Milk bottle parts

Didn’t know where else to put this… @mcdanlj feel free to move it if there is a better place.

I have for some time been playing with and enamored by the notion of making plastic parts from milk jugs.

I think I finally have a process that works, mostly from trial and error and lots of YouTube watching.

In this case, I wanted to make an adapter part of my Automated Shade project. I need to adapt a 6mm motor shaft to drive the end of the shades cardboard tube.

My Current Process:

  1. Cut up the milk bottle in strips (this is tedious). 1" x 1" or 1" x (length of dish).
  2. Put in a blender on chop to create granular plastic … sort of. This is hard on a blender so don’t use your wives if you want to stay married. So I got one at a thrift store. Alternately cutting longer strips and laying them in the dish will work but you may have to add more on top of the molten plastic to get the thickness you want. I have also tried a paper shredder but lots of jams.
  3. Put strips/granular plastic in a pyrex dish with oven paper (keeps it from sticking). This stuff is really sticky when hot.
  4. Heat in a toaster oven @300-350 until the plastic gets translucent but not so hot it starts to turn brown on the surface. Toaster oven also from thrift store. I tried a bread-making machine but it heated slower. Perhaps a future control hack.
  5. Pull from oven periodically and tamp out air bubbles with a 2x4 or something that fits in the dish. Air bubbles are hard to get out because the sticky plastic creates a seal around anything you stick into it, inhibiting the release of air. Mmm, brain fart … perhaps a metal straw?
  6. When the plastic is fully translucent (no white left) and the air bubbles are minimized then pull it from the oven and let cool. You can dip in the water if you want to speed up the cooling.

Fabrication:

  • To turn tubular shapes cut the material in strips that are as wide as the material is thick ie: square strips.
  • Turn on a lathe, work held with a chuck at one end. Turning between centers will probably not hold the material strongly enough.
  • The material is a dream to turn if insure good bevel contact when turning, turn at high speed. Does not require a finishing step.
  • The material is very smooth and slippery with a lubricated like feel on the surface. I doubt that there are many types of glue that would stick (@Nedman ?)
    *I have not yet tried pouring this into a mold, but plan to. I would expect it to be difficult to mold as the material does not flow very well and is incredibly sticky.
  • I would expect this material to cut easily on a cnc but it needs better thickness control. I am thinking of some kind of press while it is molten.

So why not just 3D print it.
GOOD POINT, does this method have an advantage?

*Stronger? I know its a strong dense material and threads and cuts great.
*Lubrication properties?




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Might be a problem if you’re lactose intolerant!

Cool.

You could always raid the neighbors recycle bin @HalfNormal :wink:

@donkjr Milk jugs are typically made from HDPE (High Density Polyethylene ). HDPE is one of those plastics that is difficult to glue. Seems there are some specialty adhesives out there that will work with HDPE, like this one from TAP

https://www.tapplastics.com/product/repair_products/plastic_adhesives/tap_poly_weld_adhesive/435

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I’ve been thinking about recycled milk bottle polyethylene myself. I have commercial polyethylene stock for turning and milling and it pains me to put milk jugs in the recycling bin when it feels I might recycle them at least as effectively myself… So thanks for sharing!

AFAIK polyethylene would usually be injection-molded rather than poured. I have seen but don’t have links handy to tutorials on home injection molding. Might be worth looking for those?

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Do not forget to pre-prepare the surface to be glued.
Surface tension will not let plastics bind if there is no prior preparation.

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What preparation do your suggest?

Flame the surface. A torch cooking flame is enough.

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Sample here:
https://www.youtube.com/embed/h-9yhanz5DE?

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Thanks I had no idea…:slight_smile:

In industrial environments, plasma systems are used to prepare the surface. With the right treatment, even the PTFE can be stuck.

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Two thoughts come to mind reading this. Maybe adding water to the blender in the blender method of pelletizing would help. And pulling a vacuum on the pan of molten plastic would de-air it.

I tried the water in the blender and it really did not improve it much. It seems that the plastic gets to a certain size and then it just flies around and doesn’t cut much more.
However that size is ok for melting.

Yesterday is dawned on me: “Put the whole jug in the toaster over”. That worked took about two minutes to melt a jug once temp was reached. My plan it to just keep adding jugs and see how that works.

I wish I had a vessel I could pull a vacuum on, I do have a pump :(.

Buy a pressure cooker on Craigslist? :grin:

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Man I am off the thrift store this is a great idea…thanks … thanks!

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With the meteoric rise of the much safer instant pot and its derivatives, there should be a huge glut of old pressure cookers.

Thrift store is a great idea. I should start haunting Goodwill for this purpose.

My hope is that there has never been a better time to get a vacuum vessel cheap!

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Ok collected my first jug :grin: Any idea what volume a 1 gal jug melts down to?

About one sheet of paper I think.
Takes a lot of milk …

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Weigh it, divide by the specific density of polyethylene. Result is the volume for that weight. Specific density of HDPE is 0.93 to 0.97 grams/cc. Convert units and dimensions as needed.

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Great minds, I actually had that thought right after I laid down to go to sleep last night :grinning:

Stripped off the label this morning. Not sure the best way to do this, but I ran it under some hot water to soften the adhesive and scrapped most off with my finger nail. Cleaned the residual adhesive off with some paint thinner. Put the jug in the sun to fully dry out.

So my jug weighed 2.21g and, using a specific density of 0.95g/cm3, I get a volume of 2.33cm3 or 0.14in3

Note: I cut the labels out of mine, to difficult to remove.

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