Plastica

EXTRUDED PLEXYGLASS.
ABS Go a bit slower and a bit lighter in ABS than HDPE.[53] 3 or 5 in/min and a plunge depth of 0.05"[54]

DELRIN.

• Bits: roughing path with a 1/4" end mill and a finishing path using a 1/16" ball nose mill
• Feed: 800 mm/min feed speed
• Cut Depth: 1/16" @50-60ipm or 1/8" @30-40ipm
• Stepover: 10% step over
• Material Thickness: Varies (Tested 1/8" - 3/4")

UHMW.

• Bit: single or double flute 1/8" end mill (with center point for drilling!)
• Feed: 30-60ipm
• Speed: generic dremel turned up to 11
• Cut Depth: 1/16" @50-60ipm or 1/8" @30-40ipm
• Stepover: ???
• Material Thickness: Varies (Tested 1/8" - 3/4")

HDPE.
Plastic that can easily be found in your local supermarket as a white cutting board (but also available in other colors). Only limitation is they are typically quite thin, usually not greater than 1/4"(6mm) thickness. Thicker material is available (9mm or so is sold as "half-inch" cutting boards), while larger boards in half-inch or even 3/4" thickness are available from specialty suppliers or online. Much larger and thicker panels are available from specialty plastics shops, sign shops and possibly local hardware stores.[55]

• Bit: double flute 1/8" end mill
• Feed: 355mm/m (very conservative 1,500--2,700 mm/min has been suggested --- one can trade off speed for cutting depth)
• Speed: 11,000 RPM (Dremel 4000 set to 11)
• Cut Depth: 1.5mm (as much as 2.5mm may be feasible at slower speeds)
• Stepover: 30%

We did some tests at Inventables and these settings worked successfully[56]: DIA = 0.0625 Step over% = 60 Step down = 0.045 Spindle Speed = 12,000 Feed Rate = 60 Plunge Rate = 30 DIA = 0.125 Step over% = 60 Step down = 0.062 Spindle Speed = 12,000 Feed Rate = 60 Plunge Rate = 30 One datapoint, Improbable Construct notes "2 flute 1/8" endmill, 40% step over, 1/16" cut depth, 27000 RPM, at a feed speed of 1200 mm with good results. Of course that was with dual Y motors and the double X mod." Another datapoint: 30in per minute on the feed rate, and .125 on the depth per pass.[57] A further note: "With HDPE you want to use conventional milling. It does leave a fuzzy, stringy edge when you use climb milling."[58] Rubbing the pieces w/ a towel after machining will help remove errant flecks/strands.

TWO-COLOR HDPE.
the following settings worked best with a straight fluted bit. Upcut bits make a huge mess of things. 40% stepover 0.05" step down 20IPM Feed 10IPM Z-Feed Clockwise on the engraving[59]

POLYCARBONATE.
Bit: double flute 1/8" end mill Feed: 1000mm/m Speed:20,000 RPM Cut Depth: 1mm Stepover: 2mm

ACRYLIC.
Lengthy discussion of the difficulties of milling acrylic and some solutions: bit getting "sucked" down. Note that what is sold as 0.25" thick acrylic is typically manufactured to metric 6mm (0.236"). Thickness tolerance for typical manufacture is 0.02", engineering plastics are available w/ tighter tolerances (0.005" from McMaster-Carr). Notes from IC for cutting his dust shoe:

• Bit: double flute 3.175mm (1/8") end mill

Feed: 400mm/min Speed: 20,000 RPM Cut Depth: 2mm (0.08") Stepover: n/a (through cut) Plunge Rate: 75mm/min. O-flute bits are recommended.[60] Makita RT0701 16in/min feed, 0.08" step down[61] at speed 2 (~12,280 r.p.m.)[62] 10mm cast Acrylic using 6mm Single Flute bit 2mm depth 400mm/min Feed speed.[63] Cast Acrylic: DW660: single flute end mill, 30000 rpm, 300mm/min feed rate, 75mm/min plunge. Pass Depth 0.0625[64] Extruded Acrylic: Stock Shapeoko 2 w/ stock spindle, maximum speed, feed rate 380--400mm/ min and plunge rate 100 mm/ min., Step down 0.8mm with better results.[65] 2 mm acrylic from Home Depot. Cut with 1/8" 2-flute spiral end mill. 2 mm cut depth 400 mm/min feed 75 mm/min plunge 12000 rpm spindle (300w Quiet cut spindle)[66] Re: Cutting plexiglas with standard Dremmel Cutter: 3mm 2 flute carbide Kyocera cutter Spindle speed: 13800RPM Pass depth: 0.5mm Feed rate: 1200 mm/min Plunge rate: 300 mm/min

Acrylic and Polycarbonate.
: 600 Watt router, 30,000 rpm, feedrate of 1500 mm / min, plunge rate of 800 mm / min.[67] Some users have reported difficulties w/ the above settings: 660 and 30000 RPM issues --- please test w/ scrap and report specifics.

Plexyglass.
Acrylic is also available under the name plexiglass. (untested) Feed: 200--300 in/min Speed: 5,000 RPM Using a Dewalt DW660 on a ShapeOko 2, Riley Porter was able to cut 3/8" plexiglass[68] with the following settings: Bit: 2-flute 1/8" carbide upflute w/ 1/4" shank[69] Feed: 600 mm/min Speed: Full speed Cut Depth: 1.75mm (was supposed to be 1mm) See also Cutting Cheap PlexiGlass Any Luck?

Fabrication Notes.
Extruded acrylic tends to "store" energy and may randomly crack if one presses in a part as a friction fit. This happened when I.C. tried pressing in the magnets on his DWP611 shoe and broke a couple.[70] A further issue is that it will have two separate optimal feed/speeds for cutting, one along the extrusion axis, the other at 90 degrees to it.[71] The edges may be polished after cutting by rapidly passing an open flame over them and quickly allowing the material to melt and cool. You may wish to consider misting the material w/ water[72] and/or dishwashing liquid[73] as a coolant or applied to the bit as a lubricant[74] Further Notes and References http://www.plasticrouting.com/pdf/Routing_and_Trimming_Acrylics.pdf [75] 14,500 r.p.m. and 200 i.p.m. or 18,000 and 250 i.p.m.[76] Plastics Distributor® & Fabricator Magazine: Achieving Premium Finishes When Routing Acrylic Plexiglas = Perspex = Acrylic = PMMA = Polymethylmethacrylate Cast vs. Extruded --- usually cast has a paper protective film, while extruded has plastic[77] Cast PMMA is essentially pure polymethylmethacrylate and machines well using, when possible, tools with zero top rake and a very sharp cutting edge. Brand new HSS cutters are a good option. Extruded PMMA has chemicals added to it to aid in extrusion and does not machine as nicely, tending to melt. There is a possibility of stress cracks and crazing after machining as noted above[78]

Alternatives.
Polycarbonate. It costs twice as much, but it's nicer in every way.[79]

EXTRUDED POLYSTYRENE.
(non testato) Bit: 1/8" end mill Feed: 1000mm/min Speed: 6,000 RPM Cut Depth: 2mm (0.08")

EXTRUDED PLEXYGLASS.
Stock shapeoko 2 with dremel 4000 (grbl 0.9) Feed xy: 1000mm/min Plunge Z speed: 250mm/min Speed: 13-15,000 RPM Cut Depth: 0.5mm Bit: 1-flute 1/8" carbide upcut spiral [80] Note: Extruded plexiglass is not easy to mill. The above combo is what gave me best results after some experimentation. A two flute straight cutter can be used but will cause more melting.

KYDEX.
13--15,000 RPM --- Spiral O shape bit suggested.

PVC.
available as boards and trim pieces at home center. Mentioned for cutting in 25mm thickness.[81]