Best way to make a mold for vacuform canopy?

[billn53]

I am building Special Hobby’s Lockheed Electra, which is a 20+ year old kit. The kit includes a vacuform canopy, which has become yellow and brittle with age. 
I wish to use the existing canopy to create a male mold, which I will then use to vacuform a new canopy. 
A few questions:
 

1. Does this sound like a viable plan?
2. What material is best for creating the mold? I’m looking for something that can be poured or pressed inside the existing canopy, then extracted after hardening. 
3. What (if anything) should I use as mold release?
 

Thanks,

Bill

[Stu_davros]

I have replicated numerous vacformed 43rd car windshields by filling the existing vac with plaster of paris. I rig something up to keep the vac level when upside down and pour the plaster mix in, a screw pushed into the setting plaster will make it easier to remove the cast from the vac when the plaster is set.

I've never used anything as a release agent as I've never found it necessary with vacforming.

 

Hope this helps.

 

Stuart

[tomprobert]

In  addition to Stuart’s suggestion above, Millipit is also a very good medium for making masters for vacforming. 
 

Tom

[billn53]

Thanks, Tom & Stuart. I have plenty of both Milliput and PoC, so it seems I’m good to go. And, the screw idea is a great one!

- Bill

[Planebuilder62]

Hi there

 

How do you stop the Milliput from bonding itself to the inside of the old canopy?

Regards Toby

[tomprobert]

2 hours ago, Planebuilder62 said:

Hi there

 

How do you stop the Milliput from bonding itself to the inside of the old canopy?

Regards Toby

You can buy an off the shelf release agent but a very thin coating of vaseline will also do the trick! 

[LorenSharp]

I've had some success using Sculpy instead of Milliput. It's a lot cheaper and you don't have to spend a lot of time working the 2-part epoxy to the right consistancy. MY biggest problem has been getting clear plastic the right thickness to do the job without messing up the plastic. I had been using K&S .015 Clear Plastic sheet, but this last time I used it, it wanted to pit and distort before being soft enough to use. That may have been due to the high humidity of late, But I have to get more before I can experiment further.

[Paul Lucas]

8 hours ago, Planebuilder62 said:

Hi there

 

How do you stop the Milliput from bonding itself to the inside of the old canopy?

Regards Toby

Apply a thin dusting of talcum powder to the inside of the canopy and a similar dusting to the Milliput before you press it in.

[Tarby]

I used a casting resin-plaster from Hobbycraft which was poured into the canopy itself, with external walls made from plasticine to contain the plaster where it would overflow. The release agent was Johnson's baby oil.

[bootneck]

Hi Bill,

I hope that you don't mind me asking a similar question here please.

 

How can I make vacformed curved windscreens without having an original to work with?   I haven't managed to construct the front windows of this Whirlwind as I don't know how to shape/vacform the curves.

 

 

 

cheers,

Mike

[Black Knight]

I would use, have used, polymer clay to shape the canopy, cook, and vac form over it, 

[Black Knight]

I had to go out

Only thing I have photographed at the mo

The Airfix Westland Scout; the bulged rear doors were moulded in polymer clay then vac formed over that