Vacuum forming help

[Wild Oscar]

Hi anyone in this part of the forum know wherein the UK i can get a single small canopy shaped object vacuum formed or plunge molded?

[Kenny]

You could make one yourself by thermo forming. Make a frame to firmly hold a thermoplastic (one that softens rather than chemically converts with heat and) [eg p.e.t] then heat, press onto balsa (or other plug) just make sure the plug is perfectly smooth and with nothing that will come off on th plastic.

[Wild Oscar]

Hi thankx for that i have a master in of all things vacuform WHITE dohhhh.
When i attempted to vacuform it looked a bit like a sucked sweet!! Or should i say plunge it through a heated piece of clear plastic. But I will try anything once ...
If i like it more than once. Thankx for the help.

[Wild Oscar]

Woe is me...
This was an art which i never learn't all those years ago! Eons ago when i started model making at our local IPMS branch we had loads of what i call 'old boys' These so called old boys could make you a scale model of a Bristol Blenheim out of a bottle top! And plunge molding or home made vacuforming was one of those artforms they use to indulge in. I knew a guy who use to make the most fantastic vacufom models for the Shuttleworth Trust, who could vacform your pet cat perfectly.
But alas yours truly who thought vacuforming was for girls looked to a time when resin would rule the world and even the oddest of subjects or a TSR-2 would be kitted by Airfix! Anyways I didnt pay attention at classes and strayed towards the dark side. Now in his twilight himself can only make vacuforms that look like half sucked boiled sweets dohhhh.

By the way the old boys all died!!!! And i never got back to Walton's Mountain.

[naoto]

Despite your disparaging comments regarding vacu-form, the technique does still have its uses. I have yet to see a decent canopy made of resin. I've yet to see an injection-molded canopy for model aeroplanes in smaller scales (1:144) that don't look overly thick. Okay, so my viewpoint is skewed in favor of vacu-form in that I prefer to build in smaller scales, and often build flying model aeroplanes (where cast resin just doesn't cut it as it's far too heavy).

BTW... what were you thinking about when you were trying to vacu-form using a vacu-form master?!?! Draping hot plastic over thin plastic form (and even thick plastic form made of similar material) is a disaster waiting to happen!

[Wild Oscar]

you know you were so right....

Like keeping a 1/2 ton bengal tiger in the garden an accident waiting..
No to be sensible for a mo i filled the master (vacuform) up with milliput and then plunged it... It was OK, it was the hot plastic clear sheet that wasn't... It looked a bit like Donald Trumps head!!! Or Joan Collins lattest boob job.

If your into abstract it's yours i'll send it.

Tis true i've never seen a resin canopy EVER i dont think unless its solid. I was dreaming of all those unkitted sci-fi subjects. Minus ones with canopys lol.

By the way im not bashing vacuforms some of my best friends are vacforms. It's more my inability to watch and learn at an early age.

[Chacal]

Thermoformable plastic's natural shape is a flat sheet. Heat it up and it goes happily back to a sheet (that's why you need to keep the vac-formed part "vac'ed" until it cools). Even if you back the molded original with anything, it will distort with the heat from the "to be molded" plastic. If all you have is the vac-formed original, make a male form of it pouring plaster "inside" it (on the "back" of the part). That'll not give you best detail, but as the thickness of the original will vary (because of the contour of the original plug) the same way the copy will, so they should be pretty similar, if not equal.

[naoto]

By the way im not bashing vacuforms some of my best friends are vacforms. It's more my inability to watch and learn at an early age.

Ah... I see... In my first reading of your post it sounded to me like you were bashing.

Anyway... As mentioned in the previous post, when plunge-forming as well as vacu-forming, you need to hold the plastic against form until it cools sufficently. Learned that early on when I used to plunge-form (aka "heat-n-smash") canopies for my model aeroplanes. Here's what I typically did:
1. make a male form (typically carved from wood, which was sealed and sanded so that it was very smooth)
2. make a holder for the plastic with a hole slightly bigger than the form
3. securely clamp thermoform into holder
4. heat thermoform until it begins to get rubbery and sag
5. Plunge form into plastic through hole in holder in one quick but steady movement and hold and wait 'till the plastic cools.
7. wait a bit longer while holding form in place

Obviously forming parts with a vacu-form rig will produce better results than the "heat-n-smash" method.

For opaque parts there is one option worth trying out. An adaptation to papier mache could be used for form hollow shells. Instead of the starch mixture, use thinned wood glue. This will result in sufficent stiffness and resilience that you can sand the part. Works well on larger parts where vac-forming might be difficult (used to do this to form cowlings where the depth of the part would've proven problematic). Best part is that it's probably the cheapest technique -- albiet messy.