Hdpe

[Robert Edington]

I stumbled across a video on youTube about HDPE. It showed people melting down milk jugs (or anything labeled "2" in the triangle or HDPE) and making things out of it. It turns like warm butter on the lathe and yet is pretty strong. Very easy to make and not messy.
I was wondering if anyone has made anything for turning out of HDPE. I was thinking about vacuum chucks, rotary adapters and headstock adapters.
The stuff fills up our landfills. I'm on a well, and we don't like the water's taste, so we buy water. We must use at least a gallon a day.
Has anyone melted HDPE?
What did you make?
Thanks.

RP

[Frederick Skelly]

That's interesting. I'll look forward to reading all the replies here.
Wonder if there's any reason to be concerned about fumes when melting that plastic?

[Brice Rogers]

I have melted and cast some black plastic from those semi-flexible landscape pots. I think that it was LDPE or something. But when it got to around 350 F it got sticky and flexible. I stacked strips of it in a simple mold. The strips were wrapped in the no-stick aluminum foil. I had a 2# piece of steel pushing down on the stuff so that when it got to the consistency of soft taffy it kind of conformed to my mold. When it cooled, I used the slug to make a replacement wheel for a suitcase. I could have repurposed a hockey puck or a roller wheel. It all worked, but there were a few trapped bubbles. The stuff is pretty viscous (thick) even when up to temp. Commercially they use high pressure injection molding to move the stuff. I don't know how they remove the air though. Maybe they start the process in a vacuum.

[Marvin Hasenak]

I stumbled on it a few years ago when I was looking for info about slingshots. A couple of good tutorials on their forum. I have used the process to make a few things, I use an old electric skillet for my heat source. Find multi colors of #2 plastic, and you can get some interesting "messes" out of a blank. Most plastic lids are #2 and I found them to be my best source of colored #2. Make a wood mold and line it with several layers of parchment paper, and have your stuff ready to move fast when it is melted. Wear welders gloves, it is HOT. I also heated my mold in the oven to keep it from cooling off the #2.

[Kyle Iwamoto]

I've tried. It's not as "strong" as you may think. I have not found a glue that will glue it (pen blanks). I think you have to find HDPE epoxy. I couldn't find any. It's tons of fun to turn. I would think if you kept the shavings you could re-melt it. Bowls and such may be a good idea. You need to turn it thick. Think gallon buckets, they pretty flexible, so bowls need to be a bit thicker than that. They make nice coasters. Soda/water bottle caps are "2" and you can use them for colors. Fun thing to do! Different and as mentioned, saves the landfills.

[John K Jordan]

Has anyone melted HDPE?
What did you make?

I've never tried melting any but I have turned some small things from HDPE - specifically to make tips for throwing tops. (Wood tips get beat up easily and metal tips can mar floors.) It is pretty soft.

If bottle caps are made from HDPE I can image a colorful blank made from swirling some into white plastic.

BTW, did the video instructions melt it over an open flame? If so, some caution might be good since HDPE is flammable. (Smells like paraffin when burning.)

Most of the HDPE I have is in large 1" thick sheets, maybe 4'x8'. I found these at a local metals recycling company - clean, very cheap, but with shapes cut out of the sheets. I've used more of it on the milling machine than the lathe, making brackets and insulators. It machines beautifully.

Hey, have you ever turned acrylic plastic? I got some pieces of colored 1.5" rod last summer and turned a bunch of things.
acrylic_ornament_green_bell.jpg acrylic_top_yellow_small.jpg
Cast acrylic turns nicely with gouges and Hunter carbide tools and takes a nice polish.

JKJ

[jared parson]

Ive never turned anything acrylic or plastic, but have always been curious about finishing. Is it a fairly clean surface off of the tool? Tool marks? Whats the sanding process if any? Does the turning take/need any sort of topcoat, for say, a pen? I wouldnt think so. Cool stuff.

[Malcolm McLeod]

I have melted and cast some black plastic from those semi-flexible landscape pots. I think that it was LDPE or something. But when it got to around 350 F it got sticky and flexible. I stacked strips of it in a simple mold. The strips were wrapped in the no-stick aluminum foil. I had a 2# piece of steel pushing down on the stuff so that when it got to the consistency of soft taffy it kind of conformed to my mold. When it cooled, I used the slug to make a replacement wheel for a suitcase. I could have repurposed a hockey puck or a roller wheel. It all worked, but there were a few trapped bubbles. The stuff is pretty viscous (thick) even when up to temp. Commercially they use high pressure injection molding to move the stuff. I don't know how they remove the air though. Maybe they start the process in a vacuum.

~30 yrs ago I was responsible for processing 200,000 lbs of HDPE per month in injection molding facility, making large containers (milk & soda crates/bread trays/etc). Injection molding machines use a reciprocating screw inside a heated barrel to plasticize HDPE pellets. The screw moves backwards as a plastic 'shot' passes thru a check valve and builds up in front of the screw. Entrained air is forced back out the feed chute - where it came from - - (no vacuum required typically). HDPE/LDPE/LLDPE and PETG (soda bottles) are probably the most common plastics in use for consumer products. (UHMW is a variant of HDPE, but not a lot in use, relatively speaking.)

A couple of things to be wary of: 1) Never looked, so not sure what the typical clear water bottle is made from (PETG?), but milk jugs are generally made from LLDPE (linear low-density polyethylene). It is quite a bit different from HDPE, and even LDPE. Co-mingling them in any sort of homemade molding machine may result in unexpected results - especially on a lathe. 2) All polyethylene feedstocks have a specified melt index. This index is determined by a 'flowabilty' test, but also correlates to a material's brittleness. Mixing recycled materials from different sources may give you similar unpredictable results. 3) Every melt cycle of a plastic causes some degradation (generally it gets more brittle). Be careful on a lathe.

If you want to machine or turn plastic, I think there are billets available that are largely made from recycled products. Might be safer and more enjoyable, but still let you 'get your green on'?

[Jason Edwards]

HDPE stands for High Density PolyEthylene. LDPE stands for Low Density PolyEthylene. The high and low is in regards to the length of the molecular chains and high density is slightly more dense than low density. Both will float, being just slightly less dense than water. Common sources of HDPE are water and milk jugs and detergent bottles. LDPE is more flexible and used a lot in lids, like in butter tubs. Polyethylene is flammable, but not like gasoline or oil. In the right conditions it burns pretty clean. Don't get it on you when it's hot, it will stick to your skin and burn you bad. Stuff made from high density will in general be stiffer than stuff made from low density. Most composite lumber, think TREX or something like that, is a blend of Poly Ethylene (usually high density) and wood fiber, about 50/50 by dry weight. Air bubbles in low tech melting often come from water vapor, so warm it up to 200 F for a while and get any water evaporated off before you melt it. You cannot glue polyethylene without special treatments. Super glue is usually stored in a polyethylene bottle.

[Malcolm McLeod]

... Common sources of HDPE are water and milk jugs and detergent bottles. ...

My bad. I saw your post and looked up milk jugs - they are indeed now mostly HDPE. (....My info is only 30yrs out of date.)

But this a good comparison of the Melt Index - - I recall milk crates typically have a MI of 6-8, but I'd suspect jugs have a MI of ~30?

[Aaron Craven]

I've never melted any down, but I have purchased HDPE for turning non-stick pen bushings. You can get rods from Amazon for fairly cheap and CA doesn't readily stick to it (Though it does stick to itself, which means you can still end up with a coating CA that has to be chipped off).

As for turning, it's... weird... a bit like turning acrylic, but softer. The shavings wrap around the workpiece and have to be cut off (usually you can just break acrylic loose). Definitely requires cutting techniques (as opposed to scraping).

[John K Jordan]

The shavings wrap around the workpiece and have to be cut off (usually you can just break acrylic loose).

I found that if I can get the cut started just right the dust collector inlet just behind the work can suck up the long strand as it comes off the tool so nothing gets wrapped around the spindle. A nest of "shavings" is the worst thing about turning plastics.

JKJ

[Olaf Vogel]

HDPE is also used to make large pipes for the garden, sewers, drainage etc. Some of this stuff is really thick and heavy.
I have turned these on the lathe to make parts for around the shop, speaker parts. Yes, cuts well and easily.

I've never tried melting it down. All my stuff was off Kijiji - leftovers from construction projects.

Like other plastics, it tends to dull the chisels pretty quickly

[Jason Edwards]

My bad. I saw your post and looked up milk jugs - they are indeed now mostly HDPE. (....My info is only 30yrs out of date.)

But this a good comparison of the Melt Index - - I recall milk crates typically have a MI of 6-8, but I'd suspect jugs have a MI of ~30?

Hi Malcolm, I think it's getting outside the scope of what woodturners want to know, but the I agree the melt index of an injection molded crate would be in the 6-8 range. Water and milk jugs, and detergent bottles too, are blow molded and the melt index is actually around 0.7.

For those of you wondering what Malcolm and I are talking about, melt index is a measurement of how well plastics flow when molten. The higher the number, the more it will flow.

[Jon McElwain]

Like Olaf said, HDPE is a very common material used in construction for underground pipe. We use it for pressure pipe in diameters from 4" up to 3-4' diameter. There are special machines that we use to fuse pipe sections together. Basically, it cuts a smooth end of two adjoining pieces, then melts them together. For all intent and purpose, the fused joint is as strong as the pipe itself. Any earthwork construction project with sections of black pipe is probably using HDPE. Cuts a lot like UHMW plastic - smooth and soft, but resistant to impact and has a high capacity for deflection and bending.

I have not melted it outside the fusing machine, but it would be pretty easy to do so with a steady, non-flame heat source.