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RazorJ (Industrial) (OP)
28 Nov 07 10:04
I am drilling a 1" Hole (#30 drill bit) through 304 SS. My problem is bit breakage. My parts, which are being hand drilled, is part of the problem.
I would like to know the best style/hardness of drill bit and lubricants to use. Also there has been some debate in my machine shop about the angle of the head of the bit, we are using a 118 degree bit.
Any help would be greatly appreciated.
Helpful Member!  TVP (Materials)
28 Nov 07 11:56
The following thread has some information on drilling of stainless steel:

thread281-128899: 17-4 stainless

Regarding lubrication, use a flood of lubricant specific for stainless steels.  This means it has been compounded with sulfur-containing EP additives.  Castrol Ilocut 5468 is one example:
Helpful Member!  limey1 (Mechanical)
28 Nov 07 12:02
Are you drilling a pilot hole first? If you are hand drilling, titanium coated bits should work (@85 rc hardness).
Drill rpm shouldnt be above 570 for 1" hole. What type of lubricant are you using now?
RazorJ (Industrial) (OP)
28 Nov 07 12:13
I'm using a Scotchman pure synthetic water soluble sawing coolent with a 5:1 ratio and I am running the drill at 800 RPM
RazorJ (Industrial) (OP)
28 Nov 07 12:19
I am drilling a pilot hole first.
limey1 (Mechanical)
28 Nov 07 13:25
Castrol 5468 sounds good, just make sure to flood the drill to control temperature variation. Do you have any control on feed?
RazorJ (Industrial) (OP)
28 Nov 07 14:34
Right now, every thing is manual and done on a drill press which is completley exposed. I will be automating the drill and the entire system will be enclosed.
Helpful Member!  MikeHalloran (Mechanical)
28 Nov 07 20:05
A #30 drill is .1285" diameter.  You confused some of us by stating the depth of the hole where we would ordinarily expect the diameter.

Regardless, you're breaking them by running them too slowly.  

Double the speed, at least.

Mike Halloran
Pembroke Pines, FL, USA

limey1 (Mechanical)
29 Nov 07 10:47
Good catch Mike. If it is a .1285" D drill, rpm should be @1400. If its a 1" drill, rpm @180. Again, flood it as much as you can, otherwise you will need to passivate afterwards.
NickE (Materials)
29 Nov 07 15:47
Sharp Bit, High Feed, Switch to a Sulfur Based cutting lube. (HSS with Co will help)

I love materials science!

RazorJ (Industrial) (OP)
30 Nov 07 9:42
Sorry about the 1" depth...I realized I had forgotten to specify that it was a 1" depth after I had written it.
It is a .1285" DIA. drill bit.

Could the angle of the bit also be the problem? I'm using a 118 degree bit.
Helpful Member!  tripleZ (Industrial)
30 Nov 07 13:46
Correct your speeds, feedrates, and coolant conditions, and I think you'll be able to overlook the minor difference you'll get from the tip angle or the flute pattern.  The center drilling operation should be permitting your drill to center, decreasing the chance of flex or walk.  The suggestion for TiN coated bits is also a good one.  Final suggestion: don't use the cheap Chinese knockoffs to save money.

unclesyd (Materials)
30 Nov 07 15:51
One thing I've experienced in drilling SS is the problem of clearing chips while drilling. Chips can quickly bind a drill bit and cause breakage.

We routinely drill 3.2 mm holes in SS with L/D's up to 12 with very few problems. We use both single and multi spindle drill presses.

The drill bits we use are from Guhring with the following description from a packet of 10.

Art. No 658 K
DIN 338 RH
S-Bohrer  GT1
3.20 mm

All of our precision drilling is accomplished using Guhring drill bits. We are able to have Guhring resharpen each bit 3 times without any loss of performance.

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