T-Drill S-80 - Page 74

INSTRUCTION MANUAL
74

¨NOT!¨ 

The parts of the bit: α = Clearance angle, ɣ = Chisel edge angle, 1. Cung edge, 2. Body
clearance surface (land), 3. Rake face, 4. Flute.
The patented cung geometry of the T-DRILL bit is designed in such a way that a perfect
pilot hole without burrs can be achieved at a low feed rate. However, this presupposes
that the cung edge is always kept sharp.

When the cung performance of the bit declines, it does not seem to penetrate the tube
surface easily or burrs occur on the edge of the pilot hole, it is me to resharpen. (Note!
Burrs may also be a sign of insucient lubricaon). Use of a dull bit must be avoided,
because a dull bit wears out very quickly and thus its life expectancy will be relavely
short.

The bit is resharpened at the rake face only. The body clearance surface is never to be
sharpened, because even the slightest variaon in the anding angle will radically reduce
the cung characteriscs of the bit.
For the resharpening the following equipment is needed:
- A tool grinding machine equipped with a vercally ltable rotary table
- A ne-grained, thin grinding wheel which ts in the ute
- A straight pin which ts in the cung-groove by means of which it is easier to set the bit
in the correct posion.

1. Fasten the drill shank in the clamping xture and put the straight pin into the ute. Set
the pin parallel with the slide bars of the grinding machine carriage both vercally and
horizontally. (See gure next).