We now come to the most important phase of construction, erecting the frames and buffer beams in order to provide a stable, accurately assembled platform for the rest of the locomotive. This is a very important task and one can do no better than to quote from the book titledBritish Locomotiveswritten by C J Bowen Cooke, published in 1894. Chapter 9 is called "In The Erecting-shop" and reads as follows: To get the cylinders, frames and horn blocks perfectly square is one of the chief points aimed at in building an engine. If not accurately done at this stage, the error can never be properly remedied afterwards. It does sometimes happen that through carelessness or inaccurate measurement, an engine is built slightly on the skew, and if such be the case troubles will always ensue so long as it runs. After the frames, cylinders, spectacle plates, foot-plate and horn blocks are all bolted together, the accuracy of the work is tested by diagonal, transverse and longitudinal measurements. This is very important, it being absolutely necessary that the centre line of the cylinders should be perfectly parallel with the frames and the faces of the horn blocks square with them. I will not bore you with the finer detail of the techniques actually used, as they are not really practicable in Gauge 3. However, the point is well made - a wonky set of frames at this stage leads to a wonky running engine that you will have difficulty correcting. Riveting the horns to the frames - 3 hours Before the frames are actually assembled, the horns can be permanently attached to the frame plates, although if you wish these can be attached after the frames are assembled. The task of riveting the horns to the frames must be the most boring, tiresome and repetitive task that you will have to undertake and complete. Some folk might say "who needs horns on a Gauge 3 scenic type locomotive"? I suppose that this is a fair point if the frame material is say 3 mm thick, however with thinner material it is necessary to add strength to the frames particularly just above the axle box cut outs, and provide bearing surface for the axle boxes. The picture below is of one horn riveted to a frame plate, prior to milling the bearing surfaces to the final dimension. The picture also illustrates that the horn must be placed in such a way as to leave a gap of 3/16 inch below the horn, in order to allow for fitting the horn-keeps made of ¼ inch brass angle at a later stage. Yes, I know the horn keep angle is upside down and the hole is in the wrong place!
The process of attaching the horns is to first of all drill 6 holes in each horn, that makes 24 holes in all, with a drill slightly smaller than the final drill size. Some designs recommend using 1/16 inch rivets, but this generally applies to horns of greater depth e.g. 40 mm. Remove the burs and place a horn upon the inside of a frame held in place with a small G cramp.Tip- Makeabsolutelycertain that you place each horn in the correct place, it cannot be moved after riveting. When the horn is in the right place, checked with a set square, and clamped up tight, drill the first hole through with the same drill size used to drill the horns. Remove the horn from the frame and open out the holes for the 3/32 rivet by using a 92 thou. drill. I drill each item separately as the drill can easily break at this stage when the horn and frame are held together. Clamp up again making sure that everything is square using a small set square and drill the second hole diagonally opposite and drill through as above, later opening out to fit the 3/32 rivet - seen in the picture below with the frame supported on a Nippy vice. Continue until all holes are drilled popping rivets in loose as you drill the holes. Countersink the outside of the holes, just two turns of the hand drill will suffice and bang home the rivets.
Milling the axle holes slots - 1 hour. When all the horns are riveted up, clean up the outer face of the frames with a file to remove the rivet surplus, and temporarily reassemble with 3 copper rivets just slipped into the holes to keep the frames aligned, but not of course hammered over. File off as much of the surplus from the frames and horn material holding by holding the frames in the bench vice and using a sharp flat file. This will make the milling task much easier. The advantage of retaining the flat reference edge to the top of the frame is that this facilitates achieving perfectly parallel axle box sliding faces as you will now see. Position the frames vertically in the mill vice as horizontal as possible. Raise up the frames from the mill table by means of a piece of scrap material at each end such that the frame top is parallel to the mill table. I used two pieces of scrap steel of the correct height such that the frames are at a right angle to the cutting edge of the mill tool. I find that trying to mill both sides of the axle box hole in one set up, the left side and then the right leads to the cutting tool snatching or biting into the material when the mill is cutting the right hand face. Instead, and to avoid this, gently mill the left side, turn the frame around and mill the right hand side. in other words four setting up tasks are needed. The picture below shows just the left side being milled. Again the G cramp comes into play by holding the frames tight together at the top and prevents snatching. Only mill one thou. at a time as steel is very hard. With care try to get the bottoms of the holes the same distance from the Top Reference edge, in the case of James this is circa 920 thou, using the micrometer to check.
Erecting the frames - 2 hours The frames are erected by drilling through the pilot hole at each end of both frames into the respective buffer beams and then tapping a 7 BA hole in the buffer beams. This task has a number of steps. Above all however, you need to be in a good mood, take great care with each task and find a good piece of plate glass to act as a flat reference surface for the final assembly. First, clamp the front beam in the vice and push home the left hand frame in the slot cut into the buffer beam. Carefully position the frame correctly on the buffer beam, by means of the footplate reference line scored onto the frame, in the case of James this is 11 mm below the Top Reference edge. When all is square tighten up, with a G clamp and spot through the hole into the buffer beam angle as shown in the left hand picture below. Remove from the bench vice and transfer the buffer beam to a Nippy vice and holding the beam vertically, drill through the hole with a say a 70 thou drill as shown in the right hand picture.
Open out the hole to 81 thou. and get ready for tapping. Tapping holes in mild steel is quite frankly nerve racking, because it is ever so easy to snap the tap if you get distracted, lose your nerve, lose concentration, bend the tap out of vertical or try to cut too much at one go. So how do you do it? Firstly use a new sharp, high speed steel taper tap. The way to success is take it easy, use lubricating oil such as 3-in-1 and only turn the tap a quarter of a turn at a time and back off each time to remove the cut material from the tap. Keep going gently and it helps to change to a middle tap every now and again rather than use the taper tap all the time. In order to keep the tap vertical to the material at the start of this task, one can use a brass dolly which looks like a small top hat drilled through just a shade larger than the tapped hole. See picture below - the finger is an optional extra in order to hold the top hat in place.
Next, repeat this process for both ends of the rear buffer beam by drilling and tapping into the brass part of the beam. Again, check carefully that the frame is positioned exactly in the right place such that the top of the frame edge is flush with the top of the buffer beam. One approach if you are not totally confident is to measure the frame depth with a micrometer and then measure again when the frame is in position with the buffer beam. If the dimensions are the same then you should be OK. With James the frame depth at the end of the frames is 760 thou. and after placed in position into the buffer beam slot, when 760 thou. was achieved we knew we were right mate! See picture below.
Prior to assembly it helps a lot to make the frame stretcher from steel round stock, or if you prefer use brass. James uses a 5/16 diameter steel stretcher 50 mm long and tapped 8 BA at each end. Time to make this was 30 minutes.
Final assembly Placing the frame upside down with the Frame Reference surface resting on the sheet of plate glass, you can now adjust the frames in order to drill the last remaining hole in the front buffer beam. A piece of plate glass from a bathroom cabinet was used and the G clamp yet again holding the buffer beam and frame plate. Adjust the position of the frame and buffer beam carefully until you reach a point whereby the assembly does not rock. This may take time to achieve. Spot through the hole with a70 thou. drill. Take the buffer beam off and drill through with an 81 thou. Drill as shown above and tap the final hole 7 BA. Finally screw up all four 7 BA screws and hey presto you have the assembled frames. Do not remove the surplus material at this stage as this task is best done when you are completely happy with a balanced non rocking rolling under frame. Total time to attach the horns and erect the frames is 6 hours 30 minutes.
Next - Part 7 will be as special look at engines from Scotland.