[TheForge] 2 tapping questions, oops 3

[Joe Chadwick]

On Mon, 11 Feb 2002 08:59:44 -0500, Barking Crow wrote:
 >I was doing some tapping yesterday and came across a reference to sharpening
 >the tap. Anyone know how to sharpen a tap?


Sharpening a tap is analogous to sharpening a router bit or a mill. You 
don't want to do anything to mess-up the diameter, profile, or relief 
angles. It's the contact face that needs to be dressed. If you do the 
nitric acid dip, the thread profile will get ragged, which will cause much 
more stress on the tap in use - and we all have our share of broken tap 
stories...but the cutting face won't be helped at all.
I dress my small and medium taps with a Dremel (it ain't the big time here, 
but hey, it works). Use a cylindrical stone with a diameter a little 
smaller than the flute. I have a couple of stone "slips" used to sharpen 
carving gouges that I use for large diameter taps. Cover the flute with 
layout dye if you have it (is layout dye available in bottles anymore? all 
I've been able to find is the spray can...) or use a magic marker. With the 
axis of the tap parallel to the stone, lightly touch the tap to the 
spinning stone with a little more pressure to the face your're trying to 
sharpen and the nose of the tap. This is where most of the wear occurs. The 
dye helps to gage where and how much metal is coming off, and helps 
indicate whether the face of the thread meets the adjacent faces with a 
crisp edge. You shouldn't have to mess with the relief angles.
I have bunches of used and second-hand taps and dies that I sharpen this 
way. The light touch is important because very little metal is removed. 
Also if you're holding the tap in your fingers, you'll know in a hurry if 
its over heating- but then you shouldn't be pressing that hard to begin 
with....