Re-using Old Broken Taps

rwm

Robert
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Mar 25, 2013
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I know y'all have a pile of broken taps just like I do. I have never seen anyone post about re-using these.
I just happened to have my makeshift tool post grinder set up on the lathe when I ran across a nice 3/8-24 tap I had broken the tip off.

42663115370_033a4b44ac_h.jpg


I used a diamond wheel to carefully put a new taper on the broken end of the tap. I used about a 10 deg bevel and that seems right.
I decided to try some others:

30602247838_34e4df0aa4_h.jpg

Other than being short, these look like factory taps. I confess I have not tried them yet but I think they will work fine. Has anyone else done this or have a tip?

Robert
 
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This also seems like a way to "sharpen" an old tap since most of the cutting is done with the first few teeth.
Robert
 
This will not work as well as one might expect, tap sharpening attachments all have a cam action that provides the relief necessary to facilitate cutting so the tap will "bite". A "sharpening" such as is described would be like a lathe tool with no angular relief on its cutting face.
The angle used to sharpen a tap is a function of how many threads are chamfered by the particular grind for the taper, plug, and bottom tap styles, such as, a bottom tap may have only one thread chamfered, a plug tap may have three threads chamfered and the taper tap, even more, and the angle used would control how many threads are chamfered, depending on the pitch.
 
I was putting some 2-56 set screws in propeller clutches last week. I'd start the tap on the mill, then hand tap with a bottom tap to depth. Second hole, I bottomed the tap, broke it off half way up. I threw that clutch away, sharpened (by hand) the tap. Three flute, I tried to emulate the 30º side of the thread and put about 10º relief on the end. I used that tap on the next 17 clutches. No, I don't do custom tap sharpening.
 
Hi Tom,

Are you saying that you start a new hole with a bottom tap ?
 
This will not work as well as one might expect, tap sharpening attachments all have a cam action that provides the relief necessary to facilitate cutting so the tap will "bite". A "sharpening" such as is described would be like a lathe tool with no angular relief on its cutting face.
The angle used to sharpen a tap is a function of how many threads are chamfered by the particular grind for the taper, plug, and bottom tap styles, such as, a bottom tap may have only one thread chamfered, a plug tap may have three threads chamfered and the taper tap, even more, and the angle used would control how many threads are chamfered, depending on the pitch.

Interesting. I'm glad I posted because I did not know all that. I will let you know how it goes when I use these.
I just inspected some of my factory ground taps and they do indeed have relief behind the cutting edge.

Robert
 
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