3.6 SCREW FASTENING SYSTEMS
Direct Fastening Technical Guide , Edition 22
3.6 SCREW FASTENING SYSTEMS
3.6.1 SELF-DRILLING SCREW FASTENER SELECTION AND DESIGN
3.6.1.1 DRILL POINT SELECTION
Top material to be drilled Bottom material to be drilled
Total thickness to be drilled
Top material to be drilled Void or insulation
Bottom material to be drilled
Total thickness to be drilled
Hole diameter larger than screw threads
Top material Void or insulation
Bottom material to be drilled Total thickness to be drilled
Drill Flute The length of the drill flute determines the metal thickness that can be drilled . The flute itself provides a channel for chip removal during drilling action . If it becomes completely embedded in material , drill chips will be trapped in the flute and cutting action will cease . This will cause the point to burn up or break .
Point Length The unthreaded section from the point to the first thread should be long enough to help assure the drilling action is complete before the first thread engages the drilled metal . Screw threads advance at a rate of up to ten times faster than the drill flute can remove metal . All drilling therefore should be complete before threads begin to form .
Drilling through wood to metal If your application calls for drilling through wood over 1 / 2 " thick , a clearance hole is required . Select a fastener with breakaway wings for this type of job . The wings will ream a clearance hole and break-off when they contact metal surface ( minimum metal thickness 0.06 ") to be drilled .
Drilling capacity — material thickness recommendations ( steel to steel )
Thickness of material to be drilled ( in .)
0.500 |
# 2 Point |
# 3 Point |
# 4 Point |
0.400 |
|
|
|
0.300 |
|
|
|
0.250 |
0.250 |
0.200 |
0.210 |
0.220 |
0.100 |
0.100 |
0.110 |
0.140 |
0.175 |
0.175 |
0.175 |
0.100 |
0.110 |
0.110 |
0.110 |
0.035 |
# 5 Point 0.500
0.250
Screw Diameter
# 6 , # 8 # 10 # 8 # 10 # 12 # 14 # 12 # 14 # 12
Note : Meets or exceeds ASTM C1513 . Gray or black areas represent total thickness of all steel including any void spaces between layers .
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