Making a Mold?

Post by **nick69** » Fri Feb 22, 2008 5:14 pm

Does anyone know anything about making molds?

I have a VERY rare wing mirror for one of my cars and lots of people want me to make casts of it in plastic/resin.

Ive had a hunt around and wondered if anyone has any knowledge on this subject?

Nick

Post by **Orkney** » Fri Feb 22, 2008 5:48 pm

Whats it made from ? What do you want to cast it in ?

Edit : sorry replied too fast see you want to cast in plastic/resin - both can be wildy diffrent in producing - so whats the original made from? a pic would help.

Post by **MoggyTech** » Fri Feb 22, 2008 5:48 pm

You can use Polymorph from Maplins. Nylon granules you put in hot water, then take an impression to make a mold.

Post by **nick69** » Fri Feb 22, 2008 6:11 pm

I think its made of cast ally.

This is the mirror as a whole but I only want a mold of the base so I can do a couple of copies as they are no longer in production.

Post by **Alec** » Fri Feb 22, 2008 6:19 pm

Hello Nick69,

one thing to be careful about is to design the mold to have a slight taper, unless it is a flexible mold.
I.e., if you want to cast the illustrated base and it increases in section toward the mirror end, it will not release from a solid mold. You can split them, of course, but you will have a flashing mark to deal with.

Alec

Post by **nick69** » Fri Feb 22, 2008 6:24 pm

Yeah I think it would have to be a 2 part mold due to the shape, as you noticed it does have a fluted top aswell as bottom.
I can deal with the flash/join after as long as it works

Post by **Orkney** » Fri Feb 22, 2008 6:36 pm

For what its worth take it to bits and take the base to your local foundry/forge man. If you cant find one in yellow pages or online then go speak to a local welder who's likely to know of one. (they do still exist)
looking at it it may have been a diecast looking at the recess where it meets the door/wing - that said though its not a rocket science job to do that in a sand mould.

Post by **nick69** » Fri Feb 22, 2008 6:59 pm

Surely Die cast will be an expensive way of doing it?

Sorry ive never had anything like this done before.

Post by **Orkney** » Fri Feb 22, 2008 7:04 pm

Yes die cast would be - that need moulds tooling. Traditional sand casting does not. You take the original to the guy, he uses it to make the pattern in casting sand, takes teh original out and pours.
Job done and you just need to clean it up - as i said would be less expensive than you might think and if its a really rare part then get a few extra made, flog em and pay for the whole project

Post by **nick69** » Sat Feb 23, 2008 7:49 am

Ill look in to the sand casting, thanks for your help and advice.
Nick

Post by **paulhumphries** » Sat Feb 23, 2008 10:09 am

What is the mirror off ?
I'm sure I've seen similar, if not the same, on 1970's US cars so it might be easier to simply buy via Ebay USA.

Paul Humphries

Post by **nick69** » Sat Feb 23, 2008 10:55 am

It is off a 70 US car but the base is 1 year specific which you cant get anywhere. Ive only managed to find this one after a 5 year hunt.

You have seen some very simlilar but not the same. Its the base that is different on them all.
Mustangs, Cougars, Torinos, Fairlanes, Montegos, Cyclones etc etc all have the same bullet head but different bases.

Post by **Alec** » Sat Feb 23, 2008 3:35 pm

Hello Nick,

I did reply yesterday about sand casting but the post seems to have disappeared?

If you use the original to make the sand mould, the finished article will be smaller, as the casting shrinks as it cools. Sand cast patterns (usually wood) are made oversize for this and the pattern maker has some special rules to measure the job. These rules are graduated with a compensation for shrinkage of the casting and there is a differnet rule for each metal.

Alec

Post by **Orkney** » Sat Feb 23, 2008 4:13 pm

will be smaller, as the casting shrinks as it cools

Wow live and learn ! they never mentioned that in metal work !
makes perfect sense though.
Would it make a noticeable difference on smething that size though ?

Post by **overider** » Sat Feb 23, 2008 4:35 pm

In this months copy (March 08) of Complete Kit car is a big 7 page spread about a guy who made a car from scratch out of different composite materials using different techniques you might get some idea’s from this???

Post by **les** » Sat Feb 23, 2008 7:55 pm

M

Would it make a noticeable difference on smething that size though ?

Probably not, as any holes you need to drill look like they will be away from any edges, from memory aluminium shrinks 1'' in 48.

Post by **nick69** » Sun Feb 24, 2008 8:21 am

I went down the local Foundry yesterday as I knew they were in and they are not interested in doing small jobs such as this

The guy said that resin is rock hard and in some cases harder than metal and maybe try a home cast in a 2 pt plaster mold. He said as long as I put some steel reinforcement by the screw holes there shouldnt be a problem.
Might be worth a go in the short.

I have emailed a couple of other places to see if they would be interested.
One chap last week wanted £700 for the mold alone

Post by **nick69** » Sun Feb 24, 2008 8:23 am

overider wrote:In this months copy (March 08) of Complete Kit car is a big 7 page spread about a guy who made a car from scratch out of different composite materials using different techniques you might get some idea’s from this???

If not it would still be interesting reading, thanks ill get it.

Post by **paulhumphries** » Sun Feb 24, 2008 9:41 am

Casting "one off's" is quite common for model engineering.
Seek out your local club (maybe via a night school course) and I'm sure you will find someone who will help.
This is a well known "cottage industry" type model engineering suppler who are usually helpful -
http://www.users.zetnet.co.uk/college-engineering/

There are numerous books on the subject and a quick look on Amazon finds these -
http://www.amazon.co.uk/Successful-Cold ... 677&sr=8-2
http://www.amazon.co.uk/Foundrywork-Ama ... F8&s=books

Paul Humphries

Post by **nick69** » Mon Feb 25, 2008 7:09 am

Thanks Paul, I did order one of those books this weekend.

Cheers