Re-using Old Broken Taps

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.
 
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.
Click to expand...

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
 
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.:eek 2:
Sorry.
(i.e the thread depth is greater on the leading edge than the trailing edge)
Click to expand...
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.
 
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
 
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
Click to expand...
You are correct, that is what I was trying to say.
 
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.
 
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.
 
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.
 
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 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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