How to drill straight?

[BobK207]

Pat-

Great reference! Thanks for posting the link.

Now we have some guidelines about drilling holes in glulams.

As most have posted, not a great to be drilling a gulam.

I think what bothers me the most is that a gulam is an engineered & manufactured assembly. Made up of selected pieces of timber that are placed in specific regions of the beam, especially the bottom (tension) face of the beam. So from a strength point of view, the bottom face is critical. Drilling a vertical hole that removes material from a critical location

As an analogy consider a reinforced concrete beam with 4 pieces of rebar (kinda like a 4" wide glulam). The report that Pat provided says that the hole really reduces the beams effective width by 1.5x the hole diameter. In the case of A 5/8" hole this means an effective material removal of nearly 1". So it would be similar to cutting one of the 4 pieces of rebar.

Would any of us cut one piece of rebar out of 4? Probably not.

Would cutting that piece of rebar result in a major reduction in beam strength? Depends on where the cut was made.

I guess this is why so many light or fan installations on glulams use surface mount wire mould.

cheers Bob

[Red Green]

"MiamiCuse" wrote in news:acadnf1-N6u4UHPanZ2dnUVZ [e-mail]:

Drill the opposite of what you think you should. :-)

[Boden]

Yes.

[Stormin Mormon]

Buy two lengths of chain, about two foot long. Hire two helpers. Put a screw about a foot or so away from the hole, so the chains are at 12 and 3 o'clock. Let the chains dangle, they will be plumb. Have one helper at 12 o'clock, the other at 3 o'clock, guiding you. Using the chain to see if the bit is plumb.

[David Combs]

----- Same, but split up:

This screw is screwed into the bottom of the beam, facing the floor?

Beams are narrowish, so the screw will be on either one side of the hole-to-be or on the other -- ie only two possible screw-positions. Yes?

Here's the first place I get lost. The imagined clock is mounted on the bottom of the beam?

On the side of the beam?

Where does 12 o'clock point to -- the ceiling? Parallel to the ceiling?

Let the chains dangle, they will be plumb.

(Three dimensional space this stuff lies in.)

Have one helper at 12

Same question.

Is one standing in front of you, and the other out to your right?

Now, what do these helpers do?

guiding you.

Using the chain to see if the

And how does this work>?

Thanks!

David