Vacuum Forming

[Kazzer]

I've been messing with fiberglass and molds for some time, and not having much practical experience of laying up boats, I thought I'd take a look at vacuum forming, before I really settled on a technique. HWSNBN got all of a quiver when I mentioned I'd like to give it a whirl, so -with more ado - my son Jon and I started on a plenum yesterday. It's 6' long and a foot wide. The frame is wood, but if this works, we'll get a metal one welded up.


Next job is to make the oven. I have figured out the wire, ni-chrome 23 ga, about 15' long, and the ceramic posts are being ordered. I'm going to line the oven with Hardybacker cement board.

More to come!

[greenman407]

Cool Mike! Full Speed Ahead!

[trout]

6' huh, perfect for a certain hull you have been working on? I am very interested in your posting Mike!

[He Who Shall Not Be Named]

Don't burn the place down, Mike!

[Scott T]

You might pick up a used ceramic kiln and use the parts of it for a large oven.

Scott T

[Kazzer]

I've decided to go for a gas system, and purchased some more stuff today.
My first buy was the heater. Costing $80. It runs from a propane BBQ tank and even has it's own spark igniting device.


The heater is in the foreground, the pipe reducer fits over the heater, 2 x 3' lengths of ducting make the oven, a couple of end caps and and angle reducer. That's about all there is to it.




My first job was to cut the top off two sections of ducting, one half is retained for the lid, and the smaller part on the right here, has a reinforcing strip attached which hides the rough edge.

A little later and I have the majority of the box pieced together. These pre-formed duct sections are a snap!


Here's the 6' long piece of duct, with the top cut off. End-caps are on and all it needs is a few bracing straps to keep the sides from flapping and for the lid to rest on.





Here's the almost complete set-up. Noted the tapered reducer fits perfectly over the heater, which stands on the floor. ( A safety feature - I hope!) I have to secure the end-cap, but first I need to add about 6" more length to the box.

So far -so good! Tune in tomorrow for more exciting adventures from - my basement!

[herrmill]

Safety features???!!! We don't need no stinking safety features!!!



My acrylic bathtub factory would be green with envy if they saw your set up.

[george]

Hi Mike

From what I can see of your heater setup, I think your going to have a problem. All your heat is coming from one end and not from other sides. Think of a stove oven, as it "bakes" it surrounds the item in heat. Your`s you will get lots of heat on one side and less heat on the other side. Plus the metal will dissipate the heat on the other end away from your heat source, you will have your plastic unevanly heated.
George

[trout]

Mike, looking at your heating side. With the duct coming from one side, wouldn't that heat one side of your plastic faster then the far side of your heating box? Or did I miss some baffles to ditribute the heat? Or am I just wrong?

[Kazzer]

Let's get some gas burning before we make any decisions here. If this heater is throwing out 25000 btu into a 6 cu foot space, I doubt there will be much in the way of variation throughout the chamber.

We'll see!

[Scott T]

Might I recomend one of these dual purpose units.



Scott T

[Kazzer]

My son Jon and I have been hard at work today, shopping for parts and tinkering with our former boxes.

We decided to insulate the metal heater box with Roxul, so bought a bunch of that. we also fired up the heater for the first time, and checked the temperatures.
Here's the heater fired up. Heat was reasonably even, but I think it will improve with the plastic sheet covering the top of the box.

Here's Jon checking the temps with a laser thermometer. We have a metal cover over the box for now.

Our best shot was a test run of the plenum pulling the vacuum with our Wet Vac.

We don't have any plastic sheet yet, so we cut up a heavy duty garbage bag. I know its not the same as the thick plastic, but it's obvious we have a good pull on the vac.

[He Who Shall Not Be Named]

For a given differential pressure, the force acting on the sheet is proportionate to the surface area of the plastic subject to the differential. So, the shop-vacuum, which pulls only a few inches of Mercury is fine for big sheets, but you'll need a proper vacuum pump and volume tank for the smaller work.

So far, so good. Good sound DIY fabrication on display.

Man! If you and Jon can start pulling good quality 30-60" inch long hulls ... Katie, bar the door!


David

[Kazzer]

Our first attempt today was exciting! We got everything ready, tweaked here and there, then lit the heater and plonked the new sheet of plastic on the heater box.

And waited ------

as predicted by some, one end heated up and the other froze.

Back to the drawing board! Darn!

I'm no longer sure gas is the heating answer.

[Virgil]

Mike

You might want to install one or more Muffin fans to keep the heat circulating. That's what I do and it works great.

Virg