drilling cast iron

[Robert Mahon]

Another thought:
Unless the thickness of the cast-iron will support at least 5 full threads (1/4"), I'd suggest you through-drill it and use good hardware for fastening.

Cast-iron does not have the strength of steel and I'd be concerned the threads will pull out.

[brian lanning]

Another thought:
Unless the thickness of the cast-iron will support at least 5 full threads (1/4"), I'd suggest you through-drill it and use good hardware for fastening.

Cast-iron does not have the strength of steel and I'd be concerned the threads will pull out.

I'm just drilling through holes. There's threading already in the other piece.

I didn't get to drilling it last night because I had to stop at sears and order a compucarve. (there's my drive-by)

brian

[Brian Dormer]

I have to - unfortunately - disagree about how "easy" it is to drill cast iron. I was in a similar situation (needed a hole in my table saw deck to attach something). I tried for a good hour - small bits - big bits - dry - oil. NADA. The only dent was the dent I made with a punch to mark the spot for the hole. I gave up and went to "plan B".

It was an old (probably 1970's) Craftsman benchtop TS. I doubt that the top was made of anything exotic. But it was like trying to drill Titanium.

Truthfully, I *MUST* have been doing something wrong - I was using some older (but still servicable) drill bits (I didn't want to risk trashing my good ones). But out of 3 different bits - I got nowhere.

I don't think the bits were any worse for wear. All I did was make some heat.

I'll throw myself on the mercy of the experts - what did I do wrong?

bd

[Mike Henderson]

I have to - unfortunately - disagree about how "easy" it is to drill cast iron. I was in a similar situation (needed a hole in my table saw deck to attach something). I tried for a good hour - small bits - big bits - dry - oil. NADA. The only dent was the dent I made with a punch to mark the spot for the hole. I gave up and went to "plan B".

It was an old (probably 1970's) Craftsman benchtop TS. I doubt that the top was made of anything exotic. But it was like trying to drill Titanium.

Truthfully, I *MUST* have been doing something wrong - I was using some older (but still servicable) drill bits (I didn't want to risk trashing my good ones). But out of 3 different bits - I got nowhere.

I don't think the bits were any worse for wear. All I did was make some heat.

I'll throw myself on the mercy of the experts - what did I do wrong?

bd

Can you drill mild steel with your drill bits? Find a piece of mild steel somewhere, maybe 1/4 inch or thinner and see if your drills and technique will drill into it. If not, the problem is there (in your drills or technique) and not in the cast iron. You should use standard HSS twist drills and not drills with brad points that are sometimes used in woodwork.

I'm not an expert but I've been told that in really old cast iron it was possible to get hard nodules but that the modern techniques used to produce and cast iron have pretty much eliminated that.

Grey cast iron usually drills even better than steel (as someone earlier mentioned) because some of the carbon converts to graphite during the cooling process. The small grains of graphite cause the iron to fracture, producing dust swarf rather than ribbons. Additionally the graphite provides some lubrication during the drilling.

Mike

[glenn bradley]

I'm gonna say bit problem BUT, that is only based on my experience. I was using a semi-used El Cheapo bit from one of those Ryobi kits that folks buy you for your birthday. No problem at all. I didn't even drill a starter hole first. If the bit doesn't start peeling off chips from the start, something is different than my experience (wow, that sounds smart, huh?). This does make me wonder as this was "new" cast iron. I have not drilled in any of my older iron.

[David Epperson]

Way back in school I was taught NOT to use oil or coolant with cast iron. As has been mentioned the chips come out as dust...dust and liquids make mud - a very abrasive mud. We used an air jet to clear the chip/dust and to cool the bit. Go slow, clear the chip/dust often and if possible put a backer piece behind the hole so the bit doesn't grab and bind when it breaks through. Tapping is only a little bit different, but still needs the chip dust cleared often.

[Skip Thomsen]

For drilling cast iron or brass, you should always sharpen your twist drill bit with a slight negative rake. The cutting action of the bit needs to be a "scraping" action or the bit will dig into the material. This is especially important when enlarging an existing smaller hole.

And yes, you can cetainly get away with a regular out-of-the-box twist drill, but it works better and safer to do it rignt. The bigger the drill, the more important it is, too.

The negative rake thing applies to all cutting tools for cast iron or brass, like milling-machine bits, lathe tools, etc.

[Rob Blaustein]

For drilling cast iron or brass, you should always sharpen your twist drill bit with a slight negative rake. The cutting action of the bit needs to be a "scraping" action or the bit will dig into the material. This is especially important when enlarging an existing smaller hole.

I've drilled holes in my TS wings using regular drill bits (usually cheapos) for metal work but I have noticed some biting from time to time. I usually sharpen them with my Drill Doctor. Could someone please explain the negative rake thing and maybe describe how you would put one on a drill bit?

[Robert Mahon]

Easy to do, a bit harder to explain.

A drill has a 59 degree included angle across the leading edges of the cutting profile. Hold the drill vertical and look at the drill so you can see this angle. Now rotate the drill 90 degrees so you can see one of the sharp cutting edges and the leading edge of the spiral flute. It is this edge on both flutes that must be "Dubbed" (ground to make it more vertical). A slight negative angle will also work well.

If this is not done the drill will bite and pull itself into the metal. If it locks up the torque from the motor will be transmitted to your wrists. If using a powerful motor, you may be injured or have the motor torn form your grip.
DO NOT USE THE DRILL LOCKED IN THE ON POSITION.

As stated by another, this technique is also used with Brass, Bronze, AMPCO Bronze, etc.

Also, do not use a drill having other than a standard 59 degree cutting angle, which includes Brad-point type.

Lastly, older cast-iron should pose no problem unless it was made during the Industrial Revolution. Although the processes have improved, the composition hasn't changed much in the last 50 years. Rarely is a hard spot in exactly the place you start to drill. If something like that is experienced, I suspect the drill was made cheaply and useful only for drilling wood or plastic.

Use a HSS (High Speed Steel) drill. If necessary, buy a new drill of known quality.

I hope I haven't confused you with this.

Good ain't cheap and cheap ain't good.

[David Epperson]

I have to - unfortunately - disagree about how "easy" it is to drill cast iron. I was in a similar situation (needed a hole in my table saw deck to attach something). I tried for a good hour - small bits - big bits - dry - oil. NADA. The only dent was the dent I made with a punch to mark the spot for the hole.

I don't think the bits were any worse for wear. All I did was make some heat.

I'll throw myself on the mercy of the experts - what did I do wrong?

bd

The only time I've ever seen that happen, the man doing the drilling had the drill in reverse. But I'm sure that wasn't the case this time.

[Gary Keedwell]

With the size of the drill (.201) I would not be too concerned with resharpening your drill bit. Using a hand drill, as opposed to a drill press, you will not be able to give the bit the force it would need to really catch that hard. Just be careful and slow it down (feed) when you think it will breake through. In my experience it is starting the hole and ending the hole that usually has any problem of "catching".

Gary K.

[Roy Wall]

With the size of the drill (.201) I would not be too concerned with resharpening your drill bit. Using a hand drill, as opposed to a drill press, you will not be able to give the bit the force it would need to really catch that hard. Just be careful and slow it down (feed) when you think it will breake through. In my experience it is starting the hole and ending the hole that usually has any problem of "catching".

Gary K.

Gary - Robert,

I was thinking of using my drill press to get perfect perpindicular holes drilled in the CI fence of my band saw. Maybe I should just use the hand drill and use the "CLUTCH" setting on a low #?

I can clamp the fence securely to the drill press table..though....

[Gary Keedwell]

Gary - Robert,

I was thinking of using my drill press to get perfect perpindicular holes drilled in the CI fence of my band saw. Maybe I should just use the hand drill and use the "CLUTCH" setting on a low #?

I can clamp the fence securely to the drill press table..though....

Hi guy, I would clamp it and not worry about it. Just start the hole slowly, without a sudden thrust, and finish slowly. It might grab a little when it breaks through, but no big deal. Don't be afraid of it, especially if your clamping it.

Gary K.

[Robert Mahon]

I agree with Gary.
It is always better to use a drill press when an accurate hole is needed. In this case, doing it by hand may result in an oversized hole, which will compromise the thread. There is also less chance of the bit "grabbing". Set the RPM to about 1500 or so, which is fast enough to get the job done but not so fast as to burn the point. Also, while you have the piece under the spindle, start the tap with it in the chuck rotating the spindle by hand, which will assure a straight thread.