Pilot holes for large drill bits

[stealthwolf]

I used a 20mm forstner bit to give me a well 10mm deep. I need to drill a 10mm wide hole through the timber (45mm thick).

I used a 3mm wood bit so it would centre perfectly. On a test piece, using the 6mm wood bit next meant the hole was off centre. So on the main work, I used a 6mm hss bit which worked. But when I used 8mm and then 10mm, the edge of the hole became splintered.

How do I avoid this?
What was the correct technique for what I wanted to achieve?
Should i have drilled the hole first and used a forstner bit second?

 

[Tigercubrider]

The edge of which hole? The small hole inside the well? Or where it comes out?
If out, then add a piece of wood under the main timber, preventing break through damage

 

[stealthwolf]

I should have taken a pic.

The forstner “hole” is a recess for the collar of a masonry bolt to rest on. That bit is fine.

The main hole for the shaft of the bolt is chipped on the forstner side. I used a scrap bit of wood for the opposite side and there’s no breakou.

 

[Notch7]

Drill 20mm counterbore first.

Thrn drill 10mm hole.

Dont drill 3mm pilot hole or increase in increments -you will end up off centre.