Know How: Drilling Stainless Steel
For many years I hated drilling stainless steel. It’s hard, it requires expensive cobalt or carbide bits and it takes a long time to drill. In other words, I had many good reasons for feeling this way. However, as it turns out, all of them were based on incorrect information.
First and foremost was the belief that stainless is a “hard” material. Because I thought stainless was hard, I would run my drill at high speed, thinking it would otherwise take forever to complete a single hole. I could not have been more wrong. Thanks to the advice of an exceptional metal worker, I learned the right way to drill stainless with standard High Speed Steel (HSS) drill bits.
Stainless is actually a relatively soft metal, at least in its initial state. What stainless tends to do is “work harden” fairly quickly when heated, and drilling at high speed creates a lot of heat. When stainless steel work hardens, it becomes very hard and extremely difficult to drill.
Here is the right way to drill stainless steel:
Start with a sharp drill and have it turning as slowly as your drill or drill press will allow. I set my drill press to its slowest speed or run my portable drill as slow as the trigger will allow.
You need to exert a lot of pressure on the drill bit—as much as it will bear. Small bits can be a challenge because pressure can cause them to bend and break, but you can put a lot of pressure on any drill bit that’s ¼in or larger. You will know if you are exerting enough pressure if a continuous spiral of material comes off the bit as it turns. The photo above shows the kind of stainless spiral you should see as you drill.
You must keep the drill bit and stainless material cool. Machine shops have a continuous stream of lubricant that they spray onto the tip of the drill bit to both cool the drill bit and the stainless and to lubricate the cut. When you’re drilling stainless onboard, in a boatyard or a home shop, that is not possible.
However, what you can do is regularly stop drilling and drip some oil onto the bit and in the hole. If you have a helper, you can also have them place a few drops on the bit as you are drilling to speed up the process.
Ideally, you want to use cutting oil, although motor oil or even WD-40 will do the trick. I even used olive oil once. The key is to stop often for cooling and to make sure there is plenty of oil.
If you follow these suggestions you can quickly drill stainless using a standard highspeed steel bit that you can buy in any hardware store. I recently drilled 16 quarter-inch holes through 3/16in stainless using a standard HSS bit and when I was done, the bit was still sharp and usable.
But Be Careful! While this procedure will allow you to drill stainless, you need to take some precautions. Drill bits can snap when you’re working on any material, but the high pressure used to drill stainless can lead to a drill bit snapping and sending metal shards toward your eyes. Everyone involved in or watching the drilling must wear safety glasses.
As the tip of the drill begins to come through the bottom of the hole, there is a tendency for the edge of the drill to snag the metal and spin the piece being drilled, sometimes with considerable force, which can cut you or even break bones. Always firmly clamp the piece you are drilling to a substantial work surface.