[martinw]

Dear Steve,

....there are better men than me hereabouts.

Best wishes,

Martin

Dear Steve,

I told you so!

Best wishes.
Martin

[little bubba]

AAAAAAHHHHHHHHHHHHHHH!!!!!!!!!!!!!!!!!

I keep seeing the word "center drill", its a cross hole, you spot spot spot. Center drills are used for putting in centers for turning in a lathe, nothing more, EVER.

If you have a very large center drill, you can use the very end for "spotting". Drills get really cranky going into a 60 degree included angle and can wander off by quite a bit. Try it sometime, two holes "spotted", and two holes "center drilled". throw it up on an angle plate on the granite plate, the "spotted" holes will be much closer to where they are susposed to be than the "center drilled" holes. This assumes that people are using center drills as "center"drills and going up into the 60 degree included angle.

[brian1030]

I have found that using a spot drill with the same included angle as your drill
helps out not only with accuracy, but drills last much longer. I have found that making my own spot drills out of solid carbide on my deckel (tool and cutter grinder) is the best and most economical for me.

[dapoling]

I have a different view point on the issue of never using a center drill for other then a lathe.

While I prefer a spot drill I have never had a problem with a using a center drill to accurately locate or damage drills.

A job I did just a while back had to drill a .125 dia through a part with 14 thin legs that spanned 14 inches and had to be within .005 true position and it worked out just fine.

The majority of the holes center drilled that require an amount of accuracy are most often bored.

The main reason for having a starting hole either it be from a center or spot drill is to provide a start for the web of the drill as the web does not cut or cut efficiently after being thinned.

In this situation the center drill can be off a little as a boring endmill will clean it up from any wandering that a drill will do.