No announcement yet.

Question About Counterbores?

  • Filter
  • Time
  • Show
Clear All
new posts

  • Question About Counterbores?

    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!


  • #2
    How about 3/32" its about .0085" over .


    • #3
      You need to predrill the pilot hole. Try a #44 drill (.086").


      • #4
        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
        Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.


        • #5
          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.
          Paul G.