More power for Pontesbury Sidings - building Canopus (part 1)

As I have said previously the Shropshire Minerals Light Railway would have been a challenging railway to operate. If Col Stephens had inherited the SMLR in 1923 he would have needed heavier power than the WW1 Baldwins and Kerr Stuart Skylark he bought for the Snailbeach District Railway.

There were plenty of surplus locos in the aftermath of WW1 because of the extensive use of narrow-gauge railways in military supply, and also as public light railways had started to suffer road competition. At the time the ex-Pentewan Railway 0-6-2ST Manning Wardle Canopus was for sale at second hand dealer, in real life she ultimately ended up as a RAF Air Construction Corps loco before being scrapped.  Let’s just suppose that instead Stephens bought her for use on the SMLR – quite a reasonable assumption; he liked both a bargain, and Manning Wardle’s products (there were several on his standard gauge lines). At 2’6” gauge with outside frames Canopus would probably have been easier to re-gauge to 2’4” gauge than the 60cm gauge Baldwins.

Historic photo of Canopus in RAF service - Wikipedia Commons

The model

I purchased a Backwood’s Miniatures kit for Canopus off eBay a couple of years ago – probably paying a bit too much for it, but its long out of production with Backwoods closing down in 2016. The kit was one of the first of a breed of prototypical kits for 009 but is rather infamous for being difficult to build due to some flaws in the design. One of my favorite blogs documenting a build is this one: https://caffeine-train.blogspot.com/search/label/Backwoods%20Miniatures   The kit I bought was part built which was a bit of a risk, but what the previous owner had done had been done very well, but not without some issues.

The previous owner had made the frames and gearbox assembly nice and square and soldered them neatly. They had soldered the outside cranks to the axles, but the right lead crank had been removed, presumably to sort out a bind, so it was not a rolling chassis. The other main issue was the slide bar yoke. This had been split and patched to widen it, as its well documented that as designed it’s just too narrow to allow the lead crank to rotate behind the crossheads. However, the slide bars which are supposed to fold up out of the yoke had been snapped off on the left side – these would prove a “right swine” to re-attach.

The first job I tackled was the loose crank. As the others were soldered, I thought I better solder it back on. I attached the side rod on the left side with some of the tiny (16BA I think) nuts included. Then used the side-rods to judge whether everything was in quarter by eye – as my quartering tool wouldn't fit this type of chassis construction. Next, I slid the wheels on the leading axle fully to the right side of the chassis, and with the left side-rod loosely on the cranks I clamped the chassis into a helping hand. I swapped the bit on my temperature controlled 50w iron for a medium sized bit rather than an electrical pencil tip, as I find this much easier for soldering brass components. The whole chassis except the front left crank was submerged in a bath of water to ensure that the heat from soldering the axle didn’t melt the plastic wheel centres. I had two goes as soldering the crank – the first time the crank slipped just as I was taking the iron off it before the solder set. I then tested the chassis and found that it rolled quite nicely with no major bind. So, I slid the wheels back into place using a back-to-back gauge to get everything in line.

Next, I tackled the crossheads, one was already constructed the other was still a fret of parts. I needed to provide my own piece of brass rod to form the piston rod as it was missing from the kit. Fortunately, the previous owner had obviously read up about another of the kit’s shortcomings and had purchased replacement connecting rods of the correct length so that the crossheads didn’t foul at the end of each stroke. I found the crosshead fiddly to assemble, and had a couple of goes before I was satisfied it was solid. I used a razor saw to make sure the channels on both sides of the crosshead were clear of solder. I don’t like rivets in any shape of form so rather than riveting the connecting rod to the crosshead, I made my own soldered pin arrangement – which calls for some deft movement with the soldering iron and a paper washer to stop the solder flowing where it wasn’t required.

I then tackled the slide-bars; first reinforcing the still attached set on the right side of the loco with a fillet of solder at the yoke end. Then attempted to solder the loose ones on. I had several goes at this – and eventually got them to attach sufficiently straight. I inserted the cross-heads only to find I’d accidentally put the left side connecting rod into the crosshead assembly upside down. It meant that the lubricator on the big end was pointing down. I couldn’t face disassembling the whole thing again, so as the connecting rods are otherwise plain, I just cut the etched lubricator off and filed it flush. I then attached the crossheads and slide bar yoke assembly loose into the slot in the frame. Trialling rotation, I noted that space behind the crosshead was still very tight indeed. I decided not to add a nut to the leading cranks, with the centre and rear nuts holding the side rods tight enough that there was no need for them on the leading axle.

The cylinders in the kit are whitemetal castings to be attached to the etched brass frame with thick CA or epoxy. The left side one had been drilled out by the previous owner, but the right cylinder only had what appeared to be a starter hole at one end. I attempted to drill this out with an appropriately sized drill bit, only for it to snap off. I tried the same from the other end only for the same to happen – there was something hard in there. It transpired that the previous owner had also had an issue with a snapped off bit and it was still stuck in there. This called for some major surgery on the cylinder. I cut off the cast in piston gland and managed to get the snapped off section of bit out. By now however the hole was much too slack for the piston. So, I drilled out the central hole with a wider bit and fitted a sleeve of brass tube securing with CA, building the gland back up with small sections of concentric brass tubing.

I then tried to attach the cylinders to the slide/crosshead assembly and to the chassis, in the process of trial fitting I ended up damaging the left side slide bars. I decided to solder both ends of the slide bars – I turned down my iron and used low melt solder to attach the slide bars to the whitemetal cylinders. I found I needed to use low melt solder throughout this piece of work as it was too easy to get the whole assembly hot enough to melt other solder on joints not being worked on otherwise.

Once this fiddly piece of work was complete, I attached the connecting rods and trialled rolling the chassis before soldering up the crank nuts. I found that a little bit of filing was required on the inside of the cylinder glands to ensure that the lead cranks didn’t catch – despite leaving the lead axle crank nuts off.

With a rolling chassis I next turned to altering the trailing truck attachment. I added a washer below the chassis bolster and drilled and tapped this 0-80; I tend to use American thread sizes as I have modelled in US outline HO for a number of years and they are to hand on the workbench. A cut down 0-80 countersunk bolt attached the truck which the previous owner had made up.  I then attached the motor / gearbox assembly to the main frame, with the worm just clearing the chassis stretcher to which the trailing truck attaches. I it tested under power, and it ran reasonably well first time. Phew!

Next up was the attaching the electrical pick-ups. The sketch in the Backwoods instructions leaves a lot to be desired, so I rather did my own thing. Gluing two strips of copper clad strip to the lug on the top of the gearbox and the slidebar yoke. I formed wheel wipes from the springy phosphor-bronze wire provided, these are an inverted v-shape so there is a wire pick up running on both side of each wheel.

I tested the chassis under power on stands on the desk and it ran well, if slightly “dry”, it ran much better after I lubed everything up - Tamiya plastic-friendly grease in the gearbox and light oil on the axle bearings. However, as soon as I put it on the track it didn’t run well at all – there appeared to be some form of intermittent short. This appeared to be related to the trailing truck, as when the truck was removed the short disappeared and the loco ran sweetly.

I’ll cover resolving this issue and the next steps in a future post...