Red Eye Garage Tip #9 - How to Increase Drill Accuracy August 24 2018, 3 Comments
When drilling a hole with a large bit in a drill press, it can be difficult to line up the drill bit accurately. The larger the bit, the harder it is for your eye to precisely find the center of the bit. Center punching is a good way to increase drilling accuracy because the divot guides the drill bit and prevents it from walking while it is starting. However, it is less effective with larger drill bits because the tiny divot is trying to guide a much larger drill bit. It's like trying to stop a monster truck from rolling using a standard-sized wheel chock. It's not very effective because the chock is so small in comparison to the wheel.
It is hard to tell if the bit is perfectly centered.
One technique that I often use, when higher tolerances are required (short of using a mill), is to chuck up a pointy rod to aim the drill press at my drilling mark. I then clamp the workpiece, swap in my drill bit and drill the hole. As long as everything stays in alignment, you should have an accurate hole. I use a sharpened tungsten rod from my TIG welding kit, but a pen, scribe or center punch would work too. The skinnier, pointier and straighter the pointer, the more accurate the results.