"Buffalo" Class Saddle Tank No. 1601

Following the success of my first scratch built locomotive in 2mm scale (my Small Metro Tank), for my next engine project I wanted another saddle tank - this time an outside framed "Buffalo".

This page has been divided into two sections : Chassis, and Body

The Chassis

Chassis Drawing
Chassis plan
Basic Chassis
Basic bare chassis
For this engine I again decided to employ a split framed milled brass chassis, therefore a drawing was done in CAD to see what sort of arrangement I could employ to use a Nigel Lawton 8mm diameter motor in the saddle tank space, a 2 stage gear reduction to drive the rear driving wheels but still make sure that nothing would encroach into the open cab space. Having a nice big space in the saddle tank, I came up with the arrangement shown.

Before I could make a start on the chassis proper, I first needed a set of coupling rods. The 2mm Association sell some etched coupling rods for the correct wheelbase, but unfortunately they are straight fluted ones - I really needed fish-belly type. However, since I had the etch to hand I decided to use the Association ones as a jig to drill the axle holes (and to test the chassis later) while I drew up some fish-belly ones in CAD to be custom etched.

To start the chassis, a piece of 6mm square and 1mm flat brass strip were cut over long, and bolted together outside the extremities of the finished chassis. The idea being that the parts could be separated and rejoined at any time with these fixings. The axle centre line was scribed along the length a suitable distance from the chassis top, and a 0.5mm hole drilled where the first axle will be.

Milled chassis
Milled chassis
Coupling rod as jig for drilling
A 0.5mm drill was placed in the hole, and the etched coupling rod placed over it and used as a jig to drill the other pair of axle centre holes 0.5mm. These were then opened out to 1.5mm (axle diameter). Because I had drawn the chassis in CAD including the gear centres, it was a simple matter to set my lathe up as a milling machine and to use the dimensions in CAD to accurately drill the gear centres using the driven axle as a datum from which the gear axles could be measured.

While in the vice, the fixing positions for the 12BA countersunk bolts which are used to hold the two halves of the chassis together were drilled 12BA tapping size, the 1mm section was unscrewed from the main chassis block so that the 12BA holes could be opened out to take nylon plugs (which were glued in place and cut off flush with the outside of the main chassis block). The pair were then re-united secured with the 12BA bolts outside the finished chassis, and the nylon plugs drilled 12BA tapping size using the holes in the 1mm thick section as a guide. Once removed from the vice, the parts were again separated so the the 1mm section could have its 12BA holes opened out to 12BA clearance and countersunk. The nylon plugs were then tapped 12BA, and the pair reassembled to check that these new fixings would do their job.

Crank 1
First crank made
Crank 2
First crank used as a pattern
The embryonic chassis was returned to the mill, and milled to the profile shape of the chassis. Finally, the 1mm thick section was removed again so that the space for the gear wheels, and for the axle muffs could be milled out of the main chassis block. Once I was happy that the gears meshed correctly, and with the wheels in that it sat squarely on a piece of glass, all of the axle holes were re-drilled to accept 2mm Association phosphor bronze bearings, which were soldered in place.

Because the Buffalo class had outside frames, Association wheels with extended axles were purchased, unfortunately the wheels do not come with Fly Cranks so these had to be manufactured. A sheet of 0.018" nickel silver was used to fabricate the cranks, a 0.7mm hole drilled in a piece of the material for the spigot on the extended axle, and a 0.5mm hole was drilled 0.080" (about 2mm) from that hole - For consistency across the cranks, a little jig was made with a 0.7mm peg in it onto which the piece of nickel silver sheet was placed so that the 0.5mm hole could be drilled 0.080" away from it on a vertical drill. Finally, the crank was then filed to shape around these two holes.

Crank 1
Completed cranks
Crank 4
Finished wheels
Once I had a set of 6 almost identical cranks, they were soldered onto the end of the extended axles, and the protrusions filed flush. To complete, Association flanged crank pins were soldered into the 0.5mm hole in the cranks.

Completed chassis
Completed chassis still requiring end fixing points to be removed

The Body

Saddle Tank
Saddle Tank
On my first saddle tank engine the main thing that I felt could be improved was the appearance of the saddle tank - because the 1854 class had been a conversion the saddle tank had been filed from solid, leaving it perfectly smooth with no rivet detail. For this engine I was determined to rectify this fault. I therefore made myself a rivet press that I could attach to my lathe so that I could use the lathe dials while embossing the rivets to advance the work and so obtain an equal spacing of rivets.

Through experimentation, I found that a rivet spacing of 0.020" (0.5mm) gave a fairly good (if not completely accurate) impression of the rivets used to join the panels on the saddle tank.

But first, a pair of tank profile pieces were fretted and filed to shape from some 0.018" nickel silver sheet. These profile pieces form the "end caps" for the saddle tank. Once the profile was established, a piece of kitchen foil was wrapped around the profile and the end points of the saddle profile marked. When flattened out again, it was a simple matter to measure the distance between the marked points so that I knew how wide the sheet needed to be to form the saddle tank wrapper (from drawings I already knew how long the tank was).

A piece of 0.005" brass sheet was cut slightly over-size and mounted in a vice on the lathe vertical slide, and the embossing of the rivets performed. Once complete the resulting sheet was finished to size and carefully rolled until it fit snuggly around the end profile pieces. To complete the assembly the profile pieces were soldered in place.

Frames 1
Outside Frames
Frames 2
Frames attached to Footplate

Because the outside frames have prominent rivets around the horn block areas, the outside frames were drawn up in CAD (with the rivet positions marked). These were then printed out onto self adhesive labels which in turn were fixed to some 0.006" nickel silver sheet. The rivet positions were then embossed with a "drop-rivet" tool before the outside frames were fretted and filed to shape.

A footplate was cut from 0.010" nickel silver sheet, and the front and rear buffer beams were cut from 0.018". The buffer positions being marked and drilled 0.8mm ready for the buffer shanks. The front buffer beam was soldered into position before the outside frames were initially tacked in place where I thought they needed to go, and finally the rear buffer beam was attached. Because I purposely didn't cut the hole in the footplate for the wheels, motor and gearbox until after this assembly I did find in the end that I had to drift the outside frames further towards the footplate edge to clear the fly cranks properly.

The next stage was to cut the hole in the footplate to accommodate the tops of the wheels and the motor, etc.

Footplate 1
Footplate fretted to clear motor, wheels, etc
Footplate 2
A centre line was scribed on the underside of the footplate, and positions of the tops of the wheels and the motor/gearbox marked from that centre line. From a hole drilled through the footplate this area was removed with a piercing saw, and finished with files.

Once the footplate could fit over the motor/wheels, etc., the body fixing holes were transferred from the holes present in the chassis. Once the footplate could be bolted to the chassis, trials were made and small amounts of metal removed from the footplate and outside frames until the wheels no longer caught on the footplate or the extended axles did not catch the outside frames.

The next operation was to add the wheel splashers. For these I turned up some "dishes" which had sides and bottom only a few thou thick. Chords were then marked on these dishes which when cut off with a piercing saw provided the 6 splashers. As each splasher was added to the footplate a further trial was made to ensure that I had not introduced either a short or binding with each new addition - doing this may be slightly more time consuming but if a short is found one knows instantly what has caused it and the offending splasher can be removed or drifted slightly until all is well again.

Custom etched springs
The springs on this class are fitted above the footplate outside the splashers. Rather than fret and file 6 of these items I had included a set on the artwork I'd drawn up and had etched. The etch is a 3 layer affair which when sweated together provides a fairly robust spring. I elected to solder these springs directly to the outside face of the splashers - this may make painting more difficult later but I felt that the strength of such a ruse outweighed the potential delicacy of mounting them in small holes in the footplate a little way from the splasher face.

The buffers are fairly simple turnings, the buffer head and shank turned from 3mm silver steel rod, and the buffer housings from brass. I made more than the 4 I needed in case any were sacrificed to the carpet god. The buffer housings were soldered to a small piece of 0.006" nickel silver sheet, which was cut and filed to provide the square foot of these castings - no fixing bolt detail was attempted in this scale!

To Be Continued...