HDPE bowl fail #1

[Bombarde16]

Have been saving up my milk jugs, shampoo bottles, and containers from windshield fluid and the like to melt into blanks for turning. Here's failure number one:

It's a fun medium to turn. So much fun, in fact, that I turned clear past my target depth and poked through the bottom.

Several lessons learned. I didn't have the entire blank melted all the way through, so there were pockets of unmelted chips which, once liberated, sprayed everywhere. Studying how the experts do it, it appears that you need to add plastic slowly while melting, ensuring that each addition is heated all the way through before adding more and, essentially, covering things with an insulator.

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[Mpride1911]

How are you melting it down?

[mat60]

32 minutes ago, Mpride1911 said:

How are you melting it down?

I think they use a oven but I would like know more about this.

[Bombarde16]

On 7/27/2016 at 8:51 PM, Mpride1911 said:

How are you melting it down?

HDPE starts softening around 300 degrees Fahrenheit, well within the range of a household oven.  (Strictly speaking, this isn't melting/casting so much as it is sintering but let's not split hairs?)  Bad stuff starts to happen above 450-500 degrees; but it's more than workable at 400.  The hardest part is what to do with it once it's soft.  At that point, it's a gooey, blazing hot mess that sticks to everything it touches.

I melted this in a terra cotta pot lined with aluminum foil.  The pot conducts heat, which helps, and it's roughly the right shape for a bowl blank once it cools.  Lining it with foil prevents it from getting stuck in the pot.  You end up with a foil coated blank, but that turns right off once you get it on the lathe.

My source for information (and inspiration) was a small but active YouTube community of people making custom slingshots.  Plenty of great tutorials out there.  Once you add up all the time spent cleaning and shredding plastic, plus the energy it takes to run the oven, it's definitely the hard way to turn trash into something useful.

I've got other projects backed up and the program year is about to start, but if I do more of this I'm going to try to snag some Kirkland shampoo/conditioner bottles.  Those are a nice ivory color which, when swirled with some plain, translucent HDPE from milk jugs, give a passable imitation of mother-of-pearl.  Other than that, I've learned enough at this point to have satisfied my curiosity.  

[mat60]

Im thinking the smell from the hot plastic cant be good...Do you run a fan and a small oven in the shop?

[Gixxerjoe04]

Does it matter what kind of plastic you use?

[Tpt life]

HDPE is popular for a few reasons. The chief reason is that it retains strength after being repurposed this way. It is commonplace for a bother big reason. HDPE is used in milk jugs etc. because it is not known to release harmful agents as it degrades. We often find ou that there are things we don't know down the road, but most other plastics are known to be unsafe as they degrade. 

[Bombarde16]

Im thinking the smell from the hot plastic cant be good...Do you run a fan and a small oven in the shop?

Not really any smell at all. Again, the key is to keep the temperature under the point at which bad things happen.

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[Rex Edgar]

"Other than that, I've learned enough at this point to have satisfied my curiosity."  Well said, that statement sums up many of my partially begun projects, before some other thing catches my attention.

On August 1, 2016 at 1:57 PM, Bombarde16 said:

HDPE starts softening around 300 degrees Fahrenheit, well within the range of a household oven.  (Strictly speaking, this isn't melting/casting so much as it is sintering but let's not split hairs?)  Bad stuff starts to happen above 450-500 degrees; but it's more than workable at 400.  The hardest part is what to do with it once it's soft.  At that point, it's a gooey, blazing hot mess that sticks to everything it touches.

I melted this in a terra cotta pot lined with aluminum foil.  The pot conducts heat, which helps, and it's roughly the right shape for a bowl blank once it cools.  Lining it with foil prevents it from getting stuck in the pot.  You end up with a foil coated blank, but that turns right off once you get it on the lathe.

My source for information (and inspiration) was a small but active YouTube community of people making custom slingshots.  Plenty of great tutorials out there.  Once you add up all the time spent cleaning and shredding plastic, plus the energy it takes to run the oven, it's definitely the hard way to turn trash into something useful.

I've got other projects backed up and the program year is about to start, but if I do more of this I'm going to try to snag some Kirkland shampoo/conditioner bottles.  Those are a nice ivory color which, when swirled with some plain, translucent HDPE from milk jugs, give a passable imitation of mother-of-pearl.  Other than that, I've learned enough at this point to have satisfied my curiosity.