resin casting

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14 June 2010 at 23:03 #27298
ashley needham
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@ashleyneedham69188
Chaps. I need to make 6 off 6″ gun turrets for my HMS Nelson plank and hardboard special. 33,000 tons of superior British hardware condensed into about 44 inches.

The three big turrets have come out ok, cut from MDF on my small bandsaw and tidied up, as the sides are straight and all at the same angle, but cutting the smaller turrets has somewhat defeated me. I can make one no problem, but not six all the same, at least, not in the right time-frame. They are only an inch or so wide and all curves.Horrid.

So. I am going to have a go at casting some in resin, and to this end I have purchased some self vulcanising silicon rubber to pour over my best master, and hey presto…its so easy…

OR IS IT…anyone done this before.. have any tips ?? Can I use ordinary petroleum jelly as a release agent or Mr Sheen polish..or something specific?

is ordinary resin adequate (I dont mind a bit of work after).

Ashley
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14 June 2010 at 23:03 #3584
ashley needham
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@ashleyneedham69188
15 June 2010 at 09:13 #27302
Bob Abell 2
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@bobabell2
Hello Ashley

I had the same problem with deck window lights on Great Eastern and I used card construction….which solved the problem nidely….I needed 24 of them and it was essential that they were identical. Mine were drawn with CAD which was the secret of success

You could cut one turret out of card………….and then draw round it, for the repeats?

Or you could make a plug and press it into “Plasticine” and cast a few out of plaster?……or playdough?…………..or even resin?

Or make them from Balsa…………..on a production line………Make 20 of `em and pick out the best six………LOL

Full of great ideas Bob!
15 June 2010 at 11:56 #27303
neil hp
Participant
@neilhp
Hi ashley….I’m just about to do some casting myself for my new lifeboat model, and have always cast in GRP polyester resin.

However most casting suppliers are now casting in Polyurethane resin which does not shatter, can be sanded better and is easier to paint.

I’m just about to order from this outlet..thought you might like the contact.

neil.

http://www.cfsnet.co.uk/acatalog/Fastcast_Polyurethane_Resin.html
15 June 2010 at 18:52 #27310
Ian Gardner
Participant
@iangardner62867
Hi Ashley,

I have cast quite a number (hundreds) of figures using RTV silicone moulds and white metal. I used to use a product from Alec Tiranti as a release agent and I always found them very helpful. They did a series of booklets about casting using different materials so it might be worth contacting them for information. I’m sure they have a web site too.

Ian
15 June 2010 at 19:38 #27312
nevins
Participant
@nevins
Hi, I have done quite a bit of work with the silicone in question. my 1st question for you is what colour is it red or blue. (the catalyst colour) The reason I ask this is that the blue is more flexible and the red sets like a brick and when pulling the piece from it, it tends to split the mold.

The main thing to watch out for, is under cuts, as this will prevent the resin part to be removed. Also the thinner the mould the more flexible it is, but this may split. Trial and error is the key to this game. Any questions feel free to ask.
15 June 2010 at 22:34 #27313
ashley needham
Participant
@ashleyneedham69188
Thanks chaps.

Nevins. Yes , undercuts….wont be any as the bottoms will be flat, the turrets sit on seperate round supports which will be seperate so no bother there. Not sure what colour the catalyst is, yet! but the tin says flexible product so…

Ian…will have a gander at the website. The product….from “Hobbies”….they also sell a petroleum jelly release agent which I am banking on IS actually P.J as per the chemist…cant see any reason why not.

Neil. yup, seen loads of these polyurethane castings, used a few myself. I only need 6 in a fairly solid non fiddly shape so am banking on yer bog standard resin as being ok…we will see,

Bob. me old mucker. Plasticine. i have had mixed results using this. i find it doesnt release without distortion very well..I dare say it is lack of practice. So saying I have successfully cast some resin shields for a few Lone*Star moveable knights O.K, but these were fairly flat. Production line and balsa. I did have the same thought, balsa being soft and all that, and the numbers game is certainly a good ploy. The boat is going to have a camo later-war finish, thus either side will be either grey or green (yes) AND SO I only need three to be identical, either side (I am not silly, you know).*

Nothing wrong with casting stuff in plaster of paris/whatever (in case anyone reading is a bit dubious). Good idea, and I may well try the plaster if the resin is ..difficult.

I believe in “eye-modelling. If it looks right, is IS right. Proportion is in the eye of the beholder, whatever the drawing may say, and I always feel free to alter as per what i like the look of. Which is handy as I usually work from blown up line drawings or photos !

Lifeboats on my Titanic…for instance. There are 16, in 4 groups of four (and not enough, eh?…although the shipyard apparently wanted to fit more, White Star Line was more interested in aesthetics and limited the compliment to the totally inadequate 4 groups of 4 which satisfied the then current regulation).. BUT although in theory they should all be the same, you only need to make 4 groups of 4 the same….a small difference will not be noticed between them. Its a bit heretical..but is sure speeds up build time. I would challenge anyone to see the shortcuts I use, when the model is on the water.

The Sunderland “Shorty” is a point in question. People look at it on the water, and instantly recognise it as Sunderland. Job done. Doesnt matter that its rather square and to be honest, crude….they know what it is and their brain adjusts to the proportion of the model. Works every time.

I use the same process for my band….a good, popular number gets them all going…they hear the tune in their mind, , they all start singing it on the dance floor: the arrangement is rubbish..all unison…doesnt matter.

Need to know what people look at. I have made every single l little bit on Berengar`s Argus WW1 aircraft carrier barring the small Sopwith camels, bought at great cost….and what do people see…”ooo look at the little planes on that boat”. makes u mad!

Balsa bits need a lot of preparation I find, but MDF, when soaked well in sanding sealer, goes very solid, and is easy to finish off as it goes goes rock hard. NOT that I use it for much other than small parts!

On a previous post someone wondered about planking with MDF I believe…. My problem with this would not be the waterproofness (once painted with sanding sealer or something) but the glueability…it only seems to glue to the surface, and the top layer pulls off really easy..making it unsuitable for high-stress applications.

Sorry to blather on. Thanks for the replies. Thoughts of chairman Needham.

Ashley (supping some more wine)
17 June 2010 at 08:20 #27324
David Meier
Participant
@davidmeier28154
Ashley, your blather was a very enjoyable read. Must have been a good drop of wine.

You have given me the courage to carry on with my trawler build. I have stalled at deck level. I cant imagine myself doing the superstructure to the incredible detail that I see others achieving I just haven’t been around boats enough to visualise all the bits and pieces you find on the upper works of a boat. So I will start with the basic cabin, hatch covers etc and may be I can add a bit more from time to time.

I really want to build an old NZ sailing scow. I have the plans all ready but have determined not to start until the trawler is finished.

David.
17 June 2010 at 22:57 #27339
ashley needham
Participant
@ashleyneedham69188
Snaps. Unfinished boat, also the Glorious, which started as just an experiment in plank and hardboard for hull construction, and looked so decent I simply had to use it. The long and thin and the fat and er not quite so long . Scales similar…not sure what … 1/200 (ish). Glorious NOT planked, but having a steel deck, covered in non-slip herringbone strips…impossible to replicate at this scale. Nelson will have a paler brown than currently undercoated.

Nelson 44″ and Glorious 48″. Glorious very fast on 2x 380 motors on 6v and 25mm props…Nelso has twin 540/1 (mild) motors and at the moment 35mm brass props. Should be not so fats and that would be about right. I have made another 6 inch gun turret now and put it in a box, greased it with vaseline and mixed some red coloured rubbery stuff and filled it up.,it appears to have set ok…I will leave it a few days.

Plenty to do…painting mostly and attempting to get a good outline of the black and green camouflage pattern for the Nelson. Dont ask me, i didnt choose the colours.. Ashley
18 June 2010 at 21:46 #27350
ashley needham
Participant
@ashleyneedham69188
David…dont think too much, just DO. I build for my own amusement so am not that worried about what anyone else thinks too much (to a point !!), and just think that for every fabulous model you see on the `net or in a magazine, there are 20….others…out there hiding, of various quality, from great to not so great. But their owners all love them.

Now..I turned out the cured rubbery stuff and the mould is perfect, no sticking to the master, or the sides, and no air bubbles.

I shall be casting on Saturday !

ALSO tomorrow is camouflage day. The book I have ..Nelson and Rodney 1927-1949

the big battleships

has two small pictures, one of either side of Nelson in one of the two two camo finishes she wore.

A green and very very dark Grey was used, Grey bordering on Black. Ican do very dark Grey, and i have a humbrol tinlet of a Green that appears to agree with most of the colour pictures I have seen.

Ashley

Edited By ashley needham on 18/06/2010 21:51:22
19 June 2010 at 02:02 #27354
David Meier
Participant
@davidmeier28154
Hi Ashley.

What you say is absolutely right, I tend to worry what other people will think of it. Doing the frames and planking the hull was really enjoyable but I felt confident about that part. I will box on and will at least have a boat that I have finished and can use.

The other part of the build that I have really enjoyed doing is making the gearbox from salvaged printer gears and the little brass prop. I made the prop as large as I could thinking that it would be marginally big enough at 35mm dia. Well when I tried it in the pond fully ballasted it was doing its best to plane and the bow wave was higher than the deck. I made one 30mm dia, but still too fast and have ended up with 25mm dia with very little pitch.

Your Nelson and Glorious are looking good. Here is me dithering over one boat and you are building two at once.

Thanks for the encouragement.

David.
20 June 2010 at 18:01 #27376
ashley needham
Participant
@ashleyneedham69188
One mould, and one of 8 turrets, cast in something called”resin plaster”. I may have overdone the mould thickness??

It looks like normal P-o-P, but is much harder, and can take much finer detail.

Bargain at £7 a kilo, mixes really easily, and casts with no mess, doesn`t need a release agent..and can be done on the kitchen sink!.

Am now the now proud owner of sufficient turrets, requiring very little tidying up…unlike using fibreglass resin, which is smelly and stays sticky for a while. Horizontal line on turret is a pencil mark, not a crack!

Ashley

Edited By ashley needham on 20/06/2010 18:04:37
21 June 2010 at 18:53 #27383
ashley needham
Participant
@ashleyneedham69188
Odd stuff, this.

Looks like PoP but the few extras I had I cant break in my hand , which would be the case with PoP.

It drills ok, and not a single chip while I was doing it. I have sanding-sealered them and glassed them down with fine paper and the finish is really silky.

I have Two almost black turrets, one Grey and three light green. Looks really odd, but matches the camo on the hull and superstructure sides when fitted (hopefully).

It makes you think, the firepower of these ships….there is the power of a battleship ( 9x 16″ guns), a cruiser (6x 6″ guns) and a destroyer (3x 4.7″guns) on each broadside.oo er.

The lad is not impressed, it doesnt have an aircraft. Rodney was fitted with a Walrus for a very short period on the last big turret, but they never had a permanent flight.

Ashley
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