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Glass drilling

Saturday, January 19th, 2019

Glass drilling

 

 

 

Introduction

 

The standard tool used to drill on glass is a core drill ( Belgium standard) with ½ inch fitting. Different lenght are available, but the more common is 75 mm for a new tool. The diamond activ part has a lenght between 10 and 12 mm.

 

The first problem met drilling on glass was the chips created by the core drill on the glass bottom face. The pressure from the core drill causes glass breaking out at the end of the drilling. To solve this problem, glass was firstly drilled on a face on few millimeters and after reversed and drilled exactly at the same place.

 

The first drilling machines was machines coming from mechanical industry, with a “ water box ” addition to drive the water for the cooling inside the core drill.

 

To prevent damages or accidents during drilling, the machines suppliers has proposed drilling machines with 2 opposed spindles on line allowing drilling from the both sides without moving the glass.

 

 

 

Double spindle drilling machine from Janbac

 

The working cycle is

-Water opening for the lower spindle

-Fast climbing for the lower spindle up to somr millimeter from the glass

-Proper climbing speed to drill and drilling on few millimeters

-Lower spindle way down, water stop and core drill protection.

-Water inside the top spindle

-Fast descent till the glass surface

-Proper drilling speed adjustement

-Drilling till the bottom glass surface

-Glass carrot eviction

-Spindle rising and water stop

 

The working cycle can be manual, semi-automatic or automatic with remote control in case of large glass.

 

 

The lower core drill drills 1/3 of the glass thickness for medium glass thickness ( 8, 10 mm). But ½ for 2 mm and ¼ or less for 12 mm and over.

 

The spindles have changed over the years. Firstly mecanic, after hydrolic, then electric and now electric with servomotors for a best accurency

 

Main machine stypes present on the market

To-day the suppliers propose 3 different way to drill on glass

-Horizontal machines

-Vertical machines

-Drilling with a CNC machine

 

1/The horizontal drilling machines

-Mono-spindle : you have to reverse the glass and to drill

-The opposite double-spindles machines : the more common on the market

-The multi-spindles machines with 2 or more ( 3,4,6) opposite double-spindles  : intented to market where several different holes have to be performed  on the same glass. These machines can be positionned in line with a double edger, even if the drilling lower speed cycle reduce the double edger speed.

 

 

Multi-spindles machines from Janbac

 

2/The vertical drilling machines

These machines were introduced on the market by the Autrian Company Schraml, 15 years, under the Topdrill trademark.

 

 

 

Vertical drilling machine fromTopdrill

 

 

Contrarily the horizontal double spindle drilling machines where the drilling heads are fix, here the double spindles move on Y axe.

The main advantages for vertical drilling

-Place saving : Interesting for smallest machines, but not real for the ùore important ‘ones because teh inlet and outlet conveyors.

Les principaux avantages de ce type de machines sont

-The drilling is automatic : the glass is installed on teh inlet conveyoe and the hole is automatically carried out from teh data intered inside the control panel.

-Drilling on line and less glass manula handling : the glass can come directly from an other vertical machine ( edging, sandblasting machine..) and sent automaticaly to a washing machine. Less handling means less scratches and accidents

-Water recovering : the water drops vertically after tools cooling and is easy to recover.

 

But this machines type meet some inconveniences :

-It is not possible to drill more than 2 different diameters ( but some machines propose now a tools store with automatic changing).

-It is difficult to have the two spindles perfectly on line

-The cooling is less efficient, the water leaving fastly the core drills.

-The glass is installed on one edge, causing some vibrations and more scratches during drilling.

 

The machines has one or two double spindles, the second one being often replaced by a milling spindle. Possibility to have an automatic tools store

 

The vertical drilling machines meet a real succes from customers, mainly for the smallest machines. They represent an important need on the market.

 

3/Drilling on CNC machines

Here the market is not the same. The idea is not to use a CNC machine as a drilling machine, but to complete process a glass on the same machine including holes.

To solve the scratches problem at the drilling end two possibilities are offered on the market.

-A software and a special tool allowing to drill and after to remove the scartches with only one tool.

-An option allowing to start to drill under the glass and to finish the drilling by the top.

 

 

Intermac option to drill with CNC machine

 

Drilling parameters

1/Advance speed

The advance speed for glass drilling is about one millimiter per second for diameters between 10 and 30 mm. For lower and larger diameters the speed has to be reduced

The drilling speed is also connected with:

-The core drill supplier

-The dressing

-The cooling

-The drilling machine

-The glass

 

2/The spindle rotation speed

Strictly connected with core drill diameter and with the supplier ( Each supplier has his own rotation speed table).

Happily the modern drilling machines are supplied with electronic variator allowing to adjust immediatly the roation speed after core drills changes.

The older machines are equiped with a pulleys/Belts system not easy to use.

 

 

Main available options

1/Hole positionning

a/Laser : a laser installed in the upper spindle center indicate with a luminous point on the glass the place where to drill. The glass has to be marked. indique par un point sur le vitrage, l’endroit où se fera le perçage. Cela implique de marquer sur le verre le centre de l’endroit à percer. The water on the glass can disturb a proper positionning. The laser has to be adjusted on a regular base.

 

b/Equerres manuelles :des butées avec indicateur millimétrique sont positionnée d’un côté et sur l’arrière de la table où s’effectue le perçage. L’opérateur pousse le verre contre les butées pour positionner correctement le verre.

 

c/Butées automatiques : les coordonnées du trou à percer sont entrées sur le pupitre de la perceuse. Les butées se déplacent automatiquement. Le verre est positionné manuellement ou automatiquement contre les butées.

 

 

2/Milling

Il s’agit là de l’évolution récente des perceuses vers des centres perçage/fraisage capables de réaliser à la fois des trous et des encoches, en particulier dans le cas des perceuses verticales. La broche de fraisage est souvent différente car elle nécessite davantage de puissance et  de couple et des vitesses de rotation plus élevées que celles requises dans le cas du perçage.

 

 

Drilling, milling Janbac machine

 

3/Automatic dressing

Option permettant à intervalle régulier d’amener les forêts devant un baton d’affutage.

 

4/Compensation d’usure des outils et mesure de la longueur des forêts

Le seul système qui demeure est un calibrage manuel sur une pièce de métal ou de verre d’épaisseur connue.

Lors d’un changement de forêt ou après un certain nombre de trous on descend manuellement le forêt sur la surface de référence. La perceuse enregistre la côte par différence de pression et adapate son cycle de perçage en fonction de la nouvelle longueur de forêt détectée.

 

 

5/ Magasin d’outils et changement automatique

 

 

Conclusion