Page 378 - ISCAR(HOLE_MAKING_CATALOG_65)

USER GUIDE
TAPS Regrinding

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
that the tap, fixed between points or on the pincer, runs
concentrical. Also ensure that angle B is in the correct Picture 2
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
calculated with the formula: X = 1/2 d1 sin (ϒ)
(see picture 3). β
(d1 =tap major diameter)
Example:
Picture 3
Tap 10 X 1,5 to cut on steel
strength = 600 N/mm 2 γ

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

X = 0.25885 x10 ; X=1.29 mm Picture 4
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
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 ϕ
to the active edges), regrinding as described above is Picture 5
impractical. In this case restoration is done, by cutting Flank wear
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,
such restoration is advisable for regrinding taps
with spiral flutes. This is because regrinding Chamfer
the flutes becomes unnecessary.

New chamfer
Part to be cut away

376 ISCAR