drilling 304 stainless 4

[RazorJ]

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.

 

[TVP]

The following thread has some information on drilling of stainless steel:

thread281-128899

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:

http://www.castrol.com/castrol/productdetailmin.do?categoryId=82958627&contentId=6004344

 

[limey1]

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]

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]

I am drilling a pilot hole first.

 

[limey1]

Castrol 5468 sounds good, just make sure to flood the drill to control temperature variation. Do you have any control on feed?

 

[RazorJ]

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.

 

[MikeHalloran]

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]

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]

Sharp Bit, High Feed, Switch to a Sulfur Based cutting lube. (HSS with Co will help)

Nick
I love materials science!

 

[RazorJ]

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.

 

[tripleZ]

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]

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
HSCO EDBB
1272/7

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.