I have a Fadal 4020 with rigid tapping which I use to tap thousands of 4-40 holes into 6061 aluminum, but recently I bid on a job that requires tapping 5/8 through 1-3/16" 304 stainless plate. I know I won't be able to tap this part, but it got me wondering what the limits are for rigid tapping for future cases? The majority of my work in on aluminum so It's not a huge deal but just got me thinking? Also, what are some opinions out there for precisely tapping this size? Just curious. Thanks, Dan.
I would recommend rigid tapping up to a 1 inch 8 thread max. Use thread milling above that. I normally use thread milling above 3/4 inch threads.
If you're cutting exotic materials then that's a whole different ball game.