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| Tina :- Engine and Boiler Build |
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| andyf:
You're right about that disc, Peter. Looking at the photo in your first post, it looks a bit utilitarian - more suited to a toy than a model. It shouldn't be too difficult to come up with something more interesting; maybe a crank arm with a counterweight to "balance" the big end would look a bit more interesting? Andy |
| Rob.Wilson:
Hi Peter what about this sort of shape for the disc Just a thought Rob |
| andyf:
Rob, you've drawn just what I was ineffectively trying to describe! Andy |
| loco:
Having just joined the group allow me to introduce myself. My name is Pete Smith and I write as the proverbial horses mouth as I am the poor soul who makes these boilers for GLR and the count is over 40 complete boilers and hundreds of flange plates so I think that I know a thing or two. I cannot write everything is one session so will treat you to a number of episodes over a period of the next few weeks covering the comments made earlier by previous members. If there is anything you need to know then tell me and I will sort your problems. The next section is the preface that you will find in the 'words and music' supplied by GLR with the boiler kits. See his website for the various kits available. The drawings for the mill engine vertical boiler were first published in 1950s. The construction series was written by Stan Bray and appeared in the Model Engineer from March 1997. Since first publication there have been various changes to the boiler codes with reference to construction and testing. Builders may also find that copper sheet has been provided in Metric thickness instead of imperial. This makes no difference whatsoever. It used to be accepted practice to drill and tap the boiler shell to allow for the fitting of the firehole door and other items. This only allows about 2 or 3 threads in the soft copper and although is was possible to initially fit and make steamtight removal usually stripped the threads. This is no longer accepted practice and ALL screwed fittings to a boiler MUST be made using gunmetal or bronze bushes silver soldered in place. On NO account use brass. This gives you a safe fixing with many more threads and they can be made blind ( not drilled / tapped through ) so that even if the screw is removed no steam will emit. The weighted safety valve shown in the drawings should be replaced by a spring loaded version safer and tamperproof. It is shown for historical reasons. Irresponsible workers used to add weights to increase boiler pressure with the expected results plus an explosion as an extra. Ready flanged plates are available from GLR formed to shape and correctly spot drilled only needing to be skimmed in the lathe to fit as detailed in the series. The boiler may be fired by gas or coal. The use of methylated spirit burners these days is frowned upon by the safety people as it burns with a clear flame and is uncontrollable and easily spilt. The solid pellets for use in Mamod type engines can be used but can be expensive and leave a nasty residue. Over the last few years there has become available excellent ceramic burners and control valves to fit disposable gas canisters and other cylinders. Clean, efficient and safe, especially where the children are around. Should you decide to go for gas then there is no need for the firehole, blower or grate as the burner is designed to fit inside the boiler with a flexible pipe to a remote gas supply passing through one of the 3 slots. The air for combustion comes from underneath. This does save a great deal of work and simplifies construction. You can of course make a false door and fit to the cladding afterwards to maintain the appearance. For those of you who prefer the smell of steam and intend to use coal then the construction of the firehole ring, creating the curve and perhaps the oval and still get a good fit can be problematic and does little for your confidence. There is an easier way. Instead of using the copper ring supplied use a suitable length of 1 1/8th diameter by 16 gauge thick walled copper tube. The hole is made to the tube diameter by any suitable means. Do not use a hole saw of the same diameter as they always cut oversize. It does not matter how much sticks out on the fire side and it can be left square. Using a triangular file make a few nicks in the hole to allow full penetration of the silver solder. When assembling, file the tube end to allow it to fit. Again use the triangular file, assemble with the foundation ring and final soldering to secure. If your hole is slightly oversize then the tube should be annealed and the ends expanded to fill the gap, The outside can be finished afterwards. This will not affect the strength of the boiler but certainly allows easier construction. If you use blind bushes to hold the firehole door in place consider how to get the holes to line up. They are radial to the boiler. I suggest cladding that part of the boiler on a temporary basis, placing the door in position and transferring the holes through the cladding just to mark the boiler. They can then be drilled and the blind bushes soldered into place at the same time as the ring is secured. Perfect line up afterwards. There is another clever little way lateral thinking. Make the firebox door in the usual way but silver solder onto it a length of steel tube approx 1 diameter which is a push fit into the hole. The curved shape will align the door and it can be secured with small woodscrews. Much easier. A few moments to consider the fine stationary engine you have just built. In real life such engines rotated at 30 to 100rpm. The bearings and those on your model are designed for slow speed. Running with the motion and flywheel a blur may be exhilarating but you will soon be facing a rebuild!!!! Most of these engines will tick over at a realistic speed on 20 plus psi. I suggest setting the safety valve to 40 psi and see how it goes. The nominal working pressure for this boiler is 80 psi but its initial test should be to 160 psi. When testing your boiler do remove the gauge glasses and plug the holes as they may fail at test pressures. If you live in a hard water area look in your kettle then the small area between the firebox and barrel will soon get clogged with scale. Visit your local chemist and get some citric acid crystals used for cooking mix up a warm solution and fill the boiler. It will bubble away merrily converting the chalk to carbon dioxide. Flush out thoroughly afterwards. Happy steaming. The next exiting episode will cover stays, boiler testing and fittings. |
| klank:
Andy, Rob, Benni - thanks again for encoragement - and suggestions. Peter - thanks for taking the time and trouble to write. Rob, the superb (is it a cad rendering?) sketch is what I too was thinking of at first - but got sidetracked into picturing "locomotive driving wheel centres - with fluting". Originally I had a mental picture of a "nodding donkey" kind of pump crankshaft with counterbalance weights. Tomorrow, I'll try and draw it long hand - (I am not clever enough to use a cad programme!!) and stick it on the disc. I like your rendition - it "feels" right - and looks quite simple to make from chopping up the disc. Well, now we've got chapter and verse straight from the horses mouth on the boiler - thanks Peter. Looking forward to your next bulletin. I was afraid the Copyright Police might object if I posted what is written in the up-dated GLR boiler build handbook - it does put things in a better perspective with regards to current good practice and regulation. Best wishes Peter |
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