O no! Another broken tap thread.

[seve7]

Being the hack that i am, i have broken more than my share of drills and taps and have become fairly proficient at removing them. However this one has me stumped and im about to tap out and send it out to the EDM.

I managed to break a hss Cobalt thread former (actually 2) in some fairly deep holes. What was surprising to me was that the tap shattered like more like carbide at the top of the shank. I was unable to back them out, i couldnt get anything with enough friction to spin them out so i seeing how brittle it was i went to work with a chisel and actually made some progress, more or less prepping it for a faster edm. I had some extra time so i decided to try and drill it out, they are through holes and i have access to the other side, so i was like well if i get really lucky i can back it out or just chew my way all the way back through it. I had some decent shape carbide end mills and drills, the drill dulled almost instantly but it was pretty ready for sharpening already, the end mill was basically new and sharp and made maybe .030 of progress before it refused to go any farther, it was still decently sharp, but refused to cut, it just skated across the surface like i was running in reverse, never seen anything like that before. Just checking to see any suggestions. Ill get a couple more pics in the morning.

 

[ostie01]

I could understand EDM time for a $25000 mold but, for a $5.00 parts.

 

[Finegrain]

Put a torch to it and expand the Al, then try to back it out. Also, grind wrench flats on the shank to get some solid torque on the tap.

Regards.

Mike

 

[Scruffy887]

TIG torch and start melting the end into a blob. If your any good then melt it into a hex shape blob. Get the heat into the stock too. Before doing this check what is in your tapping fluid. Not sure but some things like brake fluid will react to the intense heat and just one good wiff could shut your kidneys down.

 

[atomarc]

seve7,

Welcome to the forum.

I can only say that with that much tap sticking out of the hole it should be as easy as falling off a log to remove said tap! I know 'talk is cheap'..but the only thing missing seem to be the flats so it sure looks like you can prevail.

Stuart

 

[aarongough]

HSS tools are heat-treated very hard, and will shatter exactly like you see there with enough force applied!

Given how much shank you have sticking out, grind the end roughly square, then use a wrench to back the tap out, should go pretty smoothly. Heating up the part to make some clearance also makes sense!

 

[DJ2]

I'm no expert myself, but I would weld (with high-nickel rod if you have it) a scrap steel bar to it and back it out. Just curious, was this tapping by hand or machine? Did you use tapping fluid that is meant for Aluminum?

 

[jrmach]

I am so glad we have this happening all the time,,,,NOT

 

[seve7]

ha, learned alot since this with dealing with this. the best lesson learned is my pilot was too small. this was my first attempt with thread forming. rule 1, i guess is use a thread forming calculator. the advice i was given was basically just make your pilot bigger than normal, i wasnt aware of how much bigger it really needed to be. also learned a bit about that tooling, iirc after the fact, i learned it was a cemented or sintered type and thats why it shattered the way it did. there was no getting it out it was kind of a difficult part to make, it was 304ss with a 3.5" deep 3/4-10 tapped hole.

 

[guest]

...it was 304ss with a 3.5" deep 3/4-10 tapped hole.

I see some R8 collets there, you're a bold man.

 

[seve7]

lol wasnt tapping with them if thats what you are thinking.

 

[litlerob1]

it was 304ss with a 3.5" deep 3/4-10 tapped hole.

R8 or not

Roll forming requires a lot of Torque, 4.5xDiameter is a loooooong way to go. Especially forming 304. I would find a CNC and Threadmill it, or I would get a Carbide bar and single point it.

Or cut with a bunch of pecks. Hell even cutting it by hand would be more successful, not easier.

R

 

[seve7]

ya, that was my exact sentiment, was like send it to the cnc guys in the next room so they can thread mill it, because uhh... im not so confident i can make this the way you want me to, atleast not with breaking shit and wasting a ton of time, which is exactly what happened.

 

[guest]

lol wasnt tapping with them if thats what you are thinking.

I was thinking form tapping that particular hole on a Bridgeport is pretty optimistic.

The collet would still be the best way to hold the tap, just so much torque required for that size and depth in that material...

Safer way would be to use a cutting tap, power tap the first 3/4" or so, then finish by hand with a big-ass tap wrench.

But I guess you figured that out.

 

[Bill D]

Would soaking it in alum and water be safe for the stainless? I know it is supposed to be safe in brass or Aluminum and dissolve the tap away. How about nitric acid.
Bil lD.

 

[D Nelson]

Heat that sumbitch up pretty warm and rub beeswax on it then screw it out.


Sent from my iPhone using Tapatalk Pro

 

[Bobw]

Would soaking it in alum and water be safe for the stainless? I know it is supposed to be safe in brass or Aluminum and dissolve the tap away. How about nitric acid.
Bil lD.

Nitric would work.. Won't hurt the stainless, but it takes quite a while... Days, if not more every time I've done it.
I'd rather chew it out with an endmill... But form taps don't have flutes (maybe one little one) and now you have a
threaded tube stuck in your hole.


And here is a cheat that I've used... Had a part a I did for a while. 304.. 1/4-28 or maybe 10-32...
Needed to be tapped about an inch deep at the bottom of a narrow slot.. With a normal tap held in a collet I
could only go so deep, so they needed to be finished by hand...

So I form tapped the top of the hole in the machine, and then finished the bottom with a cut tap
by hand.. A cut tap, in a form tap size hole goes REALLY REALLY easy...
About half the square of the tap sticking up at the top
of the slot by the time the depth was achieved..

No prints.. Just had to work, and the tapped hole needed no strength, it was just one of those pushy
plunger things, but it was really really long, and threaded the whole damn distance into a blind hole.

I actually have a pic of that part....

And NO I didn't cut that slot like that.. Some thread on here years ago, guy was
getting chatter and hanging everything out a mile, endmill in a drill chuck or
something.. So... I just had to....

 

[JS]

Just don’t break any taps it’ll save you the headache in the long run.

 

[seve7]

no doubt. the problem was the callout for having the whole 3.5 inches or whatever threaded in a difficult material and the boss deciding that not thread milling it was a good idea.

 

[metlcutr55]

the advice i was given was basically just make your pilot bigger than normal, i wasnt aware of how much bigger it really needed to be.

engineering are important!