Wednesday, 4 July 2018

Centering Holes for Drilling



When using larger core drills, it is not possible to see the centre point for drilling. So a different arrangement for marking the place to be drilled is required.  This example is to locate the hole for a clock spindle accurately bewteen the points marked by the stringers.


Find the centre point and extend lines at right angles to each other across the centre point.



Then measure the radius on each arm and make a perpendicular mark on each of the radial arms. Depending on how long those lines were, you have something approaching a box.



Approximately center the drill over the center point. In this case it is a portable drill, but the principle is the same for a pillar drill.






Lower the drill bit over the hole. The radius marks allow the drill operator to see the edge of the hole and use any two of the marks to centre the drill bit within the hole.


This procedure ensure the accurate positioning of the hole.  This is especially important when fitting to existing fixing points rather than making new ones.