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charlie coghill
11-08-2006, 08:13 PM
I have been working on the old craftsman vice that I posted a pic of a couple of weeks ago.

I have the stationary jaw brazed up and machined and found the orginal holes that were tapped and held the hard jaw on. Lucked out and hit the old hole dead on. Started to retap the holes, the first one went fine. As I was tapping the second hole I heard this crack as the tap broke off in the hole and my heart hit the floor.:( I think the tap must have been cracked as I was taking it real easy and backing off every little bit.

Tried needle nose pliers, no go, they would not budge the tap.

So now I got to thinking, the parent metal is cast iron and I have used a O/X to cut out taps out in through holes befor,but this hole is a blind hole, would my plazma cutter cut that tap enough to get it out?

With nothing to loose I gave it a try. With a couple of blasts of the plazma the tap was cut enough, that with a pin punch I was able to get the tap loose and out. Cleaned up the threads and was good to go.:D:D

This may not work in every instance but it is worth a try.

BillH
11-08-2006, 08:21 PM
thats a new one, I hear that most people simply weld a nut to it and unscrew it out.

CCWKen
11-08-2006, 08:36 PM
You are lucky and you're right, the tap must have been bad. I've never broken a tap in cast iron. Not even and old "seasoned" soap pot.

charlie coghill
11-08-2006, 11:42 PM
Bill the tap was a 5/16X18 and it broke off below the surface.
yes it is hard to break a tap in cast iron except for me.

BillH
11-09-2006, 11:51 AM
Bill the tap was a 5/16X18 and it broke off below the surface.
yes it is hard to break a tap in cast iron except for me.
Even if below the surface, they can do it. Now my thoughts are, "how do they keep from welding the tap to the sidewall?"
Thats what I love about this hobby, the ingenuity of people and all the different ways to do something.

charlie coghill
11-09-2006, 01:02 PM
Cast Iron does not cut for beans with O/X. Trying to weld a nut to a tap that is borken off below the surface may not be a good thing as the weld may sitck to the cast iron enough that it could not be removed.

Some one else may have some comments to make. They usually do :D, Just teasing guys. There is a lot of good information that comes from this site and I read it just about every day, even though I don't post too much.

pcarpenter
11-09-2006, 02:45 PM
5/16 would make a pretty small target, but I have welded to a 3/8 bolt snapped below flush. The key is that you weld down through a hole in a nut, sort of building a small bridge between the broken piece and the nut. This does not make for a very strong bond, but usually it does not take much. You weld it and let it sit and cool before turning and the expansion contraction cycle will break the bond that may have been a problem before.

Paul

BobWarfield
11-09-2006, 02:53 PM
I've definitely been mad enough at a broken part to shoot 50,000 degrees of searing plasma at it (bwa ha ha), but never had the nerve to actually do it.

Good job!

Best,

BW

motorcyclemac
11-09-2006, 06:21 PM
I have in the past heated broken taps with an oxy/acetylene torch until just short of melting the tap. Then turn off the flame and open the oxy valve and flood the area with oxygen. This caused the metal to "burn" if you will and managed to remove the tap.

Cheers
Bill

gunbuilder
11-10-2006, 11:31 AM
I have in the past heated broken taps with an oxy/acetylene torch until just short of melting the tap. Then turn off the flame and open the oxy valve and flood the area with oxygen. This caused the metal to "burn" if you will and managed to remove the tap.

Cheers
Bill

Hmmm,
Sounds like a good way to get rid of some of the carbon in the tap. That would make drilling the tap easier.

Paul