Page 736 - Iscar

USER GUIDE
TAPS Regrinding

Regrinding Picture 1
Tap regrinding takes place in two steps:
a) regrinding of relieved chamfer
b) regrinding of flutes (see picture 1)

Regrinding of Relieved Chamfer
It is recommended that the resharpening should 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 the regrinding done with the
cylindrical surface of a grinding wheel. Picture 2
Before regrinding, verify 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 β
tap axis, in relation to the regrinding surface,
of an amount X to be calculated with the
formula: X = 1/2 d1 sin (g) (see picture 3).
(d1 =tap major diameter) Picture 3
Example: γ
Tap 10 X 1,5 to cut on steel strength =
600 N/mm2
d1 = 10 mm ; g = 15° ; sin (g) = 0,25882;

X = 0.25885x10 ; X=1.29 mm
2
X

On all taps with spiral flutes, it is possible to find
the pitch of the spiral in reference to the lead screw Picture 4
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 nose, regrinding the flutes can
be done on the front area only (see picture 4).
In cases where the thread flanks are worn
(in addition 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. Picture 5
(see picture 5) Flank wear
In the absence of special regrinding machines,
such restoration is advisable for regrinding taps
with spiral flutes. This is because regrinding
the flutes becomes unnecessary.
Chamfer

New
chamfer
Part to be cut away

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