I need to drill some .687 holes in 18ga. 316 stainless.
Can I use a Uni-bit, without destroying it?
I can clamp the part down solid, and use a piese of steel
for backing, and use a drill bit.
I'll do that only if, the Uni-bit won't work.
Any other suggestions, on how to do this.
"Gary A. Gorgen" wrote in message
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! :)
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).
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
face angle than an endmill.
Use a metal backing plate for support. When the drill cuts thru, the
will just spin on the plate. Use low speed and heavy feed being careful
the cut thru point. When you get blue chips and squeaks, stop and
Gary A. Gorgen wrote:
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.
1. Oil or another coolant is a MUST! ...Unless you plan on spinning at 12
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
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).
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.
Joe Agro, Jr.
Automatic / Pneumatic Drills:
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.