Any tips or techniques on drilling bolt holes thru glu lams thru heavy steel glb hangers with glu lams in place. I can never seem to drill straight enough to get the pre drilled holes on each side of the to match with the hole I drill through the glu lam.
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I like to drill halfway thru both sides. I seem to drill straighter that way. I also drill the hole a little bigger than the bolt, if allowed, to help with lining up the hangers.
My favorite ones are the knife plates that go up inside a 16" log post.
Have fun, Dave
Some folks have a knack for this and do quite well. Others will never get it right. I'm in between. After working with foks who couldn't drill straight, I tried it and analyzed what I must be doing for the holes to come out repeatedly just a little bit off. It came down to 1) making the extra effort to position myself properly so that I could comfortably achieve the necessary lineup, 2) using a sharp bit so that I would not have to give up concentration on position to increase pressure, and 3) thinking about what was wrong with my approach each time the hole was not accurate. If these things don't do it for you, you might consider getting a different drill, one that has a different feel to it. If you don't have too many holes to drill, an air drill often is much smaller and easier to line up close to obstructions. Unless you have a lot of compressor, this can be a slow way to drill, but it is very controllable.
If Im worried about the holes on either side of the board lineing (sp?) up, I will do what Dave does and drill from both sides of the board. Its not that Im more accurate that way, its that in any bit of an angle that I am off drilling , the two holes should still meet up together in the middle ( does that make sense, picture would make things so much more clear).
Two other tips I can think of is to start off with a much small bit and just drill all the way through. That way you can see if your holes line up. If they are off, you can try compensating when you drill through with your actual size bit. If your holes line up, now you've got a nice guide hole. You can also try using a longer bit or bit extender, that way any movement of your drill from perpindicular will be that much more noticeable ( bit is 3" long, move 1/16" from perpindicular wouild be ~1.2 degrees, if bit is 6" long, move 1/16" from perpindicular, would be 0.6 degrees).
Of course, these are hangers, so even if one did drill perfectly perpindicular through the glulam doesnt mean that your going to end up on the hole on the other side of the hanger.
-m2akita
I have an old drill dedicated to being hooked up to one of those
small drill press frames. It will also drill at angles.
I've seen people hold a square (speed square would probably work) next to the drill to help make the holes perpendicular--depends how much room you have.
I had a job in which my carpenters needed to drill hundreds of 7/8" dia. bolts 17" long into 4X10's scabbed on either side of beams. Many of these holes needed to line up with 1/4" reinforcing plates on either side. In starting the hole they used speed squares of align the drill bit as the started the holes. After several inches the squares were no longer needed. This was a two-man proposition, one man drilling & the other man holding the squares.
This technique is used by boat builders whenever "precise" drilling on board the boat was required.
butch
Why not make up a few plywood frames, say 3" and 6" tall that will hold your bit square? You could put some busings in to really make it smooth.
Jon Blakemore