Page 375 - ISCAR(HOLE_MAKING_CATALOG_65)

USER GUIDE
Chip Explusion
Tap selection is also influenced by the type of hole
being threaded. Through hole tapping usually requires
a tap that pushes the chips out in front of the cutting
edge and through the other end of the hole. A bottom
hole tap must pull chips up and out of the hole. • scrap workpieces
Tap Jamming
Some possible causes of tap jamming are:
• unsuitable tap
• tap with incorrect cutting geometry
• unsuitable coolant for material
• insufficient coolant
• axial pressure (pull or push) on the tap
• core hole too small
• breaks in walls of core hole
• speed too high or too low
• swarf trapped in the hole
• incorrect alignment of tap and core hole
• tap eccentricity
TAPS
Results of Tap Jamming
• torn threads
• short tap life
• rejected threads
• tap breakage
Tap Mounting
The tap must be mounted on the axis of the core hole.
On non-synchronized machines (feed/speed) we
recommend using a tapping spindle. (ISCAR GTI, GTIN
collets, see pages 381-382)
Tapping Heads
As a rule, with non-synchronized machine spindles
(feed/ speed), the feed rate should be programmed
approximately 5-10% lower than the thread pitch. In
these cases, a tapping chuck must be used which will
compensate the difference between the feed rate and
the thread pitch. It is important that the tension spring
in the axial compensation is set to a minimum pressure
to avoid axially loading the tap. The compression
spring should be tensioned so the tap starts to cut
by compressing the spring up to one-half pitch.
Important
Verify that the correct speed has been selected.
Ensure that ample lubricating coolant is being
used. Machine and equipment stability are
essential for optimal performance and results.
Forming Taps
Forming taps (roll forming or cold forming) produce
threads by deforming the material near the hole walls
rather than by cutting the material. This method often
works well in ductile materials. However, in brittle
materials it often results in unsatisfactory threads.
Torque requirements for forming taps are considerably
higher than for cutting taps. When forming taps
are used, chuck capacity must be decreased by
25%. Forming taps do not produce chips.
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