I drilled about a 2" through hole with a brand new replacable carbide tip drill. The tip is .476. I can slip a .472 gage pin (all I need) in either end of the hole and slide it through most of the way from either side. But I can't slide it all the way through from either side. Drill tip looks OK.
So...my theory is what's happening is the same sort of thing that happens when you wring gage blocks together.
1. Air pressure from the surrounding environment is locking the pin up in the center of the hole as the air between the pin and the through hole is squeezed out.
2. Surface tension from coolant or water vapor is "gluing" the pin and the surface of the hole together.
3. When two very flat surfaces are brought into such close contact with each other, an interchange of electrons between the atoms of the seperate surfaces creates an attractive molecular force.
Got all those from a Starrett web page about gage blocks months ago.
I had to rule out the theory that my drill is drilling larger on both ends and smaller in the center for obvious reasons.
Anyone ever experience this weird behavior before?
I'm drilling cast, and the drill has high pressure through coolant.