[AT] EDM (Electrical Discharge Machining) Drilling on old tractor steel and iron.

[James Peck]

What would be the traditional way to remove a hard tap broken off in a tractor casting.?  Do you heat it with an acetylene torch until it becomes softer or do you try to burn it out?

For broken bolts that you can't drill easily, maybe the solution is a custom made hardened drill jog.

Looks like Jack can replace his lost EDM article.

https://secure.villagepress.com/store/items/detail/page/6/item/797

[Stephen Offiler] Thanks Jack.  Your comments are spot-on.  Since the original comment on EDM was aimed at me, I'll elaborate.  I conducted an experiment of cobalt drill bits versus a more modern alternative made from high-Vanadium powder-metallurgy steel.  I concluded the cobalt drill bits are far more cost-effective.  I was questioned about the EDM portion of my experiment, which I never mentioned, was never a consideration, and did not happen.  My total cost-per-hole, including the cobalt drill bit as a consumable, plus labor and overheads, comes to roughly $0.30/hole and there are roughly 2000 holes per year so grand total $600 annually to make those holes. That kind of money will never pay for an EDM machine.

[Jack] What got me started was thinking about whether EDM, now defined in this group, would be cost effective in drilling Vise Grips to mount tooling to. Reading this definition suggest EDM hole drilling is likely not cost effective in any case where a twist drill will do the job. And yes, I did not stop to think whether others commonly use the term. Stephen was getting 50 holes per bit so the Vise Grips are pretty drillable.

https://en.wikipedia.org/wiki/Electrical_discharge_machining#Fast_hole_drilling_EDM

The magazine in which the tap was EDMed out of an aluminum casting got jettisoned in a move 20 years ago. I wish I still had it.

If it is the case that EDM would not be cost effective when a twist drill could be used, then a portable EDM device for drilling out broken bolts would not work either.

I have long been fascinated with the portable machine tools offered by climax.

https://www.climaxportable.com/products/drills/

[Phil Auten] Thank you, Farmer! I was wondering just what the **** EDM was. Your advice is spot on.

[Indiana Robinson] EDM – Electro Discharge Machining
There is an old writing rule that says that you shouldn't use an acronym or an initialism in an article without first giving a definition of the letters involved. After doing that you are then allowed to use the letters abbreviation  constantly even to the point of silliness if you want and all is fine...  :-)  Most of us (myself included) break this rule constantly. One example is "PTO" = Power Take Off. That is pretty safe on an old tractor group. If you were writing for a group of pie repair shop owners you should probably pre-define it first.
I'm not really questioning James use of EDM here, we as a group define the word casual, but I took that link... I hunted all over their site and could not find the initialism defined there. I Googled it and had to look at several returns to find it there. Obviously it is only a household word among a fairly limited group of engineers and machinist. Why would they not define it up front on their site? I suppose some of it is that most sites are created by computer geeks who are not always journalist.
Back in my data processing days we discovered that the systems analyst guys were horrible at writing instruction manuals for clients to use when preparing data input. They knew their end of it but just couldn't connect with the customers. I became the interface between them and the customers.
While I'm here I'll insert one of my favorite gripes. "Nothing should go on the internet that is not dated up front. I hate it when I'm researching and can't find a date on an article then find that the article is 25 years old and the information badly out of date... Especially so on medical information that keeps evolving.
And now back to old tractors.  :-)

[James] Probably 25 years or so ago, an article discussed a homebrew low tech EDM a man had built to EDM a broken tap out of the aluminum block or head of a small engine. The article may have appeared in “Home Shop Machinist”. 
 
The downside is that the setup may have only worked in the down direction. 
 
 

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