Tips For Removing Broken Thread Taps-Maintenance Cruz
Dreaded Broken Tap
Oh how I hated breaking taps in steel. I took very special care and studied up on tap technology to avoid broken taps at all cost. I would suggest for any and all maintenance personnel to get the skinny on thread cutting and the types of taps and fluids to use with specific metals, it makes all the difference.
Anyone who has ever broken a tap knows the feeling for those that haven't it is very deflating. All the studying of taps and fluids can not totally eliminate broken taps but it does greatly reduce the issue. Seasoned veterans still snap the occasional tap. Ask anyone who works in stainless steel about breaking taps, you will probably get a dirty disgusted look and no conversation at all.
Taps, being made of very hard materials, tend to also be very brittle. I can't stress enough the use of the right tap and fluid in combination on certain materials. I have thought I was doing everything correctly and using a good cutting fluid only to jam and snap a tap. Later, the correct cutting fluid is on the scene and I tap one hole after another with no issue, it does make a difference. Also, I find many shops with a bin full of bad or damaged taps that should have been tossed out but weren't. Nothing breaks a tap faster then using a damaged tool, one turn, two turns, screech, tap jammed, gone.
Nothing like getting down to the last hole of a machining project only to break a tap. Seams to happen a lot at the end, I guess hurrying to get finished. So now the real problem, how to get the nub out of the hole. Most maintenance personnel have had this distinct pleasure that can take a few minutes, a whole shift, days, or a complete restart of a part - just miserable.
More Methods Than Tools
There are some tools out there to help remove a broken taps but, I have never found a purchased tap remover that has worked for me, although I have included a link to one at the end of this article. This particular Walton tap remover does work in some situations. Most of the time a small cold chisel and a ball peen hammer and infinite patients is required to work the tap out. I have picked up a bunch of tricks over the years to assist in tap removal and they have served me well.
When a tap breaks you hope there is a nub protruding above the hole, something to get a chisel point on. I have found there are some pre-chiseling things you can do to ease the process. Compressed air has been very valuable at times by either using it to clean debris from the hole to assisting in rotating the tap, it is a force after all. I have removed taps with just air alone on occasion by blowing in at the tap at an angle that promotes reverse rotation and also with assist of a hammer.
With the hammer and air method I would blow in at an angle and tap around the part to create vibration, vibration is a very powerful and under used force. Vibration with rusted objects, press fits, and seized pipe parts works wonders. I remember a guy who had broken an arbor press and a hydraulic press trying to separate two parts. He was at the end of his rope because now all he had left to use was a small hydraulic unit with less then half the tonnage of the one he just had broken. He asked if I had any ideas so I suggested vibration and heat. He never applied heat because he reached for a ball peen a gave it a moderate tap and "pop" the assembly sprang a part.
I will have to say that the air or air and vibration method only works with perfect conditions. Most of the time when the tap breaks not only is the tap embedded tightly but the top thread is normally mangled. A lot of the time I will grind the tap nub flat to the surface and remove some of the work material. Many times at this point I am able to press my thumb against the tap and twist it out and sometimes a little chisel to get it reversing then out with the pressing thumb.
I have had those stubborn taps, especially in stainless, that refuse to budge. At this point I generally decide on one of three options heat, cold, or impact. I have heated and cooled a tap and had it give up rather easily after the process. I have heated the work material and have been able to manipulate the tap while still hot although I general try everything else before I resort to heat.
Breaking the tap in to pieces is a last resort but an effective one. When I would snap a tap in a through hole I would give the nub a good hard smash with a hammer then fish the bits out of the hole. I have been lucky because after removing the broken pieces thoroughly I have been able to finish tapping the hole and use it. I suggest freezing the tap if possible with dry ice, liquid nitrogen,and I have even used propane. Of course using anything flammable is dangerous and not recommended and care also must be taken when using very cold substances.
I had a situation where a tech had a 2 1/2" custom built tap that broke off halfway through a hole. The tap was defective and had an inclusion in the steel shank that caused it to fracture. This tap was not budging at all and production was down. I wound up blowing a hole through the center of the tap with an air arc torch. After the tap cooled it shrank considerably due to the heat and the material removed from the center, it came out with little resistance after that.
I also have used the two tech method where I would have another tech push on area of the tap while I tap the other chisel from a opposed position. Applying pressure from two direction helps to get the tap to spin around its axis and relieve some side stress.
I have had some taps where I mixed and matched methods to find a way to get it out. If you can reach the tap from both sides you can use a punch to knock the tap from the bottom and the top to loosen it. The idea is to just tap it gently, just enough to widen the freshly cut threads just a bit. If you hit it hard you might as well just punch it out now because its not going to spin.
I love it when I can get them out fairly quickly and for the most part I do, but the stubborn ones I like the freeze and break method the best as I do not want to waste any more time. Some have told me that they have been able to weld a make shift shank on a broken tap and get them out. I generally do not even attempt this as the weld splatter can make the whole situation worse. Most broken taps are small and no real way to weld to them and the tap is very hard so welding does not work well at all. A tech told me he bores a hole in the broken tap then uses a bolt extractor. I doubt very seriously that this occurred but, I have been wrong before.You would probably need a diamond tip tool with a relatively small tip to get a hole in the tap first then the extractor probably would shear or round off trying to bite into hard tap material, might have worked.
The Right Stuff
In the end an ounce of prevention is worth a pound of cure. Obviously you can not always have everything you need and the job needs to get done but, some study and understanding may save some heart ache. Sometimes good old spit is better than the wrong cutting fluid and the right tap for the material is the most important thing of all. No matter what method you use you must wear eye and face protection as taps shatter violently sending small sharp shards everywhere, normally right at your face, I even wear welding leathers to protect my torso and arms when removing taps.
If you generally only tap in mild steel and rarely other metals your taps and fluids should be purchased for that purpose. This is case in most shops, but if you are in any food industry than you would opt for tap geared for stainless steel and a food grade cutting fluid. Tap magic fluids have been around forever and have a selection of fluids for aluminum and steel. They also have water soluble and biodegradable fluids.
If you do have a wide variety of materials that you tap on a regular basis, than you should stock for those materials, proper taps and fluids.