I could listen to that guy read a phone book.
I liked this video. There are much more exciting EDM videos, where people use it for CNC, and show the process close up, but this is good because it’s cool to see people who specialise in doing some highly specific thing.
It’s pretty nail-biting near the end, where he puts his own tap through the hole he just finished cleaning out. If that was me I’d be guaranteed to break off the second tap and have to start over.
Sometimes electricity and water DO mix, but you really have to know what you’re doing, as this gentleman obviously does.
That was like, very mellow. I feel high.
Saying “I’d tap that” for this feels like sloppy seconds.
Yah. It is kind of pleasurable to listen to experts who seem content to explain a process in a conversational tone that’s not condescending but doesn’t make things too technical for a lay listeners either.
I guess I can see paying for this in a fairly expensive part, but it can’t be cheap. For a lot of things it looks like chiseling the tap out, overboring the hole and using a helicoil would work well enough.
I’d like to see something like this portable. We break 30mm x 300mm bolts at work 1/3 of the way down in the hole every few months. Sure they aren’t as hard as a tap, but when you have put enough force to stretch/shear a bolt of that size an ez-out just doesn’t cut it.
Yeah, that was much better than tap extractors. Turns out the pros have lots of ways.
I’ve broken a few taps. 4-40 (smaller than M3) and as one of the last steps of machining a complex titanium part. Leave it to the pros to have solved this one long ago. Just drop the part in nitric acid and let the acid eat the tap. Or bleach if you have time. Only works for titanium and a few other metals, but saved my hide.
It was the horrific flood of metal blood that got to me.
you’d be amazed how well hammer welding a bit of soft steel rod on to a broken tap works for getting it back out.
The Horror. The Horror.
That’s genius. Do you heat the rod first or cold weld it? And do you turn it with Vise Grips or equivalent, or bend it at a right angle for leverage? Sooner or later I’ll probably need this.
Virtually every old tool and die maker or machinist explain things like this.
I hated the way he blew out the bits of metal while not wearing protective eyewear other than glasses.
Start by heating up some sand to around 1300F
Next, get the broken bit very hot (color of melted butter) and also heat up your soft steel rod at the same time to a melted butter temp. you are looking for 1700-2000F
Drop borax on the end of both pieces and immediately put them together end to end.
Hit the cold end of the soft steel rod hard enough to make a weld but try not to hammer so hard you deform the metal or make all of your borax flux spray out. These hits are not as hard as shaping hits.
When the weld finishes cover the whole thing in hot sand and walk away. This is to slow the cooling and prevent it from going full hard and brittle. The larger the piece the tap is stuck in the more it will act as a heat sink and cool your metal. This is not a good thing. You want a very slow cool to prevent accidental hardening and you will likely get some so you’ll need to temper it to soften it up a little. We don’t want it breaking again after all this work.
After the metal has fully cooled, heat it back to to about 600F and allow to cool again. This is to temper back any hardness you might have picked up during the whole process. This is especially needed for hard steels like A2 and W2 and whatever hard as heck steel they use to make taps from.
Both parts should now be soft(er) and solidly connected. Clamp a vise grip on the rod and slowly turn the bit back out.
Edit: almost forgot to mention, make sure your rod is between 50%-75% the size (diameter) of the tap/hole. You don’t want to hammer weld the rod to the wrong thing and it will also expand when hit so you need a bit of room to work with.
Oh, and practice hammer welding rods before trying this on the real thing. Practice is good.
Given the size of the casting that he’s working on (and the number of machined surfaces it has), that’s a brutally expensive part he’s saving.
So this could be dead-expensive and still be cheaper than a new casting.
Maybe there’s less risk of borking the thing this way? Or maybe it’s really just a matter of reach- getting to that hole on many conventional machines could be difficult, and that EDM machine seems to have a HUGE arm to reach with.
Thanks for the very comprehensive explanation.
My brain keeps reading “EDM” as “Electronic Dance Music”. I guess they could stomp the broken bit out.
