Broken tap in cast iron... anyway to drill around to get it out?

[skcncx]

What a bummer, I was hand tapping an M5 threaded hole on my PM 833TV column benchtop mill to mount a bracket for my DRO and 1 of the 4 holes I snapped the tap off flush with the surface.

I see now way of using a traditional tap extractor, so I'm wonder, could I use a very small hole saw, large enough to go around the tap with no center, like the diamond drill bit?

It was a spiral tap, and I've tried a tap extractor but there's nothing to grab onto.

I want to drill it out plug it with a larger threaded plug and then an inner hole for the intended 5M tapped hole.

Pretty much broke off flush and slightly below the surface. I really don't want to move my holes.

 

[Dave Smith]

how much of the tap is still in the hole--if only a short section, see if you can loosen it with a small punch and hammer or break it in peices (taps are brittle)to remove with blasts of air----if it is a long portion this will not work, and a hole saw will need to be tried---if a diamond or carbide grit hole saw is used run drill in reverse.
Dave

 

[hman]

Annular cutters do a much cleaner job than "traditional" hole saws. My annular cutter set includes an R8 shank. I can use it on the mill (no need for a pilot pin or drill).

 

[skcncx]

how much of the tap is still in the hole--if only a short section, see if you can loosen it with a small punch and hammer or break it in peices (taps are brittle)to remove with blasts of air----if it is a long portion this will not work, and a hole saw will need to be tried---if a diamond or carbide grit hole saw is used run drill in reverse.
Dave

Quite a bit, broke off where the tap ended, so more than .75" inch. Yes they are brittle for sure. It was cutting nicely, picked up the phone, not paying attention and just cranked on it too much... plus wrong style of tap.

I just ordered a diamond hole set on amazon, should arrive tomorrow. I'll run in reverse, though I'm not sure that'll matter with a diamond bit. I'm hoping if I can expose enough, I may be able then grab onto it. If not, I'll go all the way.

 

[skcncx]

Annular cutters do a much cleaner job than "traditional" hole saws. My annular cutter set includes an R8 shank. I can use it on the mill (no need for a pilot pin or drill).

Yea, it'll have to be a hand drill, because it's on the column of my mill. Gonna try a diamond hole saw, basically grind around it not sure if it will have any affect on the cast iron. Hopefully I can expose some of the tap and then extract it. Total tapped depth is around 1".

 

[RJSakowski]

I had that happen when I was tapping mounting holes for dust shield over the z axis DRO scale on the lathe. I was able to get enough of the tap removed using a combination of a carbide p.c. drill and a small prick punch so I could use a shorter screw. Cast iron is notorious for having hard spots and I just happened to hit one.

 

[hman]

Yea, it'll have to be a hand drill, because it's on the column of my mill. Gonna try a diamond hole saw, basically grind around it not sure if it will have any affect on the cast iron. Hopefully I can expose some of the tap and then extract it. Total tapped depth is around 1".

You'll probably want to start by using the holesaw to produce a guide hole in a chunk of aluminum, then secure the aluminum to where you'll want the actual hole. I'm hesitant to use hole saws in a hand drill because they can catch unevenly and try to wander or kick to one side.

 

[mac1911]

What a bummer, I was hand tapping an M5 threaded hole on my PM 833TV column benchtop mill to mount a bracket for my DRO and 1 of the 4 holes I snapped the tap off flush with the surface.

I see now way of using a traditional tap extractor, so I'm wonder, could I use a very small hole saw, large enough to go around the tap with no center, like the diamond drill bit?

It was a spiral tap, and I've tried a tap extractor but there's nothing to grab onto.

I want to drill it out plug it with a larger threaded plug and then an inner hole for the intended 5M tapped hole.

Pretty much broke off flush and slightly below the surface. I really don't want to move my holes.
View attachment 441646

Is there no room on the bracket or mount to relocate the hole a little L/R or U/D ?

 

[GT-6 Racer]

If you have a welder stick a rod to the end of the tap and see if it will back out. Fairly low amps so it doesn’t strike a continuous arc. Break the flux off the rod a little at the end so you can get a good stick.

good luck !

 

[tq60]

Go to harbor freight and get their small pneumatic pencil style grinder.

Then, get a couple of packs of the diamond bits.

You can also order carbide burrs in that size.

Lots of water and time, working like a dentist, you can get it out.

Was it a through hole?

Maybe you can get to the back side with some teardown.

If not, it may have bottomed out.

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