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 Post subject: Resin Casting questions
PostPosted: Fri Sep 09, 2016 3:16 pm 
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So I want to cast copies of 1/350 carly rafts/floats. Due to the size ( very small) I don't want to make a two part RTV mold...seems like over kill on such a small part.

The question is,...Can I just make a Air dry clay mold of the Part/s and when cured and hardened then pour the resin Material into that clay mold to cast the needed parts? Will it react with the clay mold and not form? ..do I need to coat the mold with release agent..or talcum powder.?

Any help would be most appreciated.

ps...I am using Alumilite system if that matters.

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PostPosted: Fri Sep 09, 2016 3:22 pm 
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gott_cha wrote:
So I want to cast copies of 1/350 carly rafts/floats. Due to the size ( very small) I don't want to make a two part RTV mold...seems like over kill on such a small part.

The question is,...Can I just make a Air dry clay mold of the Part/s and when cured and hardened then pour the resin Material into that clay mold to cast the needed parts? Will it react with the clay mold and not form? ..do I need to coat the mold with release agent..or talcum powder.?

Any help would be most appreciated.

ps...I am using Alumilite system if that matters.



So ... let me get this straight. You're asking how to steal someone's work?

Or are you the originator of the master/pattern/part you're going to pull a tool off of?

(Yeah, it's my business to know before assisting you).



David

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PostPosted: Fri Sep 09, 2016 4:20 pm 
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Yes David the master is one I fashioned.

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PostPosted: Fri Sep 09, 2016 7:21 pm 
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gott_cha wrote:
Yes David the master is one I fashioned.


Excellent Mark. I'll prepare a tutorial -- will post it over the weekend.

Stand by.

David

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PostPosted: Sat Sep 10, 2016 9:18 am 
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For open molds like that I've used plasticene for the mold. Press the master or original into the plasticene for the mold, then pour the Alumilite. These molds are "disposable" as they are deformed and destroyed removing the casting, but you just re-use the stuff for another mold, and so on... Not as accurate as RTV, but a lot cheaper. :wave_1:


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PostPosted: Sat Sep 10, 2016 10:12 am 
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Thanks for weighing in Biggles.

What I need to do is cast 45 oval Carly floats from one master I made. The parts (45-50) are small 1/2 inch and flat bottomed. Too small to utilize a 2 piece mold. I'm thinking just a simple single sided "depression mold".

I'm not familiar with Plasticine all I have used has been the Alumilite system,,...what is it and how is it used? You say it's a disposable one time mold? Like the plaster or clay would be I presume. My questioning is how hard it will be to remove the parts once cured..

Also as a note..the copies do not need be perfect in detail (another reason I won't use the Alumilite)....All I need is the size and shape so I can stack them in between gun mounts.

I'd like to hear more of your opinion on this even as I wait for Merriman to chime in with a tutorial he's working up.

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PostPosted: Sat Sep 10, 2016 7:03 pm 
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Plasticene is a children's modeling clay (NOT Playdoh!), usually available at Toys 'r Us and places like that. Platicene never cures or hardens unless you leave it out for around 10 years. Once the casting has cured you just pull the plasticene away from it. You could also chill the plasticene in the freezer so it won't stick too much to the casting. :wave_1:


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PostPosted: Sat Sep 10, 2016 9:22 pm 
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Your objective is to produce a simple open-faced mold, possessing many identical cavities, from which to cast resin parts.

Select a mold medium that is quick to work, will capture the masters shape faithfully, and will not require any special attention in order to assure a quick, clean separation of the cast resin parts once they’ve cured hard.

Yes, your air-dry clay will work as a medium, but it will require application of a mold release and, because of that mediums rigidity (once hard), can make cast resin part removal problematic, particularly so if the cavities have high draft angles.

But, why suffer all that hassle of impressing the shape of your master onto a medium that requires you to wait for it to change state from a malleable semi-solid to a solid; and then having to introduce a part-release system?

Too much work.

Instead, you can achieve a simple, open-face type mold quickly, and use it immediately, by using oil-based clay as your mold medium.

The following shows how I employed this clay to produce a tool from which many tear-drop shaped resin pieces were cast, in mass, in one casting cycle. I suggest this technique to you as a means of producing all those little raft/float parts required for you current project.

A few years ago a job called for tiny, tear-drop shaped parts, each representing a streamlined zinc anode, attached to the sides of a submarine. And I needed a lot of them. I employed oil-based clay as the tool from which those many parts would be cast from Alumilite brand polyurethane resin.

Below you see the end-game: The cast resin tear-drop shaped zincs have been painted, and transferred to the sides of the model submarine, adhered with CA adhesive.

I produced nearly one-hundred of these parts in one, quick, casting operation. This exemplifies one of the many virtues of this tool making technique.

Image

Image

I rolled out a slab of oil-based clay. Onto the face of this slab I impressed the desired cavity shape(s) with a simple master of the zinc anode, attached to a handle.
As the ‘hardness’ of this non-hardening medium is a function of room temperature, the environment is adjusted to a temperature that permits easy impression onto the clay, but does not produce a sloppy mess of the cavities(s) formed once the master is withdrawn.

Image

Make the flange face of the clay tool even with the base of the eventual resin part formed. That means the master has to be impressed into the clay to a specific depth. I achieved this goal by gluing a ‘depth stop’ to the handle of the master. I press the master into the clay till the depth-stop makes contact with the face of the clay; I stop, and withdraw the master. And move on to the next cavity forming operation.

Image

Casting resin is mixed up and poured over the work. Gop it on, don’t be shy!

Image

Place wax-paper over the resin and screed over the top of the wax paper (a popsicle-stick used here). Use a light touch. The objective is to push the resin into the cavities with very little projecting atop the flange face of the clay tool. Leave things alone till the resin cures hard.

If you have the facilities, pressurize the work to two atmospheres till the state change is completed – this will crush any small bubbles that got entrapped within the tool cavities. If not, make sure to use fresh casting resin – this will alleviate any off-gasing induced bubbling in the parts.

Image

Yank the fret of resin parts off the clay tool. Then scrub the still attached parts with a lacquer thinner saturated piece of abrasive pad. This to remove oil the parts picked up off the tool, and to etch their surfaces for priming.

Image

Place the fret atop a sanding block (outfitted with #240-grit sandpaper) and abrade the thin layer of backing resin away, releasing the parts from the fret/backing resin.

Image

And there you have it.

David

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PostPosted: Sun Sep 11, 2016 3:26 am 
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biggles2 wrote:
Plasticene is a children's modeling clay (NOT Playdoh!), usually available at Toys 'r Us and places like that. Platicene never cures or hardens unless you leave it out for around 10 years. Once the casting has cured you just pull the plasticene away from it. You could also chill the plasticene in the freezer so it won't stick too much to the casting. :wave_1:



Ahh ok thanks Biggles2. Will have to remember that. Can't believe I never heard it called by that name.

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PostPosted: Sun Sep 11, 2016 5:16 am 
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David,

I appreciate the time you spent to answer my question about mold release....the clay (soft non-hardening) already has it! Great. .
Also a good reminder on screeding to level out and reduce air bubbles.


Many thanks Sir.

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PostPosted: Sun Sep 11, 2016 8:32 am 
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gott_cha wrote:
David,

I appreciate the time you spent to answer my question about mold release....the clay (soft non-hardening) already has it! Great. .
Also a good reminder on screeding to level out and reduce air bubbles.


Many thanks Sir.


My pleasure, sir.

David

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PostPosted: Sun Sep 11, 2016 9:43 am 
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Merriman's modeling clay is just the same as Plasticene under a different name. Casting method is the same as I described. :wave_1:


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PostPosted: Sun Jan 29, 2017 3:00 pm 
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To the early question about "original work," the vendor chooses whether to sell the original product with or without copyright. The vendor will only ship the product at a price and on terms that the vendor accepts.

The threshold is copyright, not whether something is simply "original work." Provision for copyrights and patents has been in the U.S. Constitution from its beginning. Legislation defines the specific markings and wording to assert a copyright. The cost and effort to assert a copyright are zero.

If the vendor declines to copyright the original work or to license it in some way, and still sells the product, then the consumer has the legal freedom to copy. If the consumer then makes copies, the consumer is exercising the paid-up right that the vendor knowingly authorized, and is not stealing the design.

A scaled-down model in a publicly-known medium like resin of a public-domain design like a life raft, or an entire warship, might be difficult for a vendor to defend as original work that he can copyright. A model of a licensed private design, like of a car or a fictional character, is different because those designs are (typically) copyrighted.

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