How to drill straight?

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I need to drill a 5/8" diameter hole through a laminated beam that is 16" deep. This beam is sitting 10 feet above the floor across a room support part of the roof. So I will be standing on a bench drilling from below pushing the drill up.
I need this hole to be perfectly vertical as I will be passing a rod through for a ceiling fan.
I know in the past when I had to drill through something much thinner like a 2x4, I often end up with a slanted hole.
What can I do to ensure my drill is perfectly vertical?
I cannot afford to make a mistake and redrill.
Thanks,
MC
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get a drill guide; it's a base with two guide rods,and your drill chuck tightens down on the guide's own drill chuck shaft. it's adjustable for 90 deg or angles. Home Depot and Lowes will have them.
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Jim Yanik
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On 3/29/2008 3:22 PM Jim Yanik spake thus:

I second that emotion. Have one of those rigs I got 25-something years ago which has served me well in many similar situations. Not too expensive.
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also,some dowelling jigs can guide a drill bit perpendicular on a flat surface.You're limited in drill sizes,though.May be OK for a pilot hole.
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MiamiCuse wrote:

If it were me, I would drill the hole through the beam, then hang the ceiling fan from the beam and use the hole for just the wire.
In the off chance that you MUST do it like you are stating, then there isn't really an inexpensive method of making SURE that it is perfectly plumb. I would assume that you are using an auger bit. If so, then you can take a block of wood say six inches thick and, using a drill press, drill a hole straight through the block. You can then use the block as a guide for your drill bit to hold it square with the bottom of the beam.
I have also used torpedo levels to line up my auger bit, then drilled by hand, checking every so often with the level to make sure my bit is plumb. When I can't get the level on it anymore, then it will usually guide itself the rest of the way.
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Robert Allison wrote:

I wouldn't invade the beam at all- I'd build a hollow 'U' out of matching wood that fits over the beam from below, and trim out so it looks like it belongs there. If the beam is sloped, you can make it look like the added block was for purpose of giving a flat mounting point.
Hard to give good options without seeing it.
-- aem sends...
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16" is a long way to drill "perfectly straight" by hand.
I also assume you're using an auger bit (at least 18 to 24" long)
Got any of the glulam left over? Practice.
Hot gue or "affix" in some manner two framing squares at 90 deg to each other & parallel to the axis of the hole to be drilled.
Use he square to eyeball the straightness of the hole, a "spotter" is helpful
....drilling the hole a bit over sized (3/4") will give you some forgiveness
per Robert's suggestion why not just drill the hole for wiring & figure to do the mechanical mounting a different way. A 5/8" "nutplate" would do the trick.
cheers Bob
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MiamiCuse wrote:

Personally I would avoid drilling through the beam that way and would instead hang the fan along the side of the beam. If I were going to the trouble of deep drilling through the beam, I would be going large enough to feed 1/2" rigid metal conduit through to allow the power to feed through "invisibly". With a beam like that you can support a fan rated box from the beam with a couple lag screws if you're going to be routing power to the box along the beam anyway.
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On Sat, 29 Mar 2008 19:13:40 -0400, "MiamiCuse"

A perfectly made 16"-deep hole will be difficult to make, and how to keep a hand-held drill plumb and steady is another problem. Perhaps, clamp a table-top drill press to the beam and use various length 5/8" bits?
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wrote:

HD and Lowes both sell long auger-style bits,and you can even add extensions for deeper holes.

Yikes!
didn't you READ the guy's post? "So I will be standing on a bench drilling from below pushing the drill up."
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Could you make 3 sided jig?
Start with 2 vertical pieces of wood clamped to the beam.
If the beam is wider than the drill body, use filler strips below the beam. If the drill body is wider than the beam, the filler strips would go between the beam and the vertical pieces.
The idea is to sandwich the drill body so it cannot swing side to side.
Once this "channel" is in place, close off the back side with a board so you can put the back of the drill body against it to prevent back and forth movement.
If the drill can't go side to side or back and forth, your hole should be straight.
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On Sat, 29 Mar 2008 19:13:40 -0400, "MiamiCuse"

I tried to think about it. Nothing, would persuade me to drill a 5/8" hole through a 16" deep lam beam - just for a ceiling fan arrangement.
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Agree, that is why them make surface mounted boxes. .
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A 5/8" hole through a 4" wide beam reduces the load capacity by 1/4. Unless your beam is oversized you may damage it enough to cause it to fail.

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Pat wrote:

Please don't top post.
In addition, I would like to hear from the engineers in here about the validity of the above statement. I do not believe it for a minute. This is done quite often and I would be surprised to learn that it compromises the integrity of the beam. Unless you meant to say by 1/4 of 1 percent.

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Robert Allison wrote:

It depends on more information than is provided here but the load carrying capacity is decreased by AT LEAST 16% and it could be 25%. The smart thing would be to not drill this hole.
Boden, PE

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On a LAMINATED beam?
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Jim Yanik wrote:

Yes.
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Robert, I believe he's assuming that removing the hole material will reduce the effective width of the beam & thus the load carrying capacity.
I'm with Edwin & the others....drilling through the beam isn't a great idea
but the actual capacity reduction depends on the beam width, the location of the hole & whether the beam is currently bending stress, shear stress or deflection limited (which depends on the depth & span)
for a 16" deep beam, the span has to be in the vicinity of 16' or so (or greater) to be deflection limited....if the beam performance is deflection limited then a 5/8" isn't going to change the deflection performance that much. It will boost the local stresses so it should be checked to make sure the allowable stress aren't exceeded.
cheers Bob
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BobK207 wrote:

Thanks, I was having nightmares about the dozens of beams that I have either drilled holes through, or seen holes drilled through. But then, almost all of my jobs have required an engineer to write a letter for all of the oddities that the city just can't stand to pass without professional opinions on paper. I think my PEs would have mentioned something if I were compromising loaded beams by as much as 25%.
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