Royal Navy Submarine C1 (1906) 1/48th scale

[PICKETBOAT]

Hi all

The completed masters for the conning tower, nose, tail section, aft diving planes, rudder and assorted engine breather pipes were then grouped together on a single base. This was surrounded with a light weight plastic card wall creating a box into which RTV silicon rubber will be poured. All surfaces and detail inside the box were then sprayed with release agent.

The RTV (Room Temperature Vulcanising) silicon rubber was carefully weighed, mixed with catalyst and thoroughly mixed. Careful attention was taken so that the catalyst was well mixed in leaving no RTV silicon un-catalysed. I mix mine in an old milk carton with the top cut off, making sure I stirred in the silicon at the bottom and in the corners. What ever you mix the stuff in there has to be plenty of extra space as the next stage can cause it to expand by X 5.

The mixture was then quickly moved to the vacuum chamber to be de gassed. Mixing in the catalyst creates lots of bubble. The silicon is supposed to be self de gassing but this is only partly true. Getting all the bubbles out is essential to creating a good mould.

I built my own vacuum chamber for de gassing. As you can see it looks pretty �Heath Robinson� but it works fine. It�s basically the bottom of a propane cylinder attached to an old pump removed from a domestic deep freezer. I takes about 1 min to reduce the internal pressure to 25 inches of mercury. It�s then left for 3 min before repeating. This machine probably infringes about 100 health and safety regulations so if you build one like this take care. Vacuum chambers have to be pretty strong but generally speaking if you get it wrong they leak rather than catastrophically implode.

The de gassed silicon is then poured into the mould, pouring into one corner and allowing the silicon to flood across, reducing the chances of trapping any air bubbles.

[PICKETBOAT]

Hi all

The remainder of the fittings were manufactured and arranged on a second square base. These are many of the smaller fittings, cleats, fairleads, the conning tower hatch, forward hydroplanes, cowl vents, deck mounted compass, sections of engine breather pipe etc. Just as before they were sprayed in primer before being encased in a temporary plastic card wall.

[PICKETBOAT]

Hi all

Again the RTV silicon rubber was mixed, de-gassed and poured into the box. I hit a slight problem here. The bench in the workshop is built in as part of the building. I noticed that when filled up, the silicon was starting to overflow the moulding box at one end?

My workshop is a re-cycled moveable steel building on legs. It turns out that over the years one of the legs had slowly sunk! I used some thin wooden strips to level the moulding box on the bench, to get the job done. I will jack up my workshop and make it level again very soon.

Cure time (pot life) for this silicon is listed as 6 hours, but this depends a lot on temperature and humidity. I raise the workshop temperature to 20C and leave a tub of water on the bench. I then tend to ignore the project for 24 hours. When it sets, the silicon is initially very pliable and it�s at this point that it�s easiest to get it off the master. The rubber continues to harden for about another 24 hours.

You will see that a scalpel has been used to make incisions in the rubber to make it easier to get the final castings out without damaging them, particularly the fine or complicated ones.

[Folgore]

Hello PICKETBOAT

This is an interesting subject! I really love these bow torpedo doors.
It must be cool to see a movable version of this design

Sincerely

Chrischan

[PICKETBOAT]

Chrischan

Welcome back.

These outer torpedo doors would only be seen when the sub was in dry dock, but they must have been amazing things to see when they cranked them open. They must have looked like some giant prehistoric insect blinking it's eyes. I have no chance of making them function on this quite small model. It would require a model maker with greater skills than me. Getting the internals (propulsion and dive controls) to work is going to be a bit of a brain burster as it is.
I saw your model collection spread across the dining table. Where are you going to start?

Good modelling

[Ltm109]

Hi Picketboat,

How do you handle the undercuts (where you have a round object but this is a one piece mold)?

Watching this with great interest.

Lou

[PICKETBOAT]

Lou

The silicon is very flexible and if de gassed correctly has a reasonably high "Shore" strength. This is its ability not to tear. When removing the mould from the master it is sometimes necessary to use a fine sharp scalpel to create some relieving cuts to get the mould off the fittings (eg the flat diving planes). Some additional relieving cuts were also made after getting the mould off to make it easier to extricate the finished castings.
You get more confident about the ability of the materials after a while, and at the end of the day, for items with big undercuts, it is possible to scalpel the whole silicon mould in half. Elastic bands can then be used to hold it together during the casting process.
I have added pictures of the first resin cast fittings out of this mould.

[PICKETBOAT]

Hi all

The second sheet of cast resin fittings was "boxed up" and covered with silicon rubber. Because it carries the the conning tower and tail section it ended up quite a large deep mould, using a lot of silicon. Its always a bit of a trade off. Make one or two sheets holding all the fittings, or make up lots of individual little moulds (extra work, less silicon).

In the end the silicon mould came away from the master reasonably easily although two of the diving planes broke away and remained embedded in the silicon. This was not a problem as a couple of fine relieving cuts with a sharp scalpel quickly enabled me to remove these components and the cuts needed to be made anyway to enable the eventual resin castings to be easily extracted.

[PICKETBOAT]

Hi chaps

Well here is the "proof in the pudding". I poured the resin into the second mould today and cranked the pressure chamber up to 50 PSI. The first casting out of the second mould was good, picking up all the detail. I now have two sets of casting which comprise about 85% of the external fittings for this C class submarine. Some simple components (for example the aft fins supporting the rudder and diving planes) will have to be made up from brass sheet on the finished working model, as they need to be a bit more robust. Cast in resin they would have been fine for a static model but would be too easily broken on a working model.

The next stage is to return to the hull plug and coat it with silicon rubber as the first stage of making the two part hull mould.

[Neptune]

Most brilliant work there. Love how you explain/show the moulding method and it sure came out great. Can't wait to see that come together. Quite an impressive pace of construction as well!

[PICKETBOAT]

Thanks for following Neptune

Apparently the essential thing with working submarine models is to keep top weight down, so that the ballast on the floor of the (outer) hull really does work, keeping the hull upright and stable. I will use the same procedure adopted with all my other surface models and try and "build in lightness" as the model aircraft guys term it.

The resin conning tower and nose cone were cast solid, but when I eventually remove them from the casting base I will try and machine out some of the resin core leaving them at least partly hollow.
The plus with casting all the fittings in resin is they will withstand prolonged immersion. If I had used wood for any of this I know that eventually moisture would get through the paint finish and ruin it.

Still lots of work before all the bits come together and it starts to actually look like a submarine. I am very much looking forward to sailing the finished model along side, and hopefully underneath, the rest of my fleet.

[PICKETBOAT]

Hi all

I have now moved back to the hull plug. The two halves have been mounted on strong base boards. Again they were glued (PVA) and screwed down. The glue was intended more as a gap filling so there was no crack along the joint between the plug and the base board.
The base board can be thick ply, MDF or as in this instance some 20mm Foamex board left over from a job. Thin ply is hopeless as it turns into a banana.

The base board has been primed and sanded to render it smooth and non absorbent.

I am now ready to start creating the mould for the hull.

Sorry about the messy workshop but it has to "earn it's keep", and there is lots happening in there at the moment.

[PICKETBOAT]

Hi all

I am pleased that I am not the only one interested in these early submarines. A fellow model maker has just alerted me to this rather nice working model of a C class sub, built at 32nd scale by a German model maker. Well done who every you are. The bow wave looks particularly accurate.
Lets hope I can do half as well as this at 1/48th scale.

[sandy]

No pressure Steve...

[PICKETBOAT]

Hi all

For those who followed the first part of this build, sorry for the delay.

Having to go out and earn a living sure does get in the way of REALLY important things like building ship models. Work meant this build slowed, then stopped, but recently I managed to get a little done.

While casting the resin fittings to detail the model exterior I thought the same techniques could be used to manufacture the end "bungs" for the internal water tight compartment. This, as I have already said, was a clear acrylic tube 60mm diameter by 300mm long.

I turned masters for the two bungs from lime wood (bass wood), each having a groove to carry a neoprene rubber sealing ring. The aft bung also had an internal recess which will house the main motor. The two projections (yellow arrow) are for mounting the master while encasing it in silicon rubber and they will also provide the entry points for the poured resin on the finished mould.

Each end bug also has a horizontal slot on its inside surface. Into this will locate the clear acrylic tray which will carry the main functioning components of the model.

The finished wooden masters were then primed to fill the grain and to give a smooth non absorbent surface, vital for making a good mould.

[PICKETBOAT]

Hi al

The styrene walls of the "mould box" were added by tacking them in place with CA. This was a repeat of the same process used for casing other fittings. You can use tape. Whatever securing method you use it has to be easily pulled apart after the silicon rubber has set, to make it easy to extract the mould. The joint has to be leak proof. The silicon is pretty thick stuff, but it will pour out through any gaps and spread across your workshop if you give it a chance!

Apart from the recess for the main motor and the slot for the components tray I kept these end bungs simple. I could have cast in reinforced exit points for the rudder and diving plane activating rods, but at this stage I was not certain where these would be. The end bungs are thick enough to be drilled and machined for any additions. There is also the possibility that these could be adapted for use on another future submarine build, another reason for keeping them simple.

With the rubber "O" rings in place these end bungs just push into the end of the acrylic tube with a nice neat fit.

[Goodwood]

Glad to see you back at it, PIGBOAT!

How far d'you think you are from sea trials?

[PICKETBOAT]

Goodwood

Sea trials are a long way off I'm afraid. The hull plug is here, sitting on my work table and I need to make the moulds from it. These projects are a long slog at times.
I am also considering designing a photo etch fret containing all the really fine detail. This would have to be made up "out of house" as I don't have the skills for making this.

[Mr. Bean]

This is a very interesting subject. You must have been doing this for quite some time, the mold quality is fantastic.

Mick

[PICKETBOAT]

Mick

Thanks for your praise. I have been experimenting (in what little spare time I have) for over 6 years, but can remember my very first attempts nearly 40 years ago using modelling clay and GRP resin.
You would not believe how many failed experiments have ended up in the rubbish bin! My early attempts were clumsy and not very detailed, but as I went on, got more confident and picked up new tips the success rate increased. A study in perseverance.

When it works it is very satisfying.