Tap hole in bandsaw cast iron table

[Dave Rosner]

Have a grizzly 14” bandsaw and need to drill to tap 2 holes into the cast iron table. Everything I’ve read says any bit that works with metal will work and it’s relatively easy.

I bought the heftiest 13/64 bit at the store and tried lots of my other HSS bits I have too. But so far I can only get a small dimple. Should this take really really long or are these machine tables different kind of cast iron that can’t be drilled?

Anyone else do this successfully?

[Mike Cutler]

Many times.
I don't know why you're having trouble, 13/64th's is a relatively small bit. I know folks think that you don't need cutting fluid for cast iron, but I always found it helps.
Are these quality drill bit's? What's the speed of the drill?
Odd.:confused:

[Mike Kreinhop]

I've drilled and tapped several cast iron tables. I've always used a little cutting fluid (or light oil) and a slow speed on the drill motor. Trying to drill fast with cast iron doesn't work.

What size thread are you trying to cut? I assume the 13/64-inch drill is the pilot hole and you have the correct drill for the tap you will be using.

[Wade Lippman]

Probably going too fast; you need slow for metal. A little oil, or even water, helps. If all else fails, try a masonry drill.

[Van Huskey]

A little oil and a speed of between 75 and 100rpm should work for CI.

[Dave Rosner]

I’m trying to tap for a 5mm bolt if I remember correctly. There isn’t an exact fractional not but whatever I came up with was close enough on the charts.

Could it be that I need to put a lot of force into the drill? I might try to do it on my drill press too.

Some of the machinist sites talk about a layer of extra hard cast iron on some things. I’m going into the corner of the table that is about an inch or so thick. Not sure if that matters.

I’ve tried slow and fast and even hammer drill..

[glenn bradley]

Something is going on here. I’ve drilled three eights inch holes in cast-iron using a battery powered hand drill at about 200 RPM. Very easy.

[Van Huskey]

Something is going on here. I’ve drilled three eights inch holes in cast-iron using a battery powered hand drill at about 200 RPM. Very easy.

I agree a hole less than 1/4" shouldn't be hard at all. My first thought was bit but he said he tried multiples. I have drilled much bigger holes in CI tops with a hand drill and crappy Asian bits and normally don't lubricate, CI generally self-lubricates. I guess it could be unusually hard (but Grizzly?) worst case get a quality cobalt bit, probably with a 135* point.

[Bill Dufour]

Do not hammer drill! you can crack the cast iron. I would switch to a 1/8 bit for a pilot drill. Saw table should not be hardened. Poor casting methods may have made chilled iron near the edges.
Bill D.

[Marc Jeske]

You may be applying insufficient pressure, and/ or too fast rpm.

Steel and Cast Iron needs WAY more feed pressure than drilling any wood.

Watch a few Youtube videos to see what type of cutting action you want to see.

If the above was your problem, and pretty sure it is, you may have dulled the bit some by burnishing it.

Marc

[Mike Kreinhop]

I’m trying to tap for a 5mm bolt if I remember correctly. There isn’t an exact fractional not but whatever I came up with was close enough on the charts.

The drill size for the M5 tap is 4.2mm, which is about 0.1654 inches. The 13/64-inch drill is 0.2031 inches, so your M5 bolt will have a looser fit and won't take much torque before it strips out the threads in the table. If you can't find a 4.2mm drill, the #19 is the closest match at 0.1660 inches.

For what it's worth, I buy all of my SAE and metric drills and taps from McMaster-Carr (www.mcmaster.com). If you can't find the correct drill locally, McMaster-Carr has fast delivery.

[Richard Young]

Just checking that you are running the drill in forward position and not backwards? Sometimes i forget to reset switch position after backing out of a hole.

[John K Jordan]

Some of the machinist sites talk about a layer of extra hard cast iron on some things. I’m going into the corner of the table that is about an inch or so thick. Not sure if that matters.


Some people anneal the cast iron before machining. I've never tried that - would need a good sized oven or a way to cool very slowly.

If the carbides are just on the surface, maybe you can use a diamond bit on a dremel or something to get through. I've drilled and tapped cast iron but haven't run into the need for anything other than standard drill bits. I know you can buy diamond drill bits but don't know if you can get one that small, and even if you did tapping might be a problem. I might start thinking about another way to do the job.

JKJ

[James A. Brown]

I am retired now but worked in the machining trades for 40 years so know a bit about machining most kinds of metal. First, if you can't drill it you would never be able to tap it. A tap will be much more brittle than a drill so if a good quality drill won't go through it just forget it. I also agree that the drill is probably toast by now and you will need a new one. A few drops of motor oil should be a big help and absolutley use some on the tap. Sometimes cast iron does get harder near the edges of a casting so if you can move the holes further away from the edge that might also help.
IIRC a 13/64 dia. is the correct size for a 1/4-20 thread, whatever size threads you choose use the correct size drill. If the hole is too big for the thread size the threads will pull out too easy. If the hole is too small it will be harder to tap and the last thing you want to do is have a broken tap in the table. Good luck, Jim.

[Bill Dufour]

Beware of carded taps and tap drill sets at the hardware store. I have seen them with the wrong tap drill where they just throw in the closest fractional size. If it is too hard to drill consider a through hole with nut on the bottom. The nut could be epoxied if needed.

[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.

390206


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.

390206


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:
416159

[michael langman]

Good eye Lee. That would surely cause the problem.

[Kevin Beitz]

Make sure the drills turning clockwise looking down....

[Ole Anderson]

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:
416159
Actually the Irwin Turbomax is designed for metal cutting in much the way Dewalt Pilot Point bits are. Not to be confused with brad point bits which are designed specifically for wood. I have found the pilot point bits work rather well in most metals.

[Osvaldo Cristo]

I am not a Metallurgist but I guess there is a wide variation on cast iron.

My limited experience on the subject had found one very easy to drill and one completely impossible for mere mortals...

[Tom M King]

Sometimes even in the same casting, there can be relatively soft areas, and harder than it seems like possible areas, depending on the care in the whole casting process. The engine block I had to rethread those large holes is was some very nice cast iron by (or for) John Deere. Google "drilling hard cast iron", and you'll find some interesting stuff. There are special drill bits made for drilling really hard cast iron, with designs like three carbide flutes, and an unusual looking grind. I just figure that if a Cobalt bit won't do it, that it's over my head.

[Jim Andrew]

Most of the steel used is recycled, and sometimes, old ball bearings get dumped in with other steel. I bought some 4" channel iron, and drilled holes in it, and found a couple holes where it broke my 1/2" drill bits. Started with 1/4", then 3/8" and finished with the 1/2".