Drilling / Countersinking Holes in Tablesaw rails

[Alan Lightstone]

I need to drill several holes in my SawStop tablesaw rails to install a cast iron router table. To have clearance for the Biesenmeyer type fence, I'll need to countersink the holes, just like the saw comes with.

My question is, how do I drill those countersunk holes in that steel? I'm assuming that my wood countersink bits can't do steel. Are their specific drill bits made for this task?

Also, is my drill press necessary for the task, or can a 36V Bosch cordless drill accomplish it?

[Don Zielinski]

Hi Alan,

Unless your countersinks specified wood only they are generally high speed steel and will be fine for the job. You do not need a drill press as the
countersink will follow the hole. The holes are probably 5/16 -3/8 so I would keep the drill speed under 500 rpm.

Don Z.

[Bill Edwards(2)]

Do you have a 1/2 inch or bigger twist drill (bit).

I would think it would provide the countersink you need.

(just guessing)

[Don Zielinski]

A large drill will work in a pinch but the point angle is too shallow. drills for mild steel are 115-135 deg and a standard countersink is 82 deg.

Don Z.

[Keith Westfall]

A large drill will work in a pinch...

But you won't get a very smooth countersink!

[zayd alle]

But you won't get a very smooth countersink!

Nor will your screw seat in the countersink due to the mismatched angles. Pay the $12 and buy a HSS countersink bit from Sears, even if you wear it out for just these holes.

[Lee Schierer]

Buy one of these countersink bits at your local hardware store or big box for about $4. It will work just fine, if you drill by hand drill keep your drill speed down.

[Alan Lightstone]

That's the approach I took, Lee. What speed should I use? Is oiling the bit necessary during drilling?

The approach is to drill the center hole first, then essentially cut the countersink / smooth the edges, correct?

[John Coloccia]

Unless you're drilling through thin aluminum where it really doesn't matter, it's never a bad idea to lubricate your bits. Everything will just work better. If you try to use the countersink like a normal bit, you will probably be rewarded with a chattering cut. I prefer to countersink in metal with a slow speed and a higher than normal pressure. This will "lock" everything together and help to prevent the chatter. Once it starts chattering, you'll probably never get rid of it. You'll also never see it again once the bolt is in, so no big deal in this particular application.

[Lee Schierer]

it's never a bad idea to lubricate your bits. Everything will just work better. If you try to use the countersink like a normal bit, you will probably be rewarded with a chattering cut. I prefer to countersink in metal with a slow speed and a higher than normal pressure. This will "lock" everything together and help to prevent the chatter. Once it starts chattering, you'll probably never get rid of it. You'll also never see it again once the bolt is in, so no big deal in this particular application.

Chattering when countersinking on a drill press is also a function of the play between the rack and pinion gear on your quill. If there is much play, the countersink can chatter pretty easily. Unelss your drill press is really tight, you want to apply good quick downward pressure to a stop point and not try to sneak up on the desired final depth.

[Alan Lightstone]

Thanks guys. Great advice.

[Chip Lindley]

Countersinking has been well-covered. How about drilling holes in metal? Accurately finding where the hole center will be, comes first. Mark the spot with a prick punch. Then dimple that mark with a centerpunch. Now your bit will not wander and scar the surface! It will stay centered where you want it.

A drill press is nice for drilling OR countersinking. Feed pressure is steady and the depth stop can be set for uniform countersinks in every hole.

[Alan Lightstone]

Learned something new. Had to look up what a prick punch was. Why can't you just use the center punch?

[Alan Lightstone]

OK. Drilled the holes with the drill press - no problem at all. 7/16" Holes.

But when I tried the countersink (I got a Hitachi 5/8" titanium one at the BORG), it doesn't do anything. It just spins to its hearts content and doesn't cut into the metal (Despite pretty significant pressure).

What am I missing here?

[John Coloccia]

How hot did you get the steal when you drilled the hole? It's possible to harden the steal if you get it too hot. I doubt you did that but it's possible. Maybe this is a stupid question, but are you sure you're not up against a depth stop or the end of quill travel? I know I know...dumb question, but I figured I'd ask anyway.