Tapping speeds are determined by many factors. The main ones are:
Tapping speeds can be calculated using:-
TAPPING SPEEDS SHOULD BE DECREASED IF: |
TAPPING SPEEDS CAN BE INCREASED IF: |
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Speeds given are for machine tapping using HSS taps, and are given in feet per minute.
MATERIAL |
FEED SPEED (SFM) |
LUBRICANT |
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Aluminium |
70-90 |
Soluble oil |
Aluminium alloy |
50-70 |
Soluble, light base or lard oil |
Brass |
60-100 |
Light base oil |
Bronze |
30-40 |
Light base oil |
Copper |
60-80 |
Light base oil |
Gun metal |
50-60 |
Soluble, light base or lard oil |
Grey cast iron |
30-60 |
Dry or soluble oil |
Alloy cast iron |
15-30 |
Sulphur based oil |
Malleable iron |
20-40 |
Soluble or sulphur based oil |
Magnesium alloy |
50-70 |
Soluble oil or paraffin with lard oil |
Nimonic alloy |
10-12 |
Very high pressure cutting oil |
Plastics |
50-70 |
Dry, freeze spray, liquid soap |
Mild steel |
30-50 |
Sulphur based oil |
Carbon steel to 4% |
20-40 |
Sulphur based oil |
Carbon steel to 7% |
20-30 |
Sulphur based oil |
Carbon steel 7%+ |
15-25 |
Sulphur based oil |
Steel alloys to 60T |
15-25 |
Sulphur based oil |
Steel alloys 60T+ |
10-15 |
Sulphur based oil |
Stainless steels |
10-20 |
Sulphur based oil |
Tool steels |
15-25 |
Sulphur based oil |
With so many variables affecting tapping speeds there may need to be some experimentation to find the ideal. A good rule is to start at the slowest speed and work up.
Many factors can affect the quality of a tapped thread. Some more common problems are listed along with probable causes.
POOR THREAD FINISH |
OVERSIZE/BELL MOUTHED |
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EXCESSIVE TAP WEAR |
COLD WELDING |
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TAPS BREAKING |
TAP TEETH CHIPPING |
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In order to minimise problems the following rules should be followed: