SpudFiles

After doing a bit of research as well as conducting a few experiments, I am happy to announce a few (probably) new concepts to the SpudFiles forums. These techniques include casting PE (polyethelyne) and stamping heated PVC parts and components.

A while ago, I created a thread to discuss the possibility of melting down PVC for casting. After this was deemed to be quite pointless, I redirected my attention towards shopping bags. I proceeded to burn my first bag, having a bit of trouble at first. I tried to cast a slug in a small piece of 1/2" Sch40. Unfortunately, it came out pretty crappy, looking more like a web than a slug. But at the base, was a small glob that had formed. It was very smooth, and it was good and hard. Eureka. Afterwards, I turned to a multi bag method of prepping several bags at one to speed up production (one bag doesn't yield very much at all, I'm afraid). I used a butter cookie tin and instead of cutting the bag into strips, I cut the bag into two large squares, put them on top of each other, rolled them up, and cut the roll into two rolls, which is much faster. I burned at least five bags. I let the plastic cool (wafer thin in the tin) and it came out easy. I cut open a soda can and put in the chips. I built a very small fire and put the can near the burning wood. I let the chips melt. It covered the bottom, and came out a nice round disc about 6mm thick at the center. It was however slightly brittle, and the plastic was filled with air pockets and was matte gray with a lot of spots, looking like cookies and cream ice cream. if one could come up with a faster way to melt the bags, this method would be great for making your own plastic.



I devised stamping parts while I was thinking about mass producible weaponry. After gaining a hell of a lot of experience in working hot PVC on my High School Robotics team, I decided that by using pneumatic rams available from both McMaster and Fastenal, it would be possible to build a cheap and effective form of punch/stamp press. This would be useful for producing lots of the same thing quickly, like rifle receivers, grips, and butt stocks. All that would be required would be a heat gun, the ability to make stamping dies from wood, (fairly easy with good tools) and the need to stamp something out. Possible applications include sales, cheaply arming a large inexperienced airsoft/nerf army (haha, like that could happen) and just making a lot of stuff.

You can buy HDPE beads in the craft/sewing area of Wal-Mart. They use them to stuff small pillows and such.

I use them in a plastic injection molder when I make light weight, ball bearing tipped slugs for my copper gun.



Edit: Inevitable engrish.

no no no gippeto. you need HEDP (high explosive dual purpose) tips

Sweet. Any info on how to melt those effectively?

Google is your friend.

http://www.maropolymeronline.com/Proper ... 20Prop.asp

Straight ethylene glycol (boils @ 197C) in a double boiler? Use an electric hot-plate and do it outside.

Get permission FIRST.

Keep a fire extinguisher handy. Wear proper safety gear, molten plastic and skin don't get along well.

Interesting, but what advantages does it offer over good quality epoxy casting?

there is no way you can get 197C in a double boiler, as water boils at 100C. You could get 197F though. If you need 197C, then you need to use that hot plate.

if u don't mind coiling wire than u can make something like a large glue gun or a heated funnel. when its hot u put the plastic bags on it. whatever melts will drip out the bottom and into whatever u want. burning makes any plastic brittle.

You don't put water in the bottom of the double boiler.

You use straight ethylene glycol (automotive anti-freeze) in the bottom.

Put the plastic beads in the top.


Jack, cost would be my first thought, but then there's the double boiler, the hot plate, the extension cord, the fire extinguisher, the PPE, etc.

Not to mention, the risk of 3rd degree burns.

Then there is the matter, that if temperature is not STRICTLY controlled, the castings will shrink at different rates depending on thickness, etc.

This leaves you with hollows, and other defects which will likely cause the part to be rejected anyway.


Epoxy/resin casting looks better all the time.

I have still yet to see any kind of brand name mentioned or and description of the case for finding the right epoxy. Tips?

It depends on the project. Look on the package and it describes what type of material it is designed to adhere to. You can find dozens of types of epoxy at any home depot or hardware store. Just read the package and decide what works best for the project. I have found that GENERALLY the longer it takes to set up, the stronger it is. If you still have doubts, go ahead and pick up some JB weld, that stuff works for almost any situation.

Epoxies and resins differ by brand, type, cure times, strength, viscosity, and a bunch more variables I can't think of right now. :occasion5:

I have used 30 minute epoxy from Great Planes, JB Weld, LePages 5 Minute epoxy, polyester and vinylester resins, and even 5 minute epoxy from the dollar store.

Lower viscosities, and longer cure times are better when the part is "deep" and you want air bubbles to get to the surface, or when working with glass cloth.

The thicker and or faster stuff might be better when the parts are not deep, or where certain properties are required/desired. (mechanical strength, or speedy set so you don't have to hold it overnight)

In the end, it really depends on "what" you're trying to accomplish.

The only problem with epoxies/resins that I can readily think of, is their limited tolerance for heat.

Meh, I just want something that I can readily cast/mold.

Bondo fibreglass resin for "deep" stuff.

Glass re-enforced bondo for thin stuff with slightly better strength.

How's that for straight to the point?

Exactly what I needed to hear. Thanks Gippeto.