# Molding your own plastic.



## chadne (Mar 28, 2006)

Can anyone point me to a site to buy materials to do this? There must be a way to make your own plastic and then mold it, but I'm not getting any hits except for people willing to do it for you?


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## MadMag (Mar 29, 2006)

chadne said:


> Can anyone point me to a site to buy materials to do this? There must be a way to make your own plastic and then mold it, but I'm not getting any hits except for people willing to do it for you?


 
I don't want to discourge you, but plastic parts are actually hard to do at home with limited equipment. The raw plastic usually comes as pellet form. Then it must be heated and injected under high pressure into the mold. You have two costly items. The molding machine and the mold itself. Molds are made of high quality steel and are made by machining or EDM (Electrical Discharge Machine). You cannot just pour plastic like metal and have a strong part. Making the mold is expensive....the resulting part can be just pennies. It sounds crazy but you can actually machine a nice looking metal part using milling machine at home much easier that molding a cheap little plastic part.

The best thing is to find a shop that does small prototype runs. And have them mold the parts. Again, the parts will be cheap but they will want good bucks for the mold itself.


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## gadget_lover (Mar 29, 2006)

Doesn't it depend on the plastic you are working with? Well, that and the quality.

I saw a documentary on TV that showed a "cottage industry" making plastic bottle caps. They were literally casting these things in their living room. 

Then there is vacuformed plastics. That's actually a popular hobby for some folks. Make a model, suck hot plastic sheets against it, voila! A replica. See http://www.studiocreations.com/howto/vacuumforming/ for an example.

There are casting resins you can buy at tap plastics, hobby shops and such. The results can be very good.

Like Madmag said, in most cases you have to make a very good model from another substance before you can mold it in plastic.

Daniel


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## IsaacHayes (Mar 29, 2006)

theres low temp plastic you can dip in simmering water them mold with your hands until it hardens. Good for making crafts and stuff, but not much else. I wonder if I still have that stuff!?


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## schill (Mar 29, 2006)

IsaacHayes said:


> theres low temp plastic you can dip in simmering water them mold with your hands until it hardens. Good for making crafts and stuff, but not much else. I wonder if I still have that stuff!?



Stuff like this? I've never used it, but I'm tempted to pick some up.
Makezine blog entry 
www.shapelock.com


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## MadMag (Mar 29, 2006)

Maybe I am a little spoiled from working with industry that has lots of money for molding. From the above post's I guess there are some easy low cost methods for home. But still it may depend on how good and strong a part you need. I am still learning, maybe simple parts can be made easier than I thought.


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## JonSidneyB (Mar 29, 2006)

for a custom one of a kind mold to be had, expect around $25,000 for injection molding.


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## Mrd 74 (Mar 29, 2006)

Maybe we could be more helpful if you were more specific as to what you want to produce. If your project could be made from polyurathane resin(liquid plastic) cast in RTV molds it would be cheap and easy to do.


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## chadne (Mar 29, 2006)

I just want to build a housing for a 5mm led based lamp. I'm guessing I could make some type of mold from foam coat it with something like wax to prevent the plastic from attaching, and then injecting the material -- sort of like 5 minute epoxy but stiffer. I just don't know how to do it, and haven't found the right material. I found a sight about mixing 1 part sulphur to 4 parts graphite and heating to around 240 degrees, but that's about it. I'm also contemplating fiberglass resin as a possibility.


thanks in advance for any input.

Chad


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## IsaacHayes (Mar 29, 2006)

schill: I think I had friendly plastic back in the day. This stuff looks the same only in a big ol tub of it! It's given me some ideas for stuff I could use it for sometime..

chadne: Sulphur and graphite? Sounds like a pyrotechnic mixture lol. 1hour 2-ton epoxy is pretty strong, if left to cure for a few days. It's very hard plastic when finished. A RTV mold probably would work for it...


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## ZaVoo (Apr 1, 2006)

Dave Gingery has a fairly low cost solution.
I have a copy around somewhere...

As I recall the basics of it are an aluminum block with a round bore for a piston to force out the plastic. A ceramic heater cartridge is used to heat the plastic and an oven thermostat for temperature control.

I took a few short cuts and used a 1" copper pipe coated in JB Weld (to electrically insulate the pipe) and wrapped it in nichrome wire. Fibergalss insulation surrounds the pipe. The pipe is supported by two 1" copper pipe brackets that accept 1/4" allthread.

I placed an end cap on the bottom of the pipe (with JB Weld) along with an aluminum knozzle that I turned to a slight taper to insert into a mold.
The piston is a turned piece of aluminum mounted on all thread, which in turn connects to a level and fulcrum to apply pressure. (Grounding the handle or wearing rubber gloves is a good idea if you want to avoid any tingling)

The temperature control consists of a light switch with a dimmer function. You can measure the current passing through the wire and use the datasheet to determine ambient temperature. Or, if the JB Weld starts smoking you probably have the current too high. I think most thermoplastic (pop bottles, milk jugs, etc.) melt around 350˚ F.

If I were going to start a new project using plastic injection I would probably take the time to build a new machine closer to Dave's design, or atleast include a thermostat.

Having said all that, the hard part of the whole process is making the mold. You definately need access to a milling machine or a lot of patience on a lathe.

James


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## olephart (Apr 2, 2006)

There's a swell 2 part epoxy type product call Accra Glass. It's sold exclusively by Brownell's, a gunsmithing supply house of inpecable reputation. Easy to google it.

It barely shrinks when cured, can be filled with metal powder for added strength and is machinable when cured. It can be dyed many colors prior to curing (uniform color throughout) and releases easily from any mold coated in common paste wax. You can use light cardboard or similar materials for a mold.

There are other similar products on the market, but I don't have enough experience with them to make a recommendation. The Accra Glass is an exceptional product.


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