broken tap

[T.L.A.R. eng]

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.

[ZipSnipe]

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?

[T.L.A.R. eng]

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.

[msomerville]

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.

[Mcgyver]

Originally Posted by ZipSnipe 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 . 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

[l u k e]

Originally Posted by ezdoesit 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?

[l u k e]

Originally Posted by T.L.A.R. eng 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.

[T.L.A.R. eng]

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.

[Mcgyver]

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

[gmfoster]

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