I don't know specifically about pedal taps, but many, or perhaps all taps can be found that are sold in sets of three, each tap having a 1,2, or 3 stamped on it. This enables you to do the inital shallow threading, then proceed with the remaining two taps while encountering less resistance to achieve the completed thread. With fine threads, especially when re-threading where you might not have sufficient metal left to support the tops of the new threads, this more delicate approach will generally give cleaner results. Using a lens, if you look at well cut threads done with the sequence of taps, or even a new sharp tap for that matter, and compare with not so nicely cut threads that still will hold, it is clear which results are preferable.
Dennis Young Where there are third generation machine shops in Hotaka, Japan
> One trick that we used to use was to clamp, face-to-face, an old crankarm to
> to the one being threaded to pilot the tap into the crank being rethreaded.
> Later, we scored a set of pedal taps that had a reamer/pilot built into
> them, so that wasn't such a big issue. The trick about starting from the
> back is primarily for straightening out threads when some shmuck has forced
> the pedals in crooked--a common problem with over-the-counter sales (that,
> and putting the wrong pedal in a crank). Typically, only the threads in the
> face side are buggered. You can get the tap started straight on the good
> threads in the back side of the arm, and the tap will often restore the
> threads on the other side well enough to hold the pedal. Sometimes a little
> thread reapir epoxy is necessary as well. When that failed, we reamed them
> out and put in an insert, as long as it was an aluminum crank. Steel cranks
> went in the junk. Obviously, one would go to greater lengths to repair a
> rare crank. Almost anything can be fixed, if you have the time and money.