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How to Precisely Drill Holes without Precision Equipment May 1, 2009

Posted by Ruzter in Assembly, Fabrication.

Tools needed:

  • Jiffy Marker
  • Micrometer (ok, this is a precise but affordable tool)
  • Square
  • Scribe
  • Centre Punch

Here is a fairly typical way I build a part:

1) Draw an area about centre on the piece of metal to be drilled

2) Using a square and a scribe, scribe a line roughly center of the piece. I leave some room so I can mill the end off later. Colouring with marker makes the scribed line show up much better.


3) Color again, but measure how far the holes are from the top edge. Gently drag the micrometer along the edge, scribing the coloured area. You would think this wouldn’t work very well, but it really does and I haven’t had problems with the line being too close to the top because the micrometer wasn’t square


4) Use center line to scribe distance of hole from center along the horizontal line you just made.

5) Centre punch


6)Repeat for all the holes


7) Drill small pilot holes. It is amazing how much even a 1/8 inch bit can wander on a press drill even if it is centre punched. Mind you I have fairly tight tolerances.


8 ) Cut to length and take off the sharp edges.



9)Clamp to a 2nd piece and drill the second one.



10) Test fit the pieces. If one or more holes don’t line up perfectly, drill out the hole to a slightly larger size. This is where my 200 piece drill bit set comes in very handy!


At this point, it is time to realize that you measured two of the holes wrong and you have to decide to start over or modify the part that was suppose to bolt on… 😉

11) Later I will mill the edges square in my cross-slide and drill press setup.



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