The recommended hole size for tapping is usually not the best. There is no one perfect size, but you can often do a lot better by considering the thread percentage.

The deal with thread percentage is the recommended tap drill sizes you find in most online charts and on the tap packaging are for 75% threads. That’s conservative from a strength standpoint, but aggressive from the standpoint of over-stressing your tap. Premium tap makers like Guhring actually recommend 60% to 70% percentage of thread for most applications because it significantly lowers the torque force required to tap without giving up much thread strength. That means you’re way less likely to break the tap and you’re sacrificing very little holding strength.
You can learn a bunch more from our article on tap drill sizes, but now you know enough to greatly reduce your chances of breaking a tap.
Our G-Wizard Calculator includes this powerful Tap Speeds and Feeds Calculator and a whole lot more. Try this more powerful calculator (and much more) just by signing up for our 30-day trial. That’s right–most of the calculators can still be used after the trial expires. For example, you can still access the Thread Database with it’s percentage of thread table.

Tap Forms 5 2 6 download free. full

To sign up, simply visit the G-Wizard page or click this button:

Need to Program Tapping on a CNC?

We’ve got you covered with this great article on tapping g-code. It even includes information on our easy Conversational CNC Wizard for tapping.

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