Drilling holes in cast iron with portable drill

[george wilson]

Cast iron is used for machinery because,as said,it is self lubricating. I am an experienced long time machinist,and know it is cut or drilled dry.

There was a company years ago which tried making large jointers with steel tables. They got grooves in them soon,and the practice was abandoned. It was Oliver,I think.

[Norman Hitt]

As George stated (and ask any machinist), cast iron is typically drilled dry, as it is self lubricating. I used to own an automotive machine shop, and have drilled many holes in CI over the years.

You do not need to step the hole in small sizes either. Simply drill a pilot hole, and then use the correct bit for the tap that you will be using. Using a countersink on the top of the hold before tapping is a good idea.

A cordless drill will work just fine. Use a sharp bit and keep good pressure on it when drilling. If you have access to a Hougan mag drill, then fine, but it's overkill (and not usually used to drill the small holes that you'll probably use to mount the feder).

The exception to the rule is if the cast iron that you're drilling is of extremely poor quality, and has hunks of unmelted recycled material in it. Then, it's anybody's guess.

Be sure to check the bottom side of the casting for ridges before you start to drill. If you catch the edge of one with your hole, it may cause your tap to break when you tap it.

I've tapped CI both with, and w/o a tapping fluid. It seems to work fine either way, but usually I'll use a small amount of tap-magic as a precaution.

+1 on "everything" you said. One thing NOT mentioned here is that when bit starts out the back side, you need to ease off on the pressure but keep a good grip on the drill, because the bit will try to grab the remaining bit of metal and run on through (like a bolt in a threaded nut) and this will many times cause a chip/chunk to break out on the backside. You can also prevent this if you have room to clamp a piece of hardwood on the backside the same as you would when drilling through wood to prevent tearout on the backside of the hole. (and yes, drill it dry)

[Rich Engelhardt]

Cast iron is used for machinery because,as said,it is self lubricating. I am an experienced long time machinist,and know it is cut or drilled dry

Ok - that's good info & worth every bit of the six bucks I paid to be here.

Next logical question would be - do you tap cast iron dry also or use a lube?0
(I know Scott mentioned it - but - I'd like to hear what George says - (he's a grumpy old fart just like me & we think alike - just kidding )

Using a countersink on the top of the hold before tapping is a good idea.

? I'm not real clear on what that means?
Slightly bevel the hole with a countersink?

FWIW - I'm just getting ready to drill/tap my CI table saw top so I can put a mount on it for an outfeed.

[Scott T Smith]

Ok - that's good info & worth every bit of the six bucks I paid to be here.

Next logical question would be - do you tap cast iron dry also or use a lube?0
(I know Scott mentioned it - but - I'd like to hear what George says - (he's a grumpy old fart just like me & we think alike - just kidding )


? I'm not real clear on what that means?
Slightly bevel the hole with a countersink?

FWIW - I'm just getting ready to drill/tap my CI table saw top so I can put a mount on it for an outfeed.

Sorry Rich, I had a typo. You're interpretation is correct - slightly bevel the hole with a countersink.

No offense taken re asking George's opinion - I pay a lot of attention to his thoughts as well.

[Chip Lindley]

Aside from personal experience, I take my advice to drill CI dry, from The New American Machinist's Handbook (1955). Basic machining principles have changed little for those of us using HSS tooling in older machinery in a home shop.

Drilling CI creates powder instead of a curling chip. Dulling of bits is hastened by the slurry created by oil as a lubricant. Dry drilling allows the iron particles to be lifted by the drill flutes. Frequently blowing out the bore with compressed air is advised.

No doubt in commercial settings, there might be a trade-off between production speed, and bit sharpness with the use of a lubricant as coolant. But, carbide tooling is utilized there also.

[george wilson]

To avoid your drill grabbing when coming through the other side of cast iron,plexiglass,or brass,grind a vertical flat on each cutting edge of the drill bit. It will have a scraping action and will not get sucked out of the opposite side and crack the plastic or cast iron. Nor will it get sucked out the other side of brass and break your wrist by the drill suddenly twisting.

I had to drill some 3/4" holes through some brass with a powerful hand drill. The first hole nearly got my wrist before I could let go of the trigger. The drill was geared down to 850 RPM,and was very powerful. After that,I ground my bit
thus,and had no further problem.

Some guys were operating a hi-fi shop,and made a speaker enclosure from plexiglass which was very expensive. They said they kept breaking a lot of plexiglass drilling through it. I showed them how to sharpen their drill bit,and they were then able to make the cabinets cheaper,and perhaps sell some!! I didn't think a clear plastic enclosure showing the speakers and all the wires was attractive,personally.

It is good to drill a pilot hole the size of the drill's web first. The web doesn't cut well,and pushing the web through by hand is work.

[Rich Engelhardt]

grind a vertical flat on each cutting edge of the drill bit.

George,
You lost me there.

I'm not sure what that refers to?

Also - should I tap lubed or dry?

[george wilson]

On the front edges of the drill bit where the cutting action takes place,grind the cutting edges vertical to the axis of the drill,so the drill has a scraping action rather than a cutting action. They used to make drills for brass. Their flutes ran straight up the drill bit rather than spiraling. Their cutting edges,or lips,were therefore vertical. They looked like the straight fluted bits found in the wooden handles of old eggbeater drills,except the brass drills were made of HSS. You can simulate their cutting action by grinding the cutting edges vertical,even for only 1/32" it keeps the drill from grabbing when it breaks through.

[Rich Engelhardt]

Gotcha!
Thanks!

(just kdding about the GOF - you Da Man George)

[Phil Thien]

What works really well for this, BTW, is those portable drill presses with magnetic bases that mechanical contractors use for drilling holes in i-beams, etc. They're very expensive, but man they're neat.

Back in about 1986 (I was about 20-YO at the time) one of my jobs was to write code that controlled machines that polish nuclear fuel rods. They used these magnetic drill presses from time to time when upgrading/changing machinery. They had one where you could secure the base, and then very precisely align X/Y with little knobs. It was slicker than snot.