Tapping 3/8-24UNJF in 304 1/8 hard steel
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  1. #1
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    Default Tapping 3/8-24UNJF in 304 1/8 hard steel

    I'm looking to (drill and) tap some 304 1/8 hard stainless tubing at 3/8-24 UNJF about 1" deep. Is it a good idea to try this in a lathe? I see a few taps listed at MSC but none long enough to get to full depth. I may need a custom tap. Annealed 304 sounds bad enough. How much worse will 1/8 hard be? Is there a better way?

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    Quote Originally Posted by robert123 View Post
    I'm looking to (drill and) tap some 304 1/8 hard stainless tubing at 3/8-24 UNJF about 1" deep. Is it a good idea to try this in a lathe? I see a few taps listed at MSC but none long enough to get to full depth. I may need a custom tap. Annealed 304 sounds bad enough. How much worse will 1/8 hard be? Is there a better way?
    I'm not exactly clear on what you're trying to do. Are you working with 1/8" wall tubing and tapping a hole in the end?
    If that's the case a 1" hole isn't very deep. And define the term "hard". Are you dealing with a heat-treated part or are
    we talking about mill-run "pre-hard". The latter will be tough but you should be able to tap it with a quality tap--fully
    heat-treated material will be a crap shoot...

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    Lathe will be fine. BORE the tube I.D. to the max minor thread diameter (bore to get the I.D. concentric!)
    MSC lists over 200 spiral point taps ... you should not select the cheapest one!

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    your "J" thread will have a modified minor diameter. 304 is very well suited for form tapping. When you say 1/8 hard, you'll find it to be a bit tougher than 1/9 hard.

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    To get the depth you need grind away the shank to clear just above the thread.

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    I have recently found 304 SS tubing to vary greatly in quality. I haven't gotten any certs on any of it, some from McMaster (costs on material with certs is a lot more expensive)some a customer provided. I am guessing China has infected another market with garbage material. Fortunately the parts I were making were in small lots. I would first off make sure the material is sourced from a quality domestic or European mill. I like using titanium nitride coated drills and taps on 304.


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