What's the secret to drilling stainless steel?

[Bacon8tor]

I'm working on the wing spars on my Onex and having a heck of a time updrilling the stainless steel outboard pivot plates, W18-15. Granted it's thick stock but sometimes even new high quality bits just spin, dull, and make no progress. Sometimes a bit will smoke a little then get through. I might get two or three holes with that bit before dulling. I'm using high speed and cutting fluid. Is this normal? Should I just plan on a new bit for each hole?

[fastj22]

slow speed. don't let it get hot. Getting hot only work hardens the stainless steel and makes it harder. Same thing for drilling out stainless rivets.

[wlarson861]

In order to drill stainless steel you need to use a Cobalt bit. Nothing else will cut the stainless steel or titanium in the gear legs with any degree of success.

[pchuckie]

I don't have experience drilling SS on aircraft parts, but tons of experience drilling SS shower surrounds. Like previously mentioned, slow speed and good bits. Most people drill holes way to fast and way to much pressure.

[Bryan Cotton]

Slow speed, high pressure, oil.

[mike.smith]

Like REALLY, REALLY, REALLY slow speeds! A snail's pace.

[DCASonex]

Along with slow speeds, make sure bit keeps cutting. Stainless Steel is such a poor conductor of heat that very localized high temperatures can quickly develop, both hardening the Stainless steel and damaging the bit. Use of light pressure, thinking it will save the bit, does just the opposite. New sharp bits will cut with less pressure. In general, for most all materials, not just SS, 135 degree spit point bits are good for first holes, but the old standby 118 degree bits are better for enlarging holes as they are less apt to grab with pressure.

David A.

[Bryan Cotton]

Here is a short video showing the slow speed.
https://youtu.be/8zfjsZKSmuY

[sonex892.]

Along with slow speeds, make sure bit keeps cutting.
David A.

David makes a good point with this. If there is no metal spiraling out immediately, something is wrong. Stop or it will get hot real quick. If it is a new bit and you are going slow. Not using enough pressure is most likely the problem. If you have heated the metal you can expect to throw away every new drill used to fix that hole.

Using the correct technique and cutting fluid I used to get 50 to 100 uses from 1/8" bits in stainless electrical cabinets. Pilot drilling requires more pressure than updrilling. Just never get it hot

Steve
Sonex 892

[paulonex]

plates on the onex wing joint are made of 4140 to my understanding and are not SS
Having said that the drilling comment in general are correct
Note 4140 has corrosion resistance properties, but is not classified as a "stainless steel"