Centered Drilling in Pole End Grain
Thoughts on how to drill centered, matching holes in the end of poles so the poles can be connected end to end. March 26, 2009
Question
I'm making some wood flag poles that need to be collapsible. Each 8' long by 1 1/4" diameter pole will be cut in half and a 3/8" threaded metal insert needs to be inserted in one end, 3/8" hanger bolt on other end.
My question is: how do I drill a straight, perfectly centered hole in the ends of the poles? I'll have to drill a 1/2" diameter by 1" depth hole for one end and pilot drill about a 5/16" by 2" depth hole for the other end. I may have to do a lot of these so I am willing to set up a jig. I also have a horizontal slot mortising machine so maybe this could be used.
Any ideas?
Forum Responses
(Architectural Woodworking Forum)
From contributor L:
The easiest and most efficient way would be a lathe. If you have a horizontal borer that is capable of using the bit you require then you can set up a jig using a piece of wood with two intersecting 45* angles cut out of it to form a 90* groove in the board. The dowel will rest in this groove and be self centering. You just need to get the height and left to right correct and then you could bore perfect holes all day long.
From contributor J:
Have you done a test model to determine whether this design is strong enough? A 1" deep anchor in endgrain doesn't sound like much.
From the original questioner:
The "flagpoles" are actually going to be posts for a "chuppah" used in Jewish wedding ceremonies. I just called them flagpoles for the posting. There won't be much lateral forces on the poles so I thought 3/8" threaded inserts would be sufficient for this application. I'm having trouble finding anything longer than 5/8" depth for the threaded inserts. No, I haven't done a test model but wanted to get the boring down so everything lines up after.
From contributor C:
If not a lathe, then a fixture has to be built to hold the pieces, either on a drill press or for use with a hand drill. Properly done, a fixture would allow all the pieces to be drilled identically.
From contributor B:
I vote for the lathe. Fixed pole and spinning bit. You might want to consider a slight chamfer on the ends of both sections where they will meet. No matter how accurate the drilling you will not achieve an absolutely perfect match of the two ends coming together. The chamfer will disguise minor misalignment.
From contributor J:
You could take double 2 x material, get a 1 1/4 hole saw and drill a pocket. The hole saw will have a 1/4" pilot bit which will center on the bit, you than can put the end of the poles into that socket and drill them. Either use the 1/4 as a pilot or enlarge it to the diameter you need.
From the original questioner:
Thanks for the suggestions. I found a Newell post-centering device that kind of looks something like what contributor J suggested. I will try to duplicate using my own hole saw but think that I will still have to set up a jig on the mortising machine. To take care of the shallowness of the threaded insert depth and instability issue, I thought I could bore twice as deep and insert two inserts, making the depth about 2" instead of 3/4". Thanks for all the help!
