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idolman · Newbie Joined: 24 Sep 2007 Posts: 10

Im new to the forum and have no knowledge of thermoforming. Ive looked at many commercial machines and the cost for such a machine is crazy. By looking at many of the home made machines made by people on this site it seems possible to make the heater inexpensive compared to commercial heaters. Can nichrome wire be used to manufacture such a large heater that would work with 1/4+ plastic?

drcrash · Posted: Tue Sep 25, 2007 10:12 am Post subject:

I think nichrome would work fine for a really big oven.

The hard parts of making a big machine are the mechanical parts... rigid enough frames, a way to quickly move a huge sheet of plastic from oven to platen, and pumping enough air to suck it all down.
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idolman · Newbie Joined: 24 Sep 2007 Posts: 10

If the heater was a top heater, only he plastic and its frame would have to drop down onto a female mold (which is a 28 ft / 7.6ft boat hull). The plastic would not be too heavy and id think the frame would not have to be to heavy duty.

I would think the heater would be the largest obstacle as the female mold appears alot easier to effectively apply enough suction to pull the plastic into shape.

Any ideas?

jegner · Posted: Tue Sep 25, 2007 12:46 pm Post subject:

Sounds like a doable project. Try running your oven size through the oven calculator and see what numbers you get. My guess is, NiChrome wire will do just fine. You may need to make a series of smaller oven units, and daisy chain them together to make one long oven. Over/under is then only way to do this. The macine support would have to be either overhead suspension or some sort of external rack.

Vac-forming a boat hull. Wow. Cool! There have been board members here making airplane canopies, and trooper armor, and RC cars, but a full scale boat, thats what it's all about.

Jr Branham · Novice Joined: 09 Jun 2007 Posts: 28 Location: Georgia

Wow,
Where can you get plastic in that size? Can the hull be done in two sections, and joined at the keel? I have seen some big plastic-hulled boats, but, I think they were rotocast. Interesting project, keep us posted on the progress.
Jr. B

jegner · Posted: Tue Sep 25, 2007 2:05 pm Post subject:

I think you can get HIPS on a roll. Take a look at the professional plastics site, in the HIS section. The pic they show, is HIpS on a roll.

Still, seems like a crazy project! I love it.

idolman · Newbie Joined: 24 Sep 2007 Posts: 10

"Over/under is then only way to do this"

Are you explaining 2 ovens (heaters), 1 on top and 1 below the plastic? I was considering only 1 above heater.

I found a few suppliers that can do 12ft wide and basicaly unlimited leangh (shipping is another obsticle). My hope is that i can form a UV protected abs that is shiny(atleast on 1 side) to enter the female hull mold first to give close to a gellcoat type sheen, followed by a polypropylene type plastic sheet second, followed a by a stringer support system (also plastic formed poly or abs). Also hoping the sheets can form over eachother without distortion. Suction holes will need to be drilled into the bottom of each layer and filled in later. That should complete the hull. Then the inner floor would be abs consistant with the first layer of UV abs, as well as the final top cap. All will be bolter together as a standard fiberglass vessel. My hope is that the entire vessel can be completed using under 6 sheets of 28 X 8 sheets and virtualy ready to add marine hardware.

idolman · Newbie Joined: 24 Sep 2007 Posts: 10

kayaker43 · Expert Joined: 13 Jun 2007 Posts: 175

Sounds ambitious and the success will likely depend on the plastics used. There are some interesting co-extruded sheets used for spa applications that use a hard shiny (acrylic) surface on one side with UV resistance, and some other plastic to back it up. Should be available in any length for a price? Spas also use thermoformed shells back sprayed with chopped fiberglass for strength.

The TJ ovens use much less heat than normal because they are trapping it in a closed chamber, and even then heating times are very slow. I'm using 1200 watts per sq ft. with great success with an overhead oven, but its pretty well optimized. Custom builders often throw in twice that much heat, then spend thousands on controls to turn it down till it sort of works. Not very efficient that way, but easier than spending time to get it right.

1/4 inch is about the limit for one sided heating, but can be done if the watt density and wavelength are pretty close. Otherwise the rays won't absorb fast enough, or will cook the surface. Do your shopping for heating elements, then give me a call, I'm working on some modular elements that fit into common suspended ceiling grids so it should be easy to configure any size you can imagine.

Crunch some numbers first, you will need huge power for an oven that size and a huge vacuum system. The transport mechanism will also have to move some decent weight a few feet in about a second.

Overall it should be doable, but work out the plastic properties on a smaller scale before committing. I forget the name, but there was a sea kayak made with thermoformed halves and it was pretty nice. I think it was some polycarbonate blend? Lots of canoes too, but they seem to have dull soft surfaces, probably ABS?
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