Welcome to
Steve's Britannia
1.1/2" scale Allchin Traction Engine
Bodywork and Chassis Parts
  1. Tender  
I have started by separating the tender from the horn plate assembly. The tender is made from brass and has been fully soldered so there will be little I can do on this. It appears to be watertight although steel screws have been used to secure the fairlead brackets to the rear and could be a weak point. The top one came off but the bottom one is nutted inside the tank.
The filler lid needs fitting and one of the hinges are missing. Anything removeable has been stripped off for refurbishment and the tender body given a blow-over in the shotblast cabinet.
The horn plate assembly has been dismantled and the various bearing blocks removed. The spectacle plate and front plate were riveted to the left-hand horn plate and these have been ground out. These will be refitted using 6BA screws to aid later dismantling. The stiffening plates between the strap and the main bearings needed some attention and the curved strengthening angle on the spectacle plate needed making and fitting.
All the parts have had a session in the shotblast cabinet in preparation for painting.
  2. Perch Bracket  
The perch bracket had been made but not completed. After cleaning up, I made the two corner pieces for holding the front cover in place and also the lamp brackets mounted either side. The front cover plate is a piece of 20 swg brass shaped to fit the underside of the smokebox. The smokebox also needed the mounting holes drilled and these were spotted through the perch bracket. The opportunity was also taken to paint the inside of the spud pan with black enamel.
  3. Main Bearings  
I'm not quite sure how Jack managed to get the holes on one of the main bearings so far offline but the tools available to him at the time were limited to a drilling machine and a Myford Super 7. This was modified by milling away the lower section, bolting in a piece of mild steel and then redrilling in the correct places. It can't be seen once the engine is assembled.
The holes in the lower stay were opened up and an additional temporary stay made to help keep things square during reassembly. Screws will replace the rivets used to fix the spectacle plate and backplate to the horns. Space is a bit restricted for getting the nuts on the main bearing bolts and I think this would have worked better with tapped holes in the bearing instead. Too late now, though.
  4. Chimney Base  
The chimney base had been turned but needed to be drilled and riveted to the smokebox and this was done on the mill with the rotary table. The smokebox also needed the chimney hole machined and both jobs were done at the same setup. After the chimney hole was drilled, the chimney was bolted to the smokebox through it and the mounting holes drilled.
The small blower tube hole needed making and this was very carefully made using a slot drill because of the steep angle at entry. I also drilled all the holes for the chimney rivets. Finally, the chimney cap was polished up, the rivets fitted, the chimney painted with high-temperature paint and the various parts assembled together.
  5. Winding Drum Guard  
The drawing suggests making the winding drum guard from brass but I have made mine from 1.1mm (45 thou) mild steel sheet as there is a ready supply of this material in the skip of a local tinbashing firm. However, first I needed to make a former from some 20mm MDF. This was cut from a redundant kitchen end panel. The outline of the guard was traced from the drawing, then transferred to the steel sheet, although the centres of the two circles were accurately marked and centre-popped. There is no hole for the third motion shaft but I need to mount a former behind here so will drill a 4mm hole and fill it later. The large inner ring will be cut away later.
The rim of the guard was cut from another piece of the material, 20mm wide by about 500mm long. Meanwhile, the former had a boss screwed to the back and was then turned to 6.660" diameter, allowing two lots of 45 thou for the material thickness. The body of the guard was roughly cut out with about 1/8" extra to get the basic shape, then scrwed to the former. The outside of the guard has approximately forty dummy rivets set around the perimeter and holes for these were drilled next, missing out the five positions that cross the 3rd motion shaft, seen as felt-tip marks on the plate.. Hughes suggests 1/32" dia rivets but I have opted to use 3/64" rivets instead. These were drilled at 9 degree intervals on a 6.562" dia PCD with a 1.2mm PCB drill.
The strip was formed freehand around various formers - the screwcutting gears came in handy here because of the wide range of diameters - and the ends trimmed to meet as a butt join at the bottom. The clamps were used to keep the top section in place whilst shaping. At this point, I removed the plate from the two MDF formers and placed both metal parts in the pickle to remove all the galvanising. Once these were clean, a joining piece was rivetted to the rim with four 1/16" steel rivets. The rim was then placed on the plate, aligned with the holes for the dummy rivets and clamped in place with four engineers clamps, ready for silver-soldering.
However, all did not go to plan! I didn't use enough clamps and I probably got the assembly a bit too hot. The outer plate lifted at the two sides and the whole thing distorted in just about every direction. I was able to get one section soldered by extra heating and using mole grips to close the gap but the other side didn't want to play. I left it all to cool and this is the dismal result. Luckily, I was able to get the centre pressed somewhere near flat by leaving it under the hydraulic press for an hour and I was able to close the gap on the side by using a hacksaw blade to saw away some of the silver solder, then pressing closed in the vice. This was then patched up with silver-bearing soft solder. Next job was to remove the waste from the centre and, for this, the formers were once more screwed to the assembly. This was then loaded onto the rotary table and a 1/8" dia slot drill used to cut a channel at the correct PCD.
The rest of the work was cleaning up the perimeter on the linisher and with sanding drums, drilling the dummy rivet holes around the third motion shaft cover, plus redrilling all the other holes, then setting the 3/64" diameter rivets into place. I've been very lucky in being able to recover this. You'd think that, by now, I would be able to solder two bits of tin can together without making such stupid errors but such is life. I will get the brackets made next, plug the small hole and then the guard can be primed and put away.
  6. Tank Filler Lugs  
Although I had primed the tank and it's fittings, the water filling pocket on the side of the tank needed to be repaired because two of the hinge lugs had broken off. These tiny little lugs had been soldered on but I didn't fancy trying to fix two new ones on so approached the job a little differently. Getting the fitting free from the tank was a made more difficult because the heads of the upper fixing screws had to be chiseled off and the pocket casting re-drilled and tapped. The other two lugs were broken off and a recess milled along the back of the pocket 1/8" in from the back and 1/16" down from the top. A strip of 1/8" x 5/16" brass was then soldered into this recess.
Next, the brass strip was milled away to leave the ends flush and the top 1/8" above the lid-seating face of the pocket. The bottom of the casting is at a slight angle so a thin packing strip is being used on the moving jaw of the vice. Setting up to hold the pocket for the next operations was more interesting as there are no two parallel faces to work with. I could have made a mounting plate and screwed the pocket to it but that would lead to it's own set of problems. Firstly, I mounted the pocket onto a 6" length of 1/2" x 3/16" ground flat stock with a very small home-made G-clamp. The pocket is resting on the fixed jaw and the brass packing lifts the support bar by 1/16".
Meanwhile, my pair of small angle plates were mounted on the mill table and trued up, leaving a small gap between them for the clamp to go through. The parallel fixed to them ensures they are in the same plane and can be used to clock them square. The pocket and it's mounting bar were then fixed to the angle plates with the top of the bar flush with the top of the angle plates which are, in turn, exactly equal height. Finally, because there is only a single clamp holding the pocket, a pair of bracing supports were added below the casting to prevet any sideways movement.
The lugs were formed by cutting away the surplus metal with a 1/8" dia end mill to a depth of 1/8". This leaves a 1/16" thick joining strip of the parent metal below the lugs which should be stronger than four flimsy lugs just soldered on. The tops were rounded with a file and sanding drums in the dremel. Final job on the pocket was to drill the hinge pin holes and were mounted in the vice as shown. The centre of each pair of lugs found by eye using a needle point in the chuck. At this size, it is easy enough to get within a couple of thou of dead centre although I am sure that many model engineers would throw their hands up in horror at such a practice. The holes are No.60 (1.02mm) and spotted with a No.1 centre drill. At 3/8" deep per pair, it would be pushing my luck to use PCB drills.
  7. Dummy Throat Plate  
The Allchin uses a dummy throat plate and this was made next from 1.1mm mild steel sheet. The first job was to make a former from 20mm MDF and, after getting the width correct, I used a router cutter on the mill to form the radius along the two edges. After bending, I set about drilling the rivet holes. Because this is a single-use former, I used it as a backing plate on the mill and drilled all the holes using the DRO for positioning and a PCB drill for a one-pass operation.
I also marked out the cutaway for the boiler barrel using a cheap-and-nasty woodworking tool to scribe the outline. The waste was removed using an Abrafile which cuts round corners.
The mudhole lids are quite a prominent feature on this engine and there was a pair of brass castings amongst the parts. The only work required on these was an 8BA tapped hole in the centre. An adjustable angle plate was set at forty-five degrees and the throatplate set up as shown. The centre of the bend was set by eye, as was the base of the throatplate. The hole was roughed out with a 3/16" slot drill and finished with a 5/16" one.
A pair of mudlid bridges were made from 1/4" square mild steel but longer than shown on the drawing. The centre was marked out and centre-popped, then they were loaded to the four-jaw chuck and trued up. Next they were faced off by 1/32" to leave a 7/32" diameter boss in the centre. An 8BA clearance hole was drilled through and a couple pf milling operatuions undertaken to relieve the underside.
A different setup was used to reduce the arms of the bridges, one side first, then flipping over and maching the other side. The rest was tedious handwork, filing and polishing to round off all the edges and form the finished shape. With the mudlids fixed to the throatplate, this is now ready to paint and fit to the engine.
  8. Smokebox Ring  
With the boiler mounted between the hornplates, attention was turned to the smokebox end. This required a spacer to be made for fitting between the smokebox and the barrel and was fabricated from a strip of copper, bent round a former and silver-soldered at the join. A line was scribed around the outside with the height gauge set at 3/8" and the ring pressed into the smokebox until level with the line. The 1/16" dia rivet holes were then transferred through. The cutaway in the ring is to clear the one of the chimney mounting screws. Once they were all drilled, the job was transferred to the lathe and the front of the ring turned away until flush with the smokebox. I'm holding the work on the inside of the smokebox door ring for this. I took small cuts along the diameter rather than plunge the face because of the risk of digging in; it's all too easy to for the tool to drag itself into the job when using the racking handle.
The bore needed opening up to fit on the barrel but there was also some distortion to contend with so the hide mallet helped in getting a snug all-round fit. I had to change over to the other jaws for boring as the door ring wasn't running true enough. With the two parts married together, the cutaways for the various screws were transferred to the rim of the barrel and these were filed to suit. This is the smokebox with the ring in situ and both the chimney and saddle bolted on. These are needed to ensure that the smokebox is orientated correctly to the barrel and that the chimney is truly vertical in both planes.
  9. Next Item...