Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => Engineering Techniques and Materials. => Topic started by: Colin Bishop on November 22, 2018, 06:37:29 PM

Title: Moulding - best method?
Post by: Colin Bishop on November 22, 2018, 06:37:29 PM
There is a lot of stuff on the internet on the subject of moulding items. Years ago I made some lifeboats for a model liner using a material called Meltamould which was a red meltable rubber which could be poured over a master to create a hollow mould.

It doesn't seem to be available anymore.

What I want to do is to create a mould of a ships's lifeboat from a plastic master and then use that mould to create hollow lifeboats using GRP resin and tissue so they can be fitted out with internal detail. The original stuff didn't need a release agent, the boat just popped out once the resin had set.

Does anyone know if there is a current equivalent? I don't want a solid moulding, I want to lay it up within the mould.


Thanks.


Colin
Title: Re: Moulding - best method?
Post by: plastic on November 22, 2018, 06:45:20 PM
I'm particularly interested in this myself - I've got to make a bunch of small gun turrets so a reliable, simple, fool-resistant method would be handy.
Title: Re: Moulding - best method?
Post by: Hellboy Paul on November 22, 2018, 07:02:48 PM
Hi Colin, is this it??
https://www.cfsnet.co.uk/acatalog/CFS_Catalogue__Flexil_Vinyl_Rubber_554.html


Paul..
 
Title: Re: Moulding - best method?
Post by: Colin Bishop on November 22, 2018, 07:11:18 PM
Paul,

Thanks. I did look at that but just wonder if heating to 170c might damage the plastic master. I think there may be lower temperature alternatives.

Colin
Title: Re: Moulding - best method?
Post by: Subculture on November 22, 2018, 08:06:48 PM
Just use a decent RTV silicone rubber. Self releasing and won't damage the item.

e.g. http://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/rtv-silicone-rubber/addition-cure-mould-making-silicone-rubber-rtv.html
Title: Re: Moulding - best method?
Post by: Neil on November 22, 2018, 09:05:09 PM

Colin......….Go along to your local dentist and ask them if they will sell you a bag of their "dental moulding  compound"...….or just google it...…..


there are a good number of the types around………….that is what I used to mould model lifeboats before I started using the more expensive RT rubbers.
Title: Re: Moulding - best method?
Post by: Allnightin on November 22, 2018, 09:12:39 PM
What size is the original master and is it finished on the inside as you will have your copies?  The silicone suggested by Subculture can be used to make a casting that is detailed on both sides and using a polyurethane resin.  Casting that way is likely to be quicker than laying up grp etc.
Title: Re: Moulding - best method?
Post by: Colin Bishop on November 22, 2018, 09:33:22 PM
Thanks for the suggestions. I just want something simple really. The master (which I havn't made yet) will be 6cm long and 2cm in beam so quite small. I onlu need to make up shells with external detail as of the several boats aboard the ship I will only be detailing the internals of one of them as the others would normally have canvas covers.

The dental moulding seems interesting Neil but on Googling it they say it dries out and shrinks quite quickly. Is that your experience?
RTV sounds OK but there seems to be a lot of stress on the need to get the air out caused by the mixing process.


Colin
Title: Re: Moulding - best method?
Post by: Howard on November 22, 2018, 10:58:28 PM

Colin,
 If you look at my SD14 build you will how I made my lifeboats  as I to wanted open ones turned out really well. one master and as many copy's as you want.
                                         Regards Howard.
                               
Title: Re: Moulding - best method?
Post by: Howard on November 22, 2018, 11:04:03 PM

so sorry Colin my photo's seam to have gone I'll have to try and reload them from my file's
                 Regards Howard.
Title: Re: Moulding - best method?
Post by: Subculture on November 22, 2018, 11:15:40 PM
You're over theorizing, Colin. The rubber will de air perfectly adequately for this application without resorting to pressure or vacuum.

Having said that, a lifeboat shouldn't have much if any undercut, so you could just make a hard tool from resin and glass, which would save money on buying additional material.
Title: Re: Moulding - best method?
Post by: Colin Bishop on November 22, 2018, 11:22:17 PM
Not theorising, just reading the instructions on the data sheet but I'm happy to accept your practical experience. I actually have an old plastic lifeboat that I intend to add planking and some other external detail to for a master.

Colin
Title: Re: Moulding - best method?
Post by: Subculture on November 22, 2018, 11:36:31 PM
The manufacturers and suppliers will tend to give best practice methods. Without degassing the rubber, you may get some air entrapment, but it will be very small, and with hand lay-up this makes little to no difference.

Alec Tiranti is another good supplier of moulding materials including silicone rubbers, and they also do good user guides better suited to hobby builders.
Title: Re: Moulding - best method?
Post by: T888 on November 23, 2018, 05:32:34 AM
Hi Colin,
If you look back in my build log for 1/48 HMS QUORN you will see, a brief section on how and what I use to doing cold casting. Hope this will help.
Title: Re: Moulding - best method?
Post by: TailUK on November 23, 2018, 09:18:13 AM
PM me, Colin.  I might have something that'll serve your turn!
Title: Re: Moulding - best method?
Post by: Colin Bishop on November 23, 2018, 11:00:41 AM
Thanks everyone, and for the offers to mould the boats for me. I think I have enough to be getting on with for the moment - some food for thought and I will investigate further. As well as the lifeboats there are many other multiple detail items so it may pay me to have a look at moulding some of these too. In anycase, the lifeboats are a way won the line at the moment as I'm still working on finishing off the hull!
It is a scratch build so I really want to make as much as possible myself as long as it doesn't entail a disproportionate amount of effort.

Colin
Title: Re: Moulding - best method?
Post by: Brian60 on December 06, 2018, 11:28:19 AM
I'm a little late to the party but this is as cheap and as good as anything, I have used this method a lot since finding it on Youtube.
Fill a plastic bowl with water and add about a tablespoon of liquid detergent like Fairy liquid. Then get a tube of bathroom/kitchen silicone sealant - the cheapest you can find, mine are about a euro from the local euro shop, you can go to Poundland or B&Q it doesn't matter.
Squeeze the entire tube of it into the water, it looks like a string of sausages, then making sure you have wet hands, begin to mould it into one homogenous blob, after 5 to 10 minutes it will amalgamate and begin to stiffen up. Take it out and place onto a backing board massage to the thickness required and then press into it the part you want to duplcate, allow to dry for an hour or so, you can press it with your fingers to test hardness. Remove part once stiff and begin your lay up process.
The only things you have to watch is that it is genuine silicone that you buy, and that you do NOT use polyester resin. It works with epoxy and polyurethane resins no problem. But polyester has a reaction to silicone and the finished surface will never dry, it just remains tacky forever.
The whole process takes less time than it has taken me to type this!
Title: Re: Moulding - best method?
Post by: Tombsy on December 08, 2018, 02:00:47 AM
I recently tried a Smooth-On casting and mold making kit, it uses two part pourable silicone rubber and a two part liquid plastic. I used it to make some 1/8 scale Rolls Royce Merlin exhaust tips for the Executone hydroplane I’m building. The kit and instructions were great not sure if the products or something similar are available to you in the U.K.
http://https://www.smooth-on.com (http://https://www.smooth-on.com)

https://www.modelboatmayhemimages.co.uk/image/JnzgP (https://www.modelboatmayhemimages.co.uk/image/JnzgP)
(https://www.modelboatmayhemimages.co.uk/image/JnzgP)
Title: Re: Moulding - best method?
Post by: nemesis on December 19, 2018, 05:08:08 PM
Colin, The dental stuff ( alginate) is no good for what you want, it loses the water content quite quickly and consequently shrinks, a lot. It is perfect for what it is used for ie taking dental impressions and even then they should be cast within 15mins or you may find that your dental plate may not fit properly. I suppose, if you are conversant with this material you could have some success. I always use silicone by Dow Corning for mould making. nemesis
Title: Re: Moulding - best method?
Post by: Colin Bishop on December 19, 2018, 05:17:04 PM
Thanks, I have noted all the useful advice and suggestions but casting is still some way away on this projet at the moment as I've been busy with other things.
Colin
Title: Re: Moulding - best method?
Post by: Neil on December 19, 2018, 06:04:05 PM
Colin, The dental stuff ( alginate) is no good for what you want, it loses the water content quite quickly and consequently shrinks, a lot. It is perfect for what it is used for ie taking dental impressions and even then they should be cast within 15mins or you may find that your dental plate may not fit properly. I suppose, if you are conversant with this material you could have some success. I always use silicone by Dow Corning for mould making. nemesis



good shout nemesis...……..didn't know that...……...only ever used the stuff once to cast some vents for something I was doing early in 1986 and then left the rest untouched...……………..had no idea it would shrink...…..sorry for the duff info Colin.
Title: Re: Moulding - best method?
Post by: Colin Bishop on December 19, 2018, 06:32:33 PM
No problem Neil. Thanks for taking an interest.
Colin