Drilling 316 SS

Aukai

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I have 40 5/16 holes to drill in 1/4, and 3/16 316 SS plates, I have both Cobalt, and Carbide drill bits. What I'm wondering is if cool mist spray is enough lubricity, and cooling, or my next option would be drizzling cutting fluid, which is better, and what bit?
 
Cobalt is just fine, even HSS will be ok. Turn slow (150-200rpm) and feed hard with liberal amounts of dark sulphur cutting oil. I would even consider a step bit for that thickness.
 
This sounds like exactly the project I just had, but the SS that I was drilling was only .125”.

I used solid carbide drills and (drizzled out of a sewing machine oil bottle) dark thread cutting oil. Surprisingly, solid carbide center drills would often break, so I skipped center drills.

The USA made drills would wear out after about 25 holes.
 
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I have been making some die holders out of 316SS just this week. Drilling and tapping. No problem using cobalt bits and anchor lube. Tapping the 8,10,12 screw holes at .400-.500 deep was slow going but doable.

I would probably shy away from carbide as the 316 seemed “grabby”. I used a carbide insert to bore the ID of one holder. It was an interrupted cut. Great finish but even the lightest passes caused the insert to fracture.
E071A8E4-DE16-4901-B55E-8024992018BD.jpeg
 
Stick with the cobalt. The most important thing is consistent feed when drilling. Don't stop and dwell or it will work-harden in an instant. The stuff is gummy and likely to grab and fracture a carbide drill if you're not really careful. I mostly use Anchor Lube for tapping 316, although for successive drilling, I will set up the power downfeed and depth stop, and dribble tap-magic from a needle bottle. Good luck.
 
Thank you David, what down feed rate would you use, I think I have .0016,.0031,.0063?
 
Thank you David, what down feed rate would you use, I think I have .0016,.0031,.0063?
I assume your using a cobalt jobbers drill, 5/16" with no pilot hole. If that's the case, here is where I'd start. The following is from FSWizard iPhone app:

screenshot_154.jpg

I'd do 300 RPM, at your 0.003" downfeed rate (1.41in/min feed rate divided by 311 RPM = 0.0045" revolution). If you don't spot first, use a Screw-Machine rather than Jobbers length bit - they are stubby and less apt to dance around. This would be ideal IMO:


It helps if your cobalt drill has 135° point tip. I spot 316 with 140° spotting drill and use 135° point bits. This is the spotting drill I have for holes under 3/8":


Hope this helps.
 
After drilling tens of thousand of holes in 300 series stainless, I found these procedures best. Never use a pilot hole. Use fully ground drill bits. I found that relieving the centre web on the drill bit to practically nothing was effective. In addition, aggressive down feed worked well. Pussyfooting around will only work harden the hole perimeter. Don't wait for the drill bit to squeal before changing to a new drill bit.
 
I have been making some die holders out of 316SS just this week. Drilling and tapping. No problem using cobalt bits and anchor lube. Tapping the 8,10,12 screw holes at .400-.500 deep was slow going but doable.

I would probably shy away from carbide as the 316 seemed “grabby”. I used a carbide insert to bore the ID of one holder. It was an interrupted cut. Great finish but even the lightest passes caused the insert to fracture.
View attachment 437873
Nice looking results, but why 316 (or other SS)?
 
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