International Association of Penturners - View Single Post - Drilling Holes in Blanks
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Old 08-12-2017, 12:47 PM   #4 (permalink)
KenV
 
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Join Date: Oct 2005
Location: Juneau, Alaska.
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A sharp well ground drill bit really really wants to center on a rotating object. For small bits and not very deep holes a hand held handle with a drill bit drills centered holes very nicely.

As size increases and depth increases the torque to hand hold becomes excessive and mechanical aid of the tailstock comes into play. The bit still wants to center, and the trick becomes one of getting the tailstock rams and drill bit holder lined up with center of rotation. (Note that physical center of the blank and center of rotation are often not quite the same.)

It helps a lot if the drill bit is close to parallel or right on the centerline of rotation.

One of my lathes does not hit center nor stay aligned with center line of roation unless I carefully push the tailstock against the back of the bed.

Crud in morse tapers, dings on arbor tapers, etc helps get the alignment off.

I test by using "unph" to push the loose tailstock forward to make light contact with the blank and drill bit (blank turning at low speed) to see if self centering is happening.

Bit first be sure you have a really sharp drill bit and have marked the center of rotation.
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Ken Vaughan
Old Apprentice Machinist - Back in Alaska
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