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Post by jcsteam on Jul 8, 2020 15:33:01 GMT
Hello all, How do you go about scaling the full size plans down for a model locomotive, i know for the likes of 5" gauge divide the measurement on the drawing by 11.3 to get the size in 5". However what else is there to consider when scaling plans for a working miniature version of the full size locomotive. I can understand the boiler will need the internals looking at and apart from the outside appearance, the boiler will have to be a complete redesign with calculations done to prove its strong enough for the job. Other than the boiler what else needs to be considered when scaling down from full size to make sure the loco runs. To pre-empt the question, the loco is a Beyer Peacock Well Tank 0-4-0 locomotive built for the Great Northern Railway. Only two were built numbered No.13 & No.14, and its taken me a year to source a usable drawing which was originally drawn out and shown in a book called Locomotive Engineering and the Mechanism of Railways Vol II, Written by Colburn Zerah 1832-1870. The Illustrations are all D K Clark's work. I want to build it without cab in original form in 1856, both loco's having been reboilered and an addition of a cab later, as well as the dome been moved. In my opinion it became a bit of an ugly duckling after the rebuild but they carried on until 1916. Both been scrapped. Prior to finding the drawing i only had three pictures of the loco. Which i will find and add to the post later on. An image of its rebuilt form can be seen hereThanks in advance for any assistance and advice. Regards Jon Edit: Here is the engine in original form before been reboilered as described above. Screenshot_20200707-103021_Gallery by Jon Cameron, on Flickr Screenshot_20200707-103302_Gallery by Jon Cameron, on Flickr
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stevep
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Post by stevep on Jul 8, 2020 16:02:28 GMT
Jon, when I built my Stanier 2-6-4T, I started with Martin Evans' drawings, but on finding a dimensioned G.A. drawing, realised that lots of the measurements were very wrong. So I continued building it, as you say, at a scale of 10/113, and as far as I was concerned, it turned out fine. I did refer to various other designs that were being published at the time to check the sanity of some of the dimensions (thickness of connecting and coupling rods, valve travel, port sizes, etc).
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Post by jcsteam on Jul 8, 2020 17:05:20 GMT
Steve, My issue is really there is no scaled drawings or published plans for this loco. So all I have is the general arrangement drawing, and a black and white photo. I know that scale loco's need some alterations if they are to actually run. But I need to know what I need to consider and what can be left pretty much scale dimensions. For instance, wheels turning the flanges and treads to 5" gauge standards, as opposed to the standard drawn full size treads? Do wheels need widening?
Do cylinders need to be reduced/increased from scaled sizes for the loco to run?
Regards Jon
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Post by Roger on Jul 8, 2020 17:18:19 GMT
One of the challenges is to make the working parts look scale even though the nuts and bolts are probably too small to be functional. If you scale everything, you'll likely end up with something that's too delicate to be practical.
I'd fit as many dummy nuts and bolts as possible and use one or two larger hidden fixings to actually hold parts together.
I made a conscious decision not to use anything smaller than M1.4 for holding things that needed to have some strength. Smaller than that usually means the nuts and bolts are Brass, and that's hopeless for anything other than decorative attachments in my opinion.
Some things such as handles and levers can be made from Gauge Plate instead of Mild Steel. It's just as flexible, but you can bend it a lot further before it reaches the elastic limit, so it feels more rigid. That way you can make those parts a little thinner and closer to scale than you might otherwise.
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stevep
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Post by stevep on Jul 8, 2020 17:22:55 GMT
Jon, turn the wheels to published standards - flanges and treads. I personally always turn driving wheels with parallel tread, as most model engineering tracks have vertical rails. If the rails were canted in (like on full-size) then the treads should be tapered to match. I turn carrying wheels with a tapered tread, so they self-centre.
There is always a lot of discussion on the size of pistons - big or small. Big ones can use more steam, but will work well at lower boiler pressure. Smaller cylinders can use less steam, but will have a reduced tractive effort (for the same sized wheels).
Check the published designs of similar sized locos, and use something similar to them. Whether that is bigger or smaller than scale doesn't matter, as long as the (scale) cylinder outline is big enough to take the bore you decide.
I think ports and valve travel will nearly always be bigger than scale, so again, it's a good idea to check the valve gear dimensions of similarly sized published designs. You may have to work back from the dimensions to design your valve gear, but at least (as has been discussed in these pages recently) you will have all the design parameters (lap, lead, valve travel, etc.) to get reasonable answers.
As you rightly surmise, the boiler will need to be specific to the model - but you can use a lot of plagiarism here too. The boiler on my Stanier is Martin Evans' "Ashford" design, with a slightly longer firebox, and the tapered shape produced by layers of lagging on the parallel boiler barrel.
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weary
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Post by weary on Jul 8, 2020 18:37:28 GMT
Hello Jon,
To add to the comments above -> Your loco main-frames are going to be thicker than scale The axle-horns are liable to be thicker than scale too, The space required by the (internal) valve-gear will also almost certainly be more than scale dimensions. These will reduce the 'free' space between the frames affecting the capacity of your well-tank. There is also the issue of an axle-driven water-pump; if you want to fit one then the drive that will also reduce well-tank space - the pump ram etc., could be within the well-tank, thus hidden but slightly reducing capacity. Fitting an (emergency) hand-pump without it being too obvious, especially with an open cab, may be a challenge too - should you want to do-so. I see the original has 'oilers' fitted on each side of the smokebox. There will almost certainly be space for an oil pump immediately behind the front buffer-beam under the smokebox or somewhere under the cab floor, however these locations may be visible to a 'low-level viewer', and the drive may well, you guessed it, impinge on the free space between the frames.
Once you start drawing the frames, wheels, piston-rod axes, drive components, and valve-gear out you will spot where compromises between scale and overscale will need to be made.
It looks a great project and a characterful design!
Regards, Phil.
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mbrown
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Post by mbrown on Jul 8, 2020 19:24:57 GMT
I have built three models from drawings of the prototype and am now working on a fourth. Much depends on the quality of the drawing you have. You say it is a General Arrangement, but is it fully sectioned and showing all parts clearly, or is it basically an outline?
I built my Burma Mines loco from a highly detailed GA and most parts are to scale (1.25" : 1' which is not far off a 5"g standard gauge scale). I confess that I used a photocopier to blow up the drawing to scale size and then used the dimensions shown on the drawing to cross-check when measuring off (which is bad practice but sometimes unavoidable). For the valve gear, I designed it with a simulator programme, but it actually turned out almost exactly as the prototype - I had adopted "standard" 3.5"g cylinder dimensions, adapting some castings meant for Martin Evans's "Jubilee", and by chance the ports on that design were almost precisely to scale for the prototype, so the valve gear was very close to the drawing although I started from first principles. I had to make some other concessions, either because I didn't have enough detail to go on, or because my hands are too big to fix bolts in scale spaces. As you say, the internal parts of the boiler had to be designed from first principles, and some of the fittings were scaled up a wee bit for ease of operation, but, for example, all the pipe runs are as on the GA.
In contrast, my LYN was built from a Baldwin Erecting Diagram which shows some detail and dimensions but not many. For that loco, I adapted a lot of bits and pieces from other designs, often re-modelled to look like the original. So I used cylinders and valve gear from LBSC's "Virginia", and took the frame outline off the Erecting Diagram but made it in one piece with a fabricated smokebox saddle instead of the saddle being cast with the cylinders. I didn't have any details of the cab fittings so had to make them to resemble the original as far as I could see it from photos, cribbing things like Don Young's combined injector steam valves and clacks. Things like the regulator were from other designs, the plate work was to the dimensions on the drawing and details from photographic evidence and so on.
My Bagnall 0-4-2T was built from an outline drawing intended for 4 mm modellers so its internal parts are not much like the original although it looks the part because the main dimensions are to scale. It uses parts from other designs - "Netta" cylinders, "Purley Grange" valve gear (adapted for direct drive), and a boiler based on "Boxhill" but with a flat grate. I adapted other castings such as "Rob Roy" chimney, "Boxhill" dome and so on.
If you look at published designs, especially LBSC and Martin Evans, you see how standard designs and dimensions of parts recur again and again - the same standards can usually be worked into a design with a different outline.
Not sure if that helps, but there are several ways to approach this task But congratulations for choosing an interesting and probably unique prototype! There is immense satisfaction in building something that follows a long-lost design like that.
Malcolm
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Post by jcsteam on Jul 8, 2020 19:38:23 GMT
Hi Phil,
Everything that you say doesn't bode well for the scaled down plan, been a well tank there is a tank under the smokebox and behind the buffer beam at the front, this pretty much fills the remaining space at the front end, so lubricator will have to be thought about. Also there is a second tank that fits around the valve gear, between the frames, so axle pump is ruled out if it's to be kept scale or as you say build one into the tank. Although before the rebuild/reboiler it did have crosshead pumps, feeding two clacks on the side of the boiler. With the two cross head pumps feeding the boiler on a common clack, and an injector to a tank on the riding trolley this would be the two feeds for the boiler. A hand pump could also be fitted to the riding trolley however this is now 3-4 clacks needed, and only two places to put them as drawn. I know putting clacks on the backhead is frowned upon as this can sometimes mean temperamental clacks not functioning correctly due to heat.
Water feed to the boiler seems to be one thing to think about. Also a rather important one!
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Post by Deleted on Jul 8, 2020 19:50:14 GMT
Hi Jon
Re questions about boiler layout, have a chat with Paul Tompkins (Southern Boiler Works), I'm sure that he could make some workable suggestions and you'd have the added insurance that whatever he suggests will pass for the boiler test.
Pete
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miken
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Post by miken on Jul 8, 2020 20:03:17 GMT
Do you really want 2 cross head feed pumps? You could just fit 2 injectors fed from your riding trolley to your 2 back head clacks. Then if you feel you want a hand pump as well you can tee into the side of one of your injector delivery pipes with a second in-line clack valve. Ive done that a couple of times although now days I dont bother with fitting hand pumps, just use injectors and fill my cold empty boiler with a hose pipe pushed onto the blowdown valve. Also, when building from works drawings, it is difficult not to finish up with a slightly over width model. Especially when you have outside valve gear.
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Post by jcsteam on Jul 8, 2020 20:03:35 GMT
. You say it is a General Arrangement, but is it fully sectioned and showing all parts clearly, or is it basically an outline? Malcolm Hi Malcolm, Yes the plans I have found, show a side elevation, a sectioned side elevation, a sectioned top view, plus six sectioned end views through the engine, although I need spend time figuring out which drawing shows which section on the loco. Regards Jon
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Post by jcsteam on Jul 8, 2020 20:10:34 GMT
Do you really want 2 cross head feed pumps? Not really a case of want, as it's more to make and get working correctly lol. However the full size has them fitted so if I'm making a scale engine then they need to be there even if they are dummies, but they may as well be there serving a purpose. Regards Jon
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Post by jcsteam on Jul 8, 2020 20:23:48 GMT
Hi Pete,
I've given the boiler a little thought, (Not much I'll admit), but with the dome on top of the outer wrapper, above the Firebox, (need to upload those photos so you can see what im working with), as the original boilers were, then caution and calculations need doing to allow the stays on top of the inner Firebox, that will strengthen it enough. I'm actually thinking of traction engine design here with two or possibly three pieces of paired angled copper rivetted together to form a brace. Though I'll get the chassis drawn up first before I go too deep into the boiler.
Jon
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mbrown
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Post by mbrown on Jul 8, 2020 20:24:59 GMT
A well tank certainly does add complications..... that's one thing that put me off modelling a Darjeeling "B" Class. But you can either bite the bullet and go for the well tank, and think through how to make the steam and exhaust connections around it etc, or leave it out (or make a dummy) and go for a water tank on your driving truck. I reckon much of the pleasure of modelling from drawings of the original is seeking how close you can get, and working out what compromises are inevitable or desirable - a matter of pitting your wits against the challenge.
The problem with clacks on the backhead are mainly about feeding lots of cold water in around the firebox. A clack for a handpump, which may only be used for emergencies or to fill the boiler from cold, wouldn't cause problems there.
Malcolm
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Post by jcsteam on Jul 8, 2020 20:34:36 GMT
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Post by jcsteam on Jul 8, 2020 21:11:37 GMT
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mbrown
Elder Statesman
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Post by mbrown on Jul 9, 2020 9:04:38 GMT
Those are very helpful drawings.
Two things stand out - the valve gear is going to be very inaccessible if you include the well tank, and it appears the boiler is fixed to the motion brackets (which was common practice in the mid 19th Century - the two Fletcher Jennings locos on the Talyllyn were originally like that). The idea was that the boiler gave structural rigidity to the frame. That is not a good idea with a copper boiler on a model so you'd need to devise a more usual way of holding the boiler down (expansion brackets beside the firebox) and would have to ensure that the frame was rigid enough without a mid-point attachment to the boiler. Beefing up the frame thickness a bit would help, but would then put more restriction on space for the valve gear.
So I think you will have to work out some compromises, but with drawings like that, you can still make it pretty close to scale, I should think, even if you have a dummy well tank or leave it out entirely.
Good luck
Malcolm
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Post by jcsteam on Jul 9, 2020 9:47:40 GMT
I was thinking on the dummy well tank, have a removable cover to allow access for oiling the valve gear then replace the cover all looks as it should, There would possibly be space for a cylinder oil tank too, connected to the valve rocker on a shortened arm to limit the travel. it is possible but i'm not decided yet as removal of the tanks will leave very little on board water space available. I think practicality will rule in this area.
With regards the boiler, i wont be fastening it to the motion bracket but at the smoke box and rear as you say sliding on the frames, using two pieces of angle and a clip which i have seen in another design, (it escapes me which one though). The motion bracket will just be larger radius, so that it sits one mill further out from the copper barrel. Once under the insulation and cladding, it'll not be noticed, and without the inclusion of the angle to fix to the boiler. Frames will be 1/8" as that seems to be a pretty standard thickness through all the designs i have seen in 5". There is a lot of cross braces on this frame so i wouldn't think rigidity will be an issue. Hard part for me is figuring out what might need to come apart for future maintenance and what can be riveted on the frame and what needs to be secured with screws for removal.
Regards
Jon
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don9f
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Post by don9f on Jul 9, 2020 19:04:10 GMT
Full size locos with backhead mounted injectors/clacks usually deliver the water into the boiler through internal pipes, taking it to the front end, reducing the problem of shock to the much hotter firebox. I would like to fit scale backhead fittings to my Austin 7 project and am currently thinking about how to achieve this.
Cheers Don
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mbrown
Elder Statesman
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Post by mbrown on Jul 9, 2020 19:08:33 GMT
That sounds ,like very good thinking. Many tank locos have an almost negligible amount of water space when translated into model size.
Your solution regarding the boiler and motion plate is exactly what was done to the Talyllyn locos when they were rebuilt for the first time in the 1950s. Unfortunately the firm who did the job (at very low cost) didn't realise the importance of the motion brackets/boiler connection in giving rigidity to the whole assembly, so they suffered from frame flexing, loose cylinders and leaking smokeboxes for years until rebuilt a second time in the 1970s. You won't have that problem with the well-stayed frames in this design.
If you have rivetted joints in and around the frames, but may need to take them apart later, you could use round head screws with no slots. I am doing that on the tender for 99 3462, and an 8 BA slotless screw head (from EKP Supplies) is almost indistinguishable from a 2 mm rivet head.
Malcolm
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