Having a wrench guide virtually eliminates the breakage of taps. Sherline’s web site has “Machininsts Tips”, and number 7 shows a wrench for holding small taps. I have made a similar wrench.
The brass sleeve is the guide, and is held by a mill collet.
When I tap the four holes in a reel foot, spindle height is a problem. There is room for neither a standard tap wrench or a Jacobs chuck. The new wrench solves this problem.
I was skeptical that the set screw would provide enough grip for the tap, but so far it has been OK.
North Branch Reels 
I’ve grinded a small flat on my taps so the screw locks it in place. I published an article on a similar device in Home Shop Machinist. Nice blog. Congrats.
Marcelo,
Yes, the flat is a good idea. I have been using small taps and free machining material and, somewhat to my surprise, have not had a problem with slip.
Dave