Drilling 316 Stainless

Howdy again, feller metal reckers.
I have some 1/4-inch 316 SS thru-the-wall bulkhead tube fittings that I
need to a 17/64 hole straight thru - just large enough for a 1/4-inch OD
tube to slip thru without binding. The stop has a .18-inch ID, so I
started from the tube end with a 3/16 cobalt bit, then increased the
size gradually until I got 1/4-inch all the way thru with little
trouble, taking it slow.
I then put the 17/64 bit in (same cobalt, mfr, point, etc) and it
drilled fine starting at the tube end. But when it gets to the thick
wall MPT end, it stops and I can't get it any further. I also trying
going at it from the MPT end and won't penetrate at all.
There's a good chance I heat hardened the fitting by letting it spin -
the tip glowed orange before I realized what was going on.
Anyway, that's where I am. Any suggestions from the stainless folks?
As a last resort I can enlarge it with a round rat tail file, but would
rathe have a nice smooth round surface.
I'm using Swagelok but could not find that fitting on their website.
Good products, but website is nothing like McMaster:
Photo of the same type of fitting, different make - 1/4 tube x 1/4
male:
formatting link

9546388
Spec page:
formatting link

Snuffy Sniffs (No relation)
PS -- Larry? Pay attention and yew mite git some smarts.
Reply to
Snuffy "Hub Cap" McKinney
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"Snuffy \"Hub Cap\" McKinney" fired this volley in news: snipped-for-privacy@earthlink.com:
You hardened it long before that happened! Most stainless steel alloys work-harden easily, if you're not cutting a clean, thick chip with each turn of the tool. "Taking it slow" with stainless should only refer to the rotational speed of the drill; you should drill aggressively, taking as much of a cut per turn as your equipment will tolerate -- but probably never less than five to eight thousanths per turn.
The INSTANT the bit starts to 'skate', even a little, you're screwed.
You could cut it with a carbide end mill, but it doesn't sound like you have equipment to keep that centered as you go.
You say you want it to "look good". You can do that with a file. You have to be careful and deliberate, and check your work often (with a 17/64" drill bit as a gauge.)
Oh... and 17/16 is hardly a "slip fit" for 1/4"! That's more like putting a needle through the 'tight' opening of the Holland Tunnel!
Lloyd
Reply to
Lloyd E. Sponenburgh
You have work-hardened it. 316 will work-harden if you look at it cross-eyed. You need to be aggressive and *consistent* with your feedrate. I once drilled hundreds of pieces of it on a Herbert turret lathe, and I had to be as mechanical as a robot to keep the feedrate consistent, or it would harden right up.
You may or may not be able to cut through the work-hardened skin with a fresh drill bit and a lot of pressure, or perhaps with a carbide bit. Or you may break the bit in the work and then youre screwed.
It's easy to anneal, however. The spec sheets say heat to 1100 - 1120 deg. C and quench "rapidly." They don't say how rapidly, but I assume they mean water-quenching. It's like the opposite of annealing a martensitic steel. Annealing also boosts the corrosion resistance.
Good luck.
Reply to
Ed Huntress
Carbide . You might get lucky and find a concrete drill that will open it up to 17/64 , and they're cheap at the BBS's . I'd have gone to the desired diameter in one step , Low speed and push it hard .
Reply to
Terry Coombs
Correction on the annealing temperature: it's 1010 C to 1120 C (1850 F to 2050 F).
Reply to
Ed Huntress
Yes. Step-drilling is not recommended in 300-Series stainless, unless you have a torque limitation.
Reply to
Ed Huntress
Drilling 316 (and most stainless) requires the same thing, Turn the bit with as much torque as you can and stand on the feed handle. You want to cut it fast, almost to the "If I pull any harder the bit will break" point. If your not getting a nice thick chip tour going too light on the feed.
Lots of good ideas, Myself I'd anneal it. Toss it in the press and PULL that handle.
Reply to
Steve W.
Carpenter Tech has a book on line about machining stainless steel. Lots of good information about drills for stainless drilling and what the angles s hould be. Also information about drilling to 4 or 5 diameters on the first go and then pulling the drill out to clear the chips. And then drilling a couple of more diameters and clearing the chips. And finally getting to w here you only drill one diameter in depth and then clear the chips out.
Another tip is to use a center punch with a three sided end so you have les s problems with the center punch work hardening the starting point.
And using a split point drill to minimize work hardening.
But what I thought was interesting is there was nothing about whether one s hould or should not drill a pilot hole. Other sites on the internet say dr ill a pilot hole. Maybe it is because Carpenter Tech says use a split poin t drill and the other sites say nothing about split point drills.
I personally am likely to drill a pilot hole a bit bigger than the web thic kness of the drill used to complete the hole. It lets you feed the drill fa ster. So you might have some work hardening from drilling the pilot hole, but you can feed faster when drilling to final size. I might be influence d by the fact that I have some small diameter split point drill , but no l arge ( over 1/4 inch ) split point drills.
But I agree with low speed and lots of pressure.
Dan
Reply to
dcaster
formatting link
Reply to
Steve W.
Welp, I dun did it. Many THANKS to the wise men, wise ladies and wise guys! You're info has saved the day for me! The job will ship tomorrow unless I drop something.
When I stopped last night, a 1/4-in hole was all the way thru, but not enough clearance for the tube. Still couldn't get 17/64 thru the last 1/16-inch*. Today I read all the good advice, sharpened the old bits, put on some Sousa marches for motivation, and keep hitting it. Tried several lubes and transmission fluid worked the best. 3 bits and 10 minutes later got 'er done.
Thanks again!! (Larry, the thing to learn from all this is -- next time take it to a machine shop.)
*
1.5875 mm for metric fans.
===
I have some 1/4-inch 316 SS thru-the-wall bulkhead tube fittings that I need to a 17/64 hole straight thru - just large enough for a 1/4-inch OD tube to slip thru without binding. The stop has a .18-inch ID, so I started from the tube end with a 3/16 cobalt bit, then increased the size gradually until I got 1/4-inch all the way thru with little trouble, taking it slow.
I then put the 17/64 bit in (same cobalt, mfr, point, etc) and it drilled fine starting at the tube end. But when it gets to the thick wall MPT end, it stops and I can't get it any further. I also trying going at it from the MPT end and won't penetrate at all.
There's a good chance I heat hardened the fitting by letting it spin - the tip glowed orange before I realized what was going on.
Anyway, that's where I am. Any suggestions from the stainless folks?
As a last resort I can enlarge it with a round rat tail file, but would rathe have a nice smooth round surface.
I'm using Swagelok but could not find that fitting on their website. Good products, but website is nothing like McMaster:
Photo of the same type of fitting, different make - 1/4 tube x 1/4 male:
formatting link
9546388
Spec page:
formatting link

Snuffy Sniffs (No relation)
PS -- Larry? Pay attention and yew mite git some smarts.
Reply to
Snuffy "Hub Cap" McKinney
I'd use solid carbide drill myself. They can get red hot and stay sharp. The Chrome oxides are nasty to drill through.
Martin
Reply to
Martin Eastburn
Just get a real carbide drill - 100% carbide - not a concrete type - those are not tough enough and might "unbraze".
Martin
Reply to
Martin Eastburn
Yup , that's a possibility . I've never had it happen , and I use a couple on the lathe from time to time . But Snuff had a one-time part , I figgered he wanted the least expensive option . I've learned the hard way not to work/heat harden the part I'm working on .
Reply to
Terry Coombs
One thing I learned here when I first got on this group was not to center punch hole locations in stainless. Passed that on to a number of electricians working on my 316LSS control enclosures. Mark it with a felt tip or pencil, hit it hard with the drill.
Pete Keillor
Reply to
Pete Keillor
that I need to a 17/64 hole straight thru - just large enough for a 1/4-inch OD tube to slip thru without binding. The stop has a .18-inch ID, so I started from the tube end with a 3/16 cobalt bit, then increased the size gradually until I got 1/4-inch all the way thru with little trouble, taking it slow.
drilled fine starting at the tube end. But when it gets to the thick wall MPT end, it stops and I can't get it any further. I also trying going at it from the MPT end and won't penetrate at all.
- the tip glowed orange before I realized what was going on.
would rathe have a nice smooth round surface.
Good products, but website is nothing like McMaster:
formatting link
9546388
formatting link
I'm using a hand drill. Next time what about setting up the vice outside and running a hose on the part slowly? Maybe set it up in the wife's flower garden and kill 2 birds with one stone.
Reply to
Snuffy "Hub Cap" McKinney

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