'Turns out a ping-pong ball is 40 mm in diameter.

I'm trying to build a check valve.

I need to drill a fairly precise 40-mm hole in a 3/4 x 1 1/4 PVC adaptor.

Do "they" make drill bits that large?

Any other suggestions on constructing check valves?

Can one get fairly precise Teflon spheres for building check valves of various sizes?

As a machinist, I envision you creating your check valve, and driilling a 40 mm hole with a drill to fit a 40 mm ball I do not think will work. You need to get a hole saw, perhaps, that is say... 38 mm, that way your ball won't come out of the hole. You want to create a precise hole, a drill bit or hole saw would waller around, making the hole larger than you intended. Start with a smaller size, that way your hole won't be too big. You would probably also need some sort of rubber seal to seat against the ball, and I wouldn't think that a ping pong ball would be very efficient as a seal anyway. How much pressure are you attempting to hold? Perhaps one of those rubber balls you buy in a quarter machine would float? You'd only be out a quarter, and if it floated, you could use a smaller diameter, maybe a standard and readily available drill would work.

Balls to 1" are available at Industrial Supplies (http://www.smallparts.com).

As Trandy states, drill bits won't work, they drill triangular holes. There is a kind of hole saw that will cut a precise size hole. It mounts a cutter in an adjustible mandril with a centering hole. It must be used with a drill press. Not too precise.

An adjustible wood boring bit MIGHT work if it was in a piece of flat stock.

If I understand what your trying to do. I think your trying to enlarge a hole. In that case drill a hole. The problem big bits do exist, but they are not the right way. If this was a hole one might use a big bit and then an adjustible reamer to get a nice round hole.

Big bits in an end of a PVC fitting will just grab.

Boring heads for milling machines can guarantee a nice round hole that size so would a lathe.

It's probably difficult getting a countersink that big too.

Soapy water makes a nice lubercant.

Yep, have machine shop skills too.

Hey Chip, What are you attempting to accomplish? Why not just purchase a 1 1/2" check valve? Regards, Tom

I am wondering about the ball.. Seems a FLAPPER would work better here..?