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Saturday 30 August 2014

GBL BoB - Part 6

I fell headlong into the Brunswich Green trap for a BR(S) period livery.

The GBL BoB lining, number, nameplate and shield were removed by rubbing white toothpaste over them with an old tooth brush. This was a tip from RMWEB which recommended toothpaste as it does not have a chemical composition that could damage the underlying plastic. The toothpaste is effective but also removed the paint finish revealing the black plastic beneath, which was unaffected showing no scratch marks from the rubbing.

The body work was sprayed with Halfords grey primer and then Brunswich Green (Humbrol #3) after which I thought the green looked too bright compared to photographs of the prototype. (I know paint matching to photos is a big no, no). I started to research further and found that Brunswich Green is a misnomer for what should be called BR(S) Dark Green. A couple of model paint manufacturers supply the 'correct' green but I was not sure these were definitive for BR(S) locomotives of the late 1950s early 1960s. Furthermore, some commentators recommend a lighter shade than the correct green because of the effect of light diffusion on normal model viewing distances of 25 - 75 yards in 4mm scale. I looked at my loco stock from Hornby, G.R. Wren and Mainline and they all had different shades of green for the same period and even different shades across Hornby locomotive classes! I realised I had entered the minefield of paint matching. I decided to mix my own paint to achieve a shade somewhere between the dark Hornby green and lighter Wren green. The Mainline colour was far too light.

My mix was made from what I had available, Humbrol brunswich green 3 (gloss), green 30 (matt) and gloss black Interestingly, the mixing of gloss and matt gives a silk finish like the finish of proprietary models.

The first spraying looked OK in natural light but appeared too light in artificial light and of course whilst still wet is darker than when dry. Very difficult to get right but further refinement of the mix gave a finish that fared better in natural and artificial light and sat well between the Hornby and Wren paint finishes. However, in full sun it takes on a lighter shade! (I'll live with that). I can't give the paint proportions as it was trial and error.

Some detailing has been added. The pipework below the cab was made from soldered copper wire and replaced the GBL modelled pipework, which was totally incorrect for this side of the cab in the photo. Vacuum pipes, steps and screwlink coupling added to front buffer beam.

More to do - details and lining etc.

To Part 7

To Part 1

Monday 25 August 2014

GBL BoB - Part 5

I spent ages comparing the buffer beam position and size against a scale drawing of the locomotive trying to decide where the main error was, what to fabricate and where to make the cut.The dimensional errors are the valance height, buffer beam height and the height of the vertical panel above the buffer beam. All need their height increasing to match the scale drawing.

Of particular concern was the valance above the front bogie that curves around the front because cutting into that and fabricating a replacement could be tricky. I noticed from prototype photographs that some locomotives in the class do not have a valance. I then checked out the actual engine that I am modelling (to be revealed later) and found it belonged to be one of these. This makes the modification much easier. It was a simple case of a straight cut with a razor saw to remove the valances and offending buffer beam parts.

The replacement buffer beam was designed and 3D printed in three parts that were then cyanoacrylate glued together and to the body. It is difficult to show the detail because the white plastic tended to bloom in the photo. I have played about with it in a photo editing application to try and reveal the detail. Trust me, it looks better than seen in the photo.

The circular Southern ring on the front of the smoke box door was very carefully dremelled away with the grinder attachment so that just a small remnant remained. This was scrapped away with a scalpel, which leaves a more shiny surface that the dremel does. Finally, this area was polished with the dremel polishing pad attachment.

The white areas are to be painted.

Finally, I was pleasantly surprised to see that a Zero 1 chip can be located within the body without interference or modifications. It is stuck with double sided tape on top of the chassis weight.

To Part 6.

To Part 1.

Thursday 21 August 2014

GBL BoB - Part 4

Here is the 'Great British Locomotives' Battle of Britain body fitted to a Hornby motorised chassis.

And this is how it was done.

1. Coupling Peg

The coupling peg from the GBL pony truck was cut off and glued to the tender coupling and excess removed so that the tender and locomotive coupled closely ensuring it still went around curved track without hindrance.

Getting the peg to mate with the loco chassis was troublesome because the chassis part has springy electrical pick-ups that tend to push the lightweight tender upwards off the track. I did not want to cut off the pick-ups, even though they are not used in this implementation, because I wanted to keep the chassis intact as possible in case it is redeployed in the future. So, by a combination of spacing off the chassis coupling by about 2 mm and thinning the peg flange an acceptable fit was achieved.

2. Chassis Modification

The width of the body is narrower than the cylinder block on the chassis, which needs to slide/locate inside the body by a few millimetres. I had to grind back the cylinder block and relieve a bit of the central protrusions to achieve the fit. I don't think this upsets the fit of a genuine Hornby body if it was decided to fit one later.

3. Body Hacking

That red slide bar bracket also locates inside the body. It is not practical to cut it back to fit so, the body sides were thinned to 50% of their thickness in the area of the cylinder block and slide bar bracket.

Further relief was created as shown in the photo to accommodate other parts of the chassis and a new chassis screw fixing block fitted. Whilst cutting out the internal ribs the Dremel sliced through the body at the roof line leaving a slot a few millimetre long! This was filled with a slither of plastic card, which can just be seen in the photo top of this posting. Once painted it will be fine.

At the other end of the locomotive GBL had made provision for the Hornby chassis locating lugs. But, either the body overall length is shorter than Hornby or the bulkhead position is incorrect (I suspect the latter) because the motor bracket wants to stick further into the cab. The bulkhead is poorly detailed so I had no qualms lengthening the lug locating slots to allow the motor bracket to fit, which cut into quite a bit of the detailing. It would be possible to modify the motor bracket to avoid or minimise this modification but once again I wanted to keep the chassis as original as possible.

A new floor was fabricated (to be painted) because on the GBL model it is part of the chassis. The chassis resting block in the photo is where the locating lugs rest.

The bulkhead is not easily seen normally and with driver and fireman fitted even less of  this bodgework will be noticeable.

For those wanting a working Southern liveried locomotive then that completes the project. For me it is not the end. Here is a list of further work I'll be undertaking.

  • Correct the front buffer position and size
  • Remove the Southern ring from the smoke box door
  • Re-livery to BR period, early totem
  • Fit nameplates and shield for a west country class
  • Fit window glass
  • Fit Hornby speedometer cable
  • Fit a Zero1 chip
  • Anything else that I think of

Monday 18 August 2014

GBL BoB - Part 3

This is the disassembled locomotive body.

Only the body is required. Note it is hollow with strengthening ribs inside.

Motorised Chassis decisions

My first thought was to 3D print (I have a printer) the chassis, bogie and pony truck and buy a motor, axles, gears and wheels. A nice, cheap project to print some of the components. I looked into the cost of driving wheels and motor, which came to nearly £30 alone so, had second thoughts. It was going to take quite a bit of time to design and not be cheap!

Why reinvent the wheel when Hornby produced a nice motorised chassis. I looked into buying the individual components that make up its motorised chassis, all can be obtained apart from the metal block it seems. I started to total up the cost of parts and gave up when it went above £50. I also looked at a chassis kit available from a kit manufacturer and this came to £35 without wheels and motor.

I went onto Ebay and found several complete Hornby motorised chassis. Snapped one up for £34 + postage not knowing for sure whether it would be suitable but as the GBL model is a copy of the Hornby (albeit the 1980s model) there is a low risk of a serious mismatch.

Here is the GBL body and Hornby motorised chassis. The body internal ribbing needs to be removed and some other modifications to do before they will fit correctly..

Project cost to date £46.98 + tender wheels and coupling from spares box and DIY 3D printed tender chassis.

Average used Hornby model (high tender) price £81.

To Part 4

To Part 1

Wednesday 13 August 2014

My Dapol M7 Bogie Wiper Contacts Broke

If you have insulated frog turnouts then failure of the bogie electrical pickup renders the locomotive pretty useless as it will stall on the frog without the bogie pickups conveying that additional source of power at the other end of the locomotive to the driving wheel pickups.

The bogie wipers make contact on the electrical collection strip that is fixed to the chassis. It is not a very reliable connection and if you fiddle with the wipers trying to remake a failed contact then they will eventually break, most likely on the bend. Furthermore, if the bogie is removed and refitted then the wipers can get trapped between bogie and chassis weakening them.

I have never liked the fallibility of this part of the design but cannot think of an alternative to convey power from the bogie to the motor whilst allowing it to be removed for servicing. But I have come up with a method used to repair broken wipers. This only works of course if there is still part of the wiper remaining.

I used 0.2mm wire. One end is soldered to the chassis collection contact and the other end to the bogie wiper. We have to take care not to melt the plastic. Just a touch of the iron and solder on the contact and wire is enough to form a solid joint.

The wire needs to move in unison with the bogie as it rotates on its pivot. This is achieved with an omega loop formed in the wire (although in practice mine is a semi-circle). The loop opens and closes in unison with the bogie as it rotates. There is some spring back of the bogie but no more than the original and it goes around 9 inch curved track without derailing.

This is a far more reliable electrical connection than the original design but removal of the bogie is now compromised. If it needs to be removed for servicing I'll probably have to desolder one end of the wire(s).
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