I have just broken a recently new 2-56 tap off in a 3/8 inch deep hole in 7075 aluminum. Has any one ever made a hollow hole saw to try and render out the offending tap piece? I thought of trying drill rod to make the cutter then harden it. Kind of like a small hole saw, then tap the hole for a plug of metal and re-do the 2-56 threads. I don't have a lot to work with except time. Any thoughts?

If you have some time you could make a edm from the home shop machinist lay had a book you could buy. I have one i made, it will do just fine.

If you have a bridgeport or knee type mill, simply use a small diameter solid carbide endmill to drill the broken tap loose!
Do this by first getting on the exact location, then rais the knee very slowly to let the carbide take light cuts on the hardened tap metal! You may need two or three carbide endmills, but the tap should come out!

If you can do this from the opposite side, the tap may just un screw too!

I cannot reach the back side of the hole as it is a blind hole. I would love to build the edm, just didn't want to use it for this. If I use the edm, what happens when the tap material is gone? Are there threads left?
I know the tap was jammed at the bottom of the hole as I heard the tap "tink" then it was jammed and would not retract. It seemed to come loose, then without any resistance, broke off flush.
I seldom ever have any problems with hand taps but you know how it goes with the importance and care given to the project, things seem to happen expotentially. I will try the carbide end mill first, Thanks guys.

Since this is Aluminum. Do a search for Acid and Broken Taps here or on the web. Nitric acid, sulfuric or hydrocloric can disolve the tap without doing harm to nonferrous base metals. It would be a good idea to test the acid effects on the aluminum, but the right mixture/recipe should do the trick.

DC

for such a small tap size i would suggest sending it out for edm which will be cheap to have done ,i like to burn out taps with old carb endmills but with that dia. of a tap , 1/16 is all you going to get in there and to burn 3/8 of an inch you would be sol , too high of a chance of destoying the threaded hole

Guess you need to decide if it's worth it before you do anything....2-56....pretty small.....most anything that you attempt to drill it with will most likely break unless the broken surface is pretty flat......

I know the feeling, ya spend heaps of time on a job and then it all goes down hill in a second.
Only recently I had to remove a broken tap from a piece of 6061. It was an M2.5 tap about 10 deep and luckily I had a 2mm carbide cutter, just milled it out no probs. Cleaning out some of the remaning tap did pose a few dramas but in the end it all worked out.
Hope you get it out
Good luck

Thanks to all for the advice, I appreciate the wealth of knowledge on this site. Gary

If it is critical to saving the part, look for a local die shop. Give them a call and see if they have a tap-burner. We have one in our shop that we use to save large castings when we break taps off during machining. It gets very expensive when you have to scrap a $300 casting that has a couple hours of machining already invested in it due to a small broken tap in a hole. Hope this helps!!

like One says, or use Alum....

http://bbs.homeshopmachinist.net/showthread.php?t=6747&page=2&highlight=aluminium+broken+tap

http://bbs.homeshopmachinist.net/showthread.php?t=6747&page=2&highlight=aluminium+broken+tap

thank you all. I just found a lot of thing i forgot i had read befor.
They said if you don't ues it you forget it

Finally, today, the other broken tap was removed. I had two 2-56 taps with approx. 3/8 in. broken off flush in a crankcase for a 1/5 scale Kinner K-5.
I took all the advice and used two methods of extraction. I first re-searched and built an EDM and spent alot of time learning alot of NEW things. Using the EDM, the first of the two taps was burned out. Good feeling!
Last night, while reading at modelenginenews.org I saw where an Alum solution was heated to a simmer with the part immersed would remove the broken tap. I had never heard anyone heating the solution, so today I tried it on the other tap.
Amazing, 5 hours later, a clean hole with the threads still intact! The crankcase was a little dis-colored from the solution but cleaned up again with steel wool.
Thanks again guys for the help, now I can go back to turning parts, I allmost can't wait to break off another tap............. no maybe not.

So let me get this right? You researched and built and EDM machine to remove a broken tap? I would have followed Widgitmasters advice first and used carbide endmills , bullnosed preferably. Or if the aluminum can be scraped , just start over. But I will tell ya I am impressed, any pics of the EDM?

It seems that with a lot of time on ones hands, allmost anything is possible.
I just couldn't get myself to purchase a carbide end mill that small and risk destroying it, so the other routes seemed most likely to do what I wanted.
The EDM I built isn't very powerfull, as I used what I had on hand for substituted parts and it took quite a long time to burn through the first tap.
I am going to rebuild it with better components, then maybe pictures.
The Alum was definately the quicker way to go, but like I said, I have quite a bit of time on my hands and I like a challenge. It was definately a great learning experience and I HATE to machine the same part twice if I don't have to.

I don't think you would have had much luck trying to remove a broken tap with a carbide endmill that small. It may do the trick on bigger holes, but for a hole .375 deep the tool will break.

I have never heard of using alum before. Learn something new every day.

So let me get this right? You researched and built and EDM machine to remove a broken tap?

Zip, put yourself in the home shop paradigm, we all have an edm as well every other conceivable machine and contraption on our to do lists, the broken tap just changed the priority ranking :D. I so far out on multi-generational tangents of building projects to permit forwards movement on other projects that i no longer remember where i'm trying to get back to. kind of like a Douglas Adams book.

Gary, was the edm freelance or did you follow a published design? i too would like to see pic and learn more about your edm

If you have some time you could make a edm from the home shop machinist lay had a book you could buy. I have one i made, it will do just fine.


I'm interested in this. Is there any information on line you can post a link to?

Finally, today, the other broken tap was removed. I had two 2-56 taps with approx. 3/8 in. broken off flush in a crankcase for a 1/5 scale Kinner K-5.


Have you concidered takeing it to an anodizer? The process will eat the tap out of the aluminum without destroying it.

I found the basics on modelenginenews.org of how an EDM works. With the basic concept in mind I built the first unit as a test rig to experiment with. It worked but was slow and not as powerful as it should have been. I made my brass anodes from very small brass tubing soldered onto the end of a 2-56 x 1 inch cap screw with a fixture to guide it into the offending hole. An interesting side note that the brass tubing was hollow and ate through the first tap leaving a very thin piece that went into the center of the anode. I have currently taken the rig apart to make a better power supply. Mechanical vibrator coils with large capacitors are definately not efficient and somewhat dangerous. It would be nice to have a unit that can work by itself without keeping such a close watch on it. I will post pictures when I finish it.

check out village press who publishes home shop machinist. Robert Langlois wrote a multi part article some years ago on building an edm. i believe they still sell the article in the book form. Ive the original articles and its written so an electronics novice can understand (I'm safe then). I saw Robert demonstrate his once at TSME and it worked well. its on the to do list somewhere, but not until i bust a tap

Ben Fleming publishes a book on a home made EDM that is very complete and pretty easy to build. It is serve driven and can be built for around 100.00 depending on how fancy you get.

"The EDM How-To Book"

by Ben Fleming.
Fleming Publications..ISBN 0-9767596-0-8

Garry