Correct Size Knock Out Hole Punches

[Pollys13a]

Hi all,
What would be the correct size for a 12AX7 B9A tube socket, a K8A 6V6 octal socket and if different what might be required for rectifier sockets?
Thanks.

[professormudd]

depends on the type of mount and the brand, in my experience.... Best to just get a couple of good step bits and you should be covered. Just my $0.02.

[wpaulvogel]

The size for a 12ax7 is .750 inches
The octal size for Belton sockets is 30mm (1.18in) I use a 1.25 inch punch.
You have to be careful with knockout punches because they are for conduit and the size listed is the actual pipe size. The punch makes a whole for the size of the coupling and it’s larger than the pipe.
I use Greenlee chassis punches. They were expensive but I’ve punched many holes with them and after you attempt step drilling , you’ll buy punched chassis or you’ll find a different way. The Greenlee punches are VERY SLICK!!

[pompeiisneaks]

I've used several brands and all of them were slightly different sized...

~Phil

[sluckey]

Greenlee also makes a line of punches called "Radio Chassis" punches. This is what you really want for punching tube socket holes. The size on the box is the actual diameter of hole.

[wpaulvogel]

^^^^^^^^ THOSE ^^^^^^^

[M Fowler]

I use Belton sockets so for 12AX7 I ordered 18.6mm off internet and .30mm for the octal socket.

Many other types of sockets are larger and the Greenlee knockouts can be used for those or a step bit.

Mark

[dorrisant]

I use the Greenlee punches... .75" for noval, 1.21885" (1-7/32) for octal. The timing marks on the outside make lining up holes right where you want them very easy. You won't get a cleaner hole without a CNC. Ask you local pawn shop if they have them... maybe show them a picture to jog their memory.

[johnnyreece]

I bought a pair off a forum member somewhere...can't remember which one. But, when I need holes in steel chassis, they're the bee's knees! If memory serves me correctly, I use the same size as Tony mentioned. I do have step bits for other size holes (holes for grommet, fuse holder, power cord, etc.).

[mwelch55]

I tried hole saws and did not like using them. You have to deal with the pilot bits breaking and it is difficult to extract the metal from inside the hole saw. Also, in my opinion, hole saws are too dangerous.

A friend loaned me his Greenlee knockout punches and they were good, but I decided I like the step drills better, especially for the price.

I like the way the step drill bits don't get caught like regular drill bits do. I bought an inexpensive set at Harbor Freight and I have used it to drill holes for 8 tube amps and about 30 effects pedals. The set I have can cut holes for pots and jacks and also novel and octal socket holes.

[dorrisant]

I corrected my post above to show that it is a 1-7/32" hole punch that is perfect for Belton octals.

Here is one for $45... someone should buy it for this price https://www.ebay.com/itm/265486317303?c ... 1&mkcid=28

Just to be clear. The timing marks on the Greenlee punches are key. If you don't use them, then it is difficult to get proper alignment.

Make a center line between two or more sockets. Carry the line past the centers by about an inch. Measure off the back of the chassis, etc. to keep the sockets square to your chassis.

Make equally spaced lines perpendicular to your last line for the spacing you want. Carry these lines past the center by an inch as well.

Strike a center and drill out to slightly larger than the draw bolt. In this case it is a little less than 3/4" so I used a step bit to bore a couple of steps past 3/4".

Align at least 3 of the timing marks on the cup with the center lines you've drawn. Tighten by finger and recheck the alignment before you put the wrench to it.

I follow this with a ream to clean up any slight burs. Just a few minutes and you have perfectly placed holes.

[sluckey]

I corrected my post above to show that it is a 1-7/32" hole punch that is perfect for Belton octals.

I use 1-3/16" for a more better fit.

Using the alignment marks works well if you have drilled an oversize hole, but if you drill a 3/8" hole you don't have to fuss with it.

[dorrisant]

I corrected my post above to show that it is a 1-7/32" hole punch that is perfect for Belton octals.

I use 1-3/16" for a more better fit.

Using the alignment marks works well if you have drilled an oversize hole, but if you drill a 3/8" hole you don't have to fuss with it.

I know what you mean. You are mostly right... but I'd pay money to see you put a 3/4" stud through that 3/8" hole without screwing it up.

3/8" hole is perfect for the 3/4" hole punch for novals.

No offense intended! I absolutely understand that you know what you are doing.

[sluckey]

I know what you mean. You are mostly right... but I'd pay money to see you put a 3/4" stud through that 3/8" hole without screwing it up.

Yeah, that would be tough.

I probably would not have made that remark if there had been pics attached when I replied. All my radio chassis punches have 3/8" draw bolts. I don't have any with a bearing.