Plastic Smithing: How to Make Your Own HDPE Plastic Anything (DIY Plastic Lumber)





Introduction: Plastic Smithing: How to Make Your Own HDPE Plastic Anything (DIY Plastic Lumber)

How to make really good hard plastic while reusing and recycling plastic bags at home! Via this method, you can make ANYTHING you want to, out of hard, lightweight, real plastic that's astoundingly durable. It comes out very similar in texture to recycled plastic lumber.

best of all, this method involves no fumes!

I'm gonna show you how to make plastic wheels for your robot!

I first heard about stewing plastic bags to make new things from Dave Huebsch's book " Village Assignment " about interesting adventures had while running a charity/NGO (" Common Hope ") in Guatemala. He, amazingly, repaired the bottom weight-carrying main bearing of a washing machine with a big plastic disc made of stewed plastic bags, which actually was such a good stand-in replacement that it held up for several years. (and here are some more Guatemalan Handy Tricks)

I had to try it right away, and the first couple times I just burnt plastic, until I came up with this method.

By the end of this, you'll be able to make yourself a knife sheath, mold around your shoes and make DIY hard-toe sneakers, wheels, bearings, bushings, or any kind of plastic part! Take pictures and post them in the comments!

Step 1: Materials

Collect all the plastic bags you can get, they shrink down a lot.
Shredding them will make your final texture finer.

Use an old pot that you aren't going to use for food any more, or get one secondhand for really cheap at a thrift store.

Find a stick or something else you can use for a spatula.

I liked the clothespin a lot because I could pick things up as well as stir.

Oh, and oil! (I used canola because it was right there next to my stove. If you're, for example, making a bearing you can impregnate it with your personal favorite grease.)

So grab your favorite oil, here's why:

Plastic bags are made of LDPE (low density polyethylene) which melts at 248 F.

I got the temperature wrong and tried doing this in a homemade double boiler filled with water (to regulate the temperature to water's boiling point), which, of course, just made hot plastic bags.

After the double-boiler mistake I re-read the LDPE melt-point and discovered my folly! So I came up with melting them in oil.

Cooking oil boils around 350, which is far too hot for plastic, and which you don't want anyway (splashing boiling oil = no fun unless you're a hun), so I keep it to a nice low-viscosity canola oil heat and things work just fine.

If you wanted a smooth, non-oily finished surface, consider using wax instead.

ALSO: oil is not required per se --
if you had a constant temperature hot surface that you could guarantee to keep down around the melting point, you could do this just fine with no oil or wax!

Step 2: Add Oil, and Stew.

It doesn't really matter what polyethylene you use, you can melt HDPE plastic bottles in too, if you want.

That is, Resin Identification Code #2 and #4 are both good.

Polyethylene Terephthalate, that is PETE/PET or #1, may also work.

EDIT: Thanks to reader concern, I will state what may not be obvious from the pictures: there are no fumes. There's no smoke, no fans, no inhalation hazard. If there's smoke or fumes, you're doing something wrong and you're burning the plastic. That's why you use oil for temperature regulation.

The plastic bags do this alive-shrinky thing that looks really neat, so I took a video!

Step 3: Mash It

When it's tacky like chewing gum, start mashing it around to get the different bag-lumps to stick to each other. A hand blender would be exceptionally helpful in this situation, but I chose to merely wreck one of my mom's forks instead.

Step 4: Get Moldy

Now, while it's still pliable, put it into the form you want!

Since I'm just experimenting, I grabbed a salsa container that looked about the right shape for a wheel mold, and a wine bottle to make the hole in the middle.

I don't know any special techniques for molding and casting, but matt, rachel, bilal, paul, freemanmfg and smooth-on do!

If you were a molding ninja, you could make a plastic positive of your own face!

Step 5: Freeze

Let it cool like cookies, or if you're impatient, make it cool faster in the freezer.

Step 6: Enjoy!

There's the finished thing. It's got a lot of visual texture/color swirls, but it's actually a pretty regular surface. The circle turned out very well, and you can carve on this, machine it, turn it, and drill it, if you want something more precise.

This shows the finished product, the wheel, as well as another disc I made, and a video of just how surprisingly bouncy homemade plastic is.

Improvements to make:

I'd love to try using wax, instead of oil, so that the final surface is less greasy.
Shredding the bags beforehand would probably give a more homogeneous texture.

Also exciting! If you machined down a brick like this into large-ish chunks, you could feed them to your homemade injection molder! DIY action figures, hooray!

2 People Made This Project!


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Hi, I think the google videos are broken. I guess re-publishing the videos on youtube would be possible, then re-linking to them here. Please do, I want to see melting plastics! :)

Sorry - My dyslexic fingers again - Should read create strips 3/4" square, or 5/8"square!

Hello all. I am just getting started in Pen making. Will the finished plastic turn on a lathe OK? I could easily make a mould to create strips 3/4" square, or 58" square which are the requirements for a slimline pen. Has anyone any idea how many plastic bags it would require to make a 6"X3/"x3/4" bar? And what oil would be best for this project? I also have an induction hob! Grateful for any replies, John. PS cutting on the lathe will be by carbide cutters. Thanks, John

Can the plastic bags and bottles be melted down enough to pour into a mold like pouring molten metals?

Use a toaster oven ($10 at my local thrift store) heat HDPE, PP, PE or LDPE to 375-400F for an hour, take it out knead it like taffy, repeat 2-3 more times, then let it cool under pressure (I use a wood mold and c-clamps). You end with a hard, solid plastic with no voids that you can drill, cut, sand, polish into just about anything! I make tool handles, washers, repair parts, coasters, cutting boards, etc. The finished product is better and stronger than store bought!

Ok so how will I know exactly what type of plastic the bags are made of? Is there a symbol to look for or what?

Thanks :)

Plastic goods are supposed to have the resin code on them. Its difficult for Bags ( shopping bags ) The bags are 99 % of the time LDPE

Could I get opinions on whether or not my idea will work?
-Use an induction cooker to heat a pan filled with HDPE material and a little oil to about 250 degrees. Heat and stir until evenly melted. (I think the induction cooker has the means to maintain a steady temperature.)
-Make a wooden mold that uses a 2x4 for a bottom and has wooden sides and ends. Line the mold with parchment paper.
-Pour (or drop) the melted HDPE into the mold. Lay a piece of parchment paper on top.
-Place another 2x4 on top that's the exact same size as opening on the top of the mold. Clamp the top down and allow to cool.

This should create a solid block of 2x4 HDPE. The length will be limited by how much HDPE I can melt at one time. I'm hoping I can create 2x4 lumber and build a small bench.