Drilling & Reaming

DRILLING

Although standard drill bits are generally acceptable, specialized bits are available to optimize performance with Bayblend ET1000 sheets. Overheating, gumming and induced machining stresses pose the greatest difficulties. Sharp drills and bits designed for plastics and proper drilling speeds alleviate most difficulties.  Table 1lists common problems and remedies.

 Table 1 - Common Drilling Problems and Remedies

Fault	Probable Cause	Remedy
Hole too large	Unequal angle on length of cutting edge Burr on drill	Properly regrind drill Properly regrind drill
Rough Or Burred hole	Dull drill Improperly ground drill Too coarse feed Inadequate lubrication	Regrind properly Regrind properly Reduce feed Correct to remove heat
Breaking of drill	Feed too heavy in relation to spindle speed Dull drill grabs in work Inadequate chip clearing	Reduce speed or increase speed Regrind drill Check application setup
Chipping of high speed drill	Improper heat treatment after regrinding Too coarse feed	Follow manufacturing recommendations Reduce feed

Drill bits for plastics generally have wide polished flutes to reduce friction as well as spiral or helix designs to remove chips quickly. Drill point angles for plastics typically range between 60 and 90 degrees, with smaller angles for smaller holes and larger angles for larger holes. The suggested drilling speeds for most Bayer MaterialScience plastics are between 100 and 200 feet per minute. Table 2 lists common feed rates in inches per revolution for a range of hole sizes. Under ideal conditions — good cooling, sharp drills and efficient chip removal — considerably faster feed rates are usually possible.

Table 2 - Feed Rate

Drilling Conditions
Drill (in)	Feed (in/rev)
Up to 1/8	0.001  -  0.002
1/8 to 1/4	0.002  -  0.004
1/4 to 1/2	0.004  -  0.006
1/2  to 1	0.006  -  0.008

For smoothly drilled holes, remove most of the plastic with a roughing drill, then finish and size the hole with a second drill. Or, as an alternative method use a two-step drill as illustrated in Figure 1. For accurate work, and to minimize drill breakage, consider using jigs with a guide bushing (see Figure 2).

 Figure 1 - Two Step Drill

The first step removes most of the material. The second step makes a fine cut to size.

 Figure 2 - Drilling Jig

 

For accurate work, use a drilling jig with a hardened drill bushing.

Some rules-of-thumb for drilling thermoplastics include:

• Use carbide-tipped drills because they resist gumming and maintain edge sharpness longer than standard drills.
• Avoid cutting oils and cooling liquids because they may create chemical compatibility problems and will have to be removed after drilling.
• Use a forced-air stream for cooling.

Consider a water spray mist or water-soluble coolant when a forced-air stream cannot provide sufficient cooling.

REAMING

Reaming creates smooth finishes and precise hole dimension, making it ideal for determining final tolerance in prototype parts. Additionally, reaming removes gate vesting or flash from holes, as well as enlarges drilled or thermoformed holes. As in drilling, reaming requires sharp cutting edges and relatively slow cutting speeds to prevent heat build-up and gumming.

 

• Introduction
• Mechanical Properties
• Thermal Properties
• Environmental Considerations
• Design
• Assembly
• Machining
  • Drilling & Reaming
  • Sawing
• Finishing