Molding Question - Comments Please

[tonyG2]

My main problem in molding is the damn clay. No matter what I do, no matter that I use sulphur free "clean" clay, it sticks to the master and the mold like crazy glue. Mold release makes no difference.

Anyway, was chatting with a guy at the loval hobby shop and his uggestion was to avoid the use of clay entirely.

This was his suggestion. My question is - does itwork and what are the downsides (on the basis of TANSTAFL)

1. Build the mold box as usual but leave out the clay.

2. Raise the part or model to be cast above the base (for example on a round section of Lego etc)

3. Pour in the rubber as normal so it comes halfway up the side of the part to be cast.

4. cut out depresessions in the set rubber - to act as keys for the upper half of the mold. Place some sections of sprue onto the upper face of the set rubber to function as pouring channels.

5. Add the rest of the rubber. Let set

Separate the mold as normal. Clean up the pour channels with a sharp knife. Fill the hole left by the rod that raised the part above the base using miliput.

Is this going to work? Sounds a good way to avoid the crappy problems inherent in using clay.

[Kylwell]

It works so long as the part is bilaterally symetrical enough that you can do that. You may also need to trim off the little bit of flash that will form around the part as the mold material cures and shrinks.

I'll admit, claying a master up is an art. An art which I have yet to master.

[rpauly]

try putting a sheet of plastic wrap on the master before you clay it up.

[en'til Zog]

I used to put the master 'up' on needles to suspend it in the middle of the molding area. Worked a treat. Never worried about the needles leaving channels in the rubber since they were so thin.

And before you pour the top layer, entombing the master, spary both it and the surface of the first layer with mold release so the two separate easily.

Model ON!

[tonyG2]

Needle idea sounds good.

Will give it a go.

Thanks

[modelnutz]

Have you tried using WED clay ?
Find it at Michael's ..... made by Laguna...about $ 6.00 for a few pounds.
Get the gray stuff.

MUCH easyer to work than other clays ( I've used them all )
Works super easy...cleans up with water.

On the other hand...have you considered doing a cut mold ?

[futch]

3. Pour in the rubber as normal so it comes halfway up the side of the part to be cast.

won't give you a clean 2-part mold. the rubber will create a meniscus (sp?) around the master which will create bad seams. secondly, you can't "fill" holes in a mold. the oil in the rubber prevents adhesion. epoxies will simply get dislodged after a few casts.

personally, i use playdoh for my (adhoc) molds. i scrape it off then washes the remainder off with hot water (around the master part). then apply the top half of the mold. downside is that the guide marks shrinkso you cant do anything too deep.

the other point i wanted to raise, try mold sealant before using mold release.

otherwise your materials are suspect. people don't normally have these issues.

[Kylwell]

*smack* Mold Sealant. I spaced that.

Yes, Sealer works wonders. Recently cast up a copy of a river tumbled lava rock. 2 coats of mold sealant followed by two coats fo mold release and it cast up beautifully.

[Scale Solutions]

Paint the side of your pattern that will be in the clay with liquid latex

Wayne Pugh
Scale Solutions

[Kekker]

I had the same problem - with the plastic sticking to both the mold and the master. Solved it with regular enamel thinner - with the normal modeling clay it just dissolves it away. I would wipe away as much as possible, and then go to q-tips dipped in the thinner to get the rest. Worked pretty well.

Kev

[vaderman]

I find that a little rubbing alcohol on a paint brush and then wipe off with a cloth works well.

Scott