One inch hole in stainless?

I need to add a one inch O2 sensor bung into a stainless exhaust pipe. I know that it is difficult to drill stainless. Would it be best to use a drill or a hole saw?

Shotgun.

Seriously, Doc Hess should be able to help with this one.

ummm I guess miata is not the go to answer for this one huh???

Exhaust pipe should be pretty easy to do. Are you sure you need a 1" hole? I bet you only need about 1/2" or 3/4" hole. The bung OD might be 1", but you don't need a hole that big. Just big enough for the sensor to go through. A drill is preferable, but a decent quality (not HF) hole saw will do it too. Use some real cutting oil like Tap Magic if you want to use the hole saw again. I chewed up plenty of 3/4" 16ga 304 with a hole saw in my HF tubing notcher jig.

Dr. Hess wrote: Exhaust pipe should be pretty easy to do. Are you sure you need a 1" hole? I bet you only need about 1/2" or 3/4" hole. The bung OD might be 1", but you don't need a hole that big. Just big enough for the sensor to go through. A drill is preferable, but a decent quality (not HF) hole saw will do it too. Use some real cutting oil like Tap Magic if you want to use the hole saw again. I chewed up plenty of 3/4" 16ga 304 with a hole saw in my HF tubing notcher jig.

Never thought about that. The O.D. of the bung is one inch, so I assumed that it would be recessed into the hole. The bung is straight cut on both ends, so it would take some filler if I cut it smaller. How deep should the sensor itself extend into the exhaust pipe? This is for an after-cat sensor if it matters.

Drilling stainless is real tough on a drill or a holesaw. I would suggest a hole saw, lots of oil, and DON'T DRILL FAST!! Max out the speed, drill bit/hole saw go away very quickly. I have done a lot of this and have had the learning experiences you don't need. I never used any exotic oil, anything thicker than WD40 did the job.

Do you have a die grinder and a carbide bit? Start with a teeny hole and work your way out.

Isn't that bung the same as a spark plug helicoil?

Dan

I use a step-bit

Grtechguy wrote: I use a step-bit

I can't remember if I used that or just a selection of progressively larger drill bits. Wasn't that hard or time consuming. The hole didn't need to be 1". Just wide enough for the O2 sensor to stick out of. Its probably closer to the inner diameter of the bung.

Grtechguy wrote: I use a step-bit

In thin sheet or tubing.. These things are GREAT.

I dunno about the step thingie in stainless Might work. I have a small HF set of those and it works well in aluminum.

No, you don't need to sink the bung into the tubing. I just mount them flush to the tubing. Grind a little on the bung to get the contour to match the exhaust better. Fill it in where it doesn't fit. Put an old sensor or old large size spark plug in the bung when you weld it to make sure it keeps its shape. You can also beat the tubing a little flatter right there if you have to.

The last one I put on is on the front cylinder pipe just in front of the brake pedal in this pic: It's a stainless bung from DIYAutoTune.com welded to the chrome plated drag pipe (no baffles, great to piss off wimps on Honduhs.)

ignorant wrote:

Grtechguy wrote: I use a step-bit

In thin sheet or tubing.. These things are GREAT.

Worked great in a pile of 1/4" and 3/8" plate the other day too. I love unibits!

Bryce

The HF step bits are crap in anything harder than aluminum. I have a real live Unibit brand step bit and that thing is impressive. I was drilling something thick (like 1/4") once, the chips started coming out PURPLE . I stopped quick and was absolutely sure I had roasted the bit. Nope, still works great.

Jensenman wrote: The HF step bits are crap in anything harder than aluminum. I have a real live Unibit brand step bit and that thing is impressive. I was drilling something thick (like 1/4") once, the chips started coming out PURPLE . I stopped quick and was absolutely sure I had roasted the bit. Nope, still works great.

so true. i roached the HF one drilling some 3/16 plate out because i needed a 3/4" hole

I figure you're going to weld the bung in place with some kind of welder. Use whatever that is to burn a hole in the pipe and dress it up with a die grinder and a carbide bit. Quick and painless.

Plasma cutter is tha' BOMB!!