Drilling 316 stainless question - SMALL HOLE - TINY BIT!!!! = breaking

the.hogman · Jul 7, 2015

I am having a heck of a time. I am having to drill press 1.15mm (.0453") holes clear through 3/16" SS 316 round. According to charts I am calculating about:
(45 SFM x 12) \ (.0453 x pi 3.14) = RPM 3,600 with a feed of .001"

Does this make sense? I have never worked with stainless before and this seems like the RPM is so high it just asks for rubbing and work hardening. I "common sensed" it and run about half that speed, but it really doesn't seem to matter. Additionally, I am center punching. I am sure this doesn't help either.

I am using HSS oxide 118 degree bits. Whether I use coated or not, I am breaking every bit I have in stock.

I have a very solid steel work piece jig so rigidity is not a big factor right now.

HELP! Do I go cobalt, 135 degree split point bits? I really appreciate all of the knowledge on here. I am open to any suggestions.

billzweig · Jul 7, 2015

1.15mm holes should not present a serious problem. Breakage of your drills can be the result of quite a few issues:

1. The drill is not running true. Many chucks are not accurate when it comes to small sizes, and it also possible that the drill press itself has some runout.
2. Misalignment between your centre punch and the drill. Try using a small centre drill to start the holes
3. Pecking the drill in and out is better than feeding it straight through. How deep are the holes?
3. A play in the quill down feed. This can suddenly pull the drill fast down when coming through the material.

JRIowa · Jul 7, 2015

Don't know where you got 45 SFM, we don't even run CF8M castings that slow. That makes your RPM real low.

Use 60-65 SFM. RPM should be around 5,500. Don't c'punch. Coolant or oil.

A few years ago, we had a part with 147,000 small holes. Material was Inconel and 1/2" thick. IIRC, we broke less than 100 drills.
JR

allloutmx · Jul 7, 2015

JRIowa said:
Don't know where you got 45 SFM, we don't even run CF8M castings that slow. That makes your RPM real low.

Use 60-65 SFM. RPM should be around 5,500. Don't c'punch. Coolant or oil.

A few years ago, we had a part with 147,000 small holes. Material was Inconel and 1/2" thick. IIRC, we broke less than 100 drills.
JR

A part? wow

Do drill presses have that many R's?

Id get some 135dg split point drills.

Are you drilling into the round or into the face?

67Cuda · Jul 7, 2015

When JRIowa says "we", he's referring to the mouse in his pocket.

Tom

FredC · Jul 7, 2015

We have drilled lots of holes at sub par RPM and not had any issue. It happens all the time in screw machines without drill speeders. Center punching will definitely work harden the entrance but slop in the drill press handle will contribute a lot more to work hardening. If you are cross drilling definitely go with a 135 split point. I had an old foreman grind a 150 degree angle on a drill for cross drilling and it worked. You are using name brand industrial quality drills and not something you got at a hardware store (probably Chinese), right?

Mtndew · Jul 7, 2015

the.hogman said:
I have never worked with stainless before

If you've no prior stainless steel experience, 316SS is going to make you go bald.

That being said, it does cut pretty good once you get the speeds and feeds right.
According to my charts you want to go 2278rpm and 1.18 ipm feed for a .0453 HSS uncoated 2 flute drill.

the.hogman · Jul 7, 2015

All great comments and thoughts. I am using quality bits, but I am second guessing the spindle runout. I am cross drilling the rod by the way. And you caught me on the SFM. You are dead on that I had it too low. Agreed that I need the higher RPM! Given the correct RPM (the press won't run fast enough, only 3,070), the solid work piece jig and good bits (118, though), I am going to tear apart the spindle and see what is going on in there. I do notice that I get a little slop as it extend it. I'll bet that is the issue. I have some cobalt 135 splits on the way. Once I get them and go through that spindle, I'll post back.
You guys are the best.

billzweig · Jul 7, 2015

FredC said:
We have drilled lots of holes at sub par RPM and not had any issue. It happens all the time in screw machines without drill speeders. Center punching will definitely work harden the entrance but slop in the drill press handle will contribute a lot more to work hardening. If you are cross drilling definitely go with a 135 split point. I had an old foreman grind a 150 degree angle on a drill for cross drilling and it worked. You are using name brand industrial quality drills and not something you got at a hardware store (probably Chinese), right?

Split point and bigger angle are definitely making it easier. And a sharp drill. I always resharpen the drill after a certain number of holes, depending on the materiel. If you doing this kind of work frequently, you might consider getting a small drill grinder like the Christen/Alina. This will allow making a perfect split point at any angle.

JRIowa · Jul 7, 2015

Allout ~ When they don't go that fast, you just build one. 12 spindles. Now, a lot of the stuff is done on a horizontal Mazak with a 12K spindle.

Cuda ~ I used to manage that department along with several others. That was back when I was smarter. Now, the kids know much more than I do! Don't matter now, 23 days to go until retirement.
JR

jscpm · Jul 7, 2015

* use a bushing

* use a split point, 135-degree bit; if you are capable of grinding your own tip use a 140-degree lip angle and 12-degree lip relief angle

* do not center punch (as above use a bushing to locate the tool)

* typical SFM for SS is 30, but can range as low as 10 and as high as 50; however, considering the small diameter of the hole here you may want to ramp it up even further as JRIowa says to 60-70.

* sharpness is absolutely critical for SS; do not accept factory "sharpness", hone your tool to razor sharpness

Ray Behner · Jul 7, 2015

JR,
Glad to hear you're retiring....I guess. Just make damn sure you stick around here.

Cole2534 · Jul 7, 2015

JRIowa said:
Don't know where you got 45 SFM, we don't even run CF8M castings that slow. That makes your RPM real low.

Use 60-65 SFM. RPM should be around 5,500. Don't c'punch. Coolant or oil.

A few years ago, we had a part with 147,000 small holes. Material was Inconel and 1/2" thick. IIRC, we broke less than 100 drills.
JR

That 24" whisper trim cage?

Davis In SC · Jul 7, 2015

billzweig said:
1.15mm holes should not present a serious problem. Breakage of your drills can be the result of quite a few issues:

1. The drill is not running true. Many chucks are not accurate when it comes to small sizes, and it also possible that the drill press itself has some runout.
2. Misalignment between your centre punch and the drill. Try using a small centre drill to start the holes
3. Pecking the drill in and out is better than feeding it straight through. How deep are the holes?
3. A play in the quill down feed. This can suddenly pull the drill fast down when coming through the material.

A Servo Drill press would make this task easy.. Up to 20K spindle, a very sensitive feed lever, and a knob that controls the depth stop, and a dial indicator the read the depth. Works great for "Pecking" a thou or 3 at a time.. Sounds slow, but it goes quickly... Drill never pulls down.. I also agree about not center punching.... Touch the location with a center/spot drill, and do not move part until hole is drilled.

allloutmx · Jul 7, 2015

JRIowa said:
Don't matter now, 23 days to go until retirement.
JR

Congratulations! Im 45% jealous. Does this mean I will finally get a cigar? :cheers:

HuFlungDung · Jul 7, 2015

Run the piss out of it and feed slow = sure way to failure. In a manual machine I wouldn't bother running the snot out of it, try a moderate speed and a heavy feed. A proper chip should just auger itself up the flute quickly.

A stream of coolant is a practical necessity to keep the heat buildup to a reasonable level, because stainless is a poor conductor and there's double the heat intensity down in the hole, compared to regular carbon steels. That is when the HSS lips of the drill get stir-welded into the part and true 'work hardening' begins. IMO, you could hammer the shit out of a piece of stainless all day and it wouldn't get a damn bit harder (it will get real springy, though), but mix some HSS with it at high heat, and then you've got something.

billzweig · Jul 7, 2015

Davis In SC said:
A Servo Drill press would make this task easy.. Up to 20K spindle, a very sensitive feed lever, and a knob that controls the depth stop, and a dial indicator the read the depth. Works great for "Pecking" a thou or 3 at a time.. Sounds slow, but it goes quickly... Drill never pulls down.. I also agree about not center punching.... Touch the location with a center/spot drill, and do not move part until hole is drilled.

For drilling holes in the 0.2mm- 1.5mm range (and I often get to do it) I modified a "Leitz" metallurgical microscope with a fast spindle, ultra sensitive feed and through the spindle viewing. Makes the job so much easier. For small holes like this the machine must be rigid, vibration free and super accurate spindle. I have an Albrecht 0-1/16" drill chuck, but mostly prefer to hold the drills directly in the 8mm collets that the spindle takes.

A nice device for small holes is Albrecht Micro Drill Adapter. It is held in the larger drill press chuck and has a sensitive feed:
http://www.use-enco.com/1/1/79688-albrecht-micro-drill-adapter-micro-drill-chucks-adapters.html

JRIowa · Jul 8, 2015

Cole2534 said:
That 24" whisper trim cage?

36" FB. Body was F91 with Inconel liner. Cage was Inconel with Alloy 6 liner. Cage was over 6' tall. 147,00 3 stage holes. Each stage took just over 72 hours of drill time. That was the "Million $ Valve"!
JR

JRIowa · Jul 8, 2015

allloutmx said:
Congratulations! Im 45% jealous. Does this mean I will finally get a cigar?

No more cigars. They took out half my left lung in March. I get my last session of chemo next week. Can't even drink a beer until August.
JR

allloutmx · Jul 8, 2015

JRIowa said:
No more cigars. They took out half my left lung in March. I get my last session of chemo next week. Can't even drink a beer until August.
JR

Sheesh. Sorry about that. Good luck with your recovery JR

Drilling 316 stainless question - SMALL HOLE - TINY BIT!!!! = breaking

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