Learning to vacuum form

[dnl42]

The prologue. I'm working on a Gavia/Eduard 1/48 Lysander Mk III SD. The kit's canopy has 5 parts, the windscreen, 2 sides, a top, and the rear sliding section for the aft compartment. The fit of the side and aft sections are a little sketchy. At some point I had acquired a Part PE canopy frame set. While the set includes clear plastic for the 2 flat side sections, user-supplied plastic is required for the top and aft sections, which are both curved. I was able to get some Evergreen 5 mil clear sheet from my LHS. Sadly, my attempts to curve the plastic result in crazing when I tried to use a heat gun and significant clouding when I tried hot water. 

 

 

Over the years, I had thought about getting a vacuum forming machine, and decided now was the time. I was originally going to get that blue unit from Amazon, Ebay, &etc., but I found this surplus NIB dental vacuum former for just a wee bit more. That box next to it is some manner of dental plastic that was included with the unit. This plastic is pretty thick and slick stuff. I doubt it will be useful for modeling, but it's turning out to be quite good for learning.

 

For my first attempt, I plunked down a handy form--a brass jaw for a Panavise--and fired it up. Well, at least I proved the device worked. It appears I didn't heat the plastic enough. As I was cleaning up that part, I realized that plastic vise jaw covers could be handy. I put in both jaws and tried again. The molded parts were much better formed, but the bottom edge was iffy. I then realized I needed to raise the mold off the vacuum bed, so I cut some wooden "craft sticks", a.k.a. popsicle sticks, to size and placed them beneath the jaws. This was much better. I think I understand the approach.

 

Here are my various attempts. The 2 examples above the brass jaws are the best. Not perfect, but the best so far...

 

I think I'm ready to carve a mold for the aft canopy section next. It's a simple developable surface, so that part will be easy.

 

@Black Knight has provided some advice on how to avoid wasting a huge 5 in square sheet of plastic for making a small part. He suggested making a 5 in square MDF blank with a hole in the middle to mount a smaller sheet of plastic. 

[Black Knight]

For shaping up a canopy; get some polymer clay, aka FIMO or Sculpey. 

Its a heat setting plastic clay.  Un baked its like moulding clay or plasticene. When its baked its hard and set and will withstand the heat needed for vac moulding. Soft or hard it can be trimmed with a modelling knife

 

Two ways you can go when you raise the master part up off the vac bed.

1. wider and deeper, basically down a bit then at an angle outwards. 

2.  narrower.

 with 1 the vac will pull the soft plastic down and out allowing you to get the master out easy

 with 2 the vac will pull the plastic down and in and you need to cut this base area off before getting the master out for another try

 

Not all clear plastic will stay clear when its heated and vac'd. 

I use plastic marked PET - its the stuff on vac formed packaging. I save it all and have had family save it for me

[dnl42]

@Black Knight, more excellent advice!

 

I was thinking of carving basswood (lime) for the Lysander because of the simple form. Clay should be easier still! My wife makes jewelry with heat setting plastic clay. Clearly, I'll need to get my own supply...

 

My craft stick experiment above was clearly your #2 example. I've seen the #1 example in the vac formed canopies I've used in the past and is my plan.

 

I guess my first experiment with the clear sheet I already have will prove its usability. I'll look at plastic packaging differently now. I can just imagine "Honey, I really think you need this! It would look/feel/taste/be fantastic!" 

[Black Knight]

remember; the soft plastic will copy what is on the master. The master needs to be really smooth for canopies, not so fussy on white plastic parts. Even very fine grain marks on the master will show on a canopy. I had a finger print on the polymer clay show on a canopy!

If you use any wood for a canopy master, use a filler over it and smooth the heck out of it. Conversely, a bit of marking on the not-canopy part of the master will help tell which part to cut away

[dnl42]

The learning continues! I made a master using Sculpey clay. The first attempt was under-sized, so I added some epoxy putty and filed it down to shape.

 

It's actually quite handy as I was able to reshape the canopy frame PE to a smoother shape. I tried it out using that dental material and found a little more filing and polishing was needed

 

I then tried with some rescued vac-formed packaging. Unfortunately, an edge pulled out of the frame on both attempts and I couldn't get it soft enough.

 

Both attempts failed, but at least it looks like the master is smooth enough!