View Full Version : Question About Counterbores?

02-15-2004, 02:39 PM
I have never used or seen one of these up close and have question about this type of counterbore. With the type indentified in the link below, will I need to use a drill bit to drill a hole for the pilot on the counterbore to fit in or does the pilot on the counterbore act as a drill? I have been using a special HSS step drill with a cutting .093 head and a cutting .156 body. These are quite expensive at $17 a piece and I was looking for and alternative. This model and size of counterbore would work perfectly. I am just not sure of the pilot section of it. If it does not cut, then where would someone find the exact size .085 drill for it? Thanks for any help!


02-15-2004, 03:23 PM
How about 3/32" its about .0085" over .

02-15-2004, 05:16 PM
You need to predrill the pilot hole. Try a #44 drill (.086").

Spin Doctor
02-15-2004, 09:51 PM
I've got a set of these at work alongwith the #screw c'sinks. Available from Do-All. Can't think of the brand right now but top notch tooling. But you do have to have the right size pilot drill unless working in the mill

Paul Gauthier
02-16-2004, 01:55 AM
Normaly one drills a hole first. If the counterbore pilot is 3/32" dia. or .0937" one should use a of same dia drill. I have not seen couterbore pilots that also cut the pilot hole, perhaps because counterbores are normaly shallow to accomidate bolt or screw heads, but they are certainly possible in a given situation.

Paul G.