View Full Version : DIY EDM broken stud or tap removal

07-13-2005, 06:24 PM
Anyone seen any plans for how to perform edm removal of a broken stud or tap?

James D. Clark
07-13-2005, 06:53 PM
I've never seen it done but I know there is a way because they removed broken taps out of high value aluminum castings where I worked. That's a good question.

07-13-2005, 06:59 PM

Electrical discharge machines (EDM) is a process not a plan that is used to basicaly burn away the metal(tap). Are you asking how to do it or looking for instructions? Usually these are dedicated machines used to perform the task of removing a broken taps, drills, burn holes in metal ect... You would not (usually) find a home user with one of these machines. If you need to remove a broken tap there are other methods you might be able to use. I might be missing the point of your question, if I did I appologize :cool: If I have missed the point please re-state it.

07-13-2005, 07:19 PM
Believe it or not, I'm actually asking if anyone out there has any plans for a do it yourself system for edm hole boring. I have heard that over the years various magazines have published plans for building your own. Apparently they use a stepper motor to move the electrode closer to the work and maintain the arc distance based on voltage sensed across the arc. I've seen references on the net to published plans in old popular mechanics and some machinist publication. There is a book out there, but I was hoping someone had some plans I could look over to determine the feasability. I would be doing this solely for the enjoyment of it, although I would have the occassional use.

James D. Clark
07-13-2005, 07:41 PM
Here are some plans. Don't know how good. Just found them by searching for "edm plans". Good luck. Let us know what you come up with.


07-13-2005, 07:41 PM
Tap burners,or disintegrators are machines that I have gotten quite familiar with since around 1975,I ran one When I worked in the toolroom at the local plant where I worked for many years.I burned out broken taps daily,usualy from big dollar parts that were near completion,before a tap or drill was broke in them.Burning a tap used to be an effective,but slow proccess,though modern manufacturers are advertizing amazingly fast speeds,for their new machines.I also used this machine to burn coolant holes in solid carbide endmills,for a local tooling manufacturer,but this is very slow,at approx. 6 hours to burn an 1/8" hole,approx. 4" deep in carbide.The biggest drawback,would have to be the cost of the machinery and supplies,not to mention the time consumed,doing this.We had a Camman at the plant and new cost was around $25,000.00,but I have owned a used Camman and a used Electro-arc that I used in my shop at home and they cost me around $1,000.00 each,from auctions,but needed some TLC and tooling and the special coolant ,electrodes and rubber collets,are'nt cheap either.There are also some units avaliable for under $5,000.00 new,that adapt to a drill press.The principal with these machines is this:a hollow electrode is held in a coolant fed chuck,similar to a drill chuck,then the electrode is fed with a low voltage DC, current ,that actualy erodes or burns away the tap at a very slow rate,while the coolant keeps any heat out.Most of these are fed by an adjustable rate of vibration.The idea,with a tap,is to use an electrode,just large enough,to burn the center out of the tap,hence the flutes will fall out,or can be picked out,causing no further damage to the threaded hole.I hope this helps a little,but I have also included some links that may help.





Mike W
07-13-2005, 08:28 PM
The Home Shop Machinist magazine had a series of articles on building one. I belive the whole set is available.

07-14-2005, 12:26 AM
This should keep you busy for a while:


07-14-2005, 10:44 AM
Is this anything like ECM? electro chemical machining?

Why not just remove a tap with an easy out or a tap extractor???????


07-14-2005, 12:33 PM
In these days of high speed CNC. machining,tap extractors are usualy useless.Tap extractors work well as a tool used to get hold of the broken tap,but if the tap is fused in,then there can not be enough pressure asserted on the extractor to remove a jammed or fused tap and the extractor will break.When a tap or drill breaks in a high speed setting,it is often fused into the part and often has broken because of heat and expansion,due to lack of lubrication or the tap's getting dull.While removing a broken stud or bolt with an ez-out works fine,it is not that simple with a hardened tap or drill.The only practical means of drilling a tap or drill,would be with a solid carbide drill bit,but they are extremely expensive and quite fragile.If the part with the broken tool is an expensive,multi-operation part,the cost of safely burning a tool out,is negligable,to most industry.I have found that a part can be saved about 90-95% of the time and often in the other 5-10% of the time,where the tapped hole is damaged beyond repair,at least the broken tap is removed,so the hole can be redrilled,and a helicoil can be inserted,to salvage the part.I beleive that tap burning is still considered to be a type of EDM {electrical discharge machining}.


07-27-2005, 06:43 PM