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Old 05-30-2017, 09:22 AM   #1
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Default Which size Core bit for octagon box

I have been using a 1/8 bit to drill into brick, outlining the box with small holes with great success.
Now I've been asked to add additional octagon boxes for security lighting to the side of some row townhouses. I have to add 8 in total.

Do you guys normally use 4" or 4-1/4" for core bits to fit octagon boxes?

I know 4-1/8" is perfect for fitting an octagon into drywall but with the vibration of the bigger drill, I'm wondering if a 4" core bit will actually make a better fitting hole.
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Old 05-30-2017, 09:34 AM   #2
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Go 4 1/4. The fixture will cover it up. Verify first so you can sleep at night .
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Old 05-30-2017, 09:38 AM   #3
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Trace the box, score it with a diamond blade angle grinder, smash it with a hammer.
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Old 05-30-2017, 10:54 AM   #4
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If you want to be a tightwad, the 4" bit is also good for 3.5" conduit (rigid and EMT - both same size! look it up if you don't believe me )

I don't know if you'd ever care about that, it would be of value for me. I don't work on big service laterals or etc. but I use that for wall and floor penetrations for big bundles of cable.

Of course if you have to do octagon boxes again maybe you'd rather have the exact right bit.

How much slop you'll get when drilling really depends on the concrete, and the bit. A dry diamond core bit in block makes a nice clean hole in seconds, no slop. A percussion core bit in mushy basement concrete with big aggregate is sloppy.

If you mark your spot and make 3/8" holes at the corners before you drill with the 4" bit, I bet you could get a really perfect fit.

If you don't get a perfect fit, you could scrap one octagon box, turn it over and smash it face first into the hole with a hammer. Putting square pegs in round holes is the mark of a man. (Some dweeb came up with a SDS hammer bit that works this way, drives a box shaped bit through the concrete.)
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Old 05-30-2017, 11:06 AM   #5
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If you want to be a tightwad, the 4" bit is also good for 3.5" conduit (rigid and EMT - both same size! look it up if you don't believe me )

I don't know if you'd ever care about that, it would be of value for me. I don't work on big service laterals or etc. but I use that for wall and floor penetrations for big bundles of cable.

Of course if you have to do octagon boxes again maybe you'd rather have the exact right bit.

How much slop you'll get when drilling really depends on the concrete, and the bit. A dry diamond core bit in block makes a nice clean hole in seconds, no slop. A percussion core bit in mushy basement concrete with big aggregate is sloppy.

If you mark your spot and make 3/8" holes at the corners before you drill with the 4" bit, I bet you could get a really perfect fit.

If you don't get a perfect fit, you could scrap one octagon box, turn it over and smash it face first into the hole with a hammer. Putting square pegs in round holes is the mark of a man. (Some dweeb came up with a SDS hammer bit that works this way, drives a box shaped bit through the concrete.)
Normally I see eye to eye with you but the bit for box hole si think is great if you need to do a series of them on one job, it would save time and make a good fitting recess.

Would I buy it for an every now and then single hole, nope!
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Old 05-30-2017, 01:24 PM   #6
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Rent a SDS hammer drill with a 4" bit. I would never waste my time with a small bit and outlining anything. If you are worried about the bit drifting first, drill a 1/4" pilot hole in the centre and use that for the core pilot bit.

It will be slightly larger then the box, which then you can mortar in place; done it a million times (well maybe not a million times, but enough that it feels like a million).

Cheers
John
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Old 05-30-2017, 02:21 PM   #7
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I'd never tool up for such a rare penetration.

I'd go with a right-angle grinder -- which is nearly a universal tool -- and which I can control like a wand.
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Old 05-30-2017, 02:27 PM   #8
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If it is likely to be exposed finished work, I roto zip it using a tile bit. If it is going to get plastered over with stoe or something like that then I use a diamond blade in my mini grinder and cut a ton of slice cuts and break those out with a screwdriver and hammer after. Then I mix up some fast healing cement mixed with plaster of paris , or just by quickcrete and seal it all in if it needs a bandaid before the finish guys get to it.
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Old 05-30-2017, 02:31 PM   #9
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There is nothing wrong with making the hole bigger.

Drill the hole with a 4 1/4" bit.
Tapcon the box to the brick or throw a spacer behind it and screw into the sheathing behind the box.
Install the light with the canopy that will cover it all.
Profit.
Sit down and eat your bacon sammie while watching the other guys play around with rotozips and angle grinders.
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Old 05-30-2017, 02:34 PM   #10
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With all due respect to you guys that like the grinders and that type thing, those methods really sound labor intensive and time consuming.

How much depth can you get off an angle grinder? Maybe 1 1/8" max?

Getting paid by the hour is one thing but if it was my dime I'd use the core bit I have or rent the right size.

In soft brick I've drilled out the majority with the largest corebit possible and then a chisel in a demo hammer to clean the edges up.
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Old 05-30-2017, 04:25 PM   #11
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With all due respect to you guys that like the grinders and that type thing, those methods really sound labor intensive and time consuming.

How much depth can you get off an angle grinder? Maybe 1 1/8" max?

Getting paid by the hour is one thing but if it was my dime I'd use the core bit I have or rent the right size.

In soft brick I've drilled out the majority with the largest corebit possible and then a chisel in a demo hammer to clean the edges up.
I can't remember the last time I faced something like this.

Around here, this would be a very odd-ball task.

I'd shift gears, and attitude, if I ran into this all the time.

I'm insanely over-tooled as it is.
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Old 05-30-2017, 04:39 PM   #12
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I like diamond bits and core drills, because of the smooth cut. But there is always a right tool and a wrong one for the job. There's also a million kinds of brick, concrete, stucco, marble, etc. A hard glazed brick can chip or shatter if you use a hammer drill. Whatever works quicker, cuts fast, does not damage the finish, and pays for itself quickly is the tool I'd use.

your results may vary
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Old 05-30-2017, 06:44 PM   #13
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The grinder just scores the surface so the other brick doesn't chip. Once it's scored either chisel it with a hammer drill, or smash it with an American made Estwing. I do it all the time, maybe twice a month. Someone always wants outlets and lights added on brick exterior.
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Old 05-30-2017, 09:22 PM   #14
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The grinder just scores the surface so the other brick doesn't chip. Once it's scored either chisel it with a hammer drill, or smash it with an American made Estwing. I do it all the time, maybe twice a month. Someone always wants outlets and lights added on brick exterior.
Get er done!
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Old 05-30-2017, 10:19 PM   #15
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The grinder just scores the surface so the other brick doesn't chip. Once it's scored either chisel it with a hammer drill, or smash it with an American made Estwing. I do it all the time, maybe twice a month. Someone always wants outlets and lights added on brick exterior.
Estwings are durn good hammers.
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Old 05-31-2017, 08:06 AM   #16
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Estwings are durn good hammers.
I don't think there are other hammers. Anything but an Estwing might as well be a rock tied to a stick.
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Old 05-31-2017, 08:27 AM   #17
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I don't think there are other hammers. Anything but an Estwing might as well be a rock tied to a stick.
And made in the USA. When I buy an Estwing, I support my American brothers, sisters and everything in between .
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Old 05-31-2017, 09:01 AM   #18
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And made in the USA. When I buy an Estwing, I support my American brothers, sisters and everything in between .
And we know you had choices, and you chose us.
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Old 05-31-2017, 09:06 AM   #19
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And we know you had choices, and you chose us.
Keep this up and you're going to bring a tear to my eye .
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