View Full Version : best bit for drilling stainless steel

01-04-2009, 04:16 PM
I have a stainless tank and I need to drill holes for the fuel sender.I have broke three bits so far and have not gotten a hole drilled.one got red hot,one broke,the last just wore flat.I was using a 7/32nd bit as I was going to use sheet metal screws.so who makes the best small bit?

01-04-2009, 04:23 PM

01-04-2009, 04:33 PM
Any HSS drill bit will work for your application… drilling 6 holes will not necessitate the use of a GOOD M42 cobalt bit. (They are easier to break using a hand drill because they are more brittle) The key to drilling is to spin the bit slow… say 250 rpm and no faster (I wont get into drilling speed charts at this point)… oh and make sure you use coolant. Evan WD-40 will work for this or splurge and buy some drill lube.


01-04-2009, 05:36 PM
Lube and low speed

01-04-2009, 06:34 PM
thanks I will pick up a few[ha ha] bits tomorrow.will ww Grainger sell cobalt bits?

01-04-2009, 06:39 PM
You can get cobalt bits at Autozone.

01-05-2009, 09:56 PM
thanks again.will be drilling wed stay tuned in lol

01-11-2009, 03:08 PM
got er done cobalt bit,oil and slow speed all with one bit. just amazing thanks

John S
01-13-2009, 10:41 PM
This will sound crazy as shiz, but a plumber I worked with told me to use elmers glue when drilling. My first thought was that he was eating it, but sure as shiz, it worked. Ive used crap dewalt bits for a long time with the glue as a lube, and with any metal, it just flakes off, cant explain how or why. Plus, it does taste kinda good.:eek:

The main error of anyone drilling/cutting stainless is too much speed. high pressure-low speed= fast cut.

Why is cobalt a better bit?

01-14-2009, 03:17 PM
John open the windows in the cabin let in some fresh air:D

01-14-2009, 03:31 PM
Why is cobalt a better bit?

Cobalt just stays sharper longer then HSS.

As a trade-off, it is brittle.

01-14-2009, 08:13 PM
Went to to a tool store today to pick up a few things and saw a 190 piece cobalt drill bit set for 100 bucks.There was alot of items one here could use. a tire rack for the spare 10 bucks.winch cable with hook k7bucks.Check it out Harbour tools.

01-23-2009, 11:45 PM
you get what you pay for.. i have that samed set and its good for a couple hole.. now that samesizes of bits from my snap on dealer i can go as hard or as fast as i want with their thunder bits and at most ill bloody a knuckle when the bit comes through the meterial.. but i use bees wax or cutting oil to drill with. their thunder bits are about the only bit that will drill out broken taps

01-24-2009, 08:24 AM
if you have a drill press or a mill go with a carbide drill or hss drill are you center drilling the holes first stainless is tough not hard so its need alot of tool pressure to cut it low rpm and oil of some kind

05-14-2010, 09:56 PM
If you're too fast and/or dull bit, and don't finish the hole , the local heat you generate will "work harden" the area and then it's exotic material time.

05-20-2010, 03:52 AM
If you know the size exactly you want buy an ROC (ROCK) drill bit, but be sitting down when you ask for the price, but that will be the last drill bit you ever buy in that size unless you break it. All the rest of the suggestions are great. Center Punch and Pilot Hole, 250-500 RPM drill press with constant lube (I use cold cut it's like a wax). irwin Unibits work well as well on softer stuff less than 304 SS, I would not try to drill anything over .250" with one though.


09-11-2010, 06:17 PM
If you are drilling,milling or threading stainless the ONLY cutting fluid to use is TAP MAGIC. it turns stainless in to BUTTER. I have used it for nearly 30 years. They make a formula for aluminum also. The Steco Corporation--1-800-643-8026 or 501-375-5644. They are in Little Rock, Arkansas. Believe me it works!!!!


Sold honda, bought hondo
10-13-2010, 05:30 AM
I have a stainless tank and I need to drill holes for the fuel sender.I have broke three bits so far and have not gotten a hole drilled.one got red hot,one broke,the last just wore flat.I was using a 7/32nd bit as I was going to use sheet metal screws.so who makes the best small bit?
I know, old thread, but a different way of doing things.
Drilling/cutting metal generates heat. It begins at the microscopic level and increases in size as long as the source is still present. Most drill lubes are a lubricant. Lubrication is intended to keep metal parts from actually touching. In the case of a drill bit the edge that cuts must burn away the lubricant before the cut can begin. Try motor oil....it vaporizes at a high temp.....bees wax, low temp, nothing at all? With sufficient pressure the cut begins immediately. Two options....water based coolant, as used in a mill...all it is water, an antibacterial to keep things
from growing in it and a rust inhibitor to prevent oxidation of the tooling.

Or plan "B'
High pressure, low to medium speed......for a short period of time...and on to the next hole..do the same thing.... what happens is....the bit gets a little warm at the cut edge...it can take it, it's harder than stainless....the beginning of the hole gets hot, it's time to let that spot cool down and move to another spot. The second you let the hole get hot it's a done deal, you just work hardened the metal and it will wreck the cut edge of the bit next try.

I used to drill vent holes in motorcycle brake rotors...sometimes 100 holes in each rotor.....2 bits...no lube of any kind and done in half an hour. I use another rotor for the pattern, clamp the 2 rotors together, chuck the finish size bit in drill press, run the drill through the pattern rotor just long enough to barely start the hole..just push and let off..do all the holes, remove the pattern rotor, chuck a bit 1/3 the size of the finish hole in the chuck. Drill with high pressure till it start to cut...and STOP go to the next hole and repeat...do 20 holes...check for heat...you might feel barely warm, but the bit won't even be hot enough to burn your finger...and if the bit doesn't get hot, it won't get dull either....

Mini Max
01-24-2011, 09:41 PM
I saw them machining Crankshafts at Weber Motors. Cutting with no fluid, including drilling the oil journals. Explained to me that the chips took the heat away. Amazing.

Old school I use turpentine, slow speed and never let it slip. I have drilled a half inch hole in half inch stainless steel with a Brace and bit at sea in an emergency. Started at 1/8 inch and worked my way up.

Skater 32
02-09-2011, 05:19 PM
Wow , youve got my vote !!! I ALWAYS USE 135 DEGREE BITS

12-29-2013, 03:27 PM
plow of the bit needs to be small and sharp. sharp rake also. Smaller the plow of the bit the less pressure it takes to move the metal.

02-07-2015, 08:19 PM
The best bits for metal are carbide. Being an aircraft structure mechanic I have no time for a dull bit. None of them last forever. You get what you pay for but a good carbide bit will drill through titanium, steel or any other alloy but your drill speed is the key to making the bit last. When they get hot they are junk. Boelube is some really good stuff for lube. Made by the Boeing company.

03-04-2015, 11:16 PM
All the above things are good advice low rpm, cobalt is the best, but an inexpensive bit will work. The best lub for stainless drilling or tapping is coconut oil. I know you think I'm nuts but try it you will see it works well on steel also and cheap at Walmart. This is what we use in the machine shop at the Space Center (Kenndy) and believe it or not for Aluminum use Goop yes hand cleaner no grit type.


03-04-2015, 11:48 PM
What's Kenndy?

03-24-2015, 08:10 AM
cracked clevis nuckle.....since i machine my own boat parts out of 316 stainless steel.....i use carbide drill bits, carbide end mills and cutting fluid. at 500$ for a pair of these they're out of their minds.