Tapping

[jorgehrr]

What is the best way (formula) to find the RPM for tapping.
I need to make a 7/16-16UN-2B thread (ID) in 12L14 steel
I know my feed rate is 1/TPI = F0.0625
Now, how do I get the RPM????

Please help, no to much experience with taps.

George

[Geof]

Originally Posted by jorgehrr What is the best way (formula) to find the RPM for tapping. I need to make a 7/16-16UN-2B thread (ID) in 12L14 steel I know my feed rate is 1/TPI = F0.0625 Now how do I get the RPM???? Please help, no to much experience with taps. George

Are you sure your TPI is correct? 7/16 UNC is 14 threads per inch, 7/16 UNF is 20 threads per inch.

You choose the rpm you want to use depending on the material and then set your feed to suit. I tap leaded steel at 1000 rpm so for 14 threads per inch the feed is 71.4285; 20TPI is F50.0, 16TPI F62.50

[jorgehrr]

Thank you.

7/16-16UN-2B not UNC. I guess something special.
I'm trying to understand the relation between the RPM and the TPI (feed of the tap going in)

Again, Thank you for your help.

George

[ajl6549]

First calculate the required spindle speed. This is determined by the type of mat'l. and tap type your using. Soft steel around 80 - 100 sfm. with a spiral point plug tap in a thru hole. Sfm (surface feet per. minute) for a given tool diameter is found with a formula. The formula are found in most machining handbooks etc.
Next you must find the feed. The relationship between the speed and the feed for a tap is the thread pitch. Another way of discribing pitch is the amount the screw, or tap in this case advances when rotated one revolution.
In the case of taps that are discribed in thrds. per inch the pitch is found by dviding 1 by the no. of thrds per inch in your case 1/16=.0625 so .0625 is your pitch. If your machine taps in ipr (inches per revolution) mode you would use that number. See below for an example:


S785 M3
G95 G98 G84 R.1 Z-1. F.0625
G80

If your machine machine does not use ipr then it uses ipm (inches per minute) and you must calculate the feed rate by multipling the pitch by the spindle speed S785 * F.0625 = F49.11. This might look like the example below:

S785 M3
G94 G98 G84 R.1 Z-1. F49.11
G80


Note: G95 is for ipr and G94 is for ipm.

Hope this helps

[jorgehrr]

Thank you guys.

I programmed 650 RPM (just a guess) and .0625 feed rate,

The thread is good.

I need to do some research of those formulas for future jobs.

Thank you all

Cheers

George

[ajl6549]

As I said just get yourself a Machinery' Handbook it's an valuable tool for any machinist.