I've just broken a 4BA carbon-steel tap. Rats. Should I be able to dril
it out with an HSS drill?
Brenda
-- anotheri
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in one word no.
carbide drill or smash it out with a punch.
all the best...mark
To expand on Mark's comment. Carbon steel is usually _harder_ than HSS. Just tends to be more brittle and doesn't hold its hardness much beyond a couple of hundred degrees C.
Mark Rand RTFM
If you can pop in I'll burn it out for you in the edm machine
AWEM
EDM machine??? Anyway, I went the "smash it out with a punch" route Left a bit of a mess, but I may be able to thread for something just bit bigger. Luckily the bolt size isn't too critical.
Are HSS taps considered "better" than carbon-steel ones? The CS one was using was a cheapie, bought at Warco's last open day. Guess I no know why it was cheap!
Brenda
-- anotheri
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EDM -> Electro Discharge Machining. Creates a series of minute explosive discharges using a copper or carbon electrode immersed in a non conductive fluid. The blast removes material from the part being machined (ie your tap). There is of the order of 100 volts across the gap which is servo controlled to keep the discharge explosive and not arcing. The current flow characteristics are carefully controlled by the electronics. Widely used in diemaking (diesinking) and very handy as soft electrodes can shape extremely hard materials.
If your hole is now too big, can you clean it up, and silver solder a plug in and start again?
AWEM
I'm thinking of filling the hole with araldite and then redrilling. An buying an HSS tap!
Brenda
-- anotheri
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EDM machines interest me - I'd like to build one sometime. I'm particularly interested in their use for complex shapes rather than sinking into a tap. Maybe shaped electrodes, or CNC.
Is yours commercial, one of the published designs, or your own development ?
-adrian
If Araldite isn't strong enough for the threads then drill and tap a big hole - say 10mmm if as I recall the original hole was 4mm - then araldite in a bolt, grind it flat, and drill and tap into the bolt.
You can flat face, drill and tap the end(s) of the bolt in the lathe if grinding might mar the suface, then screw it in place using a 4mm bolt and suitable spanner, then remove the bolt once the araldite has set.
Adrian,
Mine is a commercial Eurospark H425 of 1970's vintage, and weighs in at about 1.5 tons.
AWEM
Sounds pretty substantial !
Why so much ? I'd have expected an EDM machine to be fairly lightweight, since there aren't any cutting forces. Though the ones I have seen were fairly large wire units with a protective cabinet and a fair sized rack of control gear, so the ancillaries made it heavy rather than a massive casting.
What dielectric fluid do you use in it ?
-adrian
lightweight,
massive
The base casting is very substantial as the table has a hydraulic rise and fall tank system to surround the work with dielectric. The servo sinking bit is also quite chunky as it is designed to take large lumps of copper for big diesinking. The very large three phase transformer adds to stability! I'm using IONOPLUS IME-MH from Oel-Held (
AWEM
Much
I'd already gone the araldite route, and I think it'll be stron enough, but good tip, thanks. I'll file it in the "to be remembered drawer for next time.
Brenda
-- anotheri
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It can be a bit more complicated than that.
If tapping under power then HSS is much better and flutess roll tap even better.
However if doing things by hand a good presto carbon steel tap can b better than cheap HSS. Carbon steel can keep theredge better at lo speeds.
Try and buy quality, Dormer, Presto, WNT.
Ebay is a good source of taps and dies, if you buy when the price i right.
Steve Larne
-- Steve Larne
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