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

[skcncx]

Thanks all for the input....

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.

Yes, great idea, without a center pilot bit, I'll do this. And someone else commented on reverse, I was thinking more about the bit and a diamond but doesn't have a direction... but reverse is more important if I can catch and grip on the tap... reverse will help back it out if I get lucky.

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

I can by making my backing plate different, it's a large backing plate I'm mounting DRO arm to and other stuff.... I've already drilled and counter bored it... so ideally I'd rather not re locate.

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.

I've had few people suggest this.. my welder is setup for aluminum but I never thought about using stick rods, I can do that with my multi purpose welder. What amps do you think would work? Never stick welded, just MIG aluminum is all I know.

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?

Not a through hole. I have a die grinder and roto zip tool I'll have to give this a try if my diamond hole saw try doesn't work.

 

[GT-6 Racer]

I’d try a 7018 rod 1/8” or 3/32”. Stick it hard And just pull the stinger clamp. Maybe 60-80 amps. You really don’t want to start a proper arc With such a small tap. Test amps on a piece of scrap. I’ve had good luck with this if the tap snapped due to bending. If bottomed it will be harder to get loose.

 

[ChazzC]

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

I have a handful of small diamond hole saws just for this purpose, but have been lucky enough to be able to grab the broken end with a pair of Japanese screw extraction pliers.

I did once use a small diamond bit to dig a broken 2mm ball-end hex wrench out of an M4 set screw in an Aluminum knob. It took a while, being careful not to damage the threaded hole but eventually dislodged the remains of the driver and made a deep enough hole in the remains of the set screw for an easy-out to grab it: you may be able to do the same in the end of the tap.

 

[Dhal22]

There is some great help being provided here. Makes me smile. 'Cause I know I might need it someday!

 

[tq60]

Canot see the tap in the photo.

If you can see the flutes, meaning there are open spaces, then the dentist act is best here.

Rotor zip is huge for this.

Smaller size tools work well.

The small burr or diamond coated but slips into the flute, and you just let it do the work going towards the middle.

If you can cut through the web in the middle, you may be able to get a screwdriver on it to get it out.

How hard were you turning it?

If it broke due to hard turn, maybe not. If you bent it, then it should come out easy.

Do this before the big stuff.

Sent from my SM-G781V using Tapatalk

 

[woodchucker]

I drilled out a broken drill bit using a masonry bit. My carbide drill bits broke trying to get it out, the masonry bit is tougher than sharper carbide. I think the masonry bit may work for the tap as well. I was drilling my Clausing mill column to install scales. I also didn't want to move the hole. Just throwing out another option that might work.

 

[RJSakowski]

I drilled out a broken drill bit using a masonry bit. My carbide drill bits broke trying to get it out, the masonry bit is tougher than sharper carbide. I think the masonry bit may work for the tap as well. I was drilling my Clausing mill column to install scales. I also didn't want to move the hole. Just throwing out another option that might work.

I have had success sharpening a masonry bit to give a decent cutting edge. Out of the box, they are usually quite dull, relying more on shock than actual cutting in use. I have a small diamond wheel from HF that works well on carbide. I am still using the same wheel that I bought several years ago. https://www.harborfreight.com/repla...-volt-circular-saw-blade-sharpener-98862.html

 

[solo]

https://cdn.mscdirect.com/global/images/ProductImages/7412923-24.jpg

I've used straight flute carbide drills with great success, when nothing else worked or broke.

 

[Jimsehr]

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 !

I had a broken tax extraction business for about 15 years and I would first try post # 9. Also car engines often have broken taps in them so I would check motor repair shop. And motorcycle shops often have this problem. And they may give you some tips.

 

[Flyinfool]

Even if you are going to try some kind of carbide drill, you still need a guide plate/drill bushing to keep the drill aligned with the hole.

Why were you tapping so deep, Scales are not that heavy 1 to 1.5 diameters of thread is all that is really needed. That is enough thread that the screw will fail before the threads fail.

Another trick I use for hand tapping where I want a longer screw is to drill a pilot hole at the exact major diameter of the screw around 1 diameter deep, then use the tap drill and tap the required number of threads. This will allow the sides of the hole to help support the screw against any side flexing but no require as much tapping depth. The deeper you tap the more likely you will break the tap. As you are tapping all of the cutting forces are near the tip of the tap. the torsional load of tapping is twisting the tap slightly and causing the thread to deform slightly. That is why taps get tighter and tighter the deeper you go. until they snap. Of course bottoming out in the hole or on the pile of swarf that a spiral point tap has pushed ahead, or even the chip buildup in the flutes of a hand tap can lock it up and snap the tap.
With a hand tap I back the tap out of the hole after every 3 or 4 turns to clear out the chips. If the flutes get full you are done.
With a spiral point tap into a blind hole I never go more that 50% of the hole depth. All the chips driven ahead of the tap will fill up the hole and cause to to bottom out way before the hole depth is reached.
Tapping cast iron needs to done more like a hand tap reguardless of the the tap style, CI does not make long stringy chips that can be pushed either forward or back it just kind of makes dust that will fill the flutes of the tap especially if you are using cutting oil, then the CI dust turns into a paste. You need to back the tap out and clear the swarf to avoid binding.