Machining Metal & Plastic
Still Under Construction 6-15-10
Plastics can be tough to machine as the heat from the cutter frequently melts and gums up the plastic. The general rule I keep hearing is to run your RPM slow and your feed fast (Half-Speed Twice-Feed). Another rule.. USE SHARP TOOLS! I have a special HSS lathe bit just for plastic.. and keep my carbide for metal. I'm told that if a cutter has ever touched metal it probably isn't sharp enough for plastic. I'm still learning, so take this as you will.
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Plastics
HDPE (High Density Poly Ethylene)
ABS
Polycarbonate
Delrin
Where to Buy -
Metals
Link to Metal Properties
Metal Identification by Spark TestThis link covers many Aluminum Alloys and their characteristics. -
Technical
Procedures
Cutting Speeds & Feeds
Design/CAD Programs
MasterCam (coming soon?)
SolidWorks or Inventor?
Plastics for Machining
ABS: Relatively Cheap & Strong. Will work for most of the projects most people work on. Glues well to itself. Easy to machine. If you take it to production, it is also easy to mold. You can buy ABS pipe & glue at Home Depot. Another good glue can be made by dissolving ABS in Acetone (fingernail polish remover). I do this by mixing the Acetone and ABS together in an HDPE container with a snap-tight lid. Bigger chunks take a lot longer to dissolve than small shavings. After the ABS is dissolved, swath the resulting paste onto two pieces of ABS and lightly clamp them together. Caution: Acetone is highly flammable and has fumes, so keep it away from flame/heat and do this in a ventilated area. Use common sense and read the bottle for warnings. Google Search for more detailed instructions before trying this.
HDPE: Think about your kitchen cutting board... which is a good source of Polyethylene(HDPE & LDPE) if you need to make something quick. This is a tough material that can be bent and will spring back. Can be worked with woodworking tools. A gummy type material that isn't always the easiest to machine. Also difficult to bond to itself... or anything else. I am told that it screws together really well. Has good self-lubricating properties.
Polycarbonate: More expensive than ABS or HDPE. Used when you need something that will be really strong and tough. Used in bullet proof glass. While it is tougher than ABS, it is also less likely to deform under pressure... this means that it could shatter when ABS might just bend. Superglue works well with polycarbonate. Also known under the trade name Lexan.
Delrin: The most expensive plastic listed here. It is strong, but usually used for it's self lubricating properties when you need two parts to slide together. Does not glue together as well as ABS or Polycarbonate, but will bond a lot better than HDPE. Good for use in fixtures. I'm using it in a sliding latch right now.
Where To Buy Plastic
- Hastings Plastics in Santa Monica carries Acrylic (brittle) and LDPE. Tell them you'd really like to have a local supply of ABS.
- www.McMaster.com Is a good source for small quantities, and they can get it to you next day with UPS Ground.
- Ebay for scrap pieces (search under Business/Industrial and Metalworking).
- Discount stores for HDPE cutting boards.
- Check the Links Page for other suppliers.
CAD/Drafting Programs
DeltaCad: A 2D CAD program that has been getting good reviews for being easy to work with. The current Version 7 from the company costs $40.
Amazon.com sellers offer Version 3 starting at about $2 +Shipping. Get the cheapest one you can since they are all the same.
EMachineShop.com CAD: Free CAD software from an on-line machine shop. Link to youtube video.
SolidWorks or AutoDesk Inventor? These are two powerful 3D Design Programs. Both offer discounted versions for students at the Venice & El Camino shops. The Full Version Professional Software costs thousands.
I started with SolidWorks, and it is not an easy program to learn. My Advanced Manufacturing class at El Camino College uses Inventor, so I switched over and it seems somewhat more intuitive (though part of this would be a result of having used SolidWorks since many of the commands and concepts are similar).
Todd from the Venice Machine Shop is a heavy user of both programs. His opinion seems to lean towards SolidWorks, as he says Inventor sometimes gets a little jammed up on some applications.
Within the Student Versions, Inventor will not let you save the file as anything but an Inventor file... and you cannot open it in MasterCam. Since SolitWorks allows me to save IGES files, which I can open in MasterCam and convert to G-Code, I've gone back to using SolidWorks more often.
Internet reviews have fans of both programs. You will probably be happiest with the one where you can get the best training. SolidWorks has a lot of good books... though it seems more schools offer classes in Inventor.
A Student Version of Inventor runs $150 for a 5 year license. With SolidWorks I paid $100 for 18 months, but last I checked the Student version was down to a 12 month term.
My Final? Go with Inventor unless you have a specific reason to prefer Solidworks.
Here is a good link to less expensive CAD/CAM packages.
