1.1/2" Allchin - restoration and completion

[springcrocus]

Adam, still waiting for access to the boiler inspector. Won't be long now, though.

Water filling pocket

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 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 prevent 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.



Although the lid for the filler pocket now fits, it's not a very nice lid - the lugs on this are too small at less than 3/32" and incorrectly placed - so I shall make a new one.



Steve

[coniston]

That's lovely work and interesting setups as usual Steve, nice job

Chris D

[springcrocus]

Shell test

I took the boiler to Broadfields today and am pleased to say that it has now passed it's shell test so it looks like I will have a steamer after all.



Now I can crack on with getting the cylinder mounted, the smokebox attached and the boiler fitted into the frames.

I'm still having problems with the Britannia regulator and the boiler inspector did say that it could be blanked off for the hydraulic test but I would prefer to get this one sorted. Everything else has been tested and I'm hoping to take it with me when I go to the club on Wednesday.

Steve

[springcrocus]

Mounting the cylinder

With the shell test completed, I have been able to start mounting the cylinder to the boiler and the first job was to mark out the position of the centre of the cylinder on the barrel. By turning the scriber upside down, I was able to zero my height gauge on the centre of the crankshaft and mark a line around the boiler at 8.3/8".



To find the radial position of the cylinder, I used a piece of 3/16" dia silver steel set into the piston rod gland and lined the other end up with the centre of the crankshaft journal, checking with the crank both fore and aft. I also made a simple clamping system out of some M10 studding and a lump of wood.



After spotting the four corner holes with a hand drill, I set up the mill so that I could drill all the holes on there. Some may enjoy drilling holes by hand but I choose a machine every time. My large vee-block was mounted first, square to the table and centered under the chuck. To support the firebox end, I fabricated a flat stretcher with a 1/4" dia hole on the boiler centreline drilled through it, fixed with a couple of screws to a pair of convenient holes in the hornplates.



A simple support was created from an angle plate and using a table clamp with a notch ground in the end. Centreheight was found by clamping the boiler into the vee-block and adjusting the table clamp to the 1/4" diameter rod in the temporary stretcher.



The next picture shows how the firebox end is supported while the barrel just rests in the vee-block.



All that was needed now was to rotate the boiler around it's axis, wind the table to a suitable "X" position and drill the four holes.



Leaving the set-up in place, the cylinder was bolted to the boiler with 5BA screws and the rest of the holes spotted through, not forgetting the 7/32" hole for the filler hole.



After drilling all the other holes, the one remaining hole was the steam feed to the underside of the cylinder and for this I chose to use a step drill although I had to be aware that I was getting close to the flue tubes in the boiler. I felt that the risk of a large jobber drill "snatching" at breakthrough was not worth taking in this situation.



To complete, all the holes were tapped freehand using a spiral-point tap which aligns itself as long as it is not forced. These taps are not cheap but they are extremely sturdy and pretty-much foolproof to use. However, considering the value in the boiler to this point, it would be penny-pinching to use anything less robust.

And there we have it. My boiler which had just passed it's shell test now has an extra twenty-six holes in it!



Steve

[springcrocus]

I've made a few more bits and pieces but none which warrant an individual write-up. The steps on the side of the tender were one of the items. The lower step was made from a block of brass rather than fabricated from brass sheet. I milled the tread pattern by setting the vice at an angle and using a rotating carbide burr to gouge the grooves.



Then the underside was milled away with a 3/16" endmill and finally tipped up by eye to form the side angles. A pair of 10BA clearance holes were also drilled for mounting to the tender.



The guard for the second motion gear was made from 18 swg mild steel using a paper cut-out as a pattern to get the shape. The rivet positions were marked out the old-fashioned way with dividers, centre-popped and then drilled 3/64". The backs were slightly countersunk and the rivets hammered flat on the inside since they can't be seen. The curvy part was bent freehand to match, then silver-soldered to the flat section and dressed all round. The fixing bracket was made from an offcut of the guard material.



The pump arm was a pig to make because it needs to be offered up to the pump for final sizing but the pump cannot be mounted afterwards because of limited access. In the end, I made it from two separate parts. The main arm had a slot milled in it with a 1/8" slot drill and the pivoting arm on the pump plunger had a pair of M3 holes tapped in it. This allowed the distance to be set after assembly and then locked together.



A bit of woodworking next, making the footboard and toolbox from obeche. Although all the parts were cut by hand, I did use the mill to get the edges flat. This was particularly useful to get the drop-front to work properly.





The hinges are standard dollshouse items and the four toolbox screws were made from 1/16" brass rod with a 10BA thread on each end and a tapped 5/32" diameter brass button screwed tightly on the top and filed to shape in the lathe - too flimsy to turn. This is where it fits.



And a few overview pictures of the engine as I start to try and bring things together.







Steve

[springcrocus]

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 of milling operations undertaken to relieve the underside.



A different setup was used to reduce the width of the arms of each bridge, one side first, then flipping over and machining 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.



Steve

[springcrocus]

Firehole door

The firehole door assembly needed to be constructed and there were many small parts to make. None of the parts were particularly difficult to make but the most fiddly parts were the door latch and keep. The hinge, hinge pin and brackets were quite straightforward.



Assembly was a little tricky and needed to be done in the correct sequence. Importantly, one of the rivets on the hinge also held the baffle plate and had to be one of the last to fit. The baffle plate had to be dressed to fit the firehole after assembly. It needs to sit 1/32" clear all round to allow secondary air to enter the firebox through the two holes in the outer door.



Ashpan and grate

The ashpan and grate also needed completing and the Allchin boasts a dropping grate for easy disposal of the fire. The first thing I needed to do was make a pair of pins to support the fire bars. 1/8" diameter mild steel was cut to length and a No.1 centre drill used to make an internal cone at each end. I originally tried using stainless steel tube but it proved to be too soft.



This allows for a punch to spread the ends and hold the assembly together and decent countersinks were made in the outer firebars to form a seating area. The firebars were assembled on temporary pins with the spacers in place and with the brackets connecting them to the ashpan lower door.



The countersunk pins were pushed through, displacing the temporary ones, and the ends bell-mouthed using a couple of lathe centres and a big hammer. The lower door was then bolted to ashpan and the whole unit became self-contained. To the left can be seen the front damper that allows extra air into the firebox.



When the catch is released, the rear of the door drops down to deposit the fire on the ground. Also seen in this picture are two of the four mounting holes.



Hughes suggests drilling and tapping half-a-dozen holes up into the foundation ring to hold the ashpan in place and three of these holes can just be seen in the ashpan flange. I think this is an unneccesary risk and decided to drill a pair of sideways fixing holes and screw the ashpan to the extended lower sides of the firebox instead.



With these items completed, I can now assemble the boiler into the hornplates for the final time and get on with the boiler cleading.

Steve

[springcrocus]

The boiler is now mounted between the hornplates for the final time (I hope), the valve gear set up and the regulator made. I didn't bother to take pictures of most of this but I did take one of how I set the eccentrics on the crankshaft. Hughes suggests using a cardboard angle plate to set them at 97.5 degreees leading and trailing the big-end journal respectively but I used an angle table set at 7.5 degrees. The eccentrics have a drilled and tapped hole at 180 degrees to the throw so a dimple was drilled into the shaft at the measured position for a grub screw to locate into.



With the cylinder and trunk guide bracket mounted, 3mm ceramic blanket was cut to shape and held in place with with masking tape. The cylinder was then removed but the trunk guide bracket left in place. One thing I discovered is that it's nigh-on impossible to mount the cylinder exhaust with the chimney in place so that has been taken off for the time being.



Card templates were cut to suit and these were then used to mark out the cleading. I'm using 24 swg brass sheet as I have quite a bit left over from the Britannia. They are made as two side sheets with a 3/16" overlap top and bottom.



Getting the cleading to be a nice fit took quite a while and I also removed the perch bracket and front wheel assembly to make things easier. Just a little more filing to get it snug around the cylinder and I can then refix the cylinder for the final time.



Steve

[springcrocus]

Overview

The IWMES is having an exhibition weekend and they put a call out for some exhibits. The Allchin has been sitting in a partlly-stripped-down condition since the beginning of the year so I've spent the last few days rebuilding where I can and finishing some of the paintwork.







There are still some parts to make and all the plumbing to sort out but it made a nice break from the loco project. I might bring it indoors when I retrieve it from the club on Sunday.

Regards, Steve