Jump to content

moulding a replacement part, is there a cheap and cheerful method?


erewhon1872

Recommended Posts

Hi all,

I have lots a part (it's an airbrake cover on a 1/48th F/A-18 Hornet) and while I have a second kit of the type I do not want to use that part as basically that just ruins another perfectly good kit.

So my question is this, is there any commercially available material for making a mould and I guess some sort of resin replacement?

As I am in the UK I'd assume that it might be something that I could get at Hobbycraft which is meant for something entirely different but can be used to create another part?

As I just want to make one part I'm looking for something reasonably cheap and cheerful rather than something that is for long production runs and might cost a small fortune!

So any suggestions gratefully received.

Cheers,

Pete

Link to comment
Share on other sites

For this I would use polymer clay, better known as Fimo or Sculpey. A small block costs under £2.

Make a pad of Fimo

Dust with talc

Press your spare part into the Fimo

Remove part carefully

Cook Fimo

When Fimo pad has cooled

put part back in

Dust with talc

Press this block with part into another pad of Fimo

Remove cooked block and part

Cook second pad of Fimo

When both pads of Fimo are ready cut an inlet for resin.

Oil pads lightly with olive oil

Put pads together and fill with resin

When resin is set you should have another part.

Also possible to use Fimo in the mould to make a part.

Lightly dust pads with talc.

Press Fimo into the cavity

press pads together

Cook the whole lot

part the pads and you should have a part.

Sounds long winded. It is. I use this method for one-offs or short runs.

This is a Fimo mould to make a French Eagle in 54mm scale; I made a dozen and the mould is still useable.

7ad0f17007181ef2810b531b3bd023ae.jpg

6624b89660bad3dde35c64aa0645244c.jpg

b8a6dd3ee6cffb2e22e8d64d0cde2d0c.jpg

  • Like 1
Link to comment
Share on other sites

+1 for Oyumaru, very easy to use, and is reuseable, and very cheap

You just drop it into hot water for a bit, and remember to use tweezers to take it out, then press it over what you want a mould of and let it cool.

sets harder than silicone moulds, it's not very fluid like silicone before it sets, more like a plasticine.

if your airbrake is smooth on the outside then just mould the inside,

I used a building product to mould with, but I'm sure Milliput would work just as well

DSC01645.jpg

upload image online

DSC01651.jpg

image upload no size limit

  • Like 1
Link to comment
Share on other sites

thanks to all for the answers, I'll investigate all the mould materials suggested.

Can anyone suggest a suitable resin product to fill the mould with?

Link to comment
Share on other sites

I've used David's Fastglas resin and hardener before. You can get it from car accessory shops.

thanks for all the info and the pictures, much appreciated.

As this is a one-off I'll go for the cheapest suggestions which would be the Fimo clay from Hobbycraft and the David's Fastglas resin and hardener from Halfords.

Can I ask how you used the resin/hardener because the products themselves (as they are for car bodywork repairs) mention fibreglass, but can the resin/hardener combination just be poured into the mould?

Cheers,

Pete

Link to comment
Share on other sites

I too use David's resin. Just mix a bit of hardener into the resin and pour it into the mould.

I add some talc as fillers into the resin before the hardener.

An even cheaper mould making material is plasticene. But only good if your item is single sided, simple in shape and you don't mind it being solid.

Press original into a block of plasticene.

Put into freezer for a while.

Remove part after the Pl. has chilled for a bit.

Lightly oil with olive oil.

Pour resin into cavity.

Sometimes the resin will stick to the Pl despite the oil but it washes off.

Mould is only good for a one-time use.

Link to comment
Share on other sites

I too use David's resin. Just mix a bit of hardener into the resin and pour it into the mould.

I add some talc as fillers into the resin before the hardener.

An even cheaper mould making material is plasticene. But only good if your item is single sided, simple in shape and you don't mind it being solid.

Press original into a block of plasticene.

Put into freezer for a while.

Remove part after the Pl. has chilled for a bit.

Lightly oil with olive oil.

Pour resin into cavity.

Sometimes the resin will stick to the Pl despite the oil but it washes off.

Mould is only good for a one-time use.

thanks for the plasticine idea, what does adding talc to the resin before the hardener do?

Link to comment
Share on other sites

Talc gives some colour, helps lower setting exothermic temperature, helps disperse microscopic air bubbles, reduces the brittleness [not completely] of the David's Fastglas resin.

I add by; >> ''umm, that might be enough'' measure

Too little makes little difference, far too much and it becomes a paste [useful as a gap filler on models though]

PS; Don't forget to allow for shrinkage of the resin when filling a mould.

Link to comment
Share on other sites

Hi Pete

some great suggestions, but I'd also try asking here in the 'wanted' section if anyone has one spare!

http://www.britmodeller.com/forums/index.php?/forum/40-wanted/

as you never know what folks have stashed away.... always worth a post.

HTH

T

Hi Troy,

did ask in the 'wanted' section here

http://www.britmodeller.com/forums/index.php?/topic/234992349-148-airbrake-cover-for-hasegawa-cf-188/

but not reply, or rather I replied to say I have ordered a spare part, trouble is I ordered it and have heard nothing more, so am exploring alternatives.

As the clay is a couple of quid and the resin/hardener combination is under a tenner then may as well give this a go and see if I can make a replacement.

Cheers,

Pete

Link to comment
Share on other sites

Talc gives some colour, helps lower setting exothermic temperature, helps disperse microscopic air bubbles, reduces the brittleness [not completely] of the David's Fastglas resin.

I add by; >> ''umm, that might be enough'' measure

Too little makes little difference, far too much and it becomes a paste [useful as a gap filler on models though]

PS; Don't forget to allow for shrinkage of the resin when filling a mould.

how do you "allow for shrinkage of the resin?

As I basically want the outside shape of the airbrake cover and can then model it shut rather than wanting an entirely new part do I have to bother about 'shrinkage' unless you mean that the resin will harden to a smaller shape than the original mould?

Link to comment
Share on other sites

If you have a two part mould, with a pouring gate, if you fill to just the level of the part you'll end up with a short moulding. Fill up the pouring gate too. As the resin hardens and contracts it'll use up the excess, or at least some of it. In fact make the pouring gate as big as you can. You can cut off the excess later but its frustrating doing the work to find its not complete.

On an open mould, pour in enough to slightly over fill the mould. The resin wont shrink away from the mould but it will shrink to a lower level. Like water in a bath. Let some out and the level drops but the water is still in contact with the sides.

For large items I make the main batch, pour into the mould, then mix a smaller batch, which I pour onto the first when it has just started to gel [harden]; this will top up the mould and the extra will become one with the main mix.

Another way is to rock and turn the mould whilst the resin sets. This will keep the resin up the sides and the shrinkage will be in the centre.

You'll need as much as 5% extra. Look at my Eagle mould. My excess resin was in that gate at the base and it was just enough.

Depending on how much catalyst hardener you use the resin will set in anything from 5 minutes to 30 minutes. Aim for the longer time. This will be a very small amount of hardener.

I mix in the foil cases which little apple or mince pies or jam tarts come in.

Mix a small amount of resin up, and let it set, so you can see how long a mix takes to set.

Another thing I do with two part moulds is to pour a little resin mix into each half and flow it around so the surface gets coated, then close the mould up and pour the resin in. Doing this helps get rid of the chance of air bubbles on the surface of the part due to air being trapped by the resin against the mould surface.

  • Like 1
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...