Prepared by Tommy Day Originator M. Stelfox

Some of you may have read the thread by Les Turnbull about building the DJB kit of this Locomotive where he ended up having difficulties in getting it to run reliably. He gave it to me to look at with a fresh pair of eyes. We both run our loco’s on the same garden railways and I have managed to negotiate the bear traps on them with my Single. The requirement are very simple – keep the driving wheels on the track at all times and have enough adhesion to provide traction. Sounds simple but this kit puts a few obstacles in the way.

The frames are a fold up into an inverted channel with the middle cut out to allow for the gearbox driving on the main axle. It is braced at the back to provide a box for the drawbar and similarly under the smokebox end to provide a rubbing plate which sits on the bogie. The back end has a subframe for driving and trailing wheels.

I do not like this method. Firstly the weight of the loco is divided between the smokebox plate and the subframe pivot, then transmitted to the axles which means with the best will in the world only about 30-40% will be on the driving axle. The attached diagram explains it

Add to this the fact that at the first bit of uneven track the front end will rear up. If there isn’t enough drop on the driving axle it spins uselessly. To fix this Les had extended the slots for the subframe axles to move in either direction – it does not add any extra adhesion.

My preference is for fixed driving axle bushes in the frames which allows weight to act directly on the wheels. The subframe would then pivot on the main axle with the trailing wheel free to rise and fall.

Where to put the bushes was the next problem as the holes in the frames curved in an arc. The tender footplate sits at 30mm above track level, the driving wheels are 54mm dia so simple arithmetic place the datum line 3mm below the top of the frames – suitably scribed with jenny callipers. Where along that line was determined by reaming out the subframe and frame pivot holes to take a 1/8th rod, When assembled the subframe was adjusted so that the axle hole lined up with the datum and held in place with sprung clips I then took some scrap etch and cut two squares approx 13 x 13mm drilled centrally to take the bushes. Before fitting them I squared off the bushes in the lathe with a chamfer to make the subframe holes clip into place easier. The right hand bush and repair plate was dropped into the subframe axle hole and tack soldered in place on the corners. The subframe was removed and the left hand side repair lined up with an extended axle resting on v blocks. When satisfied that all was square that was then tack soldered in place. And both sides finally soldered up. A 16g strip of brass was soldered between the frames above the subframe to act as a vertical stop. This was to keep the footplate parallel with the track.

The bogie is nicely built with fixed axles and weighs about 110g and holds the track well in it’s own right (makes a change) The only modification was to file back the fins above each axle bush to aid clearances

The next butchery was with the forward frames. They were 11mm deep and this was reduced to 9mm. The front cross member fouled the bogie springs and was chopped off at the frames. Now, if the c of g is placed just to the rear of the driving axle by filling the subframe and firebox with lead, there will be 1mm vertical movement on the bogie without upsetting the ride of the frames. Pickups using my method of a U shaped length of sprung wire with one end soldered to a 2mm brass rod at right angles. The other end is soldered to a pcb bus-bar. It’s not necessary to use an insulating top hat bush but it looks neater.

The final photo shows the assembled frames. They fitted the body without fouling anywhere. There was no electrical shorts and after filling the firebox with lead it did a trial run on my test track with 980g of steel resting on the tender. Final weight of the loco is about 1kg. It is now passed to Les for final testing. If the bogie fouls the frames then they can be reduced in depth to 6mm to increase clearance. My only recommendation is to consider changing the gearbox to a 3 stage one so that the motor will slip into the boiler, allowing more lead to be added to the firebox.

Turnbull21603 - Nov 8, 2017 at 9:27 PM
Firstly I would thank Malcolm for his assistance in resolving certain issues that were mainly in the design of the kit.
Regular readers of this forum recall that I was aware of problems with another example of this particular kit and actually built an apparatus to achieve a good balance of the final weight. In the event the locomotive ran freely during running but when coupled to the required test load, which is the scale equivalent of 150 tons, replicating what would have been typical load in the 1890’s the locomotive failed. The failure occurred when a load greater than 850 gram, this being a single diagram K3 PVB, with excessive wheel slip. As Malcolm has successfully built a single from scratch and repaired the other comparable single mentioned above, I handed my locomotive over to him to rectify.
The locomotive, now being back home, will now undergo a rerun of the original load tests before final completion.
Les

Turnbull21603 - Nov 9, 2017 at 1:39 PM
Achilles single, 3032 “Agamemnon “ successfully tested and capable of handling specified load. Locomotive will now be stripped down and finished in correct period livery.
Les.

StephDale - Nov 9, 2017 at 3:46 PM
John,
There is an error in your first diagram. The centre point loading can be anywhere along the top line you've drawn - it doesn't necessarily act in the middle. I can quite comfortably get a 4-4-0 to have 2/3 of its weight on the driven axles so if you used the same methodology (shifting the centre of mass to just behind the leading driver) you could easily get half, or more, of the loco's weight on the main driving wheel.
Steph

Stelfox22047 - Nov 9, 2017 at 5:00 PM
Steph
The drawing was put on by me. The drawing shows the theoretical balance as described in the diagram text. You are right that the weight can be loaded at the back to increase adhesion, But if you fix the driving axle in the frames, then you concentrate the weight between the driver and trailing wheel, a much smaller area, the adhesion exceeds the 50%. The body weight forward of the driving axle tends to pull the c of g towards the driver which is where you want it. As the front of the loco is held up by the weight in the rear, it means the bogie can lift and drop in relation to the track condition without affecting traction. On some of the garden railways we run on there are some higgldy-piggledy track ( a new technical term!) which definitely tests a single.

Les,

Greatly relieved it worked OK!!
Regards
Malcolm

Turnbull21603 - Nov 9, 2017 at 5:32 PM
I will be busy now, for a day or two, as I have now got a pair of singles to paint. After which will be the trial between two different motor/ gearbox arrangements as the Achilles is has a single stage 40:1 gearbox driving the driving axle only, whereas the Queen drives on two axles. Both are powered by the same Canon motor.
Les

Turnbull21603 - Nov 24, 2017 at 8:23 PM

The Achilles is finally completed. It is the longest build that I have undertaken. The build began in late spring and proved to be extremely difficult. The first snag was a total mismatch between the fold up tender chassis and the footplate etch, which resulted in a redesign of the footplate and a major scratch building exercise. On commencing the locomotive once again there was major discrepancies in the three etches forming the footplate. In general the build was a constant battle to make etches fit and look aesthetically pleasing and match the prototype, which after much effort and head scratching did result in a descent locomotive and tender.

After assistance in getting the locomotive to a good balance, which is the introduction to this thread, faults were found in the design which resulted in locking the compensated ashpan and a general distribution of the weight, concentrating this over the driving axle. On return the locomotive was put on my test track and managed to start a load of 1884 grams (tender not included).

Subsequent to these successful tests I decided to change the motor and gearbox. The single stage 40:1 gearbox and Canon motor were replaced with a three stage 40:1 MT range gearbox and Canon motor from MSC.

The final painting, lining and application of the various plates was completed late yesterday and the running trial repeated this morning.

The results were all that I had hoped for the locomotive comfortably handled a load equivalent, by scale, to 220 tons which is much heavier than the trains of the period when the Achilles class single wheelers were in the top link. The actual load was 2522 grams (tender not included) and the locomotive still had plenty in reserve.

I would like to thank the many members that gave me advise and especially my fellow Norfolk Mardler, Malcolm Stelfox for his invaluable assistance.

I am attaching photographs of “Agamemnon “ in her final finished condition.
Les

End of thread