Atlantic's works: Portable layout - Scenic details next

[Atlantic 3279]

I suspect my attempts to seal the skirting under the nose of Lord President to the base of the moulding box were insufficiently thorough, as I had the interesting challenge this morning of fighting a major leak of liquid moulding rubber when I filled the box! I think I have recovered the situation without ruining anything in the process, or losing either excessive amounts of rubber or time. I should be able to get a proper look at what actually happened this evening when I can invert the box and remove the base.....

[Atso]

Ouch, that sounds messy Graeme. I do hope that all is salvageable as silicone rubber isn't the cheapest of materials (although it's also far from the most expensive!). I'm very interested to see how you finish the mould and adapt it for casting considering that the master is still attached to the donor body.

[Atlantic 3279]

I'm very interested to see how you finish the mould and adapt it for casting considering that the master is still attached to the donor body.

As Corporal Jones would say, in a less than calm way, "don't panic".

I must say I haven't worked out every detail of the plan though, but I'm sure it will come together, one way or aother....

[Atlantic 3279]

This picture, although taken at a slightly later stage when I had not only removed the base of the box but had built up another course of bricks around what was previously the bottom of the box walls, and had added new shuttering at the rear to close off the previously open-ended space within the body and between the previously present skirts, does show that area that had caused trouble with leakage. In fact, one of the main side skirts, rather than the flimsier pieces under the nose, had failed to stick to, or had broken away from, the original base of the box and pushed inwards under the weight of the liquid rubber. The rough area of cured pink rubber is the result of me cutting away the excess of material. Fortunately, mostly of the cured "slick" inside the body was easy to pull away, much of it being stuck to the temporary skirts which I wanted to remove anyway. I'm sure you can see how, when the space inside the body / skirts was open at the rear, the leaking rubber was free to pour out! Luckily, I was there, and was able to quickly lift the moulding box and stand it on two pots of equal height, one under the end from which the leak was oozing. Periodically I poured the collected liquid back into the box, until the curing of the rubber made the leak so slow that I could ignore it....

Outside view of that new shuttering, built up in pieces for convenience, the profiled piece inside the boiler having been marked out with the aid of a cut body section from one of the other P2 projects. Green plasticine in evidence to seal gaps.

Production of the core piece for the mould was a process free from the trouble of major leaks - although I did fail, despite thinking about the matter quite clearly at an earlier stage, to make timely arrangements for the plug that was needed in order to produce the slot within the core piece that allows it to collapse during extraction from the master and the castings! Some quick but belated further action saved the day. I was rather glad to see how well the original body had survived, all the lining remaining intact and just one easily replaced plastic handrail knob broken off.

After a fairly messy first attempt to fill the new mould, mostly working out what to do as I went along. I now await hardening of the resin.

[Atso]

As Corporal Jones would say, in a less than calm way, "don't panic".

I must say I haven't worked out every detail of the plan though, but I'm sure it will come together, one way or aother....

Wow, two quotes, one direct and one indirect, from television shows - I'm impressed!

You're casting solution looks great so far and I'm really looking forward to seeing the casting once it's cured. The resin looks green to me, I assume that you've mixed some donny green into the resin once again.

[Mercator II]

Fingers crossed, one question, is this a straight butt up to the donor body or are you incorporating an insert piece as per EM?

[Atlantic 3279]

Definitely an insert piece again.

[Atlantic 3279]

The initial resin casting came out of the mould like this:

The next parts of the process were the modifications of this casting to produce a master "in final form".

[Atlantic 3279]

The first task was to cut the rough end off the rear of the casing, but at that stage still leaving some good material in situ aft of the final boiler band. Within the boiler, I then applied a layer of sellotape to those parts of the boiler walls that projected aft of that boiler band's line. I was then able to use various pieces of pre-curved thin plasticard to build up the necessary bridging / plug in piece that would eventually line up and reinforce the joint in a modified loco body. Doing this with the (eventually unwanted) extra length of boiler barrel still in place helped to ensure that the plug-in piece really would fit nicely inside the rear half of any other Hornby P2 body moulding. The sellotape over the contact are ensured that neither the super-glue nor the liquid poly used in building up the new layers would stick these to the part of the casting to be sawn off in the next step of the work. The casting was then cut back to a line following the rear edge of the rear boiler band, the running plate being cut back to that same line too.

Parts of the rubber core piece for the mould were then cut away in order to clear the additions that had been made within the boiler, and to open up some space under the rear edges of the running plate. This alter arrangement was necessary because I had concluded that the best way to produce the lugs that would help to line up the running plate would involve re-making them at the same time as restoring the core piece of the mould, rather than attempting to leave in place the representations of these that I had grafted on the original un-cut body (look back at earlier pictures of the underside of the body to see those original white additions). Removing the extra length of running plate above each lug, without breaking off or damaging the lug itself would, I think, have been almost impossible. Here you can see the modified casting and the butchered core piece of the mould. The re-formed running plate joint lugs are in black this time, with a "break free" temporary piece of white running plate above each. Those pieces became necessary as a means of keeping moulding rubber in the right places, once I had worked out exactly how I wanted to re-form the core piece of the mould.

With the casting worked back fully into place and the two halves of the mould reassembled the view into the rear was this.

You can see that the cutting away of rubber has broken through into the central relieving slot, and the picture below shows the view into that slot, with the open end of the mould to the left.

[Atlantic 3279]

The "action area" of the mould and the master within clearly needed to be not only carefully realigned but also held together firmly and without distortion in order to ensure that the re-made parts of the mould would line up neatly with the original parts, and that no unwanted creep of liquid rubber would spoil other parts of the mould - or leak out all over the work bench! The exposed rear part of the central slot also offered a nice opportunity for the creation of an injection port for resin. Some more pieces of Lego, some plastic rod, tube and sheet, plus some rubber bands were pressed into action.

After selective application of Vaseline to prevent adhesion of rubber in the wrong areas, I then poured just enough rubber to re-fill the boiler space and the area under the running plate. I've decided that the rest of the re-made mould will be part of the "outer". I think this will make it much easier to fill the mould with resin by any chosen method, without lots of unwanted leakage.

[Atso]

Very interesting to see how you've tackled this Graeme. Do you have ever have any trouble when you replace the casting into the mould?

[Nova]

those initial mouldings look incredibly crisp for a first casting of that piece, excellent work as always

[Atlantic 3279]

Do you have ever have any trouble when you replace the casting into the mould?

Routinely! It is best avoided as far as possible, on account of the difficulty in getting all parts to key back in to their original relationships. In a really simple mould of an "open" type, it isn't so bad. Complex moulds with wrap-around, deeply slotted, or undercut features are a real challenge. A coat of Vaseline is often necessary in order to allow the deeply recessed parts to slide home in a new or new-ish mould, whose surfaces are still "grippy". As the rubber ages the surfaces inside the mould start to feel almost as if they have been lightly powdered, and a casting will then slide in, or out, more easily, up to the point where the surfaces have become so dry and crumbly that they disintegrate! An older mould can also sometimes start to get slightly baggy compared to the master, so if any of the most delicate features of the mould are being cut out and reinstated by a localised new pour of rubber it can be difficult to keep the mould sufficiently tight against the master to prevent creep of rubber onto parts of the mould that it should not be reaching.....

[Atlantic 3279]

Providing that the main Bugatti nose casting turns out well, I should have only a few jobs to tackle before a "full" set of conversion parts for a P2/2 in either form is available. There's a chimney mould to make, which should be simple enough - streamlined double, without by-pass passage first of all, possibly other types late. A set of cylinders on a stretcher that actually fits the P2 chassis shouldn't stretch my skills too greatly. I thought about starting those two jobs in parallel with the main mould, but there's enough clutter on the workbench (and in my mind) as it is. More of a challenge will be the valve gear. The Thompson A2 conversion etch is a great start, but ideally (unless a whole new set is etched up) a fold up adaptor bracket for the stretcher is required, along with combination levers, union links and the drop-link from the crosshead for both sides of the loco. I hope my previous collaborator is able to help with this. If not, I shall have to do some asking around.....

[Atso]

Thank you for that Graeme!

That reason why I ask is that I dabbled with some resin casting many years ago and made a mistake with my initial attempt at making a mould. Not a problem I thought, I'll just slip the master back into the good half and remake the second bit. Didn't happen! I couldn't get the master back into the mould sufficiently well to stop the new rubber seeping into the resulting space and ruining everything! Luckily the second attempt was better but it proved a costly mistake. As I'd like to have another go at resin casting, your posts and advice on the subject are greatly appreciated.