Tap hole in bandsaw cast iron table

[Jared Sankovich]

Order a hss bit and ground hss tap (msc has fast shipping.) Cast is usually like butter compared to most metals (generally speaking) so I'm not sure where the trouble is coming from.

[Bill Space]

Is the drill turning in the right direction?

Happened to to me once...(insert red face here).

Cast iron has always drilled easy for me...

[Dave Rosner]

Appreciate all the inputs into this!

Here is a picture of what I am trying to do in case it highlights what I may be doing wrong. I'm going to try my drill press this evening....

[andy bessette]

There's your problem. Turn the bandsaw right side up so that gravity will help you.

[Bill Dufour]

I would guess 10-20 pounds force into the bit.
Bill D.

[Dave Rosner]

ok tried to drill a hole in a different section that is maybe 1/4" thick vs 1" thick where I've been trying to drill. Worked pretty well as everyone has said. I did change to a new bit halfway through as I assume I killed the other bit. I'll use a nut here instead of tapping it and that will work for my purposes.

IMG_0319.jpg


Maybe the 1" hole is in an area that was extra hardened...

<sorry for some reason the website keeps rotating my images...>

[Mike Heidrick]

You drilling into or next to a rib?

You drill and tap cast iron dry.

[Van Huskey]

You drill and tap cast iron dry.

Ask 10 machinists that question and you will get 11 answers.

[Martin Wasner]

That's pretty funny Van.

I just drilled and tapped four holes this morning in a tablesaw for a power feed. Dull bits, and used a cordless drill. Started with a 1/8" bit and went to 3/8" for a 7/16-14 bolt. I think I drilled each four times.

I drilled dry, tapped with cutting oil.

[Chris Fournier]

Anneal cast iron? Awesome. Please understand what what separates cast iron from steel. Cast iron is full of free graphite and is self lubricating. I've tapped dozens if not hundreds of threads in cast iron with a shop made guide and no lube.

[John McKissick]

Have you considered a mag-based drill? Great way to get good pressure and perpendicular holes

[Ole Anderson]

Watching Adam on his Abom79 YouTube channel (machinist) he sometimes runs into a hard spot on cast iron that defies a normal drill. Solution is a carbide or cobalt drill. In my limited experience, I found that cast iron was a dream to drill and tap dry with normal HSS tooling.

[Tom M King]

I know this is an old thread, but since it might turn up in someone's search, I'll add my experience in drilling, and tapping cast iron. I had to upsize, and rethread some stopped depth holes in the engine block on one of my tractors, that held the front end loader on. 5/8" threaded holes had to be upsized to 3/4", and 3/4" threaded holes had to be upsized to 7/8".

In the past I had drilled and tapped holes in cast iron without much trouble. For this job, I tried hand drilling the holes up to the correct size with a handheld 3/4" drill, and that didn't work out too good. Bits were broken, and one 49/64" bit was bent. I ended up buying a magnetic based drill press, but shortening the story to get to the threading part.....

I read what I could find on threading cast iron, and a number of places recommended cutting oil, but not regular cutting oil. There is a "dark" cutting oil that has Sulphur in it. You can even find it in the plumbing section in Home Depot.

Those holes had bottoms in them, so I could not safely risk using the magnetic drill press to tap the holes, even though that is one function of that drill press. I found some large tap handles on ebay. They could be tapped by hand, but it was a bit scary in dry holes, because I could feel the tap flexing (edited to add: might not have really been flexing, but I could tell I was close to the limit on the dry tap). Once I found out about the dark cutting oil, and bought some, the tapping went like cutting butter.

From that experience, I'll recommend using the dark cutting oil when tapping cast iron. Those large holes exposed all the weaknesses.

Also, note that taps come in different types. The commonly seen type is used for starting the hole, and for through holes. With stopped depth holes, you need a set of three taps in that size. The regular one starts the hole, there is another one that cuts the threads a little deeper, and then finish with a bottoming tap. Be careful to note what depth you are going to, because taps are hardened, and pretty easy to break. It's an extra pain to break one off inside a hole.

[Lee Schierer]

ok tried to drill a hole in a different section that is maybe 1/4" thick vs 1" thick where I've been trying to drill. Worked pretty well as everyone has said. I did change to a new bit halfway through as I assume I killed the other bit. I'll use a nut here instead of tapping it and that will work for my purposes.

IMG_0319.jpg


Maybe the 1" hole is in an area that was extra hardened...

<sorry for some reason the website keeps rotating my images...>

If that is the drill bit you are using, it is the wrong type of drill bit. That type is designed for wood. Try to find bits that look like this:
drill bits.jpg

[michael langman]

Good eye Lee. That would surely cause the problem.