Drilling really large holes - how?

[Wild Turkey]

How clean does the edge need to be?

How "round" does it need to be?

My thought is to use a drill press and drill lots of holes around the edge, then sand the waste away.  Smaller bit would leave smaller waste bumps, but would mean a lot more holes.

Another thought is to a router and a circle guide to cut as deep as you can on top and bottom, then use a sawsall to cut out the waste.  Then build a router sled to ride on the initial router cuts and then rotate it to cut the waste.

[goaliedad]

Could you cut the hole thru thinner pieces then laminate them to the full thickness?

[jteneyck]

Whoever said drill press (or milling machine) with a boring bar is on the right track.  You would need one heck of a drill press to turn an 8" diameter hole saw, if you could even find/afford one that large.  A boring bar just cuts at the end so side wall friction isn't a problem.  The problems you'll have with a boring bar are clamping and holding the wood on the table as there is no center drill with a boring bar, and figuring out how to raise the table several times to accommodate the quill extension limit, only about 3" on mine.  The boring bar will have to have a really long spindle, too.  To use a boring bar you will have to remove most of the waste first, leaving just a small amount of material near the perimeter for the boring bar. 

John

[Cooler]

Drill a pilot hole with a extended reach bit.

Then slice it into four 3 inch slices, drill and glue back together.   

Not ideal, but we make "impossible to machine" shapes in the tool room by piecing together two or more pieces of steel.

[Hank Knight]

Cooler has the solution. Short of buying an expensive hole saw or risking damage to yourself and other stuff in your shop, laminating the workpiece is the least of expensive approach that will yield satisfactory results. In addition to drilling a pilot hole for the large holes, I'd drill two more holes anywhere along the length of the workpiece before slicing it into workable pieces. Size these holes for dowels of any convenient diameter. After drilling or cutting the large holes (I'd use a router with a circle cutting jig), glue and reassemble the workpiece. Drive dowels through the two remaining holes to insure perfect realignment, and clamp.
My $.02. Good luck.
BTW, what are you building? Sounds interesting.

[Splinter Puller]

OK,  here is how I would go about it.  I would drill a pilot hole through the piece.  I would then use this reference hole to locate a circle pattern jig and use a bearing guided router bit to cut a round recess in both sides as deep as my router to go.   I would then use a long shafted smaller diameter forstner bit (or other edge referencing bit) to drill holes all the way around the perimeter just inside the outer edge to remove the core.  Last, I would use a sanding drum stacked on a shaft with top and bottom round spacers to smooth out the sides of the large hole to match the top and bottom holes originally cut with the router.  The spacers would match the diameter of the sanding drum so as to prevent from over sanding.

Presto.

[FireWood]

What you need is something like this, designed for wood:

http://www.gemplers.com/product/162452/D...ting-Auger


The challenges are going to be:

1) holding the workpiece
2) going slow enough that you don't destroy whatever is turning the bit
3) clearing the chips


If you are milling your own lumber and drilling this hole *before* the beam is dry, this tool *might* work.  Did I mention going slow?

If I was doing this, I would try and find a way to hold the workpiece at an angle such that the chips would fall out of the hole via gravity.

[wingnut]

What about a core bit?  They make them that large but they are meant for things way harder than wood. You would definitely need a chip relief hole and slow speed.  There would probably need to be a lot of clean up...

[MstrCarpenter]

If the holes you needed were in concrete, I could have had them done in less time than it took me to read all these posts. One suggestion would be to ask a few tradesmen that do concrete cutting and coring if you could modify one of their old (worn out diamond) core bits for wood. If you also borrow their drill, use air instead of water to clear the chips. Another option is to have a friendly metal shop make some for you using sched. 40 B.I. pipe. B.T.W. Sometimes when I core without a drill stand, I use the core bit to cut a disk of 3/4" ply., and anchor that to the concrete. It provides positive placement without additional holes for mounting the stand. If you do attempt to use a hand held drill, make sure it has a clutch.

[Dara]

Water jet cutter in some kind of metal shop?

Either that or blast, but that won't get you smooth sides

Its a tough one. I do like the concrete saw idea though. A bit at a time and chisel the waste as you cut the hole deeper.

How many holes?