Help with choosing counterbores.

[knifer-one]

I am looking for counterbores that have a pilot hole for inserting a drill bit. Do these come in sets or individual? I have some of the standard type where you first drill and then counterbore. I would like something that would work in 1 pass.

 

[Tony Wells]

Most counterboring tools have a small shank smooth pilot that fits in the hole in the end of the body. This will restrict the size you are drilling to that size. I don't know that they make a 2 piece tool like you mention. It's common in toolrooms to grind a full size twist drill down to the desire pilot hole, with a shoulder sharpened to cut the counterbore. I've done a few by hand and they work pretty well.

 

[churchjw]

I have a small set and I find its better just to regrind a drill bit like Tony said or use an end mill. The tools with the pilot never seam to have the right size pilot for the hole I am using it on.

Jeff

 

[george wilson]

You could make a stepped pilot,as long as the stepped part is LARGER than the hole in the counterbore. Too small,and there will be an area where the counterbore has no teeth to cut. Example: You have a counterbore with a 1/4" hole. You could make a pilot that has a 1/4" part to go into the hole,and a 5/16" part to fit the pilot hole,etc.. Doesn't need to be hardened to do a short run of holes.