Interesting thought, but I think it might be akward to work that way...gravity can be our friend!

zbrubaker Kewl....The hardest part is even heat I have found
But if you build it they will come....




Lets us know



aerogel

zbrubaker,
I like your design. It's similar to what I had in mind. Why not hinge the top box to the bottom box? Once we have softened the foam and pulled it into the form with vacuum, we want to be able to get rid of the heat quickly to "set" the foam. Hinging the heat box allows us to get rid of the heat source quickly without having to look for a place to set it. Sort of like opening and closing a suitcase?

JT

Gravity yes, but what I was really thinking about was heat distribution and control.
Because it rises, the heat would rise to the foam suspended above it. Because the foam was already in position, you could continue controlled heating until (and during) vacuum.

The heating chamber is fixed in place...the heating chamber and vacuum box are a single unit. When the foam/plastic has been heated to the appropriate temp, simply drop the frame down to the vacuum table. There is enough seperation between the two that it would be effectivly "removed" from the heat source.

I don't think hinging the two would work quite the way you think it would. That would mean the foam would have to rest on the plug when it was "cold". If you were dealing with a plug that was a couple of inches high, you probably would not be able to "close" it.

Because then you have to suspend your mold from the vacuum platform... a little harder than just setting it on the bottom, but sounds like a neat idea to try!

I am building a similar machine for "regular" thermoforming - I'm using wonderboard to build the heat box - it's made from something like cement with glass fiber reinforcing and is commonly used as a ceramic tile backer - and it's also rated as a heat shield. Got mine at Home Depot.

I'm considering using an electric dryer heating element (a long helical coil of some kind of wire) - it's made for 240V, 4800 Watts, but on 120V it'll put out around 2200W at 20 amps. I plan to snake it around in the wonderboard box and hold it in place with ceramic insulators. Add a high-current (20A minimum) dimmer control and voila!

As a backup plan I have 4 300W heating elements from a toaster oven - I don;t like this as much since I suspect the heat won't be as even...

http://members.aol.com/KMyersEFO/vacuum.htm

I plan to make mine to handle 12"x24" sheets...the hinged design would take up alot of workbench space at that size. I see the idea though, and I think it would work great for a smaller size.

zbrubaker,
From the little I have played with foam, you don't have much time to form the sheet once heat is removed. It "sets" almost immediately. What I was thinking about was a fixed frame for the cold sheet and applying heat until the vacuum is applied. This insures the foam "flowing" into the mold. I think perhaps the difference in our thinking stems from the type of of mold being used. I would use a cavity mold and I think you are looking at a plug type mold. Both of us are right.

JT

Just a thought. Could you just throw the whole thing on a propane BBQ. I am not sure how big mine is, but I know its alot bigger than my oven. Its built to distribute heat evenly. I even have a temp guage built in. I suppose it depends on if the wood in the box ignites before the Zepron forms? Could you just have the vacumn on the whole time the box was in there?

loading,
You've hit the answer in the question. Yes you can heat everything at once and have vacuum all the time, BUT everything has to be fireproof (read expensive). Heat guns, electric ovens, propane barbeques will all provide heat. The test is to produce formed parts using commonly available materials, at reasonable costs, without setting things on fire. (Hate it when that happens)
There are plenty of good ideas floating around in this thread and I am guessing that all of us will come up with a workable answer for our particular needs and not one of them will look like anyone else's!

JT

Depends Im about to start Making a cavity mold I think this process Will cost more...to do....but make More detailed and
Stiffer models

I dunno if the Box and heat guns will work its worth a shot
I think Im going to Build the Hinge version or...The slide down from the top....The best thing to use is Cermic heaters but they cost a frotune...dunno if I want to dish out the cash for it or not...



aerogel

I am not so sure Fireproof is needed. Anything you can stick in an oven you can stick in the BBQ. I think Emeral would be proud. BAM out comes another plane. Its great to share ideas. I am more of an idea copier than inovator, but if you are willing to let me pick your brains, I feel its my duty to post any idea I have. Even if its dumb, it may cause someone brighter than me a spark of intuition.

aerogel,
I'm not sure, but I think making a cavity mold will be easier with the exception of providing holes in the cavity to pull the vacuum. It may take a bit of work to get the proper vacuum in the cavity to form the part if the shape is very complex. Also, there is the implicit assumption that a male mold is available to cast a female cavity mold. I'm thinking about two piece wing molds and having to produce top and bottom male plugs>female cavity molds before I can form parts. I suspect that plug molds would be easier for one-offs and cavity molds would be better for limited production runs. Of course, I'm into production runs. With my flying skills there is no such thing as just one of anything.
For sure, the cavity mold will allow greater detail on the finished part. They don't usually put the detail on the inside of whatever we would use for a plug mold. As usual, pro's and con's. We probably need a design that will let us use both kinds of molds. There is a point of diminishing returns and somewhere in all this we have to remember that we are building model planes to fly.

JT

loading,
I wasn't trying to imply that your idea was dumb. Actually, it's a good one. Iwas just trying to point out that heating everything has some high costs. If you want to see your idea in action, do a little research on rotational molding of plastics. There is no such thing as a dumb idea. (well, there is, but it's usually mine)

JT