www.TK560.com

[user error]

Did a little digging around the net and found a few places that might be a better alternative to the Hardibacker. Not sure if this is the right stuff, but it's used in kilns and wood stoves, so I assume it'll work for a vac-oven:

http://www.ceramaterials.com/ceramicfiberboards.html

http://www.mcgillswarehouse.com/ItemsList.aspx?ProductID=109140101

Any thoughts or comments would be appreciated.

[RRK4]

It would probably work well and it would certainly take the heat better then the cement board. The only problem I could see is that the liner that I remember in kilns is like a ceramic sponge and is very brittle. The cement board may have better structural qualities.

[Fredo]

This is what you need if you plan on using 17# fiber board in your oven. http://cgi.ebay.com/Refractory-coating-Rigidizer-Ceramic-Fiber-Blanket-/130343877176?pt=LH_DefaultDomain_0&hash=item1e5919ba38m It is, I think, silicone dioxide, common name, water glass. The fiber board at 17# is still a little soft. The rigidizer makes the surface, and as deep as it penetrates much harder. I bought a case of the one inch board and 3 rolls of one inch fiber blanket and have used both in the three ovens I've built. I'm it's #1 fan here, though it hasn't really caught on with any one. I only use it because I choose not to heat the air around the vacuum former. To my way of thinking, if you are using radiation heating [on the relatively small ovens we are dealing with here], there is no reason to heat the outside of the oven. The omni directional heat loss [from most ovens] seems a waste to me. I feel it would be better if that heat is retained in the oven and re radiated as cavity radiation at the intended target. Ceramic fiber is the best reflective insulator of heat on the planet.
That's my ho and I'm sticking to it..................Fredo
_________________
If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001

[user error]

Wow, I didn't know it was that soft, figured it would be harder than the cement board. I guess if you built a steel shell and bolted the fiber board to it like James' did in the book it would be okay, but then you still have the heat loss problem that Fredo mentioned.

Speaking of which, how did you incorporate the fiber blanket into your design, Fredo?

Btw, I did find the calcium silicate board, but it was usually sold in bulk and quite expensive. I'll do some more digging and see what I can find.

[Fredo]

Here's an oven I started and set aside. http://www.tk560.com/phpBB2/viewtopic.php?t=1385 It was to be for a flip flop type former. With a couple changes, I plan on using the 1"x6" walls as part of a sliding overhead oven. The fiber board, as you can see in one of the pics, suffered some damage at the hands of ups. With the rigidizer it will be much harder.
The little 12x12 I built used only untreated fiber board and a little blanket to fill a few gaps. I didn't feel it needed any surface hardening since it gets no wear..although, I'll treat it when I order my next gal. of rigidizer. With untreated board or blanket the heating/cooling cycle, will over time, cause some surface degradation of the binders. The colloidal silica binds the fibers together when the water evaporates.
I'm using the extra blanket for a 2'x3'x6' 9000watt. powder coat oven.............Fredo
_________________
If someone has a gun and is trying to kill you,
it would be reasonable to shoot back with your own gun...The Dalai Lama..Seattle 2001

[kayaker43]

I called Ceramaterials and they only sell full cartons and only ship by truck. This is typical, you see a low price per sheet then have to buy 12+ sheets and pay $120 for shipping.
_________________
Doug Walsh
www.build-stuff.com
Hobby-Vac and Proto-Form machine plans

Also other plans books and videos for people who like to build things

[user error]

@ Fredo: Dude, that is one slick oven design! I might have to try that.

@ Doug: *sigh* Well that figures. I guess the search continues, but thanks for following up on it.