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  • how to test for drillpress run-out

    My method is not very scientific - I usually measure the bit diameter with a steel rule, drill a hole in a test piece, and measure the hole's diameter. I know that it is impossible for a drill bit to drill an exact hole the size of a bit, but what is an acceptable tolerance and how do I calculate it more accuratley?

  • #2
    Re: how to test for drillpress run-out

    To get more accurate, use calipers to measure the bit and hole. Also, do several size bits, from 1/8" or smallest chuck will hold, to the largest the chuck will hold (or that you have). Realize the run out may be more pronounced the further the quill is extended. Drill bits should be within a couple thousandths of the stated size.

    Putting a dial indicator on the smooth part of the drill's shank is a better method (a forstner bit works well for this). Slight force to the side (not running) will give you some indication of the play in the quill (again, probably most severe at full extension), and variation in the indicator needle by turning the bit by moving the pulley on top will give you the run-out. (Turning the bit by pulling on the pulley belt will eliminate you inducing any side force). Using a couple different bits will take any bit variations out of it.

    If you have a cheap drill (16" floor model Hitachi) with slop in the quill (as I have), you will get better quality holes using forstner bits when possible, as they tend to follow the hole easier and don't cut on the side as easily. Brad points with the edge tang would be the second choice. I also use an awl or center punch to start the hole, so the bit doesn't try to wander when first starting the hole.

    Using the method stated above I have 0.013" runout and can get about 0.004" side play with the quill up and about 0.007" side play with the quill all the way extended. It works fine for most of what I do. Changing the chuck or reseating the tapered shaft could make it worse or better, but I never saw the need to measure it before you asked.

    Go
    Practicing at practical wood working

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    • #3
      Re: how to test for drillpress run-out

      Thanks for your detailed reply Go! I'll give your method a try!

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