For 1/4-20  tapping aluminum (50*3.82)/.250=764 this is your RPM then divide by tpi to find you ipm 764/20=38.2     so your rpm is S764 and your feed is F38.2

Kennametal

I don't know if this topic has already been covered. I did a search, and didn't find anything. What I'm looking for is some information on spindle speed, and threads per inch for rigid tapping. My mastercam software keeps putting in insanely high spindle speeds. and aggressive threads per inch values in my programs, and I keep breaking taps. Any help would be appreciated.

I'm typically making prototype parts, so I don't always need aggressive cuts, but I always go for 1/TPI feed at RPM 400 G95 G98. It's a safe, slow speed good for most materials including stainless, but might not be good for exotics like niobium.

There are too many variables to expect mastercam to give you the right feed and speed all the time. Just find the correct SFM for the tool you are going to use and for whatever material you will be cutting.

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If a tap gets broken it won't be from a speed feed issue. I know it may sound slow but in the end way faster than burning out a broken tap.

I never understood why G95 isnt the standard for tapping.. It doesnt matter what the spindle speed is . Your feed rate is always the pitch.. For example a 1/2-13 I would usually just default to 1000 rpm and F .0769 (1/13 for the TPI)

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Shars

In any case if you need the feed for ipr format is just a simple operation 1/20=.050 so your rpm would be S764 and feed F.050

For aluminum with a HSS cut tap I do about 50sfm or for tool steel I would use 5-8sfm. With these sfm find your RPM.  I don't know if your machine needs inches per minute or inches per revolution. The sample below is for ipm.

I try to have my guys keep a constant 5ipm on all taps, the RPM is easily confirmed by the operator (multiplying it by 2)

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I'm running a 7 or 8 year old Akira-Seki vertical mill, with taps made by Kennametal... 1/4-20, 3/8-16. Broke them both right off. I ran them at 196rpm, with 14. threads per inch. My machine uses an E value for TPI...which is new to me. I'd love to find some resource material for spindle speed, and TPI, to cross reference my programs. The speeds and feeds that MasterCAM is putting out, for the taps at least, seem quite high.

I'm running a 7 or 8 year old Akira-Seki vertical mill, with taps made by Kennametal... 1/4-20, 3/8-16. Broke them both right off. I ran them at 196rpm, with 14. threads per inch. My machine uses an E value for TPI...which is new to me. I'd love to find some resource material for spindle speed, and TPI, to cross reference my programs. The speeds and feeds that MasterCAM is putting out, for the taps at least, seem quite high.

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Together, we are the strongest Mastercam community on the web with over 56,000 members, and our online store offers a wide selection of training materials for all applications and skill levels.