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What about clay as a vacuum forming material?

 
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LaughingCheese
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Joined: 24 Mar 2008
Posts: 138

PostPosted: Sun Mar 21, 2010 11:15 pm    Post subject: What about clay as a vacuum forming material? Reply with quote

Hmm, I was wondering if clay is a good material for molds?


Its a one part material (Laughing), and is fairly solid once baked! Razz
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spektr
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Joined: 07 Jan 2008
Posts: 425

PostPosted: Mon Mar 22, 2010 8:19 am    Post subject: Reply with quote

Here's what I look for in a vac form tooling material.

It will reproduce the object.
It is dimensionally stable.
It is thermally stable below the Tg of the plastic we are molding.
It is durable.
It makes sense cost wise.

GENERALLY this means to me cast urethane or epoxy tools. I rarely use plaster any more except for prototyping concepts, and then i use hydrocal or in a pinch, vinyl floor leveling compound. Simple stuff that I can make from hardwood blocks still gets made that way.

High rate tools get cast from aluminum instead of epoxys.

Now back to your question... I personally haven't found a clay that meets these requirements. They may exist, but I don't look for them because other better stuff is available really cheap. My experience is that the shrinkage of most clays is inconsistent lot to lot.

You might find the silver bullet, but I haven't stumbled across it yet.

One last thought..... If it existed, and if it was economically viable, somebody would be marketing it. That alone should answer a few questions...

Scott.
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Culvan
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Joined: 20 May 2008
Posts: 85
Location: Kansas City, MO

PostPosted: Mon Mar 22, 2010 10:05 am    Post subject: Reply with quote

spektr wrote:
It will reproduce the object.
It is dimensionally stable.
It is thermally stable below the Tg of the plastic we are molding.
It is durable.
It makes sense cost wise.

[edit]

Now back to your question... I personally haven't found a clay that meets these requirements. They may exist, but I don't look for them because other better stuff is available really cheap. My experience is that the shrinkage of most clays is inconsistent lot to lot.

Nice list and a good analysis.

I have not used clay yet, I am hoping that someone who has will speak up. I actually think it will be a good material with a few exceptions that spektr outlined.

First of all let me say that I'm referring to water based clay, not oil based clay. I assume you are as well since you say that it's solid once it's baked. Oil based clay (Plasticine and Klean Klay) will melt when heated. It is reasonably priced if you can find a local art supply store and It handles heat well.

The downsides are that as the water evaporates out of it, it shrinks. If you are trying to make a 4" block, you may end up with a 3.75" block after you've baked it. In most applications that's enough to make it completely unsuitable, but if you are looking to make something, but don't care about the exact size then perhaps you can live with that.

The other drawback is that it is brittle. You are not likely to get many pulls off of it before it cracks. However if you are just looking for a single prototype, maybe you can live with that. If you are lucky enough to get a good pull on your first try then you could fill that with hydrastone and have a better buck.

I personally have a one off project comming up. I was planning on using clay because I don't plan to do more than a handfull of pulls and the dimensions aren't that critical. I'm not sure how long it will take me to get to that project though.

Andy
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clonesix
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Joined: 19 Jan 2007
Posts: 63
Location: california

PostPosted: Mon Mar 22, 2010 10:02 pm    Post subject: Reply with quote

Clay works very well for one pull, sometimes two. After that, you need to pour stone into the pull and make a more permanent buck.

I use clay all the time. No, it doesn't need to be hard, I vac over it wet. If there is detail that might not survive vac'ing, let the clay dry out to a leather like state, and then vac over it. It works fine.
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jdougn
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Joined: 18 Mar 2009
Posts: 714
Location: Louisville KY area

PostPosted: Tue Mar 23, 2010 11:09 am    Post subject: Reply with quote

clonesix wrote:
Clay works very well for one pull, sometimes two. After that, you need to pour stone into the pull and make a more permanent buck.

I use clay all the time. No, it doesn't need to be hard, I vac over it wet. If there is detail that might not survive vac'ing, let the clay dry out to a leather like state, and then vac over it. It works fine.


What plastic are you using for the pull?
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