Problem- Threads Gulling

[dinnese]

Machine Swiss Star SR203111, Head 1, Tool Location-T1400, Operation-Tapping
(North American 7/16-32 45deg. Spiral Flute Threadshaver) running at 20 SFM. Threads Gulling. Any Suggestions?

[txcncman]

I suggest you tell what type of material and what is the measured size of the drilled hole before and after tapping.

[dinnese]

The Material is 304 S.S. Tubing. I.D is .419

[txcncman]

What % of full thread are you trying to get?

[txcncman]

From Machinery Handbook:

7⁄16–32 UN 2B Minor Diameter 0.404 to 0.411

7⁄16–32 UN 3B Minor Diameter 0.4040 to 0.4094

So, at 0.419 you are already oversize by at least 0.008. You will have an effective thread height of 0.0093. About 61% full thread. What you are probably actually seeing is not galling, you are seeing very rough, torn thread crests. Thin wall tubing is not very forgiving for most machining operations in my experience.

[hacdlux]

depending on how thin your tube wall is you might be able to get awy with a form tap,

also is there a weld seam in there ive run in to that problem before even after cutting it out

i would single point it 304 is kind of miserable to cut threads in any way

just did some 10mm studs in this used a kennametal laydown 5010 it cut like butter IT NEEDS A CHIP BREAKER