1. Chamfer Lead
Taps should be reground on the cutting chamfer periphery with
the same clearance angle as before.
The regrinding of taps is generally carried out on sizes greater
than 1/2, although sizes smaller than this may be reground where considered feasible.
Unless the regrinding is carried out in a manner which ensures all
worn surfaces are removed without heat generation, a decrease in production rates will be created.
If damage is slight the necessity to regrind may only be confined to the chamfer angle,
and the chamfer angles defined for standard taps are shown on page . . . Should it become
necessary to alter the chamfer lead length due to the component design, then the chamfer
lead angles, in terms of the “Number of threads” required, must be recalculated. It is
also important to retain the chamfer point diameter approximately the same size as the
root diameter. It may be necessary to grind back the front end of the tap before regrinding
the chamfer.
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A
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Chamfer correctly ground. All lands of chamfered portion in contact.
Point diameter large enough to permit only one thread to enter, thus
getting full cutting benefit of practically entire chamfer.
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B
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Chamfer incorrectly ground. Lands of chamfered portion are uneven as to
height, thus forcing entire cutting burden on lesser number of lands.
Result—poor threads, increased power consumption, and high tap breakage.
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C
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Chamfer correctly ground as to height of lands, but point diameter too
small, forcing entire cutting burden on small portion of chamfered section.
Result—greater power consumption and shorter tap life due to dulling of cutting edges.
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Sharpening the
cutter chamfer
Checking the cutting chamfer concentricity
Checking equipment: Dial gauge, tap located between centers.
Checking location: At chamfer, see illustration
Check values: Max deviation
- No.5 Ø = .0004"
- 3/8" Ø = .0006"
- 1" Ø = .0008"
 
2. Hook or Rake Angle
Only in emergency cases, such as when the tap is badly damaged, is the rake face to be
ground. If a tap is ground on the rake face there is a risk of burrs being produced
which cuts oversized threads on the first components. The rake face grinding must be
carried out very carefully so that the relieved edges do not have a diameter which is
too small.
For the majority of applications in both ferrous and nonferrous materials the hook or
rake angle machined on the tap by the manufacturer is satisfactory. This angle is
approximately 6 to 10 degrees. In some instances it may be desirable to alter this
angle to obtain beneficial results.
In selecting a hook or rake angle from this table, consideration must be given to the
size of the tap and the strength of the land. Most standard taps are made with a curved
face with the rake angle measured as a chord between the crest and root of the thread.
The resulting shape is called a hook angle.
Checking hook or rake angles.
Checking equipment: Dial gauge, tap located between centers.
Check values: See Hook or Rake Angles on the charted product pages. Checking location:
At chamfer and after the first full profile tooth.
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Regrinding Data
