1. Drilled hole prior to tapping too small (tap being overworked).
2. Tap not in line with hole
3. Incorrect lead chamfer grinding. Length of chamfer not equal, on each land.
4. Unevenly spaced cutting edges
5. Wrong type of tap for material of application

Tap Chips on Cutting Edges

1. Cutting face angle too acute
2. Excessive relief on chamfer lead.
3. Tap hitting bottom of blind hole, creating shock to cutting edges
4. Drilled hole prior to tapping too small
5. Tap too hard for prevailing conditions

Tapped Holes Vary in Size

1. Inconsistent work location
2. Excessive play in tap holder or machine spindle.
3. Tapping holes out of round or varying in size, this applies particularly to punched holes.

Tap Breaks

1. Drilled hole prior to tapping too small
2. Cutting edges worn or chipped
3. Flutes too wide (weak lands)
4. Flutes too deep (weak on web diameter)
5. Tap out of line with hole
6. Tap choked with chips (deep hole tapping)
7. Tap bottoming when blind hole tapping
8. Skin hardness in hole from drilling
9. Lack of lubricant