# Re-using Old Broken Taps



## rwm (Sep 4, 2018)

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.







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:





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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## BaronJ (Sep 4, 2018)

HI Robert,

Over here it is common practice to grind the end flat and use them as bottoming ones.  The other common use is to grind them for fly cutter bits or lathe tools in a holder.


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## Cadillac (Sep 4, 2018)

BaronJ said:


> HI Robert,
> 
> Over here it is common practice to grind the end flat and use them as bottoming ones.  The other common use is to grind them for fly cutter bits or lathe tools in a holder.


 Exactly what I do too.


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## BaronJ (Sep 4, 2018)

Great minds think alike


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## rwm (Sep 4, 2018)

This also seems like a way to "sharpen" an old tap since most of the cutting is done with the first few teeth.
Robert


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## benmychree (Sep 4, 2018)

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.


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## benmychree (Sep 4, 2018)

Cadillac said:


> Exactly what I do too.


Bottom taps require a chamfer with relief to cut decently, usually only one thread pitch of chamfer.


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## T Bredehoft (Sep 4, 2018)

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.


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## BaronJ (Sep 4, 2018)

Hi Tom,

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


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## rwm (Sep 4, 2018)

benmychree said:


> 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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## BaronJ (Sep 4, 2018)

Hi Robert,

The relief that benmychree is referring to is actually down the length of the left hand inside of the flute looking at the tap from the pointy end.
Grinding the tap square on the end will not remove that relief.


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## rwm (Sep 4, 2018)

BaronJ said:


> Hi Robert,
> 
> The relief that benmychree is referring to is actually down the length of the left hand inside of the flute looking at the tap from the pointy end.
> Grinding the tap square on the end will not remove that relief.



Are you sure? The end seems to be ground with taper but also with relief on the trailing part of the cutting edge of the part that is tapered. I think that is what he means.
(i.e the thread depth is greater on the leading edge than the trailing edge)
Robert


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## BaronJ (Sep 4, 2018)

Hi Robert,

My error,  It should say "right" not left.  
Just me getting it wrong   Missus keeps telling me I don't know my right from my left.
Sorry.


> (i.e the thread depth is greater on the leading edge than the trailing edge)


Yes it is !  but as you say, only along the tapered part.   
I wonder if we are talking about two different features. I was talking about the surface behind the cutting edge.


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## rwm (Sep 4, 2018)

Yes, that what I meant. Now I really need to try the non-relieved tap. I'll bet I could grind a relief by indexing the lathe spindle and advancing the tool post grinder incrementally! That may be my next attempt!
R


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## benmychree (Sep 4, 2018)

rwm said:


> Are you sure? The end seems to be ground with taper but also with relief on the trailing part of the cutting edge of the part that is tapered. I think that is what he means.
> (i.e the thread depth is greater on the leading edge than the trailing edge)
> Robert


You are correct, that is what I was trying to say.


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## benmychree (Sep 4, 2018)

The threads on a tap have a very small of radial relief,but ot is not enough to accomplish cutting, it is there to reduce drag the relief. What does the cutting is all on the chamfer, the longer the chamfer, the thinner the chip, although, I have observed over the years that a taper tap usually has more drag than a plug tap.  Taper taps such as pipe taps, have more radial relief, and cut all the way back when tapping a taper pipe thread.  Acme taps have radial relief like a pipe tap, and also cut all or most of their length to achieve full depth threads.


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## MrWhoopee (Sep 5, 2018)

I recently needed to single-point 1/2-20 internal in a blind hole in aluminum (discovered I didn't have a tap and wanted to finish). Grabbed a chipped 3/8-16 tap and ground it so I had just the end tooth (the first full tooth) on one flute. Threaded away from the chuck. Worked perfectly.


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## benmychree (Sep 5, 2018)

I'd have thought that the tap would not have proper clearance on that tooth to cut freely, that would have to be the trailing edge of the tooth if you cut on the backside coming out of the hole, it would have negative relief unless it was raised above center or inclined downwards; doing either would distort the thread angle.


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## RJSakowski (Sep 5, 2018)

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.


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## Technical Ted (Sep 5, 2018)

I agree with John that the cutting edges need clearance to cut properly. One thing to try and I have done this with some success is to grind some clearance by hand. Leave the thread profile (cutting edge) intact with only a very slight lathe ground edge, but grind away the rest for clearance. It doesn't take a lot of hand grinding since you only need a slight amount of clearance. 

YMMV,
Ted


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## benmychree (Sep 5, 2018)

RJSakowski said:


> 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.


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## Downwindtracker2 (Sep 5, 2018)

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.


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## RJSakowski (Sep 5, 2018)

benmychree said:


> 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.


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## Glenn Goodlett (Sep 5, 2018)

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.


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## eastokie (Sep 17, 2018)

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..


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## T Bredehoft (Sep 17, 2018)

BaronJ said:


> 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.


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## Superburban (Sep 17, 2018)

RJSakowski said:


> 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.


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