Tips for making a master for vacforming

[Tony C]

I would like to make a new vacform canopy for a TSR.2 long term project but having never made a master tool before, would like to ask any of you have any tips and what material I can use in the process?

 

Although I have never used it, I do have a dental vacform machine I brought a few years ago and clear PETG sheets, though I'm unsure of the right materials to use, to make the master tool?

 

Having never used a Vacform machine before, I imagine that there is a lot of heat involved, so could I use balsa or air drying clay or even foamboard or should I use something else?

 

Further but on a slightly different topic, for those that make diorama, can anyone recommend what to use, that is easily shaped, to make the base?

 

Many thanks

 

Tony C

 

PS

Please beware that I work nights, so if I don't reply immediately, I'm not ignoring anyone, I maybe working or asleep but I will reply as quickly as possible!

[Rob de Bie]

There are multiple solutions. You can use the original canopy, filled with Milliput for example. Did that with an Anigrand A-12 Avenger canopy. With an injected canopy, you run the risk of softening the detail, due to heat.

 

 

The above route will give you an oversize canopy, by the thickness of your PETG, and that could lead to fit problems. And detail will become 'soft' because it's on the inside. For my purpose, a half-fictional aircraft, this was no objection.

 

 

To solve the oversize problem, it becomes very laborious. You have to make a negative mould of the original. Done that once, long ago. I used rock-hard epoxy tooling gelcoat, followed by glassfibre and epoxy. It has to be a thin shell, because you have to drill the smallest possible holes through it. I wasted several 0.3 mm drills here.

 

 

 

I will do it again, soon. Here's the master (Bede BD-5 homebuilt), ready for waxing. It's an lot of work for a tiny part..

 

 

Lastly: PETG is finicky to use. When you heat it too long, the moisture in the plastic will boil, leading to steam bubbles. It will look like this:

 

Rob

[Tony C]

Thanks Rob,

Very Interesting, I had thought about using the canopy in the way that you describe but I was thinking of using air drying clay pushed into the inside but am unsure if it would be suitable!

 

I do have some Miliput, I'll give that a try!

 

I guess that whichever material is used, it must have a glossy and smooth finish?

You also mentioned drilling airholes, which must be to ensure that the plastic used, is formed equally across is surface. If this is correct, do all masters need airholes, regardless of size?

You also mentioned that there were potential issues with PETG, are there other materials available, that are better for the job of vacforming clear parts?

 

Again, thanks for your input, its much appreciated!

TonyC

[Rob de Bie]

Milliput is not obligatory, clay or plaster of Paris will probably work equally well. It's more a question of what you have at hand.

The master of my A-12 canopy is not very glossy and smooth, since I painted it with Revell 9 matt coal black, buffed to a semi-gloss. Maybe gloss would be better, I don't know..

Air holes are only required if you use a female / negative mould. If you have some old vacformed kits, you will often see 'pips' all over - that's where the air evacuation holes were. My tiny 0.3 mm holes left no pips on the canopies I formed.

I never used anything else than PETG - I haven't done that much vacforming! I do know that one club member got sick and tired of the steam bubbles, and switched to the plastic from report covers. No idea what kind of plastic that is.

One more comment: If you do male moulding, the base of your master has to be flat, otherwise the force of the vacuum could / will bend or even break your master. Plus your master will be stuck inside the vacformed part, and it will be really difficult to get out (ask me how I know). My A-12 master was curved at the bottom, therefore I had to build a supporting structure. That in turn was bigger than my dental vacformer could take, so I has to sand the ends aggressively, hence the white ends.

Rob

[Tony C]

Thanks Rob,

Excellent information, especially about a flat base and plenty of food for thought!

 

Cheers

Tony C