Drilling a very large hole.

opticsguy · February 04, 2025, 04:02:25 PM

First question:
I am in the design stage of a project. Curious about how to drill an 8 inch diameter hole into end-grain wood, about 12 inches deep.

Suggestions using modern equipment and also, how might this have been accomplished 120 years ago?

Second question, how to make an 8 inch diameter "dowel" to fit inside the hole? This part would be carved out on the end of a log and could not be made on a lathe.

Thank you.

Big_eddy · February 04, 2025, 05:35:22 PM

Second question - hand saw to rough shape and finish with a draw knife

Ljohnsaw · February 04, 2025, 05:48:12 PM

I'd say find a longer log so you don't have to splice one together. 😜

Resonator · February 04, 2025, 06:49:42 PM

Quotehow might this have been accomplished 120 years ago?

Guessing these would be for water pipes. Either with an auger bit with a wood T handle turned by hand, or a bit driven by a water wheel or steam engine in a mill. For the bigger diameter pipes they would have built "penstocks". Which were a continuous tube built like a barrel, out of wooden staves banded together.

GAB · February 04, 2025, 07:50:15 PM

Quote from: opticsguy on February 04, 2025, 04:02:25 PMCurious about how to drill an 8 inch diameter hole into end-grain wood, about 12 inches deep.

If someone is stealing your firewood you do not need a hole and dowel that big.
GAB

Old Greenhorn · February 04, 2025, 09:10:00 PM

So if I understand this, you want to bore an 8" hole 12" deep then make a 8" dowel to fill the hole back up? Why not just draw a 8" diameter circle on the end of the log and tell folks that you did it.

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But seriously, what are you trying to make or accomplish? There may be another approach that would work as well or better.

aigheadish · February 05, 2025, 07:12:55 AM

I am interested in this! I'm sure if it was a project I did I'd make it as complicated as possible. My mind takes me to the largest forstner bit and the beefiest drill you can find/handle, drilling out, basically, the center of the hole, but dirty, then coming in behind with chisels or maybe bowl gouges to clean up the walls.

fluidpowerpro · February 05, 2025, 01:25:07 PM

I would find someone with a big metal lathe and use a boring bar.

scsmith42 · February 06, 2025, 10:41:16 AM

My answer would depend upon what skills you have to fabricate something.

One option would be to make a boring bit out of an 8" od pipe. Basically a giant hole saw. You can drill a few inches, and then use pry-bars to break out the center wood slug, and then continue a couple of more inches.

Another option - if you have machine shop equipment available - would be to fabricate some type of Forstner bit.

You can also see about renting / buying some type of concrete core drilling bit.

With any of these options, you will most likely need a Hilti style drill or at least a 3/4" heavy duty corded gear reduction drill in order to power the bit.

Big_eddy · February 06, 2025, 12:57:15 PM

120 years ago, the hole drilling answer was probably a chisel and a hammer.

Still interested in what you are trying to accomplish. Unless the one part is to rotate on the other, a more typical approach would be a scarf joint or mortise and tenon

sprucebunny · February 06, 2025, 03:45:56 PM

Ya !!! Watcha making ???

arojay · February 06, 2025, 09:48:24 PM

Chainsaw!!!

You might have to practice a bit on some 'non critical' logs. A half dozen or so boring cuts, break out the waste and a bit of careful trimming. I've bored out squares to make wolverine trap boxes for a trapper friend.

Brad_bb · February 08, 2025, 07:34:42 PM

It would definitely help to provide more context and backround of what you are trying to do, maybe even some pictures for clarity. We don't know what you're making or trying to do. The end of the log could be shaped, roughed out first, then draw knifed, spoke shaved to hone it in. How well does it need to fit in the hole? Making the mortise, will be some brute tactics just to remove the bulk of the material. Then refine it with a gouge. What type of wood? I can't picture anything traditional that would be like this. Please enlighten us.

21incher · February 08, 2025, 09:28:44 PM

How many is the big question. I would use a 2 inch self feeding auger but with a stop to drill as much as I could out and use my long die grinder with an aggressive burr to chop out what's left for one. For many you could make an expansion bit with a big axx drill.