The Home Machinist!

Well, I knew that at some point I would break a tap and that day has occurred. Here are the specifics: the material is cast iron, the tap was HSS and 2.5 mm X .45 mm. It is fractured right at the level of the surface and I can't get a grab at the piece. The good news is that the cast iron piece is still mounted in the Milling machine and it is centered. I don't have any left hand carbide drills that small but I suppose they could be ordered. Any ideas or suggestions? At this point I'm just about out of ideas.

Thanks,
HJ

If you don't have a decent surface to engage, this likely won't work. The drill will most likely want to deflect, which will be a death sentence for the drill.

If you have a carbide drill that is slightly larger in diameter than the core diameter of the tap, use it. it doesn't have to be left handed, and likely shouldn't be, as if the tap started moving, it likely would bust the drill. If you remove the core, the remaining bits will be free to be picked from the thread.

H

I would use a ball end carbide bit, it has shorter flutes and less prone to flex, but 2.5 mm is awfully small for this kind of predicament.
Highest speed and move the knee, do not use the quill lever. As the tool meet the irregular edge of the broken tap it wants to bounce up and down. With the knee you loose the sensitive feed but in this case is of no help. just advance at glacial speed.

Smallest tip you have ,oxy-acy torch. Heat the tap red hot to soften it. Spot with a center cutting end mill to make a flat on the tap. Spot drill end of tap ,then drill slightly smaller than tap drill size.

What Mauro said.
I just removed a broken 1/4"-20 for a friend a month or so ago, just as he described.
Keep the chips blown out!

Bill

John Evans wrote:Smallest tip you have ,oxy-acy torch. Heat the tap red hot to soften it.

That won't work if the tap is HSS. It does not anneal easily, and must be cooled at a rate that is not possible without a furnace.

H

Tig weld it!

Tig weld a button on the top of the HSS tap. Heat cycle, dab a bit, and repeat until you have enough of the shank built up to grab and back the tap out.

https://www.youtube.com/watch?v=ffR2pGVGHbg

Went to the site. Gets better and better. Micro in this case but can apply.

Success!
I ordered a .081" 2 flute carbide ball end mill from Carbide Depot. The RPM's were 3600 and the knee was used to advance (very slooooowly) to the depth of the carbide ball mill. A water based lubricant was also used to keep the heat from building up. After the broken tap was machined out it was a simple matter to clean the hole and thread a brass screw in.

Thank you all!

Harper

Nice result, glad to hear of your success!

Hey, We are here to help and We work for tips.

If you have enough time and patience, broken taps and the like can be removed by grinding the center out with a piece of brass tubing and abrasive such as automotive valve grinding compound.