Drilling really large holes - how?

[Curlycherry]

I did it on a 10" thick piece of cherry with a 6" hole saw. 10" x 10" by 8' piece of wood (read HEAVY).  The holes had to be nice and finished and round on each side. No rat chewing allowed.

I held it up to my drill press with a floor jack and set it on jack stands. I used a 6" hole saw on the drill press to drill, slowly and carefully into the wood. Getting started is semi-difficult, but once the hole saw is into the wood ~1/4" it goes well.  When I got to the depth of the hole saw I pulled it out and chiseled the wood out of the center of the hole. I raised the log ~1.5" and carefully aligned it with the hole and cut another depth of the hole saw. Using this method I got about 7" into the log. Pulling the dust out with a shop vac while drilling helps prevent burning, catching of the hole saw and saw wandering.

Then I used a pilot drill the diameter of the one on the hole saw to drill down and out the other side of the log as a marker. I flipped the log and repeated cutting with the hole saw from the other side. Everything matched up perfectly and I had a perfect 6" tunnel through the log. I ended up doing 2 of them for a mantle.

Depending on the depth of the drill press stroke, you might be able to get further than 7" in from one side. That was all I could reach with mine.

[opticsguy]

OP here once again.  Thanks for the continued interest in this subject.
I had recently been boring up to 4" diameter holes in wood about 4" deep which got me interested and motivated to explore possibilities of larger holes in even larger wood. 
So far the recommendation of a masonry drill and bit set up looks like to the most feasible tool.
I see this one here which is a big investment for a home hobbyist but certainly worth exploring in the used or rental market. 
Investment in these machines are around $1,000 to $4,000 and more. 

http://www.csunitec.com/drills/diamond-c...ic/dbe-160

[Steve N]

I thought I had replied here, but don't see it. Someone else must have asked pretty much the same question in the last year. I would go to the local rental place and get a core drill. They are the gizmos that bore through poured concrete walls for utilities to run through. I have cored 8" diameter, but understand there are bigger cores than that. Depth isn't usually an issue as they are mounted on a ram arm, which gives a lot of movement, and most bits I have seen are around 12" long. The core drills are often mounted on a wall, but many are able to drill straight down, and if you had choice at the rental place I'd go that route. Put your wood on the ground, over at least 2" of another piece of wood, pile of plywood, whatever so you don't have problems with blow out. Concrete doesn't blow out, wood often does. Your only challenge is figuring how to clamp it so the action of the drill doesn't start the wood spinning. That isn't hard, but each length, width may have different solutions.

Core drill



Bit end. As crude as the cutting end is, they make surprisingly smooth holes, entry is clean, exit is the issue, but if you back the wood with a solid base under it, exit of your primary piece will be good.




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