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Making a Sandwich


MikeOxon

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Having sorted out my ideas about the make-up of the Mail Train involved in the Bullo Pill accident, I have been turning my attention to the locomotives. The Mail Train was headed by one of the big ‘Waverley’ class (a.k.a. ‘Abbott’ class) 4-4-0 engines, for which no model kits are available. The unfortunate cattle train, which the Mail Train ran into, was headed by a Gooch ‘Standard Goods’, for which the Broad Gauge Society (BGS) supply a kit.

 

The Gooch ‘Standard Goods’ engines were the most prolific of all broad gauge engines and were large 0-6-0s by any standards. The cylinders were the same 17” x 24” size as Dean’s much later ‘Standard Goods’, while the boiler was of larger diameter and the grate measured 19.2 sq.ft., against only 16.4 sq.ft. for Dean’s version. For an 1852 design, these were remarkably large and powerful engines. They did not spring into existence ‘out of the blue’ but were a progressive development from Gooch’s earlier ‘Pyracmon’ and ‘Caesar’ classes.

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Gooch Standard Goods ‘Nemesis’

 

An important feature, from my point of view, is that the boiler was identical to that fitted to the ‘Waverley’ class 4-4-0 engines, so I want to explore the possibility of converting the BGS Goods engine kit into a model of the Mail Train engine as well.

 

At first glance, the BGS kit looked rather intimidating, with a very complex pair of etched brass frets and a variety of additional castings. The instructions looked rather sparse but pointed out that “these are essentially simple engines …. less difficult than at first appears”

 

I gained confidence when I read further comments by other BGS members who have built this kit. In particular, Christopher Jones confirmed that “An awful lot of the etch - esp. in 4mm - is stuff you don't really need .… the etch also provides lots of spares (great for the scrap box) and bits for alternative versions. There's quite a lot left over when you've finished!”

 

The instructions suggest starting with the chassis and I decided to do this, especially as I wanted to see if it might be possible to alter the layout to a 4-4-0 design. The etches for the frames are in two parts, representing the inner and outer ‘flitch plates' of the sandwich frames. The instructions simply state “raise the rivet detail and sandwich a length of Bullhead rail or brass bar between the two etches”

 

I decided that I needed to learn a lot more about sandwich frames – how were they really constructed and what were the relevant dimensions? According to John Gibson in his book ‘GW Locomotive Design’, “the sandwich frame … consisted of two iron, later steel, plates, which were quite thin, 3/8 or ½ inch, with oak blocks some 4in or 5in thick between them, the whole being fastened together with bolts and nuts.” This told me that the ‘flitch plates’ provided in the kit needed to be spaced between 1.3 mm and 1.7 mm apart, to represent ‘real’ frames in 4 mm scale. There is a good description of building a ‘real’ pair of sandwich frames in Harry Holcroft’s book ‘GW Locomotive Practice’.

 

Since I have a Silhouette cutter, I thought it would be interesting to try and represent the wooden central layer between these outer plates by means of a card ‘infill’. To do this, I first scanned the brass fret at actual size, selected the frame components, and then used the ‘find edges’ filter in Photoshop to produce an outline drawing, as shown below:

 

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After a little simplification to remove unnecessary features, I imported this drawing into the Silhouette ‘Studio’ software and used the ‘Trace’ command to convert my line drawing into cutting plans.

 

The ‘trace’ software actually produced pairs of lines corresponding to the inner and outer edges of my drawn lines. To ensure that my card ‘infill’ would lie within the outline of the flitch plates, I deleted the outer lines around the edges of the plates and removed the inner lines around the various apertures in the plates, as shown in the diagram below:

 

blogentry-19820-0-13442800-1490139607.jpg

 

I cut out six sets of card frames and laminated these into a pair of three-layer frames, by means of bookbinders adhesive.

 

Before assembling the frames, I used a centre punch to raise the rivets on the outer flitch plates, following the guide marks on the backs of the etches. I then soldered a length of BGS Bridge Rail along the top inside edge of the outer (embossed) flitch plate to act as a spacer from the inner flitch plate. After tinning the inner plate, I aligned this with the outer plate, using both the Bridge Rail and the card infill as spacers. I then sweated the frames together along the length of the Bridge Rail.

 

A very important point about using card rather than, say, polystyrene, is that it was not affected by the heat of the soldering process. I was able to confirm this by removing the card infill after soldering and finding it was undamaged – barely any signs of charring. I could then wash the brass frames thoroughly, to remove any flux residues, and re-insert the infill when the frames were dry again. The card is a firm fit between the outer plates and I have not used any adhesive to hold this infill in place. I anticipate that the final painting will be sufficient, when the locomotive is finished.

 

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I felt that this was a satisfying process, which has resulted in a strong frame with a good ‘solid’ appearance, when viewed from any angle.

 

I also feel that, with the help of the Silhouette cutter both to cut out the infill and to scribe the outlines of the flitch plates by means of a diamond scribe tool, I shall be able to produce my own sandwich frames to the dimensions needed for a ‘Waverley’ 4-4-0.

 

The next task will be to proceed with construction of the boiler and how it might be fitted to alternative frames.

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  • RMweb Gold

Great work Mike, this must be a world first!

 

The result is as you mention a sandwich frame with a real sense of depth and mass. Out of curiousity, your quote mentions oak blocks but you have modelled a full wooden layer. Was there any particular reason for that?

 

I've also been trying out the Trace feature. In theory you could scan an entire etched brass kit. This could lead to copyright issues very quickly!

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  • RMweb Gold

Fascinating post Mike, I'm thoroughly looking forward to the next instalment!

 

Dave

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Great work Mike, this must be a world first!

 

The result is as you mention a sandwich frame with a real sense of depth and mass. Out of curiousity, your quote mentions oak blocks but you have modelled a full wooden layer. Was there any particular reason for that?

 

I've also been trying out the Trace feature. In theory you could scan an entire etched brass kit. This could lead to copyright issues very quickly!

I can't believe others haven't followed similar lines but using the Silhouette cutter made this approach much simpler than manual cutting.

 

Holcroft's description of the process of building these frames states "carpenters then came along and fitted slabs of oak in all the intervening spaces"  I suspect this means that most of the space, except where there were already 'distance pieces' or other fittings such as spring hangers would be filled with timber.  My 'full layer' was an aid to assembly since it acted as a jig when I clamped the the brass plates together for soldering.  i had spent some time thinking about how to keep the plates parallel before arriving at this solution.

 

Your comment on copyright is interesting.  I had thought of including a photo of the complex frets, to illustrate my point, but decided against it, for precisely this reason.

 

 

Fascinating post Mike, I'm thoroughly looking forward to the next instalment! Dave

I hope you won't have to wait too long :)

 

 

A clever way of tackling an awkward assembly. 

It took some time to get there.  A key point was that the 'fill' held the brass frames in the correct alignment during soldering.

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An interesting method Mike, I too will be following this build with great interest.

My first scratch built Rover was made with sandwich frames fretted from brass sheet and burnt fingers, oh! how I wish I'd had my Silhouette all those years ago ! Worth its weight in gold in my opinion with so many options being opened up.

 

Grahame

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  • RMweb Gold

Yes Mike very clever.  It does make a build an accomplishment for each part rather than needing the whole thing finished before you get a result.

 

Just a question, wot I fought of tonite as I red this.

 

Are you going to model the accident as the accident with smashed up locos and coaches, or as two trains rapidly approaching each other so that you can still have working models if you want to, or a crash where the parts are just lying around, the coaches of course still upright as they are broad gauge?  You have probably said this before but I have missed it.

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Good questions, Chris.  For the moment, I'm using the accident report as a recipe for building models of 'actual' BG trains, as they were running at a particular time and place. 

 

This approach has allowed me to narrow down my research to very specific areas.  The idea of modelling the smash itself does not appeal.  Perhaps I shall need to call up some alternative facts, with a very near miss that was still enough to attract a crowd of onlookers. 

 

There are lots of modelling tasks to keep me occupied for quite some time, before I shall have to make these difficult choices :)

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