Drill size calculator for tapping holes

[gellfex]

I was responding to Doozers comment, not making a recommendation. In fact, the programs help screen lists suggested Depth Of Threads
for a small variety of materials.

Not knocking you, the program's cool. Just commenting about the horror of being badly taught a little and self taught the rest.

[RichR]

Fair enough.

[Juergenwt]

Also remember that drills have a certain diameter tolerance, and typically may drill 0.001" undersize to 0.005" oversize, especially if not perfectly sharpened, and depending on how long it dwells in the hole, and other factors.

Totally meaningless. If you feel like that than why don't you ream all your tap holes?

[Juergenwt]

Or just subtract the pitch from the nominal diameter.
Works inch or metric.

-D

Absolutely right for most threads. The rest is BS. For % of thread like 50% for stainless - that is a different story.

[PStechPaul]

The recommended drill size is just a guideline. If excessive torque is needed (assuming the tap is good), then just open the hole to the next closest size up. Or perhaps use a pin gauge to determine the actual size of the drilled hole, if you need to tap to a very close tolerance of fit.

[hornluv]

Major Diameter - Pitch = ~75% tap drill
Major Diameter - (Pitch x .66) = ~50% tap drill
For inch threads Pitch = 1/TPI

As Doozer said, it works for both inch and metric threads.

[mklotz]

Major Diameter - Pitch = ~75% tap drill
Major Diameter - (Pitch x .66) = ~50% tap drill
For inch threads Pitch = 1/TPI

As Doozer said, it works for both inch and metric threads.

Why not complete the generalization...

Major Diameter - (Pitch x DOT/75) = DOT% tap drill

where DOT = desired depth of thread expressed as percentage

[754]

All I ever did was use the single page pocket chart from Cleveland and my now almost wore out Tapping handbook from Dormer, also pocket size.
If you are doing it a lot you start remembering most..