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thefatpigeon 04-13-2010 08:35 PM

method for precision hammerdrilling?
I was just wondering if anyone had some tips on drilling precise holes into concrete. I mark dead centre where i need to drill but the drill bit doesnt seem to stay on my point.

Daniel Holzman 04-13-2010 10:04 PM

The problem with concrete drilling is that the bit is often not too sharp, so it wanders. Start with a new, carbide tipped bit, use a hammer drill, and use a center punch to start a small hole. Should work better. But don't expect perfection, unfortunately the bit will walk a bit, especially if you hit a hard piece of stone in the concrete.

For real precision work, use a 38 ramset or a 22 ramset to install pins.

thefatpigeon 04-13-2010 10:15 PM

its a 7/16 inch hole for a 3/8 inch drop in anchor in a concrete housekeeping pad. the fixture has for holes in it. 3 lined up nice but the fourth needed to be reamed out with a step bit to allow the bolt to line up. doesn't look very nice. I will try making a pilot hole of sorts using the punch. used to hold a 112.5 kva transformer so using ramset wont work.

Giles 04-13-2010 10:37 PM

If I wanted a precision located hole drilled in concrete, I would first drill a smaller hole in a piece of 1/4 metal and secure it to the concrete by standing on it. Use this as a pilot guide.
I have done this many times and if I want to be "dead on" I drill the desired finish hole in the metal and finish drilling.
Securing to prevent movement is sometimes the problem.

PaliBob 04-13-2010 10:55 PM

Thanks for the hole in a plate tip
sounds good

thefatpigeon 04-14-2010 05:54 PM

ya i was thinking on making a template too since i have 7 more to install.

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