TFW’s workshop

[Tim Watson]

The Raven 4-6-2 class has stretched its legs on the MRC test tracks at Keen House.

What is also rather fun is that one of our librarians located a picture in the Club archives of the very same engine photographed by GP Keen (who became President of the MRC) at Darlington in 1925, at the celebration for the centenary of the railways. Quite appropriate that I am making a model of that engine a hundred years later.


Tim

 

[ianlbsc]

and excellent haulage, 15 with two bogies off! Astonishing. Cheers, most interesting thread!, Ian

 

[Tim Watson]

and excellent haulage, 15 with two bogies off! Astonishing. Cheers, most interesting thread!, Ian

Our 2mm FS test track is a test in all senses of the word.

Tim

 

[Tim Watson]

Now for a change of size and pace: I have re-visited the mechanism for the J50 that shunts Mrs W’s yard. This was originally made by John Greenwood in 1998 with a fully compensated chassis, which was quite a fashionable concept in those days. Unfortunately, it didn’t perform very well with the original open frame Tenshodo motor, due to vibration. I therefore made a CF simple ‘12hr chassis’ comprising a Maxon 816 motor and 1:4 gearbox, driving the centre axle via a 1:21 worm and worm wheel. This has served well in the coal yard itself, whilst the original was put to one side for 25 years. Unfortunately, this replacement chassis just doesn’t like the ramp up to the yard with its tight radius at the KX GY end and some sharpish changes in track level as well.

I was looking at the flexible old chassis and wondered if it would settle onto the track better with a coreless motor and flywheel. The chassis is fully compensated, with twin beams on each side of the frames and a midline pivot at the front.



The motor and gearbox are fully floating with the middle axle.





The Tramfabriek 816 motor had a collar made for it to fit the yoke that had originally supported the open frame motor. A rear motor-mounted tab also engages with a slot on the rear chassis spacer, to loosely restrain any arcing movement of the motor.



The improvement in performance has been transformative. The motor is of course free of vibration and is relatively low down on the chassis. The 8mm diameter flywheel does have a beneficial effect but will be replaced with a slightly longer one at 10mm diameter made of copper tungsten.

This has proved an interesting exercise, taking an historic mechanism - and re-purposing it. It would not stand up to mainline running on CF, but I’m hopeful it will now have a new lease of life in the coal yard. The CF 12hr chassis will probably get re-wheeled and form the basis for an N1 0-6-2.

The body work was looking very tired after 28 years of use and has now been stripped of paint for tidying up. It will be re-painted, probably into GNR grey, hopefully in time for showing on Mrs W’s yard on the Model Railway Club stand at Ally Pally (22-22/3/26).

Tim

 

[Tim Watson]

The big beast is back together again, having done some work on the tender. It will now be fitted with a Maxon 1016 motor and a 10mm copper tungsten flywheel. The 816 Tramfabriek motor didn’t seem quite happy and a much larger, heavier, flywheel could have very interesting properties.





Now the steps are on, it is obvious that the tender is riding a touch too high, but that is easily adjusted.

Tim

 

[Tim Watson]

There is something inherently romantic about a steam loco racing through the night with the light from the firebox reflected in the cab. So here we are, probably a first for a 2mm scale locomotive. This view is one advantage of a relatively low tender front.
.
The boiler, backhead and cab are separate components, with plenty of brass to remove to make a bit of space.

I considered using a very small LED, but that would require a resistor and a diode for reverse running, which all begins to defeat the object of using a small LED. A dear old analogue grain of wheat bulb was the solution, with the leads simply bolted to the frames, straddling the UJ for the tender drive shaft.

I may tidy up the wiring a bit and re-fit a bulb with a thin turned metal sleeve rather than the current light masking which is chrome paint.

At the moment, the light reflects too much off the metal cab floor, but that will improve when it’s all painted and matt. I wonder how many people will notice it on CF, when she’s storming up Holloway Bank with eleven on?

Tim

 

[Tim Watson]

I wasn’t too sure how well the GoW bulb would last as it was running very hot in an enclosed space. Using surface mount LEDs would not have been robust enough in this situation, but I then recalled the use of the lighthouse plastic-embedded LEDs I had used on YR tube platform. This was a good, robust, solution with the dropping resistor tucked in down the side of the worm gear head & bolted to the RH frame; with the stiff -ve LED arm bent down to act as a locating support then bolted to the LH frame. This all required a bit more clearance in the firebox, but I don’t think loosing a couple of grams of brass will affect pulling power too much…




The casing was painted with a chrome paint pen to prevent light escape in unwanted areas.

In theory, there should be a diode in circuit to prevent reverse current on the LED, but the amount of times the loco is going to be running in reverse at speed will be infinitesimal on CF. I have left a trial set-up with 12v reversed polarity power supply for 4hr and it seemed to have no effect.

The colour temperature is cooler than the filament lamp, but that can be compensated for with a wash of clear orange paint on the end of the plastic light rod, further down the line. One advantage is that operationally, the LED has effectively no draw on the engine’s power requirements: it will therefore be equivalent to its stablemates. It also looks a bit more workmanlike.

Tim

P.S. I have subsequently put a diode in series for reverse working.

 

[Grahame Hedges]

Well, I'll be jiggered. This is all very impressive and marvelous miniature craftsmanship. Can't wait to see it finished with a coat of paint.

 

[Tim Watson]

Sometimes making straight forward things just isn’t straightforward. The Raven 4-6-2 class is getting a new motor, universal joint and copper tungsten flywheel. It took five attempts to get the UJ to the correct tolerances, which are quite exacting: a stiff fit onto the 1mm motor shaft and a fraction over 3mm outside diameter, counterbored, with the drive slot cut on the diameter.



The drive shaft is 0.2mm (8thou) steel wire. The flywheel (with 3mm bore) will cover the brass UJ and the front motor bearing.

The tube at the bottom has been adapted to become a securing cap on the end of the UJ to restrain the shaft.



Tim

 

[garethashenden]

If it takes you five attempts, I don't feel so bad about my own efforts!