with the figure you've found. Quite why that's not on the drawing is a mystery. I notice that the Smokebox Tubeplate drawing is incorrect in as much as it doesn't show the forward facing flange in that view. It give the impression that there's more room than there is. Anyway, it can clearly all be made to fit one way or another, and if moving the tubes very slightly makes it easier to braze up then I'll probably do that. I'm not looking to change things unnecessarily, but I have the opportunity to do these things so I may as well if it helps. I see that some builders have added more stays to the backhead and I'll do that too. Are you planning to lag your boiler? I'm curious to know what needs to be done about that. |
John Baguley | 06/11/2013 17:31:40 |
![]() 517 forum posts 57 photos | Hi Roger, You could leave out those two outer tubes on the bottom row if necessary. The Speedy boiler has plenty of gas area through the tubes compared to the grate area and you could afford to lose a bit without affecting the steaming of the boiler. John |
Roger Froud | 06/11/2013 17:39:18 |
27 forum posts 14 photos | That's an interesting thought, I'll chew that one over John. |
Speedy Builder5 | 08/11/2013 16:06:03 |
2878 forum posts 248 photos | Roger, 'Curley' omits info on lagging, but I have seen several photos of finished models showing the brass lagging bands on the barrel. I will lag mine with a minimal thickness and brass sheath if only to hide the boiler stays. BobH |
Roger Froud | 08/11/2013 20:06:09 |
27 forum posts 14 photos | Thanks Bob. I presume the diameter of the smoke box needs to be slightly increased if it's going to look right. I'm having an absolute nightmare trying to create a 3D computer model to verify the drawings. Whichever way I look at it, things simply don't add up. The drawing for the smokebox tubeplate states 4-3/4" diameter which is clearly wrong. I can see that he was probably thinking that the boiler at that point was 1/8" thick when in fact it's 3/32" or 2.5mm (13 gauge) It also looks like he's callculated the heignt of the crown stays or the height of the firebox from the sectional view omitting the inner flange of the firebox tubeplate. Either way, it's never going to fit if it's made to the drawing unless I've made an error. How far have you got? What did you have to change to make it all fit if at all? |
Speedy Builder5 | 08/11/2013 22:08:03 |
2878 forum posts 248 photos | Roger - 160 psi hydraulic. BobH |
Roger Froud | 08/11/2013 22:20:02 |
27 forum posts 14 photos | So how much tweaking did you have to do to make it all fit? It looks to me like the tubes can't be parallel to the bottom of the boiler but slope slightly upwards.... no bad thing. Several of the tubes in the firebox tubeplate also graze the edge of the flange if it's drawn precisely to the dimensions. What diameter did you make the smokebox tubeplate? 4-3/4" isn't consistent with the 5" outside diameter at that end. |
Roger Froud | 08/11/2013 23:36:53 |
27 forum posts 14 photos | Posted by John Baguley on 06/11/2013 17:31:40:
Hi Roger, You could leave out those two outer tubes on the bottom row if necessary. The Speedy boiler has plenty of gas area through the tubes compared to the grate area and you could afford to lose a bit without affecting the steaming of the boiler. John The more I pore over the 3D computer model, the more I think this is the best solution. It's those two tubes that are causing all of the clearance issues. The smokebox tubeplate needs large scollups to be taken out of the flange and the "piston ring" joint has a similar problem. I'm not keen on doing that and the tubes are already close enough to the top of the firebox tubeplate flange. I really don't want to raise the top of the firebox crown either. I could slightly squeeze the tubes closer together or probably the least offensive would be to fit two smaller tubes there. Removing those two tubes reduced the surface area by 5.9% which doesn't seem much. Does anyone else have a view on this that they would like to share? |
Roger Froud | 09/11/2013 00:23:00 |
27 forum posts 14 photos | Ok, I've just fitted two 5/16" tubes there, keeping the same clearance as the others to the inboard tube. This works really well from a clearance point of view and means a loss of around 3% in surface area, This is what I'm probably going to go with unless there's a compelling reason not to. |
John Baguley | 09/11/2013 00:54:34 |
![]() 517 forum posts 57 photos | Hi Roger, Some years ago I devised a spreadsheet for calculating boiler parameters e.g. tube area, grate area etc. I put the dimensions of a lot of boilers into it to see how they compared. I got the tube area for Speedy to be 19.1% of the grate area with 31 tubes, making the assumption that the area through the superheater tubes would be approximately the same as the fire tubes after taking into account the reduction in area caused by the superheater elements (The actual area through the superheater flues may be more than that if you actually work it out). Reducing the tube count by two to 29 gives me an area of 17.9% of the grate area, a reduction of only 1.2%? Maybe I've got something wrong. I try and aim for a figure of about 15% for tube area versus grate area but in many boiler designs that is impossible to achieve. Incidently, in the 'Words and Music' in English Mechanics LBSC says to make the boiler barrel from 10swg or 1/8". That would explain the 4-3/4" diameter for the front tubeplate. John |
Roger Froud | 09/11/2013 08:39:26 |
27 forum posts 14 photos | Hi John, That certainly explains the difference in the difference in the smokebox tubeplate. It's tempting to follow suit and make it out of 1/8" copper, after all, the outer firebox wrapper is 1/8". I think your calculations may be wrong on the reduction. I estimated that the equivalent are of the 5 large tubes to be 8.5 small ones from the ratio of their circumferences. That gives a reductions of 2 / 34.5 x 100 = 5.8% approx. Maybe I'm missing something. Obviously your spreadsheet is more sophisticated because you must be using the surface area. Anyway, fitting two 5/16% tubes is such a neat way to get round the mechanical difficulties that I think it's the way ahead. Everything clears nicely and it isn't a struggle any more. Is that a shaping machine I see in your gallery? I haven't seen or used one of those since my apprenticeship at General Motors, 40 years ago! |
John Baguley | 09/11/2013 11:48:23 |
![]() 517 forum posts 57 photos | Hi Roger, Yes, it's a Boxford. I hadn't planned to have one in the workshop but one came up at a very good price. Couldn't resist! It's the first time I've used one since metalwork class at school 45 years ago! I'll check my spreadsheet to make sure I haven't made a boo boo somewhere. John |
Roger Froud | 09/11/2013 12:02:56 |
27 forum posts 14 photos | You're lucky to have enough space for a beast like that. I only have a single garage, and every machine I have has to do many jobs. I already have a CNC Mill, a large Warco lathe and a Jones and Shipman tool and cutter grinder so it's bursting at the seams. |
Speedy Builder5 | 09/11/2013 16:15:51 |
2878 forum posts 248 photos | JB, time to put a loft floor in your garage then ??? |
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