DJH K8 Caledonian 439 0-4-4 Kit Build

[Dad-1]

Workshop Capers,
My late buddy Ray used to work at Hatfield, for Rolls Royce & De Havilland. They had a new lad and they gave him
a spoon to stir his sugar into a cuppa. The spoon was made of a metal with such a low melting point that it vanished
as he stirred !! They didn't let him drink it !!

The debonder worked, it was only just stuck, could perhaps have just pulled apart.

Anyway, no chance of changing the motor/gearbox chassis. It's been difficult enough to get the one supplied to fit.
The gearbox drive shaft fits through the frames for the forward drive mounting & axle.
In fact the gearbox assembly can swing slightly on the main drive axle. To keep it steady I have a sponge cushion stuck
to the boiler top which holds in place. Here you can see the lead loading !!



Not cynical, but when I came to fit the sand boxes some filing was needed to get back together. I decided to look at the
illustration on page 1 of the instructions that I uncovered today. Guess what, the model used hasn't had the sand boxes fitted.
I've found that type of discrepancy in many a kit illustrations, you would think they would use a well built fully finished
model.



I'll make up the sand pipes later, I've drilled holes to mount them in, needs to be tough as they always get caught on something.



How on earth I'll do anything with the Back Head ? Painting in an enclosed cab even without the roof is almost impossible.

Another quandary - Do I buy another Zimo decoder, or fit the Hornby one that was running fine in my J15 last week, but has been
removed as the J15 is now sound fitted.

Geoff T.

[Mountain]

I would normally say to fit the one you already have, but if you are considering sound then it would be nice for this loco... But is there room?

[luckymucklebackit]

Great Project Geoff, although I did hear a rumour that when Hornby visited Bo'ness to measure up Maude for their J36 release they also took the opportunity to measure up one of the other locomotives in the SRPS collection, wonder what that could have been?

Jim

[Dad-1]

luckymucklebackit,

These 0-4-4's with such a long rear overhang are a devil to get running well.
I've not got that far yet !! At least it weighs a 'ton' and should have good traction.
I'm confident I can achieve a reasonable working loco for the straights, getting around
curves is another problem that I'm expecting. I think 1st radius will be a no go, 60" perhaps ?

Mountain, the large bunker is empty, loads of space of a speaker and chip. My concern is that
putting say £110 worth of sound would be wasted if it's a poor runner because it can't take curves.
I've just fitted a speaker into my J15 tender with the matching Zimo decoder. It works well, but
I knew that loco ran really well including 1st radius curves.

In the shed I have a SR 'Z' 0-8-0 kit, after this, Will I, Won't I ?? Do I know anyone who will make for me ???

Geoff T.

[Bigmet]

...Another quandary - Do I buy another Zimo decoder, or fit the Hornby one that was running fine in my J15 last week, but has been
removed as the J15 is now sound fitted...

No quandary at all, try it on the Hornby decoder, see if it does the job, conclude it doesn't, and install the Zimo that you have already bought against this eventuality.

(The Hornby decoder will be 'flattered' by the J15 mechanism, which presents no challenges even at dead slow, due to the flywheels and what I estimate to be a 44:1 reduction from the multistage gear train. I have some confidence in this evaluation as the most recent Hornby decoder I have experienced came in a Hornby DCC fitted B17. It couldn't manage smooth slow movement up to scale for 4mph, thereafter OK; but the Hornby mechanism with decoder removed, was smoother at dead slow on 'vanilla DC' from the H&M Duette used for DC test. The decoder was actually degrading the intrinsic mechanism performance, and there are no adjustments on this decoder to fix this.

This decoder went into a Hornby 08 which I was decoder fitting for a friend, and he was happy with the running - the 08 has 2.5x the reduction between motor shaft speed and tyre speed compared to the B17, and the addiitonal benefits over the B17 of both a larger motor and a flywheel - it would creep into motion on speed step 1 and run smoothly at scale for 0.3 mph.

Horses for courses in short. It was much the same story with the Bachmann 36-543/544 which were badged ESU lokpilot v1. These were cheap, like sub £10 at first release compared to the circa £25 for the 8 pin Lenz Silver; and produced the same on track performance when used in heavy centre motor twin bogie traction, for a great cost saving. But no good in steam locos, even with the EMF sampling and feedback carefully optimised, always some 'granularity' at slow speed.)

[Bufferstop]

The phrase "Vanilla DC" hardly fits the output of of a basic DC controller. It's raw rectified AC. If you can imagine the sinewave of AC then the output of a "DC" controller looks like the sinewave with every other hump turned the other way up. Comparing it to the output of a battery. is like comparing a cobbled road to a sheet of ice. Fitting a large value capacitor across the output of the bridge rectifier before it is connected to the reversing switch will leave you DC with a slight ripple which most motors respond to by running much quieter.

[Dad-1]

Luckily I only run DCC.

I'm trying to decide just how I arrange the pickups.
I can't see much reason to have wheel wiper pickups on the un-insulated side. In theory the
whole chassis & body will be live.
I'm fabricating a block of plastic & copper-clad with two wire wheel wipers, one for each
insulated driver.
Non-insulated wheels on the rear bogie eliminate using that, so pickup will be limited to a
rather short length of track, not ideal. I was baking today and weighed it, a kiss over 275 grams
without the rear bogie, a little over 300 with it. Quite heavy which should give a promise of
decent traction.

With my eldest son having come back from his ex-wife & children at Scunthorpe with Covid on
Tuesday I'm now just a little anxious. I'll not be rushing this or anything else !!

Geoff T.

[Bigmet]

The phrase "Vanilla DC" hardly fits the output of of a basic DC controller...

I'll try to think of an alternative term for a subjective description, applicable in the context of nominally 12V DC model railway. It became apparent early on in my participation on internet fora that 'diode rectifier bridge DC from a resistance controller' was too much for many readers; and suggestions that the deficit of understanding might be remedied by taking the physics A level course was 'unpopular'.

The basic point stands unchanged: this very rough and ready DC supply was comfortably superior at running the motor, than what should be the far more refined supply from a decoder.

[Bufferstop]

With a total lack of active components beyond the bridge rectifier the motors generated back emf forms a rudimentary self regulating system. The back emf rises and falls to almost equal that output by the power unit. The difference being the power taken to drive the train. Our physics teacher had a rather battered Hornby Dublo set in a box in the prep room, it would come out and the class would be asked to measure the resistance between the wheels and pick up. Then measure the voltage and current with the loco running. The test was to explain why the current predicted by ohm's law was not being drawn. The test was to see who'd been awake when we did motors generators and back emf.

[Bufferstop]

We mustn't forget the difference a good mechanism makes to anything that we can make with electronic tweaks.