Announcement

Collapse
No announcement yet.

formula for pilot holes

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16
    My formula is use a split point drill.

    Comment


    • #17
      Originally posted by wdtom44 View Post
      Drilling large holes with a hand drill is always a touchy thing. It is easy for the drill to grab if you don't hold it perfectly straight, especially one break through. Have a solid death grip on the drill with both hands and try to do it in a way you can still let go of the trigger instantly. Some set up the job so the cord is pulled tight in such a way if they start moving as when the drill starts to wind your wrist up it pulls the cord out of the wall.
      "Dubbing" or grinding the rake angle to zero can be very helpful trick if you need to enlarge existing holes. I have one cheap set that I have "dubbed"
      http://www.practicalmachinist.com/vb...l-bits-183967/
      Location: Helsinki, Finland, Europe

      Comment


      • #18
        Wow even thinking about it is way over the top. Start everything with a 1/8 so you don't have to prat around looking for some special size. I have a spare little drill press set up permanently with a small drill. Saves time and is a use for a small press that is too small for general work.

        Comment


        • #19
          Originally posted by MattiJ View Post
          = drill web diameter
          Spot on - only slightly more or the same as the web on the finish drill size, usually in two steps - pilot then finish.
          If it does'nt fit, hit it.
          https://ddmetalproducts.co.uk
          http://www.davekearley.co.uk

          Comment


          • #20
            I was also taught to use a pilot drill slightly bigger than web thickness, as the centre chisel point doesn't cut.

            But since that advice came out, split point drills were invented. These seem to cut all the way to the centre, and I'm now in the habit of skipping the pilot drill (when I have a full size split point available). It seems to work fine for me, certainly up to 13mm.

            Ian
            All of the gear, no idea...

            Comment


            • #21
              Wow! 2 pages of comments when we were all pretty much in agreement from the start that the pilot should be the size of the web on the main drill, or just a little larger.
              This probably doesn't apply to you guys in the US who all seem to have massive equipment (read that how you will), but even with split point drills, I tend to pilot with one or even 2 sizes when using a large (thats 1" plus to me) drill, just to reduce the power needed with the big drill. I still leave plenty to take out, to avoid grabbing. For a 1" hole, I'd probably use 3/16", followed by 1/2" followed by 63/64" or 1", depending if I was going to ream or not.
              'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

              Comment

              Working...
              X