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TAPS Regrinding USER GUIDE

Regrinding Picture 1
Tap regrinding takes place in two steps:
1 regrinding of relieved chamfer
2 regrinding of flutes (see picture 1)
Regrinding of Relieved Chamfer
It is recommended that the resharpening be executed
either on specific tap regrinding machines or on
conventional resharpening machines equipped with an
auxiliary device to generate the circular back relief.
Picture 2 shows regrinding done with the cylindrical
surface of a grinding wheel. Before regrinding, verify Picture 2
that the tap, fixed between points or on the pincer, runs
concentrical. Also ensure that angle B is in the correct
order to keep the same number of threads on chamfer.
Resharpening of Flutes
The rake angle g is obtained by moving the tap axis, in
relation to the regrinding surface, of an amount X to be β
calculated with the formula: X = 1/2 d1 sin (ϒ)
(see picture 3).
(d1 =tap major diameter)
Picture 3
Example:
γ
Tap 10 X 1,5 to cut on steel
strength = 87 ksi

d1 = 10 mm ; ϒ = 15° ;
sin (ϒ) = 0,25882; X

Picture 4
X = 0.25885 x10 ; X=.051”
2
On all taps with spiral flutes, it is possible to find the pitch
of the spiral in reference to the lead screw necessary
for resharpening. In case of using taps equipped with
a deburring tool, it is necessary to extend the flutes
according to the supplier’s recommendation. As the wear
on a tap is mainly on the chamfer area, for taps with a gun ϕ
nose, regrinding the flutes can be done on the front area
only (see picture 4). Picture 5
In cases where the thread flanks are worn (in addition Flank wear
to the active edges), regrinding as described above is
impractical. In this case restoration is done, by cutting
the chamfer away (thus creating a shorter tap) and then
reproducing the chamfer with same angle and relief.
(see picture 5)
In the absence of special regrinding machines, Chamfer
such restoration is advisable for regrinding taps
with spiral flutes. This is because regrinding
the flutes becomes unnecessary.

New chamfer
Part to be cut away

440 ISCAR