Machining plastics

Only 1 experience with UHMW, and that was today. In the mill I was making a couple way wipers for my lathe, I cut them out in the bandsaw and just cleaned up the edges in my mill. 1" cutter, very sharp American end mill cobalt, no coating, cutting around 230 rpms, slow feed. It cleaned up the edges well, not a mirror finish, but for what I am doing it will be fine.
As mentioned by others, they do not hold well in a vise.

Ymmv
Rich
 
Your biggest problem will be chip control and deburring, I just finished 1700 ABS parts in a lathe today which was a miserable mess of chips that will not break. Push the feed rate as hard as possible in an effort to make the chip as thick as you can.

With UHMW Polyethelene all bets are off, this is a messy material at best.
 
I don't care for machining any version of Polypropylene or Polyethylene. I do it when I have to. Their modulii are very low ( think wax ) which means they move under cutting loads. Drilled holes always shrink and one has to have a good grip in the part or the cutting tool can yank it out of the fixture. The molecules for both of these are very long and "smooth" so they slide easily against each other (think worms). This is unlike delrin and nylon that have a much bulkier and branched structure (including some molecule to molecule crosslinking) that inhibits molecule to molecule motion. (think trees packed tightly together). As a result, nylon and delrin have a higher modulus and are able to be used at higher temperatures.
 
Many thanks. Unless we can score some cheap Delrin or nylon, I think maybe we'll stick to 6061 which we can get from a local manufacturer who has offered us access to their drops. Sounds like the potential for mess, and/or flying plastic isn't worth the effort.
 
I have machined a lot of HDPE/UHMW with no problems, cuts like butter. No coolant needed, but use air or a shop vac to remove chips. Use razor sharp tools, and turn slower than you might think is correct and keep the feed rates up. Ignore what the machining charts say about feeds & speeds. I treat it a lot like like aluminum. Woodworking solid carbide router bits work great. The best is Onsrud 0 flute bits, designed for cutting the stuff. You want to cut, not rub the tool bit on the work. The biggest problem is generating heat caused by rubbing, this is where turning slower comes in. An end mill will take a pretty big bite in most plastics and that's what you want. Turning too fast just welds plastic to the tool bit, this is true for all plastics

Acetal machines like a dream, but it's not cheap. Again, razor sharp tools. Acrylic and polycarbonate are also easy to machine. You can use kerosene on acrylic, but the best I have found for polycarbonate is dish soap and water. Petroleum products can cause crazing on the cut edges of polycarbonate.
 
Surprised no one mentioned Teflon?
It's OK as long as you don't overheat it, then you get really toxic gas produced (cyanide or something?)
 
Should be Fluorine since that is the only atom other than Carbon and Hydrogen in Teflon (PTFE or PolyTetraFluoroEthylene).

As you already know, it is soft, like Polyethylene. The reason is the molecule. PTFE is essentially Polyethylene with some Hydrogens removed and replaced with Flourine. The long snake-like molecule structure is the same for both.
 
OK, sound good to me. Must have been some other plastic as I was doing prototypes last 3 months I worked for Tuscan Engineering.
I do remember general manager, foreman and charge-hand warning me about cyanide gas being produced from some stuff I was machining. (hey, I was 19~20 and already had the 'crazy' nickname ;))
I did wonder if I was posting about the right material as I know Polyflurotetraehelyne shouldn't make cyanide (my brother was working for a plastic supply company and could get hold of any spec sheet)
 
JimDawson said:
I have machined a lot of HDPE/UHMW with no problems, cuts like butter. No coolant needed, but use air or a shop vac to remove chips. Use razor sharp tools, and turn slower than you might think is correct and keep the feed rates up. Ignore what the machining charts say about feeds & speeds. I treat it a lot like like aluminum. Woodworking solid carbide router bits work great. The best is Onsrud 0 flute bits, designed for cutting the stuff. You want to cut, not rub the tool bit on the work. The biggest problem is generating heat caused by rubbing, this is where turning slower comes in. An end mill will take a pretty big bite in most plastics and that's what you want. Turning too fast just welds plastic to the tool bit, this is true for all plastics

Acetal machines like a dream, but it's not cheap. Again, razor sharp tools. Acrylic and polycarbonate are also easy to machine. You can use kerosene on acrylic, but the best I have found for polycarbonate is dish soap and water. Petroleum products can cause crazing on the cut edges of polycarbonate.
Click to expand...

thats the key
If the cutter has touched metal, if it doesn't slice you at the slightest touch, it is not sharp enough.
I used a 1 flute 1/4" hss bright endmill on uhmw and it cuts /really/ well, universes different than just throwing one of my regular cutters on the mill.
Note that if you aren't climb milling your finishing pass you'll get these long flappy pain in the ass burrs
 
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