last updated
01/11/2006
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Please note: we have done our best to answer the frequently asked questions below as accurately as possible but they are only our opinions and the Society cannot be held in anyway responsible for any loss or damage or other consequences of any kind arising out of any action taken by anyone as a result at all, ever, arising from this advice! |
Table of Contents
- What gauge do you recommend for a newcomer to model engineering who wants to build a steam loco?
- I have no engineering knowledge. How can I possibly make a live steam model?
- Do I have to have my locomotive's or traction engine's boiler tested?
- What sort of machinery do I need for model engineering?
- I've seen a lathe for sale which is described as having a 7" swing and BGSC. What does all this mean?
- I've often been confused by the British Railways 'Lion' emblem which appeared on the tender sides and tank sides of locos. Should it face forwards on both sides?
- Often on construction drawings or in articles I come across the term `fit`, usually something like `push fit`, 'running fit' or `press fit`. What does this mean?
- What sort of coal do you burn in your locomotives?
- What is a tool and cutter grinder and do I need one?
- Why is the wheel 'back to back' dimension on locos and rolling stock so important?
- Do you recommend buying a kit for a live steam model?
- What is laser cutting and how is it used in model engineering?
What gauge do you recommend for a newcomer to model engineering who wants to build a steam loco?
There are really three main gauges to choose from (in UK anyway) for passenger hauling, i.e. 3½", 5" and 7¼" gauge. Some model engineers build in 2½" gauge, which can haul a driver, whilst below that size we are talking large scale garden railway models which are often radio controlled. We have tracks to suit all of these!
The first criterion in choosing which gauge to build in is probably to ask yourself what you intend to do with the loco when you've built it: will it be for static display or is it to be steamed? How will you transport it around? Do you want to pull passengers? Where will you run? If you want to run on an elevated track then the two smaller gauges (3½" & 5") are ideal. If you want to run on a ground level track then the two larger gauges (5" & 7¼") are better, with 7¼" being the more stable, although some model engineers do run (rather precariously) on ground level 3½" gauge track; and 5" gauge is very popular with those who also build scale model wagons and carriages and like to run what is virtually a ground level model steam railway - there is actually a thriving national society doing just that.
The next criterion is the size of the loco. This will be governed by the weight you feel you can handle and the machining capacity of your workshop equipment and whether you can carry the loco in your car or will need a trailer. A 'small' 7¼" gauge miniature loco can actually be smaller than a 'large' 3½" gauge loco - it depends on whether the prototype is standard gauge or narrow gauge, a four wheeled tank engine or a mainline pacific with an eight wheeled tender.
If you have a particular prototype in your mind then the availability of suitable drawings and castings from the trade suppliers may force you to go for a certain gauge, unless you feel capable of scaling the drawings up (or down) and manufacturing all the patterns for the castings yourself.
The main thing to remember is that you will be beginning a project that takes the average model engineer three to five years to complete, so it's important you make the right choice at the outset.
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I have no engineering knowledge. How can I possibly make a live steam model?
With the virtual demise of engineering as a career in the UK perhaps the majority of model engineers today have little or no engineering knowledge so you won't be lonesome. By far the best idea is to join your local model engineering society where there will be plenty of experts to offer advice and guidance. Alternatively you can buy instruction books for certain models. Another idea is to follow a construction series in one of the model engineering magazines - but beware of those designs that have not been proved by building a working example!!!!
The late lamented LBSC, Lillian 'Curly' Lawrence, the father of the hobby, used to write his 'words and music' for beginners in Model Engineer magazine. Although Martin Evans carried on after LBSC, his place has probably been taken today by Kozo Hiraoka, a Japanese model engineer who writes for Live Steam magazine (USA) and has produced several books, e.g. 'Building the Shay'. Even if you don't build his designs the methods and tips he gives in his articles and books are priceless. And his designs are tried and tested before publication.
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Do I have to have my locomotive's or traction engine's boiler tested?
Not if you don't intend to steam it. If you do intend steaming it, but in private a test is still not necessary, but is advisable. If you intend to steam it in public or at a club you must have a boiler test certificate. These are either issued by the manufacturer of the boiler if it is commercially made for you, or by a society's authorised boiler testers when they have carried out an initial test to twice maximum working pressure plus a steam test to ensure the safety valves can cope with as much steam as the boiler can produce with the blower on full. Much more stringent conditions apply to the construction and testing of steel boilers (e.g. all the plate work and welding has to be certificated) than those made from silver soldered copper by amateur model engineers. Professionally constructed boilers above a certain size now have to be CE marked. If in doubt ask before you buy or start to make a boiler!
Miniature traction engines or other miniature vehicles used anywhere that the public are present must have Road Traffic Act insurance (like a car).
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What sort of machinery do I need for model engineering?
Unless building something from a kit, a drilling machine and a lathe are essential and the basic minimum pieces of machinery. Countless miniature steam locos, traction engines and stationery engines have been built using nothing more than a 3½" centre lathe which has a slotted cross-slide on which you can mount a vertical slide, enabling light milling operations.
Following the acquisition of a lathe you should probably get a bench grinder for sharpening your tools and then if your budget and space allows, a vertical milling machine.
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I've seen a lathe for sale which is described as having a 7" swing and BGSC. What does all this mean?
Lathes are classified by the distance between the bed and the centre line of the headstock, which of course will be the same as the distance between the centre of the chuck which holds the work and the lathe bed. If it is 3½" then the lathe can at maximum accommodate a loco wheel which is 7" in diameter, in other words it has a 7" swing. Some lathes have a gap directly below the chuck so they can swing larger wheels. Another dimension often quoted for lathes is 'between centres', e.g. '24" between centres'. This dimension is the maximum length of a shaft (e.g. an axle) which can be fitted between a centre in the headstock and a centre in the tailstock.
BGSC is an acronym for 'back geared screw cutting'. It means the lathe is equipped with a set of low gear ratios and can also be used for screwcutting. Whilst on the question of gears, a lathe with a proper gearbox will prove to be far less frustrating than one on which you have to take the gears apart and re-assemble them every time you want a different ratio. Imagine doing that while you were driving a car!
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I've often been confused by the British Railways 'Lion' emblem which appeared on the tender sides and tank sides of locos. Should it face forwards on both sides?
The answer is 'It depends when you were looking!'. Has he lost his ball bearings, I hear you say. No, here's the story:-
In 1956 Britannia class no. 70016 'ARIEL' was decorated with a new style BR emblem - a lion striding over a loco wheel probably describes it best. For aesthetic reasons, one presumes, the lions were made to face forwards, in other words the lion on the left hand side of the tender faced left like the one in the photo and the one on the right, faced to the right. Simple. But the College of Heralds, who govern the use of heraldic devices, got wind of all this malarkey and objected in 1959. The end result was that the design had to be changed so both lions faced the correct way, i.e. to the left. So from then on the lion on the left hand side of the loco faced forwards whilst the lion on the right hand side of the loco faced backwards. Careful study of photos and the date is obviously needed before you settle on the correct style for your locomotive or tender.
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Often on construction drawings or in articles I come across the term `fit`, usually something like `push fit`, 'running fit' or `press fit`. What does this mean?
Well the descriptions speak for themselves - a running fit will enable a pulley to rotate freely on a shaft, for example. A press fit needs considerable force, at least a vice but usually some sort of hydraulic or mechanical press will be needed. A shrink fit means that you heat up the pulley or wheel to expand it, drop it onto the shaft and let it cool down, contracting tightly onto the shaft. There are also some special fits, such as for ball bearings. There are special tables giving the tolerances, that is how much clearance or interference you need, to achieve these fits if the draughtsman hasn't specified it.
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What sort of coal do you burn in your locomotives?
We use steam coal and also ordinary anthracite which is sold by coal merchants for use in domestic boilers - it makes less smoke, less clinker and is very hot. Having said that all coal can be very variable in quality, depending on where it was mined, and some coals suits some locos whilst others do not! So you will see a variety in use. Welsh steam coal, which some still prefer, may still available. Coal is sold in various sizes, e.g. 'beans', 'stovesse', 'small nuts', 'cobbles' - to suit the size of firehole door. Whatever coal is being used it is imperative to keep raking the fire and lifting out any clinker which forms like a pancake on the firebars when the loco is working hard, stopping the air being drawn through the fire and drastically reducing the locomotive's efficiency.
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What is a tool and cutter grinder, and do I need one?
One item of workshop equipment usually considered a luxury and often not acquired by model engineers until their workshop is thought to be almost completely equipped, is a tool and cutter grinder. Most model engineers make manage with a bench grinder, using the offhand method or at best one of the several types of drill grinding jigs available. Milling cutters are discarded once they become blunt. Like so many other pieces of equipment, once a tool and cutter grinder is acquired you wonder how you ever managed without it.
With a tool and cutter grinder you can not only sharpen drills, including the four-facet method advocated by the late Dennis Chaddock, but also milling cutters, taps, reamers and even dies. Lathe tools can be accurately ground without the concave surfaces produced by bench grinders. Morse taper shanks can be refurbished and cylindrical grinding of model engineering parts undertaken. Some machines, like the 'Stent', are able to function as surface grinders too!
The machines consist of a motorised adjustable wheelhead which can accommodate a variety of grinding wheels. A typical 'standard' wheel recommended by Prof. Chaddock is a 4" diameter cup wheel of medium hardness grade, 60-80 grit size. Grinding is done on the face of the wheel, not the periphery. Wheels are mounted on quick change mandrels. A range of special attachments allow grinding operations to be carried out on the tool or cutter to be sharpened. These can vary from simple tool holders, through some capable of being indexed for milling cutters or slitting saws, to motorised devices for cylindrical grinding.
So what is available? Well, if you can afford it you can buy an industrial machine like a Clarkson which will set you back big bucks. Alternatively you can buy designs and castings from suppliers in the model engineering trade and build your own, which provides that extra degree of satisfaction when you come to use it. If you are lucky enough to find one you could buy a kit one ready-built - but check out the quality of workmanship.
Basically there are three designs on the UK market aimed at the model engineer: the Quorn and the Kennet (both marketed by Model Engineering Services) and the Stent (marketed by Blackgates). Undoubtedly the Quorn, designed by Dennis Chaddock, is the most sophisticated whilst the Kennet is the simplest. A book on building and using the Quorn is available from TEE publishing. The Stent, in addition to its other capabilities, has a long tee slotted table which allows it to be used as a small surface grinder.
Useful Addresses for drawings and suppliers of kits or ready-made tool and cutter grinders:
Model Engineering Services, Pipworth Farm, Pipworth Lane, Eckington, Sheffield S31 9EV
Blackgates Engineering, 209 Wakefield Rd., Drighlington, Bradford
TEE Publishing, Regent Street, Hinckley, Leics. LE10 0BB
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Why is the wheel 'back to back' dimension so important?
Back to back is the measurement between the backs of wheels fitted to axles on locos or rolling stock. It is a critical dimension for successfully negotiating pointwork - if you are going to run on pointwork it doesn't matter at all!
On pointwork the wheels are prevented from riding over the gap at the crossing nose or vee (sometimes called the frog) by the checkrail, against which the back of the wheel opposite to the crossing rides. Checkrails are also used on tight curves. If the back to back is too small the wheels will ride up the check rails or even jam tight and derail, if the back to back is too large, you may well derail.
The 5" Ground level Society, the 7¼" Gauge Society, and the I.B.L.S. in the USA, publish wheel and track dimensions, including back to back measurements.
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Do you recommend buying a kit for a live steam model?
In recent years some very good kits have been produced in most gauges. The best place to check these out is at one of the annual model engineering exhibitions or look at adverts in the model engineering magazines such as Model Engineer or Engineering In Miniature..
Buying a kit can be a good way of obtaining a working live steam model or electric powered 'diesel', particularly if you don't have a fully equipped workshop or lack engineering skills. The cost is reasonable when compared to buying a lathe and all the other machinery needed. However, even kits described as 'only needing a screwdriver etc' may still need a lot or work! If you do go for a kit it is still worthwhile being a society member - then you have someone to test the boiler, but more importantly, to turn to for advice if you get stuck. And you will have a track to run it on!
The Sheffield Society has hosted several rallies where around 20 Polly Models' completed 5" gauge kit locos have run very successfully on our railway - N.B. we have no commercial connection with this company.
What is laser cutting and how is it used in model engineering?
As its name implies, this is the cutting of metal (or wood or card or plastic) using a laser beam. Very accurate parts can be cutout with hole spacings for rivets or bolts, cutouts for loco frames and so on. This makes construction of, eg a loco cab, very easy, almost like a kit. The laser cutter needs a computer file (called a dxf file) which is created by a drawing using a CAD programme. So if you want your own laser cut parts you will first have to install a CAD programme (e.g. AutoCAD) on your computer and learn to draw with it! Many model engineers now combine this method of producing parts with the traditional methods.
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© S&DSMEE Ltd
Revised: November 01, 2006