Drilling Stainless Steel

[CRL]

Wasn’t disputing your method, just describing what I witnessed and was told. I’ve used a conventional shop drill press using the slowest speed the belts would allow (pre-digital controls) to drill stainless steel, and the main thing was to use lots of lube and as much pressure as the bit would stand. The main caution being to not allow the bit to spin without cutting due to not enough pressure causing the bit to burn.

[Steveruger45]

Yes exactly we are on the same page.
 On a No.74 drill bit that pressure applied is going to be critical. Not enough and it ruins the bit spinning and not cutting and hardens the SS to a point too, making it even more difficult.  Too much and a broken bit results.   So a gentle up and down of the bit into the job to get the “feel” helps a lot and like you say use plenty of coolant/lube/cutting oil.  Using a quality drill bit too. Cheap drill bits won’t cut it, pun intended, sorry I couldn’t resist

[peteski]

I really think you guys are way overthinking this.  The hole is tiny, and the steel piece is not very thick either. Carbide drill will cut right through the steel (even if it is hardened by the process).  Speed is also not that critical. The most critical to me is the backing material.  If it is too soft, the drill will break through the steel and then promptly shatter.  Just use a piece of brass or aluminum (brass is better) and just drill the damn thing! 

And yes, I *NEVER* just buy a single small carbide drills. I have many sizes in lots of 50 (full box) because I know they will break at one point or another.  I haven't look for a while, but I used to find full boxes for quite affordable price. Resharpened are ok, but used might be on the duller side.  Those bits are used for drilling thousands of holes in fiberglass-epoxy printed circuit boards, and the glass eventually dulls the hard carbide edge.  But resharpened bits are as good as new (the flute is usually slightly shortened).

[Steveruger45]

I wondered when you would “drill-in” on this Pete.  . There is a lot of truth in what you say though.  I too have “red-necked” it on occasions, even though I know better and it often works.
But I have never sharpened a drill bit in the wire gauge sizes myself, just too darn small to see if I have each fluke the same size.

[peteski]

I wondered when you would “drill-in” on this Pete.  . There is a lot of truth in what you say though.  I too have “red-necked” it on occasions, even though I know better and it often works.
But I have never sharpened a drill bit in the wire gauge sizes myself, just too darn small to see if I have each fluke the same size.

Flukes are difficult to keep even size. 

LOL!  I don't sharpen carbide drills (regardless of size).  That is why I buy large quantities of them. But I usually break or chip them before they get dull.   

[narrowminded]

The one item I'm seeing repeated here that I disagree with is the speed.  In a drill press or mill you probably don't have a speed that's too fast for this diameter, even in Stainless.  

Do some searches for recommendations for the SFPM and I doubt you'll find anything much less than 30 SFPM even for HSS drills.  Carbide can be up to and over 150 with coolant.  With oil, maybe 70 or so.  Even if you go all of the way down to 10 SFPM, with a .0225" diameter drill that will still have it spinning at 1700 RPM.  20 SFPM will be 2400 RPM.  Biggest thing is don't let the drill rub in the hole.  Cut or get out.  A nice even pressure with some cutting oil would be nice and an aluminum back up plate for blowing through.

You can search for speed and feed calculators online as well as recommendations for speeds (in SFPM) in different materials.  Take note of references to split points and point angles as they are part of it, too.  A BIG part in SS.  You'll learn things you never wanted to know.   Be aware that many of them assume flood coolant as a minimum and with just oil you may want to try half of the recommended but even at a quarter speed it's hard to go too fast with drills this small.

A quick search found this calculator.  https://www.custompartnet.com/calculator/drilling-speed-and-feed

[LKOrailroad]

I was in a machine shop years ago watching them drill a 1.5” hole in a 1/2” SS plate. The drill was making about one revolution per second (60 rpm) and was under constant pressure and a stream of coolant. The machinist told me if they allowed the drill to spin with no pressure, it would ruin the cutting edge. Very interesting to watch, but impossible to pull off without a very specialized drill press.

Interesting. I experienced similar using cheap China countersink bits in tempered hardboard while installing lighting valance and fascia. I was trying to set drywall screw heads slightly below flush. Because the hardboard was only 3mm thick and the countersink would blow right through it if pressure was applied, I tried using very light pressure to minimize the cut rate. Dulled the countersink bit to a butter knife in no time. I was using a cordless drill so the speed was not high. Granted it was dirt cheap tooling but I would never have expected glued wood to do such thing to steel so quickly.

In the end it all worked out. Oddly enough, the ultra-dull countersink bit actually gave me very good depth control because it was wearing its way through instead of cutting! Caveman way of going about it but after a touch-up sanding it delivered nice sinks.

[Chris333]

About countersinking into hard board. I've had this bit for about 25 years now that lets me countersink to any depth and has a stop. I can push as hard as I want and they will all be the same. I was going to put a link up, but when I searched I couldn't find a single photo of it. Maybe it is called something else?


This is where you pull it apart and screw to adjust the depth.

[Chris333]

Added "adjustable" to my search and found one:
https://www.appliedracing.com/window-accessories-and-nets/counter-sink-tool.html