Drilling, reaming, threading, and tapping

Drilling and reaming

For holes with small diameters, drilling is often a good option. This is also the case if molded-in holes would require expensive slides in the mold.

A standard high speed drill used for metals with a 118° nose angle can normally be used, but special drills for plastics may allow faster production rates. These drills are characterized by smaller nose angles, smaller helix angles and larger flutes, for better chip removal, and a larger back clearance to minimize friction.

Note, whereas many plastics require a positive rake angle, drills for Xantar PC must have a rake angle of 0-5° for a scraping rather than a digging action.

The table below gives some guidelines for drilling conditions. The values shown are only a rough indication, as optimal conditions depend on the specific polymer grade and the fillers used. A lower feeding speed must generally be used for drills with small diameters.

Drilling conditions

	Xantar PC	Stamylan UH	Other Plastics
Rake angle	0-5º	15-25º	>0
Clearance angle	5-15º	about 16°	10-15º
Cutting speed	5-40 m/min (16-130 ft/min)	40-70 m/min (130-230 ft/min)	30-120 m/min (100-400 ft/min)
Feed speed	0.025-0.040 mm/rev (1-1.5 mils/rev)	0.1-0.3 mm/rev(4-12 mils/rev)	0.025-0.5 mm/rev (1-20 mils/rev)

A smooth hole can be produced by first drilling a hole with a diameter that is slightly smaller than the desired size, and then finishing the hole with a second drill. A stepped drill as shown in the figure below can also be used and offers a faster alternative.

Threading and tapping

Parts made of more rigid engineering plastics such as Stanyl PA46, Akulon PA6, Arnite PET and PBT, and Xantar PC, can be provided with a screw thread by threading or tapping with conventional steel working equipment. Very fine threads with a pitch smaller than 1 mm should however be avoided and the root radius must be maximized to reduce stress concentrations. Threading can be done on a conventional lathe by removing material in successive cuts of less than 0.25 mm (10 mils). Low spindle speeds must be applied for tapping, with a feed speed between 6 and 24 m/min (20-80 ft/min).