Rectangular Tar Tank

[MikeWilliams]

I was thinking the other day that there needs to be a few more threads on here about what people are making, either for themselves or as production runs. A bit like Keith's Bubblecars. Then I thought perhaps I should put up or shut up, so here goes.

Tar Tank

This is all John Candy's fault because he suggested it! John and I have been thinking how to keep costs down and introduce a small range of kits which are entry level, but dimensionally correct and with no less detail than more up-market kits.

John's idea was that by designing a wagon kit in a series of simple parts it would be possible to cast them in resin at home and save the cost of professional casting, which is typically about a third the total cost of a kit. John made Plastikard patterns for a wagon underframe - the skeleton we call it - which he cast himself and then taught me to cast. Because the casting doesn't include a floor this needs to include the prototypical diagonal framework in order to give strength. The casting is devoid of all detail except little dimples for buffers, couplings and W irons, all of which are then drilled through by hand.

The diagonal framing prevents to use of my usual pre-bent W iron units, so we needed another way of keeping them in the right place in all three planes. The solution is the noted dimples in the solebars which are drilled through and 6BA countersunk screws and nuts used. The final location is done by eye on a flat surface, and the nuts then nipped up tight. I also assemble with Araldite to make quite sure they can't more. Home-cast resin overlays are then stuck to the solebars and headstocks to cover the screw heads and provide the detail. Since many post-Grouping railways used 16ft 6in wagons built to RCH designs, the same skeleton can be used with different overlays for detail correct for each company.

We agreed that the first wagon would be a tar tank. One reason for this is that back in 1907 they used the same 16ft 6in underframe, so the kit could use the standard fittings I already have with no need for the cost of new patterns, moulds and castings. Having said that, post-1923 patterns are on the way. My job was to make the tank. We thought about fabricating a pattern in Plastikard but there are a lot of rivets which would all need to be marked out individually. I considered 3D printing but although that would be fine for the main structure, small detail like rivets don't come out well with that process. Since some etched details like straps, corner plates and end stanchions would be needed anyway, I decided to etch the whole tank too. That still left some decisions to make: should the final product have an etched tank, or would that be a pattern for resin casting?

Well, if each kit had an etched tank, the builder would have to fold it up and either punch all those rivets, or add them through holes provided, and we thought that was too much to ask. So, the etching was the pattern, but the question of rivets remained. In my opinion half-etched rivets are horrid because they either look like discs with flat tops, or they are far too small. If they were half-etched from the back, then we were concerned that after punching those long rows of closely-spaced rivets the sheet would kink and it would be hard to fold to shape. Incidentally, the rivets are so close together that a special dolly would be needed anyway, with a flat on one or two sides. Therefore the decision was made, the artwork changed and the rivets were etched holes, into which small actual rivets would be added.

In the next instalment I'll tell you what happened when the etchings came back and post some photographs......

Mike

[MikeWilliams]

Here are John's pictures of the main chassis parts.

Mike

[keith Bristol]

looks good Mike.... Ill start a thread later in the week on the OaK foster yeoman hoppers I am making....

[hornbeam]

looking very good Mike, like the idea of a chassis for the Bachmann opens as well.

[Richard T]

At last - an underframe - this is going to be useful Mike.
Can you expand on the W irons, it sounds like you will make individual W irons available to bolt to the inside face of the solebar - is that the plan ?

Richard

[MikeWilliams]

Hi Richard.

Yes.  In the early days I had separate W irons and crossbar, but some were not keen on soldering steel, so I changed to a pre-folded single unit.  That was fine, but location of the brake V hanger required some care by the builder, so for some kits I tried pairs of W irons for each side including V hangers, and using the same crossmembers.

Because the framing gets in the way, these use the same original single W irons in which I had included a couple of holes "just in case they might come in useful one day".  I have to make sure the back face of the solebar is dead square and both the distance apart and wheelbase are not absolutely positive as in the other methods, but with care it works very well.

To make it really easy for people I'm minded to offer underframes RTR - but since I only have one actually finished at the moment, that's a bit premature!

Brakes are an issue - more on that later ....

Mike

P.S. Great to see you back.

[MikeWilliams]

The etchings were done by Precision Photofabrication Developments Limited (PPD) this time and came back quickly. All the brackets, straps, owners' plates etc came out well - better than expected in fact. Making representations of cast iron plates in this way is not so easy as some may assume because for every thou the acid etches down into the surface of the sheet, it also etches sideways. For that reason, many etched nameplates, numberplates etc are made in very thin material. I wanted to put the whole lot on one sheet to keep the cost down, which meant 18thou brass and all the lettering thickened up so that after etching it would be reduced by 9 thou either side and come out to the correct width again. Even that is not easy because if you take a letter like a "B", thickening all the lines enough for 18thou brass means that the two holes in the letter disappear altogether. In short, its a compromise, but I've done a large number of plates now and it all worked well.

Back to the tank itself. It folded up easily, but as the rivets were originally going to be half-etched from the back, I had forgotten to enlarge them sufficiently to take the actual rivets. Therefore every hole had to be drilled out by hand, and then the burrs removed with a larger drill, and then 1/32in brass rivets inserted and glued in place. At the joins, the long rivets on one plane interfered with those in the second and third planes, so many rivets had to be cut and filed to length before being inserted - a time-consuming job.  To make it worse, I had expected the rows of rivets at joints to be staggered as that would be easier to peen them over in real life, but they are actually aligned, meaning that the vertical and horizontal rivets exactly get in each other's way inside.

After several days of this - actually several weeks, but full time equivalent of several days - I've now completed all the rivets on the top face, both sides except the bottom row (all of which can be full length rivets, so quick), and just the ends remain. I totted that up today and I've "only" got 450 rivets still to do! How depressing! Drill - countersink - cut - file - insert - glue. Drill - countersink - cut - file - insert - glue. Drill - counter.... zzzzzzzzzz!

Mike

[MikeWilliams]

Here are some of the plates.

[MikeWilliams]

And here are the first rivets inserted.  The size of rivets is an art, rather than a science, as the ratio of head to shank varies between sizes and manufacturers.  I selected these as the size of each head and the gap between heads looked to be about right compared with photos of the real ones.

Mike

[MikeWilliams]

By the way, the half-etched strip across the tank is not prototypical but a) helps locate the strap in the right place; b) reduced the apparent thickness of the strap to something closer to scale.  I guess it could have been 1/4in plate at the most, which is less than 10thou on the model and would easily kink.  Model strap is actually 18thou, so if half is hidden it should look about right.

Mike

[MikeWilliams]

Here's John's resin casting for the filler.

Mike

[MikeWilliams]

Back on the job and another 97 rivets done yesterday.  I've just realised that the lower parts of the ends are completely hidden by the baulks of timber, so I could miss out those rivets.

And just as I was thinking I never want to see another rivet again John Candy suggested doing a circular petrol tank too.  Argh!!!!     (only joking John)

Mike

[John Candy]

Mike,

Well, I searched high-and-low for any evidence that a "flush" finish tank (whether of rivetted or welded construction) existed prior to the grouping but have drawn a blank.
If anyone knows of any such wagons, we shall be pleased to hear from you!

Photographs suggest that the cylindrical tanks had fewer (larger) rivets at wider spacing than the rectangular tanks (perhaps a consequence of the greater inherent strength of circular objects). I think it only fair that it be my turn to deal with the rivets next time around!

At present I am focused on the RCH dia. 98 from 1911 for a 14 ton tank on an 18ft underframe (the "skeleton" for which I am about to commence work).

This will produce both "cradle" and "saddle" mounted designs and were used for both classes "A" and "B" traffic, so there will be plenty of scope for variety in detailing (both Shell and BP, in particular, owned a lot of these and several photos exist of them liveried for the familiar "Mex Fuel Oil" traffic).

John.

[Traininvain]

Blimey! Will you be including the lateral and longitudinal tie bars?

By the way, I would like detailed articles describing the preparatory and production work involved in these models please for the G3 Newsletter. Deadline for the 1st article - approx 1,000 words + hi res images - is 15 November.

ho ho

Ian

[John Candy]

Ian,

The tanks will be fully detailed with a "proper" open underframe pattern and are expected to be surprisingly affordable....that is the aim of the new range of wagons being designed in conjunction with Mike and based around the "skeletal" underframe concept for which I am producing patterns for 18ft and 17ft 6ins over headstock patterns (in addition to the 16ft 6ins pattern already produced for the tar tank and RCH 1923 coal wagons).

The versatility of the design revolves around the supply of a range of different solebar and headstock overlays to permit the easy (and low cost) construction of a wide range of vehicles while not compromising on correct detail/authenticity.

I will liaise with Mike on producing articles for publication.

Currently, another batch of projects revolves around a "special" order from a G3S member for a complete train of fish vans (comprising 5 different diagrams of GNR/GCR/LNER Standard origin), so there will be plenty of material for future editions of the G3S Newsletter!

John.