SAFETY REMINDER : This stage involves the use of machine tools and precautions should be taken against risks involved in using tools, by wearing appropriate safety equipment such as safety gloves, eye protection goggles and dust masks. When using lathes and other rotating equipment do not wear loose fitting garments (e.g. long sleeves) or any item around the neck which may become entangled in the machines with serious or fatal consequences.
This project is NOT SUITABLE for CHILDREN.
Now that the design work has been completed it is time to get started on building the engine. We are not following an established design so unforeseen issues may crop up from time to time, after all, your engine may well be unique. The timings given for each stage are actual to within the nearest 15 minutes, no cheating. The G.A. drawings for James and Sam show that the outline of the frames are quite different so a common frame is not really possible. The overall objective is to create a model that reflects the dimensions of the prototype exactly, other than where it is necessary to adopt a dodge to overcome some constructional difficulty. The frames form the foundation for the whole engine and need to be made with care. You must choose if you want to make frames that reflect the prototypes which have humps above the driving wheels or are make them simpler with just have a dead flat top. The frames for 2 ½ inch gauge locomotives made by Basset-Lowke used 1/16 inch steel plate. Today we can use black steel plate with a thickness of 3/32 inch or 2 mm for a small tank engine. With the demise of the local friendly steel merchant it is often times necessary to purchase an entire sheet, a fate which befell yours truly, however the saving grace was that the sheet was slit into 2 inch wide lengths - enough to build engines until one attains the age of 100! The frames for James were the subject of much cogitation and raised issues that were of "no great little insignificance" - to quote Queen Victoria. An issue arose concerning the bogie. Most prototypes had small 3 foot diameter wheels that were able to move under the shaped cavities in the frames, facilitating movement through tight curves. Three engines had large diameter wheels - the M7, H class and James. The G.A drawing for the Drummond M7 reveals that the frames are bent inwards by 3 inches, presumably to allow the bogie more lateral movement. The cross section drawing for James from the NRM is for the earlier versions with small diameter wheels and does not show an inward bend. In the end it was decided to not put in the bend and see what happens on test. If clearance becomes a problem then a bend can be made in the frames later on.
Frame preparation - 2 hours 45 minutes Hopefully, water jet cut frames will be available for Sam but in order to get things moving, the frame for James are being made by the traditional metal bashing techniques. This is where the scale drawing that you have made comes into its own. Take care when transferring the dimensions from the drawing onto the frames to remember to take account of the material used for the buffer beams which are 3mm thick. In other words the frames will be 6 mm shorter than the scale drawing. To start, cut off two lengths of steel slightly longer than required and drill three holes in the right place to take 1/8 diameter copper or steel rivets which are needed to keep the plates tightly together when bashing out the final shape. Where is the right place? These holes need to be carefully placed at the front end, back end and circa mid point such that they keep the plates as flat as possible and just outside the finished frame profile. The picture below shows the position of theses rivets. Beware that frame steel does bend and can easily distort.
After riveting up, file one edge smooth as the Frame Top Reference edge, from which all measurement will be made. File one end square and blue the steel with marking fluid - <tip>do not spill this stuff on your trousers/shirt or the carpet, otherwise your wife may not speak to you for some time! Mark out the frames accurately with a scriber and odd leg calliper marking out the positions of the wheelbase, footplate, frame humps and frame bottom. The footplate top line for James is 11 mm lower than the Reference edge. Mount the frames in the vice and attack with vigour using a hack saw with a new blade as this will make the task much easier. This is where you get the feel of the material and you can also take out your frustration with politics, estate agents and anyone else you can think of. Tip- don't get too vigorous for too long otherwise regular trips to the chiropractor may be required which will exceed the cost of the tools and materials used! Clean up the frames to the marked out profile with the hack saw and files, taking care not to cut off too much - steel cannot easily be stuck back on and you do not want to spoil the frames. Drill three holes diameter 1/16 inch. One for the frame stretcher, and two for attaching the buffer beams, these are spaced 10 mm from each end and 10 mm below the Footplate line. The hole for the brake suspension bracket (BSB) was also drilled at this stage. Horn preparation - 1 hour 30 minutes The horns are made from 1/8 inch steel plate. Cut off four chunks from 1 inch or 1 ½ inch wide steel plate and trim them off to 32 mm by 25 mm, see drawing below. Then mark off the axle box space at 14 mm wide. Cut out the axle hole by making two vertical saw cuts, followed by two drill holes to enable you to cut out the chunk easily with a piercing saw (see below). File the horns to the final shape.
Buffer Beam preparation - 3 hours 45 minutes Two methods for making the buffer beams are used. The material for the beams is steel angle 3 mm by 20 mm by 20 mm which provides strength and rigidity. It is quite possible that one day your engine might leave the rails and hit the deck. If the beams are made of steel angle, little if any damage will result. If the beam is just a strip of steel plate it will probably bend on impact. The other advantage of using angle is that it provides a firm surface for attaching the footplates later on. The finished beams are illustrated below. The front beam has two small pieces of steel angle riveted to the front of the beam, whereas the rear beam uses a solid lump of brass screwed or riveted to the top of the angle During the work for the front beam the gremlins appeared. Somehow the length of beam after cutting the slots and riveting up, turned out at 98 mm long when it should have been 108 mm! This item was not going to be made again, so some head scratching - what to do? The earlier versions of Sam had a wooden buffer beam, aaah, problem solved, but no! Close inspection of the photographs reveal that all versions had lots of large rivets around the buffers. No way could 16 scale size rivets be attached to 1/8 thick steel angle. Inspiration took hold, why not make a 1/16 inch thick buffer beam with rivets attached and place this on the front of the beam, that was made too short - problem solved.
The beams are made by cutting off a length of steel angle,at the correct length, and marking out the position of the frame slots. The slots can be made with a hack saw and then enlarged with files but a quicker and more accurate method is to mount the angle on the top slide and use a slitting saw, as illustrated below. This cutting process only takes 2 or 3 minutes for each slot, although setting up the material on the lathe can take longer. The steel angle is held tightly in place with bits of scrap metal strip in the position where a turning tool is normally held. Use a slitting saw that is narrower than the required slot otherwise you are likely to end up with a slot that is much too wide.
The front beam is attached to the frames by short lengths of the same steel angle riveted to the beam with 3/32 inch rivets. It is important to ensure that these angles are attached to the beams as close as possible to a right angle.
The easiest approach for the front beam is to cut off a length of angle 40 mm long, drill the 3 mounting holesat each end. Holding the slotted buffer beam in the vice, jam a piece of frame steel in each slot and press the angle section up against the frame held in place with a small G clamp. Then drill through to the buffer beam itself, see below. After spotting the holes through into the buffer beam, or drilling right through using the bench drill, you can split the 40 mm length into two sections. If you perform this operation with each individual piece of angle, it is much more difficult to obtain a right angle when drilling the holes through to the buffer beam. Finally, rivet up with 6 x 3/32 inch steel rivets and clean up.
The rear beam is attached to the frames by means of a block of brass ½ inch thick, milled and filed down to 50 mm long and 16 mm wide. By finishing the end of the brass block in the mill or the lathe it is easy to achieve the required 90 degree angle referred to above. This block is screwed to the beam angle with two 6 BA screws. We now have the components needed for the frames, This lot took a total of 8 hours to make.
In Part 6 we visit The Erecting Shop followed in Part 7 by Wheels.