Page 294 - Hartner

The drilling process

A brief introduction to the subject of deep hole drilling

In the machining world, drilling depths of 10 x D and deeper High pressure cooling has become a matter of course
are regarded as deep hole drilling operations, whereby smaller In recent years, internal cooling has established itself for all dril-
drilling depths can naturally also be produced with gun drills. ling tools. Coolants are now living up to their name and being
Advantage is taken of the positive side effects, as for example supplied via coolant ducts to where they are urgently required.
good surface quality, low deviation from concentricity and opti- Considerable improvements in tool life and less breakages have
mised alignment accuracy. been achieved by this measure for twist drills, taps etc.
Every conventional machine tool currently on the market can be
Typical procedure with all gun drills on conventional supplied with high pressure internal cooling and is therefore also
machine tools: suitable for deep hole drilling.
• production of pilot hole. Enter at low revolutions, approx. The share of gun drills on machining centres, lathes etc. is fore-
200 rev./min, feed rate approx. 500 mm/min. ver gaining more importance. The process is therefore increa-
• setting coolant pressure and speed. sing in popularity in the machining world.
• continuous drilling to complete hole depth without chip
removal. When applying gun drills with increased length-
diameter-ratio (e.g. single fluted, solid carbide gun drills
from flute length 160 mm), we recommend machining with
reduced cutting parameters (approx. 75% of the optimal
cutting speed) up to a drilling depth of approx. 25 mm.
• switch off coolant supply after reaching hole depth.
• withdrawal in rapid feed with stationary spindle.

Deep hole drilling is not a
closed book, but can be
mastered by anybody as
All gun drills must have long as certain conditions
support for the pilot hole.
are adhered to.
Recommended cutting rates
Gun drills must never ope- for the application of Hart-
rate at full speed without ner gun drills can be found
support in the machine on the pages for the indivi-
shop.
dual types!

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