Re-using Old Broken Taps

[benmychree]

I have used broken pulley taps to make micro cold chisels, engraving tools, and center punches. I grind the profile that I need and heat the struck end to a red heat to anneal it. I had one 1/4" cold chisel that I used to cut a keyway in a piece of shafting before I had a mill. The steel is stronger that W1 or O1 and there is almost no danger of pulling the hardness when grinding.

I wonder if those pulley taps have a high carbon shank welded to a HSS "business end", as is done with drills, where the shanks are left relatively soft; this is done for purposes of good grip when chucking, and economy.
Otherwise if the taps were all HSS, heating red on the drive end would have very little effect on hardness. Lathe cutting tools and such as planer tools on long cuts can be seen at red heat at the point of contact with the work, this I have seen, and it does not degrade or destroy the tool, the trick is to use enough feed so that the superheated area of the tool falls behind the cutting edge, if this is not done, the cutting edge will be destroyed and the tool need to be reground, but the red heat will not substantially degrade the tool's abilities to cut after being reground; red heat does not have much effect on HSS so far as reducing its hardness.

 

[Downwindtracker2]

I learned early, the hard way, that taps fatigue. You would think high quality HSS shouldn't, but they do. I was gentle with them, too, I really hate trying to pick out broken taps. There is reason they are sold in packages of 10 or such like. And I've ground the end down to get a bottoming tap.

 

[RJSakowski]

I wonder if those pulley taps have a high carbon shank welded to a HSS "business end", as is done with drills, where the shanks are left relatively soft; this is done for purposes of good grip when chucking, and economy.
Otherwise if the taps were all HSS, heating red on the drive end would have very little effect on hardness. Lathe cutting tools and such as planer tools on long cuts can be seen at red heat at the point of contact with the work, this I have seen, and it does not degrade or destroy the tool, the trick is to use enough feed so that the superheated area of the tool falls behind the cutting edge, if this is not done, the cutting edge will be destroyed and the tool need to be reground, but the red heat will not substantially degrade the tool's abilities to cut after being reground; red heat does not have much effect on HSS so far as reducing its hardness.

Interesting about the welded shanks. Of the ones that I have repurposed, 2 of 6 and 40% of my pulley taps had welded shanks by a spark test.. The weld line was also clearly visible from the difference in corrosion. The welds occured between 1" and 1.5" from the upper end of the tap.

The struck ends had softened enough for an old file to cut. Thgey also show mushrooming from repeated hammer blows. The temperature at which hardened HHS starts to soften is a little over 1200ºF which is more correctly a bright orange rather than red. I use a Mapp gas torch as a propane torch won't get it hot enough. Oxyacetylene or oxypropane will easily achieve that temperature.

I have one tool that doesn't pass the file test and interestingly enough, it is the one that I cut the keyway with. The end does mushroom though.

 

[Glenn Goodlett]

I admit, I have chucked broken taps in a cordless drill and held it against a grinding wheel. I don't remember how successful it was.

 

[eastokie]

i take my broken taps , grind a flat on the broke end and light press into a 6 inch long piece of CRS,after drilling and or reaming a hole about a inch long,then grind all remaining tap cutters/flutes off so that a reasonably round end is left, keep it cool as u grind it u want to keep it hard as possible.once its ground round, i then grind a 45-60 degree angle
on it and use it as a chisel w hammer to break off broken taps and drills,bolts etc in holes of a part.simple and FREE other than your time..

 

[T Bredehoft]

Are you saying that you start a new hole with a bottom tap ?

I reaize it looked that way, but, No, I machine tap with a plug or taper, (now that I have some spiral flute 2-56 taps I'll lprobably start with them). I hand finish the hole to dpeth with a hand (bottom) tap.

 

[Superburban]

I have used broken pulley taps to make micro cold chisels, engraving tools, and center punches. I grind the profile that I need and heat the struck end to a red heat to anneal it. I had one 1/4" cold chisel that I used to cut a keyway in a piece of shafting before I had a mill. The steel is stronger that W1 or O1 and there is almost no danger of pulling the hardness when grinding.

I picked up an older Kennedy tool box at an estate sale a year or two back. There were several old broken taps, that were ground with different size ends, that I assumed were for engraving. I assume the owner had some sort of holder for them, but nothing was in the box.