Need to remove a broken tap in cast iron

Topics include, Machine Tools & Tooling, Precision Measuring, Materials and their Properties, Electrical discussions related to machine tools, setups, fixtures and jigs and other general discussion related to amateur machining.

Moderators: Harold_V, websterz, GlennW

EOsteam
Posts: 179
Joined: Thu Jan 31, 2013 1:33 am
Location: Pendleton, Oregon

Need to remove a broken tap in cast iron

Post by EOsteam » Tue Jan 02, 2018 12:43 am

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

Harold_V
Posts: 17099
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Need to remove a broken tap in cast iron

Post by Harold_V » Tue Jan 02, 2018 2:53 am

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
Wise people talk because they have something to say. Fools talk because they have to say something.

User avatar
tornitore45
Posts: 1556
Joined: Tue Apr 18, 2006 12:24 am
Location: USA Texas, Austin

Re: Need to remove a broken tap in cast iron

Post by tornitore45 » Tue Jan 02, 2018 7:02 am

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.
Mauro Gaetano
in Austin TX

John Evans
Posts: 1939
Joined: Tue Jan 20, 2009 9:33 pm
Location: Phoenix ,AZ

Re: Need to remove a broken tap in cast iron

Post by John Evans » Tue Jan 02, 2018 12:19 pm

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.
www.chaski.com

User avatar
warmstrong1955
Posts: 3136
Joined: Thu Mar 18, 2010 2:05 pm
Location: Northern Nevada

Re: Need to remove a broken tap in cast iron

Post by warmstrong1955 » Tue Jan 02, 2018 12:24 pm

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
Today's solutions are tomorrow's problems.

Harold_V
Posts: 17099
Joined: Fri Dec 20, 2002 11:02 pm
Location: Onalaska, WA USA

Re: Need to remove a broken tap in cast iron

Post by Harold_V » Tue Jan 02, 2018 4:01 pm

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
Wise people talk because they have something to say. Fools talk because they have to say something.

choprboy
Posts: 202
Joined: Sat Oct 29, 2011 11:23 pm

Re: Need to remove a broken tap in cast iron

Post by choprboy » Wed Jan 03, 2018 9:59 pm

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

spro
Posts: 7058
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Need to remove a broken tap in cast iron

Post by spro » Thu Jan 04, 2018 1:51 am

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

EOsteam
Posts: 179
Joined: Thu Jan 31, 2013 1:33 am
Location: Pendleton, Oregon

Re: Need to remove a broken tap in cast iron

Post by EOsteam » Sun Jan 21, 2018 1:14 am

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

User avatar
liveaboard
Posts: 513
Joined: Sun Dec 08, 2013 1:40 pm
Location: southern Portugal
Contact:

Re: Need to remove a broken tap in cast iron

Post by liveaboard » Mon Jan 22, 2018 1:23 pm

Nice result, glad to hear of your success!

User avatar
mcostello
Posts: 773
Joined: Sat Jan 04, 2003 10:45 pm
Location: Lancaster, Ohio

Re: Need to remove a broken tap in cast iron

Post by mcostello » Mon Jan 22, 2018 10:00 pm

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

dly31
Posts: 1042
Joined: Sun Jun 27, 2004 11:29 pm
Location: Northeast Alabama

Re: Need to remove a broken tap in cast iron

Post by dly31 » Wed Jan 31, 2018 11:21 pm

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.
Don Young

Post Reply