One thing you might check is exactly what kind of tap you are using.
If you look in a tool catalog at taps, you will see that most taps are
something like 1/4-20 h3. The h3 is how much the tap is oversize.
Oversize because a tap cuts a thread that is slightly smaller than the
size of the tap. Happens because the material flexes. If I remember
correctly h1 is .0005 oversize h2 is .001 oversize. So a normal 1/4
20 tap is an H3, but you might have a tap that is a 1/4-20 h5 or even
higher. I see in the J & L catalog 1/4-20 taps are mostly h3, but you
can buy h1,h2 h3 and h5 as well as some oversize taps that are just
sold as + .005

Dan


wrote:
I have been pulling my hair out trying to tap holes to get decent
threads. Instead they are always sloppy and oversized.

I use good technique.....tap absolutely square to the hole;
I use a good cutting oil; and I back the tap out to clear
the chips; etc.