31-12-18, 09:25 AM
When you say you ran the bit around for a minute or so, is that total drilling time per hole or do you mean you continued to turn for that length of time after you think you completed the cut?
You were right to apply light pressure and drill carefully as it's a fine bit and fragile if forced. Typically it takes about a minute to do each hole. I often used to stop after about 40 secs or so just to check visually and clear any swarf.
It is usually very easy to feel when the bit is approaching breakthrough because it gets tighter to turn in the hole. Incidentally, that's when it is at greatest risk of snapping, so go easy at that point if you're reading this and planning to follow Paul's lead.
The difference between a completed cut and a partial one is very clear to the eye. If it doesn't look like a proper hole, it ain't!
You can't do any damage by continuing to turn after making the full cut. The bit drops down into the space below the hole by about 1mm before it hits the bottom of the casting. A few more turns there isn't going to do any harm. Just be careful not to allow the bit to wobble and over-enlarge the hole you've cut.
You were right to apply light pressure and drill carefully as it's a fine bit and fragile if forced. Typically it takes about a minute to do each hole. I often used to stop after about 40 secs or so just to check visually and clear any swarf.
It is usually very easy to feel when the bit is approaching breakthrough because it gets tighter to turn in the hole. Incidentally, that's when it is at greatest risk of snapping, so go easy at that point if you're reading this and planning to follow Paul's lead.
The difference between a completed cut and a partial one is very clear to the eye. If it doesn't look like a proper hole, it ain't!
You can't do any damage by continuing to turn after making the full cut. The bit drops down into the space below the hole by about 1mm before it hits the bottom of the casting. A few more turns there isn't going to do any harm. Just be careful not to allow the bit to wobble and over-enlarge the hole you've cut.