Drilling stainless firewall *HELP*

Hi Everyone,

I am having a hard time getting my firewall match drilled. I am using Avery cobalt #40 drill bits with "off the shelf" Home Depot cutting oil. Further, I'm using my cordless drill on very low speed with quite a bit of pressure. After monkeying with this for well over an hour, I have one hole and about 6-7 trashed drill bits https://mechanicguides.com/best-cobalt-drill-bit-sets .

My question for those who have already completed this step.....

Exactly what brand, type of drill bit did you use?
Exactly what type of cutting oil did you use?

Any help on this would be fantastic!

Thanks!

No experience with this, but have you tried doing it "wrong"?

My thought is more speed and less pressure. Since you're eating bits anyway, what's one more for science?

Stainless generally wants very low speed and very high pressure.

You must be taking a chip...if not,  you're rubbing, not cutting. Also, you're generating heat, which work hardens stainless.

If you're trying to go through previously attempted holes....don't.  You may have to figure out another plan for those. Carbide burr, maybe.

I have drilled a LOT of 304 stainless.  Get a whole package of 1/8" bits, preferably at least the nitride coated ones, and short.  And a can or bottle of Tap-Eze.  Drill all your pilot holes with the 1/8" bits, using plenty of Tap-Eze.  Then go up in size until you get to what you want.

I destroyed a snap-on drill bit index at work  while drilling eight holes in 1/4" 304 stainless using Hess's method.  Lots of pressure (without breaking the smaller bits) and I worked my way up to size very slowly.  I used hydraulic fluid for lube, it was all I had.

Learn how to sharpen drill bits by yourself with a bench grinder.  It's faster than using a Drill Doctor, and stainless does not tolerate even a slightly dull bit.  As pointed out above, once you stop making chips, the material work hardens, which makes life even more difficult.  Need to go slow to keep the metal cool, lots of pressure to keep the bit biting, and sharpness is key.

I find myself touching up brand-new drill bits because the mass-production machine doesn't get them as sharp as they could be.  A well sharpened bit is a glorious thing to use.

Hungary Bill said:

I destroyed a snap-on drill bit index at work  while drilling eight holes in 1/4" 304 stainless using Hess's method.  Lots of pressure (without breaking the smaller bits) and I worked my way up to size very slowly.  I used hydraulic fluid for lube, it was all I had.

So, as usual, ALMOST what Hess said to do. It's OK, I'm used to it.  "Doc, I have this problem..."  "Do A, B and C."  Next visit:  "Doc, I did what you said and it didn't work."  "Did you do A, B and C?"  "I did A, wasn't sure about B and C was just too much trouble."  "Do A, B and C."  Next visit:  "I'm fine now."

Also, lots of pressure is not really what I do either.  Steady, firm pressure with sharp bits, and when the bits go dull, as you can see by not cutting anymore, pull them and replace.  If you start pressing harder, you MIGHT get through the stuff, but you will definitely work harden it and make a mess.

Tried step bits yet?

A number 40 drill bit is 0.098" and if we figure a surface speed of 50sfm for stainless your spindle speed should be over 1900 rpm. 

Put that drill in high gear, use lube to transfer the heat out of it, apply moderate pressure and make some holes!

As others have said, low speed, high pressure with a sharp drill bit will win the day. What I do differently when drilling or cutting stainless is use soapy water instead of cutting oil. Use it liberally to keep the bit cool, and the soap lessens the friction just enough (you want the bit to cut more than slip). Easier mess to clean up latter too. 

Also instead of using just a slow speed, I will actually pulse the trigger on the drill. The bit digs in and cuts better as its slowing down under pressure. Once almost stopped, I'll pulse it again. Rinse and repeat until hole appears.

This technique has saved many of my drill bits and hole saws from destruction when dealing with stainless.

AWSX1686 said:

Tried step bits yet?

I had to drill some 3/4"-ish holes in some thick stainless, and after I damaged one of those nice Harbor Freight step bits, I tried drilling a pilot hole and then attacked with a tapered reamer.  Hot chips flyin' and got the job done fairly quick.  A 1/4NPT reamer is just large enough to get a 3/8" NPT reamer started, and I finished with the 1/2" NPT.  (Okay, so "fairly quick" doesn't mean seconds and done, but it was a lot faster than watching a step bit turn into a cone)

Cannot be stressed enough:  If you are not making chips, stop, resharpen your drill bit, and change up your technique.  Worst case, you can do what somebody did to one of my drill bits, and just kept spinning the drill at high speed until it took the temper away and turned the bit into soft metal that couldn't cut cheese.  (Bastard dulled one of my files too, he was just running it over the metal instead of using force on it to CUT)

Remember. Slow is relative to bit diameter. It is surface feet per minute. The recommended SFM for stainless is 30 to 50.  A 0.098" bit at the top end is 1949 RPM and at the low end for super hard stainless is still 1364 RPM. A cordless drill usually has two speeds of 300 and 800 RPM. 

Here is the Norseman Feeds and speeds chart

http://www.norsemandrill.com/feeds-speeds-drill.php

And here is a handy calculator

https://www.custompartnet.com/calculator/drilling-speed-and-feed

So let that drill rip. 

And this is why I bought an ironworker; the 3/4" punch goes through stainless just about the same as through regular steel.   

If you are drilling a hole in stainless bigger than about 1/2" you might want to look for an annular cutter instead of a drill bit.  I'm slowly transitioning to them or tapered reamers for holes i can't punch.