Machinery's Handbook, 31st Edition
604 MACHINING PLASTICS Table 9. Suggested Approximate Speeds and Feeds for Drilling Various Thermoplastics a Material 1/16 in. Diameter 1/4 in. Diameter 1 in. Diameter Speed (RPM) Feed (in/rev) Speed (RPM) Feed (in/rev) Speed (RPM) Feed (in/rev) ABS 6000 0.015 2000 0.040 500 0.080 Acetal (POM) 12000 0.010 4000 0.030 1000 0.060 Acrylic (PMMA) 9000 0.010 3000 0.030 750 0.060 Polyamide, Nylon 6/6 and PA6 6000 0.010 2000 0.030 500 0.060 Polycarbonate (PC) 9000 0.010 3000 0.030 750 0.060 Polyester (PET) 9000 0.007 3000 0.020 750 0.040 Polyether ether ketone (PEEK) 12000 0.005 4000 0.015 1000 0.030 Polyethylene (PE) 12000 0.015 4000 0.040 1000 0.080 Polyphenylene sulfide (PPS) 3000 0.010 1000 0.030 250 0.060 Polypropylene (PP) 12000 0.015 4000 0.040 1000 0.080 Polystyrene (PS) 6000 0.007 2000 0.020 500 0.040 Polytetrafluoroethylene (PTFE) 9000 0.007 3000 0.020 750 0.040 Polyvinyl chloride (PVC) 12000 0.007 4000 0.020 1000 0.040 Ultem polyetherimide (PEI) 12000 0.010 4000 0.030 1000 0.040 a Using a two-fluted drill. Tapping and Threading of Plastics: Many different threaded fasteners can be used with plastics, including thread-tapping and -forming screws, threaded metal inserts, and molded-in threads, but threads must sometimes be machined after molding. For tapping of through holes in thin-cast, molded, or extruded thermoplastics and thermosets, a speed of 50 ft/min (15.2 m/min) is appropriate. Tapping of filled materials is done at 25 ft/min (7.6 m/min). These speeds should be reduced for deep or blind holes and when the percent- age of thread is greater than 65–75 percent. Taps should be of M10, M7, or M1 molybde- num high-speed steel, with finish-ground and -polished flutes. Two-flute taps are recom mended for holes up to 0.125 inch (3.2 mm) diameter. Oversize taps may be required to make up for elastic recovery of the plastics. The danger of retapping on the return stroke can be reduced by blunting the withdrawal edges of the tool. Sawing Thermoset Cast or Molded Plastics: Circular or band saws may be used for sawing. Circular saws provide smoother cut faces than band saws, but, because band saws run cooler, they are often preferred even for straight cuts. Projection of the circular saw above the table should be minimized. Saws should have skip teeth or buttress teeth with zero front rake and a raker set. Precision-tooth saw blades should be used for thicknesses up to 1 inch (25.4 mm), and saws with buttress teeth are recommended for thicknesses above 1 inch (25.4 mm). Dull edges to the teeth cause chipping of the plastics and may cause breakage of the saw. Sawing speeds and other recommendations for using blades of high-carbon steel are shown in Table 10. Table 10. Speeds and Numbers of Teeth for Sawing Plastics Materials with High-Carbon Steel Saw Blades
Peripheral Speed
Thermoset Cast or Molded Plastics
Thermoplastics (and Epoxy, Melamine, Phenolic and Allyl Thermosets)
Number of Teeth/inch on Blade
Material Thickness
(inch) 0–0.5 0.5–1
(mm) 0–13 13–25 25–76
(ft/min) 2000–3000 1800–2200 1500–2200 1200–1800
(m/min) 607–914 549–671 475–671 366–549
(ft/min) 4000–5000 3500–4300 3000–3500 2500–3000
(m/min)
8–14 6–8
1219–1524 1067–1311 914–1067 762–914
1–3 >3
3
>3
>76
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