Introduction

In addition to surfacing and edging, particular applications in the glass industry often require the drilling of holes for fixing or fitting. 

These holes are drilled by means of diamond core drills.

Contrary to the drills designed for wood and metal, the drills used for glass material consist of a thin cutting wall, which is mounted on a cylindrical tube.

72The tool components are:

·       a diamond core drill with continuous rim

·       a metal tube

·      Ba shank

During the drilling operation the cutting wall performs a circular groove in the material and as it descends, it produces a core which will dissociate itself in the final stage.

Geometry

The diameters D and D1

The core drills manufactured by Diamas Tools guarantee a core drill thickness of 1 mm and inner and outer clearances of     0.2 mm.

These clearances are necessary to avoid any contact between the glass and the tube of the drill as this would cause     chipping.

The diamond core drill is manufactured with a hole through its shank to allow coolant to flow through the centre of the drill.

The drilling depth (L1) and the diamond impregnated depth (X)

 
The drilling depth L1 determines the maximum drilling depth without considering the diamond layer (X size) as it wears out during drilling work:

L1 = 15 mm for D £ 8 mm

L1 = 30 mm for D > 8mm.

Other drilling depths L1 are available on request.

The diamond layer depth (X) varies according to the diameter:

X=5 for diameters D < 5 mm

X =10 for diameters ³ D5 mm.

The total length (L)

This dimension represents the total length of the core drill.

The standard lengths in the glass industry are L= 75 mm, L = 82 mm (for Janbac drilling machines) and L = 95 mm (for ADA and Forvet drilling machines).

The shank

The usual shank for the drilling of glass is the self-centring shank ½” Gaz, also called the “Belgian shank”.

Types of drills

FC159:  High-precision diamond core drill performing excellent edge quality.

FC161:  Long-lasting and high-speed diamond core drill designed for semi-automatic and fully automatic machines.

Conditions of Use

 The coolant system is very important, optimum results can only be obtained if the balance between the following parameters is reached:

·      the water quantity

·      the water pressure

·       the coolant slots in the impregnation.

 
The following parameters should also be considered, as they are directly linked to the core drill used: 

·      the diameter and the specification of the core drill

·      the peripheral speed

·       the feed speed and specific pressure

·       the cooling pressure.

Diameter and specification of the core drill

Compared to a grinding wheel, the diamond core drill is continuously in contact with glass. This means that the contact area for larger diameters is also greater and the down feed pressure on the core drill must be increased. 

To compensate for this increased pressure, the specifications of the diamond layer (grit size, concentration, and bond) can be optimised to feature a softer bond and to obtain the required abrasiveness.

Peripheral speed 

Coolant pressure

Coolant supply should also be studied thoroughly.

If the pressure is too low, the glass swarf cannot be removed out of the groove.

If the pressure is too high, the core is being ejected before the drill comes out of the glass and chipping becomes too important.

It is thus highly recommended to use the appropriate pressure, according to the diameter of the drill used:

Order example

1Drill type: FC159, FC161