How to Calculate Speed & Feed for Tapping

Determine the threads per inch you must provide. This figure is dictated by the bolt you are going to use. Get the threads per inch from the manufacturer or seller of the bolt.

Find out the revolutions per minute (RPM) on your drill. This is the speed at which the bit turns. If you have a variable-speed drill, choose the speed you will be using. The larger the diameter of the tap you will be using, the lower the RPMs should be. For example, a 1-inch tap could spin at a speed as low as 400 RPM. A 1/16-inch tap cold spin at 3,000 RPM.

Enter the threads per inch and the RPM into an online calculator. You can find these calculators by entering “feed and speed calculator” as your search term. Once you enter the two known figures of threads per inch and RPM, the calculator will give you the feed rate. The feed rate is given in inches per minute.

Set your drill press feed rate to the rate given by the calculator. Monitor the progress of the tap and increase or decrease the feed rate according to how the material is accepting the tap. If you notice the tap spinning without much resistance as you drill, increase the feed rate because you are cutting too fast for the metal. Decrease the speed if you see the tap smoking despite any lubricant you may apply, because this indicates that you are feeding the tap into the metal too fast.