3 1/4" hole in 3/4" thick 6061

[turbotadd]

Can a hole saw do it? Is there another quick way to knock that big of a hole out? I'd rather not spend all afternoon at it with a boring head in the Bridgeport.
Thanks,

Tadd

[Blazemaster83]

plasma cutter or if you can get the piece in your 4 jaw maybe?

[turbotadd]

Wish I had a plasma cutter... Too big for the 4-jaw.

[LKeithR]

A good hole saw with lots of lube will be fine. Th trick with hole saw cutting alum. is to have enough drill press to keep the cutter going and to keep it clean--back out periodically so you can blow chips out. Should be no problem...

[MichaelP]

A few more ways. Use chain drilling, vertical band saw, hacksaw or narrow reciprocating saw to remove the bulk and finish by boring on your mill. Naturally, if you use vertical band saw, you'll need to cut and re-weld the blade. Chain drilling followed by boring would be the easiest, IMO.

Yet more. A "poor man's hole saw", adjustable circle cutter like this: http://ecx.images-amazon.com/images/...500_AA300_.jpg But I won't envy you much.

[turbotadd]

Chain drilling it is. I knew there was a better way..
Thanks!

[BigJohnT]

If you have a manual Bridgeport scribe the circle and cut a square out then nibble close to the line all the way round then mount your boring head for final cleanup.

John

[hsm'er]

Depending on size/shape, one could use a rotary table and an end mill.

[Bob Fisher]

BigJohn, my thoughts exactly.hole saws are ok , but 3/4in is a lot.If you can clamp it on the table, should not take long to remove the bulk and finish with the boring head. If the location is critical , you need to locate the center before you start. Bob.

[justanengineer]

Depending on size/shape, one could use a rotary table and an end mill.

+1 on the end mill/rotab method. 5 minute job, maybe?

[MichaelP]

Plus 45-min setup.

But it's a good method, indeed.

[Prototyper]

I would definitely go with a hole saw, .125-.250" smaller than your target size. Chuck it up in the B'port, start the cut down maybe .05 dp, chuck up a .25 drill, and drill 4 or so relief holes along your saw line, through the plate. With a good stream of Al. cutting fluid, you will be flat out amazed how fast a hole saw will cut, with the relief holes giving the chips somewhere to go! Follow with your boring head, and you're done...

[oldtiffie]

Put it on parallel strips and clamp it to the mill table.

Use a trepanning cutter (hand-ground HSS will be fine) in a good boring head - good cutting oil and slow speed, steady pressure and clear often.

[tryfred]

Hole saw …I do it all the time…3 ¼” dia in ¾” 6061. I use the slugs to make oil filter adapters…


Joe

[darryl]

I would definitely do it with a hole saw. If 3/4 depth is too much, turn it over and finish from the other side. Keeping the kerf clear is important.

The typical hole saw uses a center drill as a guide, which works fine. If you don't want the center hole in the slug, you can remove the center drill. You will then definitely need to use a mill, as the saw will want to walk around until it gets a groove going. Without the center hole you won't have a reference if you decide to complete the hole from the other side.

The key to the whole operation is keeping the kerf and the cutters teeth clear- and use enough lube.