CF MRC

I appreciate where you are coming from Tony. In the last few years, much of my time has involved converting very pleasant N gauge locos to run on Copenhagen Fields: effective but a bit boring. There are also excellent kits available in 2mm, but they don't fit our requirements that well. I now have a bit more time on my hands, so have resumed work on a scratchbuilt P2, Lord President. I have added a few posts on the building process on the "what's on your workbench" section of the 2mm finescale section of this forum to show how it's done. The series could make an article for a magazine. I think there is a bit of a danger that railway modellers might forget how to make a working chassis from scratch; following the mantra "why can't we have a (conversion) kit for such & such..." It really is'nt that tricky to follow the old fashioned rules and make something that works. It's also hugely satisfying. Fellow dinosaur Tim

Hush hush Mr Higgs don't be so cheeky! 10000 would be an interesting exercise in brass carving and might be heavier than the P2. The A4 photo is my 7mm model: I know you shouldn't copy models but it is quite accurate... I've been working on the double chimney on 'Lord President'. These double chimneys are massive on the Greeley boilers: you can see why Mallard was able to make the steam for her record breaking run - and get rid of it - when you look at the proportions. To all intents and purposes there are no joints visible with the streamlined casing, especially in 2mm scale. I have made four A4 chimneys to date, so thought I would try a different technique for the P2 making the chimney integral with the streamlined casing. The front end started life as a white metal Foxhunter A4. Phil Kerr gave me the excellent casting, although it has undergone major re-sculpting to suite the P2. The loco body was mounted on the frames and then the frames simply clamped in the machine vice on my little Cowells milling machine. A 3.6 mm diameter mill was then used to slot out the base of the chimney to take the Kylchap blast pipes. Next, a lump of brass was double drilled for the two pipes and then filed up to shape, with the V shaped rearward extension sitting on top of the casing. This brass was generously tinned at the sides and bottom with 146 degree solder and then placed in the slotted smokebox casing. A hot iron was left for a while on top of the openings and the brass fitting melted into the casting. Any extra faring was made up with 70 degree low melt solder painted on with a hot iron. Then followed quite a lot of cleaning up. The final chimney has a reasonably seamless joint with the streamlined casing. It may be a touch too tall at the moment, but these things are often best left to have a look at with a cold pair of eyes. The final photo shows the engine doing an impression of Sir Ralph Wedgewood after Luftwaffe-based re-modelling. More on the boiler and cab later. The brass running plate is the valence, rather than the footplate itself. Tim

I have fitted the front spacer to the P2 frames. This incorporates the front pony pivot mounting as a piece of 3 mm diameter brass rod with a 12BA clearance hole down the middle. This transects the spacer and then acts as the support for the front body fixing. This tube has been isolated from both frames by gapping the PCB appropriately. The two cylinders can be seen bolted to the frames: cylinder drain cock holes have been drilled, but the pipes will be unlikely to be full length to the front guard irons. The temporary frame assembly jig has now been cut off from the pony frames. The middle photo shows the spacer extended rear wards to act as a support for the motion support brackets: PCB will be gapped when I know what these will be like, but the front body support is very clearly visible above the spacer. The cylinders have been drilled at the rear for the valve rod and combination lever support casting and the piston stuffing block / slidebar support. The photo of the A4 valve gear shows what this area should look like when complete. Tim

Making accurate measurements. One of the problems in scratchbuilding is making sure that everything stays true and level. For a number of years I have used a piece of Tufnol with two PCB tracks glued to it as a measuring platform. The gauge is set at 9.2 mm so that there is no side play of the wheels on the rails: it is also used as a coupling height gauge. To use the block, as shown in the second photo, I simply measure its thickness including the rails and then zero the calipers. Any measurements will then be accurate for height. It can also be used to scribe spot heights with the caliper tips (probably not supposed to do this, but I always have) as seen in the third photo where I am marking the centre height of the piston on the P2. Finally, it is easy to hold the little block with the engine on its wheels and check that everything is upright with a British Standard Eyeball. Tim

The Cartazzi supports and double-sided PCB rear frame spacer for the P2 have now been made (with Gary observing the process of setting up the chassis and soldering in the spacer). The rear chassis extension has been lopped off. I have worked out the body fixing - two bolt holes at the rear - fixing into the raised cab floor, the Cartazzi axle pivot arrangements and also bolted on the cylinder blocks. The quartering of the wheels in the chassis was remarkably straightforward, and these are currently held by soft muffs to allow the wheel to be removed easily. The motor-gearbox is simply laying in place (sans final drive) and needed a bit of grinding out of the boiler innards to get the required space. I still have room to be able to make a nice backhead and cab detail casting to cover the motor. Front body fixing and spacer next. Tim

Interesting comments on slates Jim. Again, on CF we use the Slaters Plastikard slates, but sanded to lose much of the relief. This moulding is better than the bricks, but still works better with a textured surface. The acreage of slates that we have rather precludes individual strips and I prefer the reliability of a solid and subtle styrene roof. Sorry to hijack the thread Ian. Tim

Nice little box Ian. One of the things we do with Slaters brick plastikard on CF is to sand down the brick faces to take away their rather blobby/shiny appearance. Tim

When we first started using these combinations they were about £60: pricey, but pretty useful. The chassis modifications are very straightforward, so your etches would be perfectly suitable for use Chris. Having cut out / filed the frames on the angle to take the motor with the worm resting on the wormwheel, I cover the chassis side of the motor / gearbox with epoxy resin and a cigarette paper. This is then araldited directly to the frames making sure that the gear mesh is kept st the correct distance as the epoxy hardens. Easy enough to tap off the motor if required done this just once when the axles on the Parks tank wore out! Tim

Actually, the Maxon 816 and gearbox is fitted in our scratch built NLR Parks 0-6-0 tank, Jinty & GN J13 (J52). It's almost a direct replacement of the old Farish armature and bearings. I had originally been a bit wary if using this in a large engine, but it's now a well proven combination on CF after 100's of miles.. It's not so much a case of having a big engine but a big wallet as the £/SF exchange rate is pretty torrid. Tim

Here's a picture of the streamlined P2 tender body, Steve. It has a core from an old Foxhunter A1 kit, but the body is a single wrapping of N/S sheet and a new back. The paper pattern used to make the shell can be seen in the picture. I'll put up pictures of the engine body when I've done the chimneys: it's faceless at the moment. Tim

Continuing the P2 chassis fettling, I carved out the notch for the motor-gearbox: a Maxon 816 with a 1:4 gearbox - shades of Rovex. This drives the third axle with an 18:1 reduction on the worm and wheel gearbox, modified slightly from an Exactoscale design now marketed by C&L. Seventy two to one is a substantial overall reduction, but our engines don't need to run fast on Copenhagen Fields. The combination should wear well. I couldn't resist putting the engine up on its wheels on temporary muffs and also to see how it sits on some tightish radius track. The rear end (bottom of the picture) needs significant tapering, but it has that on the prototype. It won't have a working Cartazzi truck, so there should be plenty of room for side play at this end. The cylinder drains will certainly not survive at the front. The centre pair of axles are a gnats whisker higher than the outer pair, which is how I like it. Tim

Interesting questions raised by your flywheel Jerry! Mechanically the UJs may wear a bit quicker because the motor is trying to shift the inertia of the flywheel via the drive shaft. Assuming the flywheel is dead true, there may not be a problem with vibration. However if the back bearing begins to wear, which it will, then the vibration from the precessing flywheel may become an issue. Easy enough to re-engineer if it doesn't work, and, as my father used to say "He who says it can't be done is liable to be passed by someone doing it!". Tim

I am now beginning to set up the frames. I have a couple of bits of old Mercontrol brass tube that are made the correct length for frame spacers, holding the two frames together with a greased 14BA bolt through them. These little tubes have seen Stirling service (so to speak) as they started off being used with the Baldwin 2-6-0 and have kicked off quite a few chassis since then. The frames simply have a couple of holes added at each end and are then assembled ready for the PCB spacers to be soldered in. The advantage over the Association jigs is that there is little by way of a heat sink and the main chassis is kept clear of bits, making it easier to work on. The extra frame extension bits with holes can be lopped off once the chassis is assembled. I think the originator of this technique was John Greenwood. The chassis is lined up with sighting rods as can be seen in the photos, any errors are greatly magnified: the out-of-parallel appearance is due to the pin cushion distortions in an iPhone camera. I now need to work out where I want the PCB spacers. Tim

I've been working on the P2 chassis today. The cylinder blocks (literally, at this stage) were super glued to the chassis sides and pilot holes drilled through from the frames (already drilled) for the eventual screw fixing. This was easier done with the frames still separated. The blocks eventually will be drilled for the pistons, rear stuffing boxes, slide bars and valve spindle guides along with being shaped appropriately. The odd shape with a screw hole in the bogie cut out is for my frame assembly jig, which I will show in the next post. The second photo shows a mod to the chassis sides. On real engines the wheel rims are very very close to the frames. The wheels do not have a rear boss which puts them nice and close to the frames, but also gives a strong chance of removing paint or chemical blacking behind the spokes. I therefore ground out and polished the frames behind the wheels to avoid this happening. An approximation of the spring shape is also visible as are the holes for the brake hangers. Tim

Started work on the driven axle for the P2. The wheels have 1/16" axles and the final gear I am using has a 2mm bore. This was bushed with a piece of acetal, centre bored to 1mm and 0.10" over length to guarantee that the gear was insulated from the chassis sides. The axles were turned down in a step collet to 1.07mm, retaining the 1/16th shoulder for the bearing/chassis. Important to put a slight 'lead' (0.95mm diameter over 1mm) on the axle end to get it to enter the muff comfortably. The wheels were gently offered up to the gear, as can be seen, but this set up will not be pushed home and used until the gearbox is assembled. For checking out the chassis a dummy muff has been made to identical width, which brings the back to back up to the correct 0.335". Should get the chassis together pretty soon - I'll probably need to narrow the front and back a bit to get it round 600 mm curves. I may make some assembling muffs with grub screws so that I can check out the valve gear easily: this is what Denys used to do. It's 40 years since I made an engine with Walschaerts valve gear! Tim

I tried millng the slots in some steel using my Cowells milling machine. This is an excellent machine but not fast enough for a small bur to mill and be driven by hand consistently. I may try it again with a different type of bur for the con rods. I am sure that there are small CNC mills out there that would do the job, but the end result would probably need a very careful clean up. Tim

I have used some amazingly complicated sorts of jigs (commercially available) when attempting to resurrect recalcitrant P4/EM chassis at the Missendon Abbey modeller's weekend. I don't think jigs would achieve the required accuracy for a 2 mm chassis: the commercial gadgets are usually no better than a British standard eyeball and common sense. Tim

The roughly finished rods were then taken through various grades of abrasive and polishing papers to get a reasonable finish. The nearly completed rod can be seen on the wheels, sitting in the unassembled chassis frames. The wheels were hand made by Denys Brownlee many years ago as indeed was the tender chassis. The P2s had very fine coupling rods, as they were made of a fancy steel alloy. Interestingly the new P2, 'Prince of Wales' will have deeper rods. The model rods are 0.9mm deep at their greatest. The final image shows the rear pivot joint indicated by a centre pop mark over the knuckle. Tim

The coupling rod was then un-soldered from the backing brass and one side of the rods reduced in height towards the flute from both sides as seen in the next two photos. The square bosses were filed to be round in shape where appropriate and then a slotting file was used to refine the slots. These files are wickedly expensive and are used to cut slots in screw & bolt heads in the watchmaking trade. Subsequently the rods were thinned down from the back between the crank pin bosses, so that they would not scrape any paint off the crank boss when rotating.

I am a firm believer in steel valve gear and coupling rods looking nice and chunky with decent bearing surfaces - because that is what steam engines have. My next engine a, P2, will obviously have a scratchbuilt chassis and needed fluted coupling rods. I always drill the frames and rods at the same time with them sweated together. The first photo shows the front axle and coupling rod hole being centre-marked with a gramophone needle ground to a cutting three sided pyramid shape, prior to drilling. Second photo shows one side rod sweated to a bit of scrap brass and the rods filed down between the bearings to leave these proud as a boss. The technique of 'draw filing' Is being shown here with the file moving up,and down the rod at ninety degrees to it. Third photo shows a small marking gauge being used to scribe the flutes between the bosses. This was fitted with a gramophone needle ground into a D shape to plough out the required shape. The crank pin bosses automatically limited the length of the flute and the cheek of the gauge was held firmly against the side of the rod, to run parallel between the crank pin holes.

This steel forging has been occupying my time a bit just lately. I'll post some pictures of how it was made in the next couple of days. Tim

One of the problems with all these new commercial models is the huge variability in axle length, even from the same manufacturer. I have some of the Farish bogie wagons for the WW1 tanks that are close to acting as spirit levels when fitted with Association wheels. Other Farish wheel replacements are much less free running. One trick to try, if the emplacement wheels are a touch tight, is to squeeze the axle boxes in a vice over the replacement pinpoints and form a new, looser, bearing surface in the plastic moulding. Tim

On my American 2-6-0 there wasn't room for thin wires as the motor and massive tungsten flywheel got in the way of any current collection from the front bogie. There was insufficient length for the requisite flexibility using thin wire: the bogies are almost square, so their tracking is easily biased by soldered wires. I therefore used phosphor bronze wiping pads lightly sprung down onto each side of the rear bogie which also took the current up to the motor brush tags (Portescap 1016). The p/b wipers also gave some springing to the rear end of the tender. Tim

Gareth With my extensive experience of American 2-6-0s (!) I would make internal frames for spilt frame pick up and dummy external versions. Extended pinpoints will be harder to make and not good for pickup. They will not stay as pin points for long if the juice is going through them. Tim

To get fine coach lining in straw and black I use the Mecanorma pens with Magic Colour inks (Goggle the names for supplies). Certainly worked easily for my Oerlikon set. For magnification I am spoilt by using high quality professional loupes and co-axial lighting. However, some of these are available at relatively low cost from the web. Quality may not be as good, but depth of field should be better than single lens systems. Massively good lighting will always help older eyes.... Tim