Drilling Stainless Steel

[GrowleyMonster]

Originally Posted by Johan Leopard51

Lots of the expected comments about bit and speed and lube - but what views on first drilling a pilot hole?

If you start the hole with a center drill, no further pilot hole drilling should be needed, normally. I find that often a through and through pilot hole creates problems with the bit grabbing and bogging the drill motor down. One situation where I do use a through pilot hole is when I want to back drill from the other side, to keep it nice and clean and reduce burr. It will grab when it breaks through, so if you make the break through point somewhere before the back side, you get a cleaner hole. De-burr, and ream if you have an appropriate reamer, and you get a very nice hole.

I do get a lot of use out of my center drills, and not just on the lathe, either. And for the actual penetration through the back side I sometimes use a small center drill, and then center drill again from the back side, and then go with the sized drill.

The only issue with center drills is they are slightly more complicated to sharpen.

If you find that you prefer drilling a pilot hole all the way through, no law against it. Nothing written in stone. More than one way to skin a cat or drill a hole. Do it like you feel it, but once you discover center drills, I think you will be an instant convert. That, and a good set of center punches and a nice hammer.

[UFO]

Drilling SS even 2205, is not hard and can be done with only HSS bits, BUT drill very slow and with plenty of lube. Start with a small pilot center hole and then go to 6mm and 2mm increments (not less) until you hit your size. Keep the speed slow and the pressure constant and take plenty of stops to re-lube. Once you get to 12mm or above you want to be around 300RPM and no more. I have made 100's of Stainless Bushes with this technique with no issues - Just gotta make sure your drills are sharp and do not overheat them.

[Opie91]

Don’t use oil for a lubricant. I know it is hard to believe but lots of fresh water works best. Use a spray bottle to keep it wet.

It removes the heat very effectively, leaves a clean cut and your bit will still look new when you’re done.

Slow with pressure as everyone else has said.

[coopec43]

Originally Posted by Opie91

Don’t use oil for a lubricant. I know it is hard to believe but lots of fresh water works best. Use a spray bottle to keep it wet.

It removes the heat very effectively, leaves a clean cut and your bit will still look new when you’re done.

Slow with pressure as everyone else has said.

Plenty of machinists would agree with you.

[Bowdrie]

Originally Posted by Opie91

I know it is hard to believe but lots of fresh water works best.

Originally Posted by coopec43

Plenty of machinists would agree with you.

I spent some time working in a machine shop that had a contract to build parts out of 17-4PH, (Bomb fuse parts for the Govt).
The cutting tools/drill bits on the lathes were flooded with a constant stream of "milk" a water-soluble solution for cutting/cooling.

[MikeLK19]

Water works great if you can keep it flowing across. The water is really great at removing the heat, as others have said, and will allow you to go faster. If you can't keep water flowing over it then, oil is better because it stays in the hole and on the bit better than just adding a few drops of water. If you use oil you will need to keep stopping to add the oil as it will be pulled away from the cutting surface rather quickly.

If your hole is deeper you need to make sure the water keeps being able to get down in the hole.

In either case, you need to make sure you do not go too fast where the bit and the stainless gets too hot. If the oil starts to smoke, if you choose oil, or the water is fully ejected out of the hole, should you choose water, you have your RPMs too high.

Cobalt would be better a little better but, high speed steel will work just fine. Either way, you have to make sure the bit and the material stays cool enough.

Like others have said, you do want to push hard enough to have a long string chip and not a bunch of small chips. If the chip comes out really long then, just take the pressure off for just an instant to break the chip.

[Iron E]

IMO, there are points to be made for water, oil, and paste.

Water (Water based coolants) - Water does an excellent job of cooling a bit. Water works best on horizontal surfaces. Water isn't as effective in lubrication as oils or pastes

Oil - While not as good as water for cooling, oil does a great job of cooling. Oil is also better at lubricating a drill bit for prolonged uses. Oil also does a good job of maintaining cooling and lubricating on non horizontal surfaces.

Paste—Like oil, Paste isn't as good as water in cooling but is superior in lubrication. Paste is also an excellent choice for non-horizontal surfaces.

So, the surface angle and depth of the cut should be taken into account.
Any fluid/paste is better than no fluid.
And, as a side note, I like the way oils and pastes collect my metal chips and swarf.

[pianopraze]

Drilled quite a few stainless steel supports for my Prout.

Harbor freight drill press and cobalt bits. Need to keep it lubricated as you drill.

[s/v Jedi]

Originally Posted by Johan Leopard51

Lots of the expected comments about bit and speed and lube - but what views on first drilling a pilot hole?

Originally Posted by Iron E

Mentioned above:

Agreed. I may go down to 4mm for pilot hole but not less as the bit easily breaks with the amount of force. With a sharp 4-5mm bit and enough force, it is amazing how well it succeeds with a good battery hand drill.