Drill Troubleshooting Guide


The number one cause of ruining a drill bit is to over-speed and underfeed the tool.  This causes excessive heat at the cutting edge, prematurely dulling the drill.  Our drills are designed for heavier feed rates.  The larger the bit, the slower the drill should turn.   Because of all the variables such as type of material being drilled, size of the hole being drilled, type of drill being used, there is no single speed any given drill should be run at.  In addition, a drill bits desired speed and feed rate can hardly be applied to a variable-speed hand held drill motor, as opposed to a drill press, with given speeds and an automatic down-feed.  It all comes down to experience.  With that said, here is a very generalized rule of thumb for drill bit speeds:

  • 1/16" - 1/8"...1200-900 rpms (occasionally faster is required)

  • 3/16" - 1/4"...900-450 rpms

  • 5/16" - 3/8"...500-350 rpms

  • 7/16" - 1/2"...375-250 rpms

  • 9/16" - 1"...300-75 rpms (and at times even slower)

ALWAYS use cutting oil or fluid

The life of any drill bit will be extended by two to five times by using a quality cutting oil or fluid.  Motor oil, hydraulic oil, transmission fluid, WD-40, water, etc. is NOT a proper substitute.  Want some motor oil on your salad?  How about changing the oil in your car by adding vegetable oil?  See, there IS a difference! Check out our DRILL DROOL on the product list.

Pilot Holes

Although 135 degree split-tip drills do not require a pilot hole, it's always easier to drill a larger hole when a smaller hole is already there.  The rule of thumb here is the pilot hole diameter should never be larger than 1/2 the finished diameter.

Chipping and breaking

Chipped drill bits are usually caused by the following mistakes:  Enlarging a hole. When enlarging a pre-existing hole using a drill bit, the hole should be 1/2 the size or less.  Example:  for a 1/2" hole, the pilot or pre-existing hole should be 1/4" or less.

Do not allow the flutes of a drill to become choked with chips.  Rule of thumb:  When drilling deeper than 4 times the diameter, the drill should be backed out and the chips cleared away.

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