How to Grind a Boring Bar

Written by sean lancaster
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How to Grind a Boring Bar
Turn your broken and dull drill bits into boring bars. (Jupiterimages/liquidlibrary/Getty Images)

Those who work in their home machine shop are always looking for methods to reduce the high cost tools. A weekend machinist can fabricate many tools for use on the machines if they are willing to spend the time required. Cutting tools used by a metal lathe are expensive if purchased from a machine supply company but the machinist can grind his own at home for a fraction of the cost. Boring bars are vital tools that allow the machinist to hollow out or remove large amounts of metal from the inside of an item on the lathe. You can make your own boring bar in your shop using scrap tools that have broken or become dull.

Skill level:

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Things you need

  • Broken or dull twist drill
  • Grinder
  • Sharpening hone

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  1. 1

    Select a broken or dull twist drill bit that is smaller than the hole you need the boring bar to work inside. You can make a number of boring bars that vary in size from large to small. Each one will be capable of boring a limited range of holes.

  2. 2

    Grind the bottom third of the drill bit flat when looking at it lying horizontally. The flat portion of the drill bit needs only to extend 2 inches from the tip of the cutting edge. Remove some of the flutes beneath and behind the cutting point of the drill. This is the relief cut for the bottom of the cutting tip of the boring bar.

  3. 3

    Sharpen the cutting tip of the drill bit using a small hone. The manufacturing of the tip provides the relief angle pre-cut thus requiring no further grinding. Due to the reduced tensile strength of the bit because part of the shaft was ground away, avoid taking deep cuts with the boring bar. If you need to cut a flat bottom hole, the boring bar will require reshaping of the bottom of the drill tip to generate a flat bottom profile.

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