Just another headache. I am running into problems with my .128 drill that I am using to drill thru 4 .09thk stacked Stainless Steel plates. It is drilling 56 holes and before it gets to the end the drill is breaking. I am running it at 1200rpm with a feed of 7.2. It equals out to .003 per tooth. I am chip breaking at .045". I am using a stub Cobalt drill. I would use carbide but we don't have any in house. Anyone have any suggestions.

Can you hear it squeal? If so, you're not feeding it hard enough. Are the corners of the drill breaking/chipping? If so, you are either feeding too fast, or it's having problems getting between the sheets.

'Rekd

Before I changed the feed and speed to what it is now...it would make it to the about the 7th hole and it would start squealing. Now since I changed the feed and speed it makes it thru about 50 holes and them starts the squealing... the tip of the drill didn't break down and the drill broke at the top by the holder.

Originally posted by Machine1
Before I changed the feed and speed to what it is now...it would make it to the about the 7th hole and it would start squealing. Now since I changed the feed and speed it makes it thru about 50 holes and them starts the squealing... the tip of the drill didn't break down and the drill broke at the top by the holder.

Are you using standar twist drills? or parabolic? or split point?

You might try splitting the difference between the first feed/speed and the ones you're using now.

'Rekd

Im using a split point 135 degree Cobalt Drill. I just didn't think that .003 chip load per tooth was that much.

Originally posted by Machine1
Im using a split point 135 degree Cobalt Drill. I just didn't think that .003 chip load per tooth was that much.

.003 isn't too much for the right drill. I would try a standard twist drill, 118° tip. The 135° tips are for softer materials, like plastics and wood.

HTH

'Rekd

Are you using a coolant?

Flood...

I wonder if the "break-through" disk is what is breaking your drills? In mid stack, if one of these disks happens to get caught between the bottom of the hole and the bit, it effectively caps the cutting edges and snap!

I would try an even more acute angle to the drill, which should be of split point grind, in an effort to make sure it penetrates the next sheet before it has a chance to break out the "breakthrough disk" of the current sheet.

Maybe try not pecking at all, too.

I'd bump to about 60 sfm .002 chip load and increase your peck.
Way too much engage/disengage going on.
jm2c

What kind of stainless is it?

PEACE:D

Workhardening S.S.
R.P.M. 948 Feed 2.84 S.F.M. 32 Gives you a .003 chip.

Free machining S.S.
R.P.M 2132 Feed 6.4 S.F.M. 72 also a .003 chip.

Info. from CNCSpeed still one of the handiest software tools I've ever used.
Oh Ver. 5.9.28 gotta get the latest update.

Where did you get the CNCSpeed software? Did you download it off of the net

its 304 SS

Originally posted by hardmill
I'd bump to about 60 sfm .002 chip load and increase your peck.
Way too much engage/disengage going on.
jm2c

What kind of stainless is it?

PEACE:D

It is 304SS...I tried these numbers and after the 3rd hole the drill burnt up. They are center drilling the hole and the tip is breaking thru 3 of the plates. Then we are coming back in with the drill. Would that have any affect of the drill? Maybe that is what is causing the drill to burn up on the corners...all the vibration that it is getting going into the hole that is C'drill. Maybe we should spot drill it? Im a little frustrated with this job. What do you think about a Carbide drill?

I'd try a high helix HSS cobalt drill before I'd try carbide, unless there is a proven coating that will prevent cratering. I'd like to know, too, if such things exist, that are successful in use in the real world.

Also, no pilot hole, maybe just a spot would be a good choice, too.

I was using a Cobalt to start out with. I think that I am going to try to run a spot drill instead of a center drill.

Originally posted by Machine1
Where did you get the CNCSpeed software? Did you download it off of the net


Nevermind I found it. Thanks

Dormer Tools series A108 fast spiral for autenitic stainless steels is the actual drills that I use for stainless. I believe these are a cobalt alloy, too, at least they look like it :) You still cannot overspeed these drills, but they do drill nice and smooth.