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General Mold, Casting and Buck Questions.

 
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n0x23
Newbie


Joined: 25 Feb 2010
Posts: 10

PostPosted: Thu Mar 04, 2010 12:41 pm    Post subject: General Mold, Casting and Buck Questions. Reply with quote

So I'm working on a budget and the price of RTV silicone seems to be my biggest hurdle right now.
I'm not even sure how much I will need, I'm guessing between a half gallon, or perhaps a full gallon, maybe 3 gallons...I have no clue. Laughing

I was thinking I could get away with a half gallon if I construct some thin-walled molds, but even then that's a purely a random guess.

I'm also considering that since I'm using cardboard, duct tape and foam, once I sculpt the Bondo on top of it, I can then fill the inside with a hard, non-shrinking gypsum plaster (Dap Presto Patch/ Fixall), then do an initial pull with a thin styrene and use that as a mold to cast the bucks out of.

Does this sound like a feasible idea?
What would be the draw-backs to this method?
Would a thicker plastic work better for the initial pull/ mold?
Are there any other budget-conducive solutions available?

I am open to any suggestions, tips and advice.
Thanks.
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spektr
Master


Joined: 07 Jan 2008
Posts: 425

PostPosted: Thu Mar 04, 2010 1:49 pm    Post subject: Reply with quote

Its done that way a lot.. some people use fiberglass to make the shell to mold the tool in. If I were going to use styrene or something thin like that, before I demold the plastic from the master, I'd build a dam out of cardboard/wood on the non-tool side of the styrene sheet and pour something cheap into it, like plaster or floor leveling compound. Demold after that sets up and the shell will be really rigid and the tool will be more accurate when you cast it into the tool side of the shell.......

Scott.
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n0x23
Newbie


Joined: 25 Feb 2010
Posts: 10

PostPosted: Thu Mar 04, 2010 1:57 pm    Post subject: Reply with quote

Thank you, Scott.
That's a great idea, I was wondering how to solve the lack of rigidity of the styrene.
Is there a loss of detail using the styrene/ mold method?

Also, regarding the fiberglass resin...Is there an issue with the resin sticking to the Bondo master mold, or am I not understanding the process that you suggested?
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spektr
Master


Joined: 07 Jan 2008
Posts: 425

PostPosted: Thu Mar 04, 2010 2:12 pm    Post subject: Reply with quote

do it your way, you understand it, it will work and you'll get a good tool in the end..
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n0x23
Newbie


Joined: 25 Feb 2010
Posts: 10

PostPosted: Thu Mar 04, 2010 2:19 pm    Post subject: Reply with quote

Hahaha. Actually I don't have a way and I don't fully understand it. Laughing
I have never done any of this before.

I'm trying to understand if the resin is poured over the master Bondo mold and if so, doesn't the resin adhere to the mold?

Along the same lines...If the styrene mold is encased in the plaster for stability and I pour the plaster into the styrene mold, is there an issue of the plaster adhering to the inside of the mold and if so, how would I extract the plaster from the mold?
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stormtrooperguy
Expert


Joined: 24 Sep 2009
Posts: 126

PostPosted: Thu Mar 04, 2010 2:46 pm    Post subject: Reply with quote

resin would stick to bondo unless you use some sort of mold release.
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jdougn
Guru


Joined: 18 Mar 2009
Posts: 714
Location: Louisville KY area

PostPosted: Fri Mar 05, 2010 9:20 am    Post subject: Reply with quote

stormtrooperguy wrote:
resin would stick to bondo unless you use some sort of mold release.


Yeah, you will need to use mold release any time you cast. Fiberglass resin uses PVA Mold Release. Do a google search on something like, "fiberglass mold making".
Here's some info on plaster mold making:
http://www.plastermaster.com/usg/index.htm
IIUC, you can get by with vaseline for plaster.
Double check this info to make sure it works for your situation....

hth, DougN
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DougN - Just in case you're wondering, I got my "rating" legitimately... by posting aimless drivel, useless advice, and pointless questions.
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jegner
Site Admin


Joined: 30 May 2003
Posts: 2144
Location: Texas, USA

PostPosted: Mon Mar 15, 2010 9:06 am    Post subject: Reply with quote

I just gotta ask, what sort of mold are we talking about?
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clonesix
Novice


Joined: 19 Jan 2007
Posts: 63
Location: california

PostPosted: Tue Mar 16, 2010 9:40 pm    Post subject: Reply with quote

Oh good, I am glad Jim asked, and I am not the only person who was confused by the description.

What are you trying to make/mold? A picture says 1000 words.

You want to mold something for fiberglass? vacufoming? Do you have the model? do you need to make the model?

This information would help to give you the right direction. Many of the products that you describe as "never done before" are dangerous to your health, and should NOT be taken lightly.

Happy to help, just need better information.
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