Proper Usage Of Carbide Drill Bits

Hey All,

I'm about to drill some hardened stainless (1/4" holes) for the first time and I purchased a 25$ spade tip carbide drill bit to do the job.

My primary drill press is a 20" 3/4HP with multi step pulley. From what I have read on here and other sites I believe the proper technique is to go high speed, don't use oil, don't peck with the drill bit and if possible have a backing where the bit exits.

My concerns lie in the world of misinformation on the internet. While I have seen the above used successfully, to a lesser extent I have seen guys go slow speed, use cutting oil, etc and also successfully drill holes.

Could you guys enlighten me so my new drill bit doesn't shatter all over my shop!

Thanks

Augus7us said:

Hey All,

I'm about to drill some hardened stainless (1/4" holes) for the first time and I purchased a 25$ spade tip carbide drill bit to do the job.

My primary drill press is a 20" 3/4HP with multi step pulley. From what I have read on here and other sites I believe the proper technique is to go high speed, don't use oil, don't peck with the drill bit and if possible have a backing where the bit exits.

My concerns lie in the world of misinformation on the internet. While I have seen the above used successfully, to a lesser extent I have seen guys go slow speed, use cutting oil, etc and also successfully drill holes.

Could you guys enlighten me so my new drill bit doesn't shatter all over my shop!

Thanks

Click to expand...

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hmmm..... you going to put that carbide drill bit in a jacobs style drill chuck on a drill press ???
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carbide drills do not like wobble or runout. they do not bend much before snapping

DMF_TomB said:

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hmmm..... you going to put that carbide drill bit in a jacobs style drill chuck on a drill press ???
.
carbide drills do not like wobble or runout. they do not bend much before snapping

Click to expand...

I think he means a carbide tipped drill from home depot,,, there a soft steel shank. I have ground the end on them and used them a lot for junk holes in hard plate. Kinda a redneck fix but it works

Augus7us said:

Hey All,

I'm about to drill some hardened stainless (1/4" holes) for the first time and I purchased a 25$ spade tip carbide drill bit to do the job.

My primary drill press is a 20" 3/4HP with multi step pulley. From what I have read on here and other sites I believe the proper technique is to go high speed, don't use oil, don't peck with the drill bit and if possible have a backing where the bit exits.

My concerns lie in the world of misinformation on the internet. While I have seen the above used successfully, to a lesser extent I have seen guys go slow speed, use cutting oil, etc and also successfully drill holes.

Could you guys enlighten me so my new drill bit doesn't shatter all over my shop!

Thanks

Click to expand...

What type of stainless, and how hard is it?

It's a solid carbide spade bit.

The steel is AEB-L cryo hardened to about 61/62 HRC. All I have now is a drill press. I have a high end powermatic 1200 1HP drill press that is probably better than what I'm planning on using but I don't have a 3Phase power source for it at the moment. Sadly no mill yet either.

The steel is only .10" or so. What are the odds of it breaking? My drill press doesn't have any noticeable slop in it.

Augus7us said:

It's a solid carbide spade bit.

The steel is AEB-L cryo hardened to about 61/62 HRC. All I have now is a drill press. I have a high end powermatic 1200 1HP drill press that is probably better than what I'm planning on using but I don't have a 3Phase power source for it at the moment. Sadly no mill yet either.

The steel is only .10" or so. What are the odds of it breaking? My drill press doesn't have any noticeable slop in it.

Click to expand...

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when drilling out a broken tap i use a carbide end mill in a cnc mill in a collet tool holder and go down .002" and up .001" and blow air on it. i keep doing that. taking to much at once or too high a feed usually does not work that well.
......... my success rate at drilling out a broken tap is about 70% ...... that means about 1/3 of time i break the carbide end mill

Please wear safety glasses !!!

plothoundsman said:

Please wear safety glasses !!!

Click to expand...

I definitely will! Fly carbide does not sound appealing. And while it's not going to break the bank I'd rather not waste a 25$ drill bit.

What is the consensus on speed and cutting oil? What speed do you use in a mill? I've heard no coolant/cutting oil unless you can constantly flood it for fear of shocking the bit and shattering it.

It's gonna Suck in a drill press either way...

Use oil for sure, and low speed maybe 350 - 400rpm. The most critical part is your set-up, It must be rigid as possible including your toolholder (drill chuck). At 60Rc your just hoping to burn through it LOL

If the drill spindle has a taper, can you pop out the drill chuck and pop in a collet chuck?

rwbaldwin said:

If the drill spindle has a taper, can you pop out the drill chuck and pop in a collet chuck?

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Its a #3 Morse Taper if I recall. However I don't have a collet chuck to put in its place. I plan on getting a mill later this year, but that is down the road unfortunately.

It sounds like you're drilling a knife blade, or something very similar. Were I trying that with your setup I'd be using a Hi-Roc drill (or something equivalent), hold the work damned securely in a vise and go at it per the drill specs. Even at that it's going to be a little bit iffy, with the material that thin you might try some localized annealing to take a few points Rc off before drilling.

rke[pler said:

It sounds like you're drilling a knife blade, or something very similar.

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That's exactly what I'm doing. Four kitchen knives went through the process without me realizing I didn't drill the tang holes...

I would have annealed the tang with an oxy/acetylene torch but I only have propane at the moment. I planned on hitting it with that before I attempted drilling to draw the temper down but it will still be in the high 50's HRC. I don't think I have a hi roc brand bit but it came in today and I'm headed to the shop tomorrow so we'll see how it goes!

When you say bit specs are you saying some should be run fast and some slow? Is this per carbide bit type or steel type? I just googled PM again and the first few threads say fast with carbide, ~2700RPM.

After drilling many holes in thin 3/16 or less in SS is to first drill with a center drill 1/16 or 1/8 . then switch to desired drill bit , slow speed , (I like Tap Magic for This ) use minimum pressure. My chose is a 140drg drill. the drill has a cutting edge (hole) to work with , being the pilot hole and doesn't have to work to make one. let the bit do the work and won't grab the SS when going through.

I would shoot for 750+ rpm but use oil and have some disposable regular steel backing to drill into to minimize the break trough.

Feed hard and dont let it rub.

i thought you were supposed to run dry, when machining hardened stuff.

Before I would trash a high dollar bit I would try a concrete bit from the lumber yard. I have drilled Wilton vice jaws with them. Touch up the edge a bit run fast and don't let them get too hot or the carbide melts out.

Put a piece steel rod (Most any thing will do) the size of the desired hole or slightly larger in the chuck and with you spindle at it's highest speed feed against the hole location until it gets red hot. Now put your drill in and drill the hole. Old knife making trick.

Do it while it's hot, 400 stainless steels will air harden.

I like that steel rod idea.

I use carbide drills pretty often. Never spade drills though, and neve that hard of a material.

That being said, here is my advice, some of wich has been stated before: dont let it rub, be very careful when you break through, run maybe 300rpm, not 2700. The material is very hard, youll burn the drill right up at high speed. Use lots of oil. Attempt to start the hole with a center drill, just a bit, not too deep. unless your drill press and chuck is really good, your drill may walk. The cutting edge of the drill will break down at the point of contact where the pilot hole forms a corner. Sort of like starting the hole with a .125 drill. It will wear out from 125 to 250. I generally dont use a center drill in a milling machine drilling operation, due to this. Chatter also occurs without full cutting edge engagement. In a drill press, your drill will wear out really fast with enough chatter.

Let us know how you make out.

Ok situation report.

First thanks again for all the suggestions. tdmidget that is a fantastic tip, I've seen it done unintentionally with drill bits but doing it to soften up the metal is a brilliant idea. Though it may not have worked for me due to one of my pin holes in the tang being too close to the edge, I would worry about screwing up my temper without some sort of cooling.

So here is what I did. The last post I read was the masonry bit idea which I agree was cheaper and less risky, so I swung by lowes and bought a couple. They failed after drilling little more than a divot. I went ahead and ruined it to see how far I could get and it was more than a pilot hole but not much.

After that didn't work I went to the carbide bit. Worried about damaging the bit I set it up by putting the blade on a small bar of mild steel which I c-clamped to a 2X3. I clamped that in my vise. I was running at about 1000RPM and did not use any cutting fluid. I used steady but firm pressure. I didn't go crazy here but the first hole took very long and really heated the steel up so after that I put a bit more pressure on it, probably 20-25lbs. That seemed to be the sweet spot, just enough to start making spiral shavings. After that I sailed through 5 holes stopping each one just a second after I felt it plowing through the mild steel. This was enough time to finish the hole on the other side but no more. Worked like a charm! Photo evidence below.

On a side note you guys had me a bit paranoid I was going to eat carbide shrapnel. I wore a full face mask and had a 2x6 between the mask and the table