Drilling Stainless

I know. If it was .125 or thicker, I've done that. It's the thin stuff that's scary. If the drill grabs, it can rip the part out of the clamps, causing much excitement.

I wholeheartedly agree with Karl... slow speed, high feed, with some sort of lubricant. I use a little Kool-Mist system when machining stainless.

I ruined several of my favorite end mills learning how to machine stainless (I'm an amateur). I "discovered" it's not like machining aluminum at all! :)

Cheers,

John L.

Hey Gary,

I've noticed that "Unitbits" are becoming a generic term, so be careful that you are speaking of a high quality purchase. And they do come with various step "lengths" now, so dependent on how many holes, and whether you can "see" the hole spot to do it, I'd try a "sandwich" with a sacrificial piece both above and below to get the cleanest possible hole in the sheet stainless. One problem with what you want to do is that stuff that thin will work-harden almost immediately if you don't do things perfect, and in trying to do that you can end up letting the drill "wander", or worse, SLIP, when you go to start. Get a cutting fluid for stainless, and use lotsa constant pressure right thru, one shot!! Do a test on scrap to get some sort of drill stop depth, as you sure do not want to do a "peck drill" in this stuff.

Sandwich top and bottom will help stop any grab and "pull-up" too. Aluminun might be good, but for sure not wood (gets hot).

Take care.

Brian Lawson, Bothwell, Ontario.

If the holes are anywhere near an edge, a punch is the way to go.

GWE

Brian Laws> >

Gary, that calls for a sheetmetal drill bit. You can't buy them. Make'em from a standard drill bit. Picture a 2 flute endmill with a centering pip. Easy to grind by hand. Similar to wookworkers bradpoint drills but a shorter pip and more negative face angle than an endmill. Use a metal backing plate for support. When the drill cuts thru, the slug will just spin on the plate. Use low speed and heavy feed being careful easy at the cut thru point. When you get blue chips and squeaks, stop and regrind. RichD

Gary A. Gorgen wrote:

There is a nice article in machinist's workshop volume 19 number 2 about grinding some nice sheet metal drills.

Sam

A Uni-bit works great because it is progressive, keeps enlarging the hole a bit at a time cutting only on the periphery rather than trying to cut right under the drill lips like a twist drill does. In 18 gage stainless I'd make the starting hole with a sharp 3/16" cobalt drill, then use the Uni-bit to enlarge it from there. Lots of coolant, low speed and aggressive feed as others have said.

Yes. I've done it, using a pretty new (and sharp) Irwin Unibit, black sulphur oil, slow speed, and a heavy hand. It wasn't even hard. But don't lose your nerve.

I didn't use a backing plate.

Joe Gwinn

1. Oil or another coolant is a MUST! ...Unless you plan on spinning at 12 RPM.
2. Work hardening is a myth IMHO. Take a heavy cut to stay "in" cool material if you can but make sure you use coolant!!! Shallow cuts leave you close to the surface where the face of the tool just generated heat so a deeper cut is usually better within reason. That size hole ... maybe a .009 cut per revolution if you can program it and not do it manually. Personallyt, I've found that a "work hardened" area seems to mysteriously un-harden when a new tool is inserted with coolant - thus it leads me to believe that the tool just got dull from overheating. Show me otherwise and I'll believe in work hardened stainless... Flames welcome, but I'm running and hiding now as this is like challenging religion. ...Did I mention coolant?
3. Sharp tooling helps quite a bit - but not as much as coolant.

I wouldn't call it a myth, but I would say the problem is overstated. Warnings about never letting a tool dwell without cutting are valid, but the fact of the matter is that most of the time you'll get away with it. But occasionally it'll bite you hard.

I recently had a couple SS sprockets that I needed to tap in order to mount shoulder screws as eccentrics on the hubs. I managed to drill them with a lot of squealing despite a sharp bit and plenty of lube, then proceeded to ruin 2 new taps without getting anywhere. I gave up and bored the holes with a carbide bar and pressed in pins instead. The sprockets were nothing unusual, 303 or 304 SS, and I never did figure out why things went so badly.

Small endmills are a bigger problem than drilling or turning simply because there's a much smaller margin between too little feed (work- hardening) and too much feed (broken tool).

Ned Simmons

Just out of curiosity, what type of lube were you using?

Generally, I try to run stainless procedures at 75% of what is considered safe speeds... It's "free" insurance for me as cycle time isn't that critical in most of our applications.

Regards, Joe Agro, Jr. (800) 871-5022

Sorry for not responding sooner. Comcast fixed something that wasn't broken, & broke it.

I'd like to thank everyone for their replys. A lot of good info, that I will keep for reference.

My wife solved the problem !

One of her firends (who she was going to have lunch with) husband, works for a company that has a CNC laser cutter.

I drew a quick print. She took the parts to lunch (I paid). Returned with finished and deburred parts.

I owe her friends husband alot of beer.

Also I'll swing any business their way, I can.

Again thanks for all of the help.

Gary, Glad it's solved. Sounds like you have found a valuable resource.

If the "bunch of holes in thin stuff" problem comes up again, take a hard look at "annular cutters".

Lard oil blend, Moly-Dee, and old formula Tap-Free with trichlor for tapping. None of them were any help.

Ned Simmons