Tap Manufacturers offer their own unique geometries
for specific materials and applications. This
chart is meant to provide general information.
For a specific tap recommendation for your application,
please consult your tap supplier.
Standard Straight
Fluted Tap
With 6 to 8 Threads Chamfer Length or Lead.
These taps do not transport
the chips out of the hole. For this reason,
they should not be used for deep hole tapping.
They work best in shallow depth through holes
and in materials that produce short chips.
Workpiece
Materials
Recommended Tap
Surface Treatments
Cast
Iron
Nitrided
or TiN
Brass,
Short Chipping
Nitrided
Cast
Aluminum
Nitrided
Short
Chip Hard
Nitrided
or TiN
Straight
Fluted Taps With Spiral Point
With 3.5 to 5 Threads Chamfer Length or Lead.
These taps push the chips
forward. The chips are curled up to prevent
clogging in the flutes. They are used for
through holes.
Workpiece
Materials
Recommended Tap
Surface Treatments
Aluminum
Long Chip
Bright,
or Cr or TiN
Exotic
Alloys
Nitrided
or TiN
Stainless
Steel
Nitrided
or TiN
Steel
Bright
or TiN or TiCN
Left
Hand Spiral Fluted Tap
With Approximately 12 Degrees
Spiral Flutes With 3.5 to 5 Threads Chamfer
Length.
These taps are mostly used
in thin walled parts or for holes interrupted
by cross holes or longitudinal slots.
Workpiece
Materials
Recommended Tap
Surface Treatments
Aluminum
Long Chip
Bright,
or Cr or TiN
Exotic
Alloys
Nitrided
or TiN
Stainless
Steel
Nitrided
or TiN
Steel
Bright
or TiN or TiCN
Right
Hand Spiral Fluted Tap
With Approximately 15 Degrees
Spiral Flutes With 3.5 to 5 Threads Chamfer
Length.
The spiral flutes transport
chips back out of the hole. These taps
are used in blind holes less than 1.5 times
the tap diameter deep with materials that
produce short chips.
Workpiece
Materials
Recommended Tap
Surface Treatments
Cast
Aluminum
Nitrided
Titanium
Nitrided
or TiN
Stainless
Steel
Bright
or TiN
Steel
Bright
or TiN or TiCN
Right
Hand Spiral Fluted Tap
With 40 Degrees to 50 Degrees Spiral Flutes.
The greater helix angle provides
good transport of chips back out o the
hole. These taps are used only in blind
holes in materials that produce long chips.
They can also be used in deeper holes up
to 3 times the tap diameter.
Workpiece
Materials
Recommended Tap
Surface Treatments
Aluminum
Long Chip
Bright,
or Cr or TiN
Stainless
Steel
Bright
or TiN
Steel
Alloy Cr-Ni
Bright
or TiN or TiCN
Soft
Material
Bright
Rake
Angle
The best rake angle for a tap depends on the material.
Materials that produce long chips normally require
a tap with greater rake angle. Materials that produce
short chips require a smaller rake angle. Difficult
materials like Titanium or Inconnell require a
compromise between greater rake angle for longer
chips and smaller rake angle for more strength.
Relief
Angle In The Lead Of A Tap
A small relief angle can be used in soft materials.
Harder materials like stainless steel can be cut
easier with a tap having a greater relief angle
which reduces the friction. Tough materials like
Inconnel and nickel can be cut more easily with
an even greater angle.
The relief angle is smaller on taps for blind holes
that on taps for through holes so that the chip
root can be sheared off when the tap reverses without
breaking the taps cutting edge.
Chamfer Length (Lead)
The actual cutting of the
thread is done by the lead of the tap. When there
are more threads in the chamfer length or lead
the torque is reduced, producing the thread is
much easier, and the life of the tap will be
increased. In blind holes where there is not
enough room to drill deep enough for a tap with
a longer lead, taps with short leads are used.
In some cases the lead of the tap is reduced
to as little as 1.5 threads. This greatly increases
torque and reduces tap life. Even when using
taps with shortened lead it is still important
to drill deep enough for adequate clearance.
It is recommended to allow one thread length
plus one mm beyond the lead of the tap as drill
clearance.
Relief Angle
In The Thread Profile (Pitch Diameter Relief)
The relief angle effects true to gage thread
cutting, and also the free cutting ability
and life of the tap. It has an effect on
how the tap is guided when it enters the
hole. If the relief angle is too great pitch
guidance and self centering of the tap can
not be guaranteed especially in soft materials.
In materials like stainless steel or bronze
the relief angle should be larger to allow
free cutting and to allow more lubrication
to reach the cutting and friction surfaces.
A bigger relief angle can allow higher tapping
speed provided the tap is guided concentrically
into the hole by the machine and tap holder.
Roll
Form Taps
Workpiece
Materials
Recommended
Tap Surface Treatments
All Ductile
Materials
These
taps form the thread rather than cut. Since
no chips are produced they can be used in
blind or through holes. Cold forming is possible
in all ductile materials. Advantages include
no waste in the form of chips, no mis-cutting
of threads, no pitch deviation, higher strength,
longer tool life, and higher speed. Please
note that the core hole diameter must be
larger than with a cutting tap. Good lubrication
is important , more torque is required, and
the minor diameter of the thread will appear
rough due to forming process.
