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Rob,
I’ve not seen hole saws beyond 6″, and wouldn’t recommend one anyway. I find hole saws, particularly larger ones, frustratingly slow cutting and prone to burn the workpiece. I assume you would be using a drill press, because holes like this shouldn’t be done freehand.
One option is to buy a circle cutter. Home Depot versions of these go up to about 6″, but you can get industrial versions with 8″ capacity. One source is Highland Hardware in Atlanta. This would be my recommendation except you mentioned turning these holes out 20-30 at a time. Your post excluded this solution, but I would use a router and jig. Much faster and with better results if you do it the right way. Plunge router, 1/2″ up spiral carbide bit, 3/4″ guide collar, and a piece of MDF with a 7 1/4″ hole – you would be in business cutting fast clean holes.
Of course, you might want to buy the circle cutter to make the 7 1/4″ hole in the first place. 😉
Good luck,
Dave
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Anyone know where I can buy a 7" dia forestner bit, or holesaw, or any other device (other than a plunge router and a jig) to drill 7" dia holes thru 3/4" CDX plywood? Production style - 20 or 30 per batch.
-Rob
*Woodworker's Supply has a 6" circle cutter you may be able to modify. Thas a pretty big hole!
*What would you run a 7 inch forstner bit with?
*Rob,I cut huge holes in 3/8 ply and drywall with hole saws from my electric supply house. "Lennox"brand.With a bit that big on a Milwaukee Hole Hawg you could sell "E-class" Disney tickets for a chance to ride it "to hell and back."Are you ready to take a ride on the wild side?!Jack : )
*Rob,I've not seen hole saws beyond 6", and wouldn't recommend one anyway. I find hole saws, particularly larger ones, frustratingly slow cutting and prone to burn the workpiece. I assume you would be using a drill press, because holes like this shouldn't be done freehand.One option is to buy a circle cutter. Home Depot versions of these go up to about 6", but you can get industrial versions with 8" capacity. One source is Highland Hardware in Atlanta. This would be my recommendation except you mentioned turning these holes out 20-30 at a time. Your post excluded this solution, but I would use a router and jig. Much faster and with better results if you do it the right way. Plunge router, 1/2" up spiral carbide bit, 3/4" guide collar, and a piece of MDF with a 7 1/4" hole - you would be in business cutting fast clean holes.Of course, you might want to buy the circle cutter to make the 7 1/4" hole in the first place. ;-)Good luck,Dave
*Could you screw a inside jig (5" O.D.) to the piece, drill a pilot hole on the perimeter and run a quality jigsaw (e.g. Bosch) around the jig? mark the baseplate perpendicular to the blade and keep that spot touching the jig. You could do 2-3 at a time. There would be less risk of "taking a ride on the wild side" than with a 7-inch hole saw. If this is a recurring theme in you life, you could mount a custom baseplate on the jigsaw with a hole 3.5" from the blade for a screw to secure the combination jig/jigsaw to the center of the hole.