Building a basic 0-6-0 chassis
The advice given to many new or would be builders in 3mm is to begin with an easy kit. I do not believe that there is such a thing in 3mm. Most kits leave a lot to be desired in terms of put together ability. Many kits are reduced etchings from other scales and do not go together as well as the were intended in 3mm In my opinion it is better to start modelling in 3mm by building a basic scratch built chassis. 3mm is a modellers scale and it is necessary to learn skills and there is no better way than to begin by building a simple chassis. Scratch building is a rewarding experience and once the basic skills are learned then no kit should hold any fear. The tools necessary will be no more than those found in any modellers tool kit and explained as needed however some means of drilling a square and vertical hole with the material being drilled would be an advantage. For years I used nothing else than a ancient Black and Decker drill stand but such items are not expensive for the diameter of holes that we will drill and a simple drill stand or drill press is recomened.
Possibly the simplest of all chassis to construct is the 0-6-0, simper even than the 0-4-0. Not matter what your chosen era or company is chances are they has a multitude of 0-6-0's. The first thing that you need to do is find a drawing of your chosen model. There are a multitude of sources for these, books, railway model magazines and specialist suppliers or societies etc. But what ever the source at least 2 copies should be reduced on a photocopier to 3mm to the foot. You can of course scale from a drawing but by reducing them to 3mm not only can you check your work as you are going but you can see what detail you will be able to model and what is not necessary because it is too small to see in 3mm anyway. Also, dont be put off by those that tell you this or that detail on the drawing is wrong, what we need for the chassis is the wheel centres, distance from the front axle to the front buffer beam, the distance from the rear axle to the rear buffer beam and a rough idea of the outline of the frames. That is more than enough to worry about for starters, absolute accuracy, if you want it, will come later. This is all about teaching you, the new starter, to build a first chassis that actually works.
The first problem is connecting rods. For the first chassis try to choose a prototype for which "off the shelf" rods are available. Try 3SMR, Branchlines or Worsley Works, all do varius sizes from stock. It is an easy job once you have learned to solder to make your own but for this first chassis let's stick to ready made.
The sideframe material comes from the K's metal stand at your local model shop in the form of brass strip. My favorite is 0.8mm thick x 12.5mm wide and comes in 305mm long sctions. I use this because it is thick enough not to need top hat bearings and has enough rigidity that it does not distort very easily when worked. It is easy to cut, file, drill and solder which is exactly what the beginer wants.
We now have the material and the drawings and the first problem to overcome is how to transfer the shape of the frame from paper to metal. Take one of the copies of the reduced 3mm drawing and just trace the frame outline with a fine red pen. Most drawings will show if the wheels have coil or leaf springs as well as the positions ofany holes in the frame. For a first chassis I would give the likes of brake hangers etc a miss. Mark the driving wheel centres and once you are happy with the frame profile that you have marked out, measure the length of the frames and cut two pieces of the frame material to that length plus 2mm. You can either saw or cut the brass. I use a large pair of tin snips, the larger the snips the less the distortion. Using a piercing saw may seem laborious but even less distortion. Lay the brasses flat on the modelling board, make sure they are flat and clean all four sides with a flat file. From now on keeping things clean is essential. Grip the two pieces of brass together with a pair of pliers and solder the ends. In other words double the thickness.
Now its time to make a choice. If you feel confident enough to replicate the red outline by marking it out on the brass by measuring then do so if not then cut out shape of the red outline paper frames on the drawing and paste it onto the brass. Double sided Sellotape is ideal. Most frames are flat along the top so take care that the drawing sits square to the top of the brass. What we want to end up with is two identical sideframes. Using a sharp centre punch, small ones are available from most good tool shops, centre pop around the red outline at about 2mm intervals and particularly changes of direction. Centre pop only ONE of the end axle positions not all three. Place the "sandwich" on a piece of small section dressed wood and drill the centre punched axle hole 1mm dia, keep drilling into the wood about 6mm deep. Place another 1mm drill shank into the hole and the wood. Place one of the connecting rods over the drill shank, If the loco has unequal axle spacings then make sure the rod is fitted the correct way round. Sounds simple but an easy mistake to make. Line up the con rod with the red marks on the paper template, press down firmly on the con rod and drill through the other end axle hole as before. Fit another 1mm drill shank or a piece of 1mm dia wire into the hole.
The next bit is important because if it isn"t done correctly the loco will not be a good runner. The centre axle hole must be drilled SLIGHTLY above the two end axle holes. Place a 150mm engineers steel rule across the two inserted drill shanks and check on the position of the middle drivers hole in the con rod. It is almost certain that all three holes in the con rod will not line up and it is important that viewed vertically you should be able to see ALL of the middle hole in the con rod. If you cant then remove the rod, turn it over and refit. now you will be able to see all of the middle axle hole. Drill the centre axle hole 1mm dia.
When you have done all this the paper template will be wanting to part company with the brass anyway so remove it. What you now have is a sandwich of brass with the frame outline clearly marked and the axle holes drilled an exact match with the con rods. The outline can be cut with a piercing saw and fnished off with needle files. Dont use anything that will distort the two brasses such as junior hacksaw or tinsnips. Open up the axle holes to 1/8" dia to accept the axles. This is done in stages and NEVER in one hit and NEVER with blunt drills. I have a set of drills bought new and never used for anything else but this purpose. Even though they have drilled countless axle holes they will last longer than me because they have never been used on anything other than brass and nickel silver. The axle at this point must not be tight in the hole and must be a nice sliding fit, not tight and not sloppy. You will note that I have not mentioned bearings. This is because with material 0.8mm thick they are not necessary in 3mm. Mark them in some way so that when the spacers are fitted the marks are on the outside of the frames. I use a single "pop" mark. File the tops of the frames flat and to the correct length and part them using a soldering iron. Dress the pair up, admire your handicraft and begin thinking about frame spacers.
Frame Spacers
The standard 12mm frame spacer fixtures (jigs guide the tool, fixtures hold the work) are 7.5mm wide and I think along with other modellers that make their own frames in 3mm this a little on the thin side. (Usual etched side frames thicknesses vary between 0.35 and 0.45 thick) The ideal spacer width is dependant upon:- the gauge of the track, wheel style, width of the brim of which ever make of top hat/straw hat bearings you use, the thickness of the side frames and the amount of clearance or side play the axles must have to allow the finished loco to negotiate the tightest curve it has to negotiate.
Wheel style:- If the wheels have a boss on the back, Chris Hardy wheels come to mind, then the thickness of that boss has to be taken into account. On the other hand Keen Maygibs are recessed so that recess has to be brought flush with the flanges.
Top hat bearings (if used):- These come in all shapes and all sizes and it is the thickness of the brim or flange that has to be taken into account.
Frame thickness:- what is the thickness of the frame material?
Curve radius:- The smaller the radius of the curve the more side play the wheels have to have to get around it. There are some fancy geometrical formulas for calculating this side play but in 3mm the following clearances give good results. 450mm rad (18") = 0.65mm. 600mm rad(2ft) = 0.5mm. 800mm rad (30") = 0.4mm. 1000mm rad (39") = 0.3mm. 1200mm rad (4ft) = 0.25mm. These are based on a long wheel base 0-6-0 and this is the total sideplay needed. It can either be all on one axle or the total of the sideplay on all axles. In reality all axles need a little side play to be able to turn smoothly and this in the case of this chassis is obtained by spacing the wheels equally using Romford shim washers, no matter whose wheels you use.
So from all this the width of the frame spacers = Back to back dimension of the wheels minus twice the thickness of the side frames minus twice the thickness of the top hat brims minus the necessary side play.
(For the chassis being built here, gauge 12mm, with no top hat bearings two 0.25mm thick washers will be taken into account along with 0.3mm side play on two axles so we will need frame spacers 8mm wide giving a total frame width of 9.6mm.)
Now isn't all this more fun than kit building? Would you ever learn all this from building a kit?
The frame spacers can be made from the same material as the frames but a I prefer to use thinner 0.45mm material as it is easier to work with when it comes to bending. The spacers are bent "L" shaped, two in number and identical. Cut a piece of brass or nickel silver 8mm wide x 30mm long and then half it to 15mm. The "L" shaped spacers should be 12mm on the long side and 3mm on the short side, if you dont have a small vice use a pair of large pliers to bend them at 90 deg. It is important that the spacers are the correct width and to help with this a vernier calliper is ideal. Once upon a time such things were the reserve of time served engineers but now digital versions can be bought for less than 10 pounds at some super markets and are a sound investment and last a lifetime for our purposes. The spacers will be fitted to the chassis so that the 3mm upstand will face the centre of the loco and the plain end of the longside will at one end of the chassis be flush with the buffer front buffer beam and the other flush with the rear buffer beam. You will also require holes to fasten the chassis to the body part of the loco so arrange these to linr up with the middle of the coal bunker and the middle of the smoke box. Drill them in 3mm scale to take a 10ba screw, 1.8mm dia.
Frame "jigs" are available from 3SMR or the 3mm Society but I prefer to use some that have been made from earth plugs taken from 13amp electrical plugs. These are 8mm wide and are drilled through and tapped 10ba then fitted with 2 10ba countersunk screws. These screws will be used to align the two frames. But in this case the frames are 0.8mm wide so the 3SMR or society ones can be used.
Fit the "jigs" to the end axle holes and slip an axle into the middle, make sure that your register marks added previously are on the outside of the frames. The frame spacers must be a good sliding fit between the frames. If you have to use any force to fit them they are too tight and will distort the finished frame. Turn the chassis to its flat side down on a piece of flat softwood or balsa, position the spacers and hold them in position with a drawing pin through the holes. Solder the spacers in place, remove the pins and the jigs and give it a good wash with Fairy Liquid and an old tooth brush.
Fitting the wheels.
For a first chassis I would advise Romfords as they are robust and are self quartering. 3 insulated and 3 uninsulated plus axles and crankpins are required. It is prudent also to invest in a Romford wheel screw driver which not only fits the wheel nuts but will also insert the crankpins. Insert the crank pin and about 2 threads from "fully home" apply just spot of superglue then screw them home being careful not to bend them. Fit either the insulated or plain wheels to the axles, it dosent matter which. Try one of the axles in the holes, it should be a good spinning fit when flicked with the finger. If it isnt then the hole needs to be made slightly bigger. My favourite tool for this is a fine tooth tapered round file turned backwards against the teeth. The file is slightly larger than a needle file and tapers from about 1.5mm to 4mm. Any good tool shop should be able to supply you one. When all the axles spin easily in the holes without any sign of tightness, and go no further untill they do, fit the wheels to the other side. Dont worry about spacer washers at this point. Drill out the con rods to 1.1mm dia or open them up to about that diameter with a tapered round needle file turned backwards against the teeth with your fingers. Line all the crankpins on one side of the chassis at either 9 O'clock or 3 O'clock and try the con rod. it should fit. If it dosent see where it is tight and open the offending hole in the right direction so that the con rod does fit. Hold the con rod in place with some insulation from electrical wire and do the same on the other side. If all has been done correctly the chassis should roll smoothly. It is no good proceeding any further until it does.
Motors.
The best advice is to fit the biggest motor that the loco in hand will accomodate and in 3mm this means the 1016 or 1020 Mashima can motors from Finney and Smith or the "open" frame type from 3SMR. (to be continued)
Fitting gears and gearboxes.
For worm gears to work properly they need to be installed with the correct amount of clearance between the worm and gear wheel. For your first chassis I would advise an etched gear cradle such as those sold by 3SMR or Branchlines and with Romford gears. I would advise also to use Romford 40:1 gear sets in 3mm and to steer clear of nylon worms and fine tooth gearsets until you have gained experience by which time you will have come to the conclusion that brass worm wheels and steel worms are the best combination anyway! Worm gears at best are just over 20% efficient and Romford 40:1's are better than most. The gear cradle performs no other function on the chassis than to keep the gearwheel and the worm the correct distance apart and to do this it must not be soldered nor fixed into the chassis. To prevent the rotation of the motor around the gear wheel a simple wire loop around the rear of the motor shaft and tack soldered onto the chassis is all that is needed.
Fold up the gear cradle and solder behind the folds. Open up the motor fixing holes so that the motor screws are a loose fit. Fit the top hat bearings and make sure that the assembly fits between the chassis frames, file the bearings so that it does. Fit the worm gear to the cradle. Note which side you mount the fixing screw and always fit it to the same side, I fit mine to the left when looking at the loco from the front. This is important because in a few minutes we are going to "run the gears in" and to fit the gearwheel in a the oposite way will defeat the objective. Loosely fit the motor using the top screw only and the fit the worm. Place two thicknesses of cigarette paper between the gear and the worm and tighten the top screw on the motor, remove the paper and the gear should just show the slightest sign of "backlash" or play between the worm and the gear. Remove the gear wheel, fit the bottom motor retaining screw, and refit the gear with the retaining screw on the correct side and the same "backlash" should be present. Solder a pair of wires to the motor teminals and connect to a controller, apply a drop of sewing machine or clock oil to the gears and run at about half speed for about 15 mins in each direction. This is all the running in that gears should need. They are now ready to install in the chassis.
Fitting the pick ups
This section was written by John Sutton and first appeared in the 3mm Society quarterly magazine "Mixed Traffic". John is a founder member of the 3mm Society and editor of "Mixed Traffic". Above all he is an accomplished scratch builder of locomotives.
It surprises me that otherwise sensible people attempt to superglue scraps of veroboard between the frames and solder to them vaguely-shaped pick-up wires which don't seem to have very lively hopes of touching the wheels consistantly. I think you need to be a little more scientific, and I like to make pick-ups which can be removed for adjustment and cleaning. This means screwing them to chassis spacers rather than gluing. The ability to tap a screw thread opens up all sorts of possibilities, and it's neither expensive nor difficult. Eileens Emporium or some similar retailer will supply 8, 10, 12 and 14 BA taper taps cheaply, and you can use them in a pin vice. I invariably use 12 BA screws to fit pick up plates, bogies and pony trucks. Drill a tapping hole in the chassis spacer, then tap it. The time honoured rulr is to take it gently, half a turn clockwise followed by a quarter turn anti-clockwise, then repeat until the thread is complete. A lick of oil or spittle on the tap will help: if you don't, the tap will jam in the hole and probably break.
The pick-up wires are soldered to pieces of thin copperclad paxolin printed-circuit board. Tour local electronics shop probably sells pcb offcuts (one is a lifetime's supply) for next to nothing. Using a razor saw, cut a strip the width of the chassis and cut this into two pieces to sit ahead and behind tha gear wheel. After final shaping, hold them in place with your fingers and run a drill through the tapped holes to mark where they6 are to be drilled. Drill clearance holes and countersink the copper surface with something like a 3/16 drill, then fix the pick-up plates with short screws, making sure that the countersinking was sufficient to leave an insulating gap round their heads. The wipers themselves are 33swg phosphor bronze wire bent- overlength for now- to bear gently on the backs of the wheels. Solder them to the pcb plates with one or two neat blobs so that they remain good and pliable. Unscrew the plates and adjust the wires if need be, then trim them to length. Connect the two plates with a bit of brass strip (from your collection of fret edges), shaped to miss the gear wheel boss if necessary, then take a fine plastic-coated stranded wire from the pick -up plate to the top motor terminal. Solder the other terminal to a chassis spacer to complete the circuit. This also holds the motor firmly in place. Mashima 1220's have a nice flexible copper terminals just made for the purpose, but those on the 1020 are vestigal, so I bent a piece of stiff wire and soldered it to the bottom terminal and frames. (Much of what I've just described applies only to Romford-wheeled chassis, of course: if you are using plastic centred drivers, you will need to gap the pcb pick-up plates, fit wipers to all the drivers and take a flexible wire to each motor terminal.)