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Reply by conifur

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Posted on Drilling holes precisely

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conifur

955 posts in 1354 days


#1 posted 04-30-2016 04:08 AM



Winters45,

I am not sure what could cause a perfectly aligned drill press to drill non-perpendicular holes. Some pure guesses are the drill bit is flexing as it drives into the wood, the drill press column is flexing (unlikely but possible), or the bit is wondering as it drills. Using a sharp bit and slow feed rate could reduce any flex, if any of my guesses are correct. And I agree, a Brad point bit or Forstner bit would help keep the bit from wondering.

I assume that the table was found perpendicular to the drill bit by using an engineer’s square set on the table and against a drill bit or true rod. This method of determining square may have enough undetectable imprecision to lead one to believe that a non-square hole problem is attributable to something other than alignment. Another method could be tried, which measures directly whether the table is perpendicular to the bit. The direct measurement method eliminates any undetected errors that may exist in the engineer’s square, steel rod, and any other things used to check for square.

This could be done with a thick block of wood (2-1/2” minimum), perhaps 12” long (the longer the better) that sets absolutely flat on the drill press table. Drill a hole deep with a ½” diameter bit into the block of wood at one end while keeping the wood firmly flat on the drill press table using a slow feed rate. Once the hole is drilled, turn off the drill press while the drill bit remains in the just drilled hole. When the bit has stopped spinning, raise the bit with block of wood still engaged on the bit just enough so the drill bit and block of wood can be rotated together on the bit by 180 degrees. In this position, lower the drill bit and the block of wood until the block of wood contacts the table. Any daylight under the block of wood, between the block of wood and the table reveals the table and bit are out of square. Then, spinning the bit and block of wood together 90 degrees checks the front to back alignment.

Jack Forsberg s method also looks like pretty good way to check for/confirm square. However the table must be flat and smooth, at least wherever the dial indicator measurements are taken.

- JBrow


-- Knowledge and experience equals Wisdom, Michael Frankowski


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