Drilling Into Cast Iron

[Keith Starosta]

What is the best type of drill bit to use when drilling 1/2" holes into cast iron? What may work the best?

Thanks!

- Keith

[Jason Whitaker]

I used a cobalt (the mineral, not the blue borg brand) bit when drilling into my cast iron table without any hitch. I believe HSS will also work, provided it is sharp. Cast Iron is not as hard as you might think, compared to steel.

[Eduard Nemirovsky]

I did use a regular HSS drill without problem.
Ed.

[CPeter James]

No lubrication is necessary as the carbon in the steel will lubricate it enough. Cast iron drills and taps easily.

CPeter

[David Christopher]

HHS drill bits are fine to do the job just make sure you bore a pilot hole first, I have found that if you drill several holes steping up a couple of sizes each time works best for me

[JohnT Fitzgerald]

I think I used HSS bits....really any decent bit should work ok. just take your time and it drills quite easily (no surprises).

[John Thompson]

I just purchased a set of reasonably price DeWalt pilot point bits that don't require the pilot hole. They work great in cast iron with speed at minimum but are a bit agressive in wood.

Sarge..

[Bruce Page]

A standard borg HS twist drill without lubrication will work fine. Cast iron IS NOT a hard material. There's no need for colbalt, M-42, or carbide, unless that is what you have sitting around.

[Keith Starosta]

Good deal!! Thanks for the info, guys!!

- Keith

[Mike McCann]

Keith

a regular drill bit would work fine. I would use a smaller bit first and work up to the larger size.

[Chris Padilla]

Depending upon the bit, I'd suggest using a punch to put a nice little mark/dimple where you can put your bit so it doesn't wander on you.

Don't forget about placing a towel or something to catch shavings if they'll fall on anything you can't easily clean up.

As everyone else said, CI drills very nicely and cleanly...with a sharp bit, of course.

[Jim Becker]

What Chris said about the punch. Then a reasonably sized pilot hole. Then the the real McCoy. Drill at a steady pace so you can control the drill, itself.

[John Keeton]

Keith, I have only one experience at this, so take it for what its worth. But, I decided I should have used a guide clamped in place - perhaps a 2" thick piece of oak thru which the correct size hole had been drilled on a drill press.

If you do a pilot hole, then double this procedure. I had difficulty with creep, but it may have been lack of the correct size pilot hole. Just a thought.

[glenn bradley]

I center punched, drilled a pilot hole that was big enough to accept the splitpoint width and drilled it out to size. No lubrication required. Drilled easily with a cheap-o Ryobi bit out of a kit I got as a gift somewhere down the line.

[Bruce Page]

Depending upon the bit, I'd suggest using a punch to put a nice little mark/dimple where you can put your bit so it doesn't wander on you.


Good point. I almost always use a center drill whether I’m hand drilling or using my mill. (comes from my machinist training).
You don’t need to drill a pilot hole when you start with a center drill…. ;)

[Cliff Rohrabacher]

Any conventional High Speed Steel Twist drill will do fine.
Cast iron is supremely easy to machine. Use no lube whatsoever. An air hose will be helpful. to clear chips.

When machining cast you need no oil or coolant because the chips come out so cleanly and do not adhere to the cutter. This means the heat will stay in the chip. Any lube you use will create an adhesive bond ( surface tension) holding the hot chips against the tool and work causing the heat to transfer to the tool and work.

In a machine shop the only time one will use a lube on cast is when it's possible to literally flood the work flushing the chips away in the stream of coolant fluid.
Otherwise cut it dry.

For a half inch hole I'd drill a pilot hole first with a .250 drill or maybe a number 7 drill: no bigger and certainly no smaller.

[Peter Quinn]

When I drilled and tapped my tables for power feeders, a machinist at work set me up with three tools. First was a prick punch to make a dimple dead center on my paper template holes. Second was a pilot bit that drills an 1/8" center about 1/4" deep then has tapered sides to add a slight chamfer to the beginning of the hole. Two birds with one stone. These are available from EMCO for around $5. This makes it much easier to get a bolt started in a threaded hole (or a thru hole without threads) than one with a square edge, and made it easier to start the drill bit and subsequent tap. The third item was a HSS jobbers bit sized to allow tapping a 1/2" #13 thread. I used a low speed (300RPM) hand held drill, just a drop of 3 in one oil to get things started, literally one small drop, not a pool.

If you are drilling holes in iron to accept bolts it is far easier IMO to tap the holes with threads than to use a nut and bolt combination, which is a real nuisance. Of course if you were say, drilling holes in an OEM iron table on a powermatic 64 to bolt it to a quality grinding router extension wing (just for instance:D) I'd only want one side of the connection threaded. The other hole you might want to make fractionally over sized, like say 9/16" or 17/32", to allow some room for setting the two tables flush.

[Gary Click]

Drills with a high Ferromanurium content seem to work very well.

[Shawn Honeychurch]

Drills with a high Ferromanurium content seem to work very well.

What about ones with a high dilithium crystal content?

[David DeCristoforo]

Best would be a bit with a high Leveright content alloyed with a small percentage of Unobtainium. But if you can't find those, plain old HHS bits will do fine.

[Bruce Page]

Peter, your "pilot bit" is otherwise known as a center drill. :)

[Glenn Howard]

+1 on using a punch first. I prefer cobalt bits, but HSS should do the trick as well.

[Vic Damone]

None of the advise you've recieved here at this woodworking site is completly correct.

Depending on the dimention of the piece and/or the size and location of the hole, cast iron can be very delecate to do some of the suggestions made so far.

http://www.practicalmachinist.com/

[Peter Quinn]

Peter, your "pilot bit" is otherwise known as a center drill. :)


Thanks Bruce, didn't really know what it was called. Works great though.