October 2018 – Roundhouse Brown Marshall Disc Signal

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October 2018 – Roundhouse Brown Marshall Disc Signal

By Simon Fletcher

Photo: Roundhouse Engineering, used by permission

This all started with a visit to Roundhouse’s open day with a couple of mates, two years ago. I saw the kit, thought “ooh, that’s nice” and bought it. The kit lay about for a few months and then I thought I’d better get on and build it. Straightforward enough… until I looked at the lamp casting. As a historical boat builder, if it has lights, then they need to work. I couldn’t bring myself to just paint the casting as Roundhouse depicted – it just wouldn’t do it justice for me. So, Plan A was to cross-drill the casting and spend ages with the Dremel hollowing it all out so that a bulb could be accommodated. I cross drilled the casting at 6mm and then lost all interest in the prospect of hours with the Dremel. I’d assembled and painted the column and platform brackets, but then put it all back in the bag.

Fast forward over a year… now getting pigged off with keeping shuffling this bag of bits around my bench, so decided to get it finished. I stared at the casting, wondering what else I could do that would avoid the dreaded Dremel. The biggest challenge with the Dremel approach was how to get an accurate finish around the lamp glass bezels; the remaining material would be 1mm or less and this felt a bit too challenging. In the intervening year or so, I had found and bought some 12mm dial glass cabochons (domed glass blobs), so knew what I had to do to the casting. Whilst still mulling the pros and cons of should the cast bezels stay or go, I came up with Plan B: do it in the lathe. That way, maybe the lens bezels could stay… and save me yet more work.

Which sounds fine, until you realise that white metal has the dimensional stability of soft cheese! So, on with my ancient 4” 4 jaw chuck and grip (ever so gently) across on pair of ‘lenses’ and the lamp base and chimney.  I suggest centring using a reference point in the toolpost; the casting is not really up to ‘clocking’ to centre. Once happy, I went through with an 8mm drill. Having done that, I set about machining out the cast ‘lens’ and rebating. As the glass blobs were a bit rounded at the edge, I’d already decided they needed a small amount of filing anyway (more later). So machining out the bezel i.d. to 11.3mm was the plan. Having achieved this, I spun the casting around in the chuck to do the opposite ‘lens’. All good so far, but how do you hold what is now a distinctly hollow piece of soft cheese to do the remaining two faces, without damaging those carefully preserved bezels? This caused much more thought, but raiding my model boat material stocks, I found some 3/8” styrene tubing. Just hand drilling (as in holding the drill with my hand; no mechanical assistance!) with a 3/8” drill produced a small step in the casting into which some small pieces of styrene snugly fitted (see photos):

Once two small bits of plastic could be used to grip the casting, without destroying my bezels, it was then possible to machine the other two faces

So now I had to bore right through to 3/8” to allow another piece of styrene tube to pass right through such that the chimney and base to be drilled… the picture is better at showing this:

Now I have four cleanly machined lens rebates, a hole for a chimney and a hole for the pole. Success! A bit of Dremel work was then done to tidy up the inner surfaces (open up the internal corners), but much less than if I’d attempted Plan A.

But all this effort will be in vain if I don’t consider the light source. Roundhouse supply a nice length of 3/32” brass rod for the disc and lamp to sit on, but this was replaced by 3/32” copper tube. Plan A had something to do with the tube forming one electrical path, but luckily my 6v bulb wires both fitted down the tube, so Plan B, Section 2, paragraph A, meant I could avoid some very fiddly soldering and assembly. A nice relief.

As yet another photo shows, the bulb (which needed some very careful fettling of both the tube and bulb potting resin) now fitted together. It just so happens that the top of the copper tube and bored out casting, when lined up, put the bulb in about the right place. I know this, because my first estimate and trial build put the filament too high up. Grrrrr…

Having sorted out the casting and illumination, it was now a case of coming up with a cap for the hole in the chimney. You could gamble on not using the chimney at all, but even grain of wheat (GOW) bulbs get warm. I was going to dome a piece of sheet brass, solder on some legs and have a push fit in the chimney… but I gave up and turned a cap up in the lathe. Some may say this is cheating: but it’s my story and I’ll cheat if I want to! The cap has four 0.6mm vent holes drilled just under the cap, too.

I’ve included lots of photos because every step in this build has its own story. This is the abridged version, honest! Only thing now is to find some red glass blobs.

Oh dear: red blobs not apparently fashionable so will have to think again. This time it was Hobbycraft to the rescue: glass paint. I needed to file down the outside diameter of the cabochons… which needs diamonds. A diamond file, or even a diamond sharpening stone does the trick. And patience.

Which leads on to the test illumination just to prove it all still works. And it does.

The glass paint is a bit strange; very thick and gloopy. I tried thin coats, but left brush marks, so opted for one heavy coat which seemed to be OK. In hindsight, maybe a slightly less thick coat would have been better, but I’m getting picky now.

Now this is where the assembly order is tricky and needs some forethought. The signal disc is intended to be epoxied on to the spindle, but I’ve never really trusted epoxy and white metal, so had decided to make some brass brackets which were to be soldered to the spindle.  The disc would then be glued and supported by brass modelling pins for structural support. I needed to do this before threading the bulb wires down the spindle for the last time. Brass strip for this came courtesy of surplus fret from a Slaters 2T slate wagon. I could then glue the lamp casting to the spindle. I also took the opportunity to add some lamp detail: a hinge and locking bar (see photo) just to up the detailing a touch. Plan properly: these details would most likely be on the platform face of the lamp when in the stop position. I knew this and planned for it and still got it wrong, so fixed it soon afterwards. Muppet!

At this point, the signal spindle assembly was pretty much complete. Hard work? Yes, but worth it. Oh, worth noting that I added a bit of tiny heat shrink sleeving over the bulb wires to protect them where they exit the spindle at the base end. You don’t want all this hard work to be ruined by the spindle chewing through the wire insulation.

Assembly of the signal post was largely as Roundhouse instructed, with the key difference that I added a short length of modelling pin as reinforcement to the platform-post joint. Thoughts now turned to the base. Rather than a simple base plate, I needed something that could house the battery pack. I’d already bought a 4 x AAA box with integral switch, so the base needed to house this. I settled on a sort of planked design. Some walnut was used for the main bearers, whilst parts of the planked ‘deck’ used other sections of walnut, where strength was needed. The remainder were stirring sticks. To mount the signal post to the base, I started to turn up some simulated bolts, but after one, I abandoned that idea and made some 10BA studs and nuts instead. Even accounting for milling up some brass bar into hexagon, it was still quicker than ‘faking it’. So the column ended up being bolted to the base. No glue required.

The ‘how do I operate the battery box switch?’ question perplexed me, but soon worked out that if I used the signal post tube as a fulcrum, that this could be done.  Again the photos show what I’m talking about. The switch blade is retained by nothing more than a piece of wood.  Of note here about the woodwork is that I use thin superglue and fillets of Kapow filler to massively improve the structural strength of the joints. I wanted to get a kind of creosoted look, so “Jacobean Dark Oak’ wood stain did the job. The stirrers needed one coat first before giving three further overall coats.

The ladder needed some brass brackets making to complete the look, and I wanted some rake to the ladder, hence the extra block riser on the base.

Looking back, this is a huge article (and I have missed out some parts) for something most would consider rather simple. But as with all such contributions, the value is in the inspiration it gives others. You can build kits as intended, or you can take on the challenge to improve upon them. This article is just an illustration of what can be done. I kind of feel guilty in having a lathe; it’s a luxury I have waited a long time to acquire and recognize not everyone is so lucky. But don’t worry: I see kits as their own challenge. You decide how far you want or are prepared to go.

In conclusion, was it worth it? The final pictures show you what the result was, so you decide if it’s an inspiration, or you think that I’m completely mad. You might also notice the signal control capstan: that I will save for part 2…

2018-10-03T08:56:25+00:00October 1st, 2018|Model of the Month|1 Comment

One Comment

  1. R Halcrow October 11th, 2018 at 2:11 pm

    A great effort I like things that work as they should

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