Drilling stainless

[nnam]

Yesterday, I wanted to drill through 2" pipes several 3/8" holes. It didn't work with HSS drill bits, even I cool it well (with stream of water). I resorted to carbide, and it worked, but I only have smaller size bits. After I maxed out the size, I used a carbide grinding bit to make it bigger.

It took a long time for the first hole, and a lot of noise. I also noticed the chattering due to drill press's low precision causes the carbide bits to chip at the cutting corners.

So I decided to try HSS again, since I drilled stainless before with them. I checked my bit for sharpness, and they are. I reground again with drill doctor, but it failed again.

I was a bit frustrated. But I thought to give it another try. So I hand grind it. That worked!

I think the drill doctor does not have a good relief angle at all. I knew this for smaller bit sizes. These are larger size drill bits and also the angle is not good for stainless.

 

[brino]

I have found that the Drill Doctor is a source of division this site.

Some love them, claim there's nothing better and put down any opinion to the contrary.
Other people struggle to get useful results.
I am definitely in the second category.

I bought one when I found a used one in good condition, but reasonably cheap. I carefully read the instructions and tried it on a few dull drill bits that I had set aside. This first time it seemed to do a decent job.

Some time later when I needed it again, I got it our, read the instructions and tried again.
I could produce nothing but garbage! I blamed myself and just walked away.
The next day I came back fresh and tried again, but I still failed.
I read the instructions, went step-by-step and kept failing.

The collets are such flimsy plastic and weak.
The method of registering the bit for rotation is hit and miss.
The last step where you insert the collet and rock it against the grinding wheel is incredibly variable.
How much do I rock it? The plastic around the collet has too much slop.

I have not used it again since. I suspect it's time to unload it on some other unwitting user.

Flame suit on!
Brian

 

[Eddyde]

You can drill most stainless alloys with HSS. The key is not stopping or slowing down, do not let the drill rub or the steel will instantly work-harden and dull the drill. Go in decisively, with firm even pressure and don't stop until you are through*. Use coolant if possible, use the lower speed range for the size of drill.
*If you must stop partway through the hole release the pressure instantly and restart with the same decisive, even pressure.
Cobalt drills will last longer than HSS.

 

[ddillman]

I had an older drill doctor and it didn't work very well. The newer one has an adjustment for the relief.

 

[Ulma Doctor]

Low speed, hard feed, lotsa cutting fluid.
Cobalt bits are higher temperature tolerant and cut longer than plain HSS

 

[C-Bag]

Low speed, hard feed, lotsa cutting fluid.
Cobalt bits are higher temperature tolerant and cut longer than plain HSS

+1, what Doc said! I pretty much do the same with anything metal. One of my favorite air drills is 300rpm wide open so perfect IMHO. I also agree on the DrillDoctor, no bueno. I can do much better with my Starrett gauge on the bench grinder.

 

[RJSakowski]

I bought a Drill Doctor 750X a couple of years ago. I find that getting the right relief requires paying strict attention to the grinding process. Although the grind may look OK, it would have a slight negative relief at the leading edge making the drill unusable until reground. I also found that setting the amount of material to be removed to a minimum helped. It required more passes but controlling the relief was easier.

 

[Reddinr]

I bought some cobalt bits especially for stainless. HSS works but cobalt is better at least from my experience. +1 on slow speed, hard feed, lots of cutting fluid.

 

[Jake M]

I have a love/hate relationship with my Drill Doctors. An older "basic" one and a newer "fancy" one. I keep them at work, because I work in a repair shop environment. The "community bench grinders" do not get kept to a standard that makes hand sharpening feasible. And bolting my own grinder to the community work bench kinda makes that community property too. So I taught myself to use the drill doctor.

Drill doctors, old or new, are capable. They don't "do it for you", it's an art form, with a lot of complicated geometry going on. Arguably, the drill doctor (and many other "more professional" drill sharpeners) require more skill, knowledge, and understanding of drill bit geometry, and have a longer/steeper learning curve than hand sharpening. But, they're concise, they store neatly, they don't have any propensity to have a groove worn into the middle of the wheel, and they're just always ready. And while it takes a while to get going, just to sharpen one drill bit, if you are able to save up a handfull (or more) of drill bits to patch up at one "sitting", they're actually kinda fast, and give consistent results.

If you're getting drills that don't have enough relief behind the cutting lips, the drill bit was not correctly "clocked" in the collet. That is regardless of what the little line up fingers said. The drill might just not be the one they though it would be when the Drill Doctor was made. Or it's one of the factory split point designs that has the huge gouge in the flute from using a fairly large wheel to grind the split point. That gouge removes the flute where the drill doctor "should" index from, so it becomes a bad reference. Either way, if the drill bit flutes are not at exactly the "standard" angle, or the flutes are partially missing, it breaks the indexing on the drill doctor, because it can not index from the cutting lips.

Fancier Drill Doctors have a correction for this, but it's crude. Very doable, but again, it's kind of an art form, as you've got to "read" the failure in order to dial in a correction.

It's a pain in the arse, but there ya go.....

 

[pontiac428]

With stainless, it helps if you spot drill first then swap to the drill. Like @Eddyde said, you gotta plunge it like you mean it, high feed rate, no dwell. Or you can peck drill, which works out well too, but you gotta peck like you mean it too. No limp-wristing on stainless, it's all about depth of cut to generate a thick chip that keeps the tool's cutting edge "under the cut" to stay ahead of work hardening. That's why spot drilling helps, you can start your cut with a jab without the usual act of controlling wander. Oil really helps with the finish.