1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Best tap for stainless steel?

  1. Apr 29, 2016 #1
    I need to know what is the strongest most reliable tap for threading 6-32 into stainless steel. I used like 3 cheap steel taps and they all broke. Any advice is greatly appreciated.

    Thank you
  2. jcsd
  3. Apr 29, 2016 #2


    User Avatar
    Gold Member

    I used to use spiral flute machine taps on various stainless steels, all about 30 HRc hardness. They worked OK even as hand taps but I would always use a drill press or lathe if possible. Just tighten the chuck with enough force so the tap will work, but then spin in the chuck when it hits the bottom of a blind hole and not break.
  4. Apr 30, 2016 #3
    Thanks for the advice, I went ahead and ordered some 2 flute spiral taps. Fingers crossed they work.
  5. Apr 30, 2016 #4


    User Avatar
    Science Advisor

    Many stainless steels work harden and so must be drilled and tapped with HSS tools.
    Some require cobalt high speed steel = HSS-Co, or carbide tooling.
    It is essential that you use a cutting fluid. http://www.bssa.org.uk/topics.php?article=192
  6. Apr 30, 2016 #5


    User Avatar
    Science Advisor
    Gold Member

  7. Apr 30, 2016 #6
  8. Apr 30, 2016 #7
    Also if you know any taps for stainless on eBay (preferably in US) please do put the link I really need to get this right.

    Thanks for all your help
  9. Apr 30, 2016 #8


    User Avatar
    Science Advisor

    I'm on the other side of the planet and I buy unusual taps from Victor Machinery Exchange in Woodside, New York, USA. They have the contacts to get special taps made to order if needed. http://www.victornet.com/departments/TAPS/100.html

    If the stainless steel you have does not finish well then you might consider drilling an oversize hole, then using an STI tap and an insert.
    That will give you a very good finish on the "recoil" thread insert. It also uses a larger tap that is less likely to break.
  10. Apr 30, 2016 #9
    I will have a look at them for sure.

    Also here is what it says on the taps that broke --- 6-32 NC HS GH3 USA 0416M4R

    By HS do they mean hardened steel? I'm guessing it's not as good as high speed steel?

  11. Apr 30, 2016 #10


    User Avatar
    Science Advisor

    Cheap taps are commonly made from Carbon Steel. More reliable, harder taps are made from High Speed Steel.
    HS is almost certainly “High Speed”, the steel goes without saying.
    G H3 is probably the finish and oversize. H3 may mean 1.0 to 1.5 thou oversize.

    Find some way to support the tap in line with the hole. Experiment with cutting fluid, oil or soap. That will almost certainly reduce breakage. Some taps in some materials produce the best finish by cutting continuously. Others require a slight advance, then a reverse to break off the cuttings. You will need to experiment to find the best technique.

    Corrosion is usually the most important parameter, but if possible select a grade of stainless that is free machining.
  12. Apr 30, 2016 #11
    I will try to mount the tap in the drill press rather than doing it by hand in that case.
  13. Apr 30, 2016 #12


    User Avatar
    Science Advisor
    Gold Member

    One thing that is important when tapping difficult materials is getting the pilot hole the right diameter .

    Using pilot holes slightly larger than the theoretical correct size eases the load on the tap considerably and reduces chances of breakage .
  14. Apr 30, 2016 #13
    Use a tap lubricant specifically for stainless steel. Tap Magic is commonly available. And never turn the tap more than 1/2 turn without backing off at least 1/4 turn. Other than that any decent quality tap will work. It's also a good idea to have a starter tap and a plug tap. The starter tap makes it easier to start the threads "square". If you start at an angle you will not be able to complete threading, and the tap will break.
  15. Apr 30, 2016 #14
    I have successfully threaded the holes. I used one of the broken HS taps and rounded it off a bit with my dremel. Afterwards I placed it in a drill press, with my piece placed in the vice. I used lots of lubricant and it worked like a charm without breakage. Drill press is the way to go for sure.

    Thanks for the help everyone.
  16. May 4, 2016 #15


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Sorry if you know this but... Are you just trying to screw the tap in or are you doing the normal half turn in and a quarter turn out?
  17. May 4, 2016 #16
    I tried it both ways without the drill press and it broke regardless. Funny thing though I just screwed it in in the drill press and it worked even without turning it back.
  18. May 4, 2016 #17
    I used ridgid for most purposes, but "working a tap" not (over working it) usually produces the desired results . Use a LOT of cutting oil and if you get in a bind stop, HSS an CHS taps will snap just as quick if not quicker than any of the cheapo taps you can buy if you over work them in stainless.

    These are pretty good:

  19. May 4, 2016 #18
    True, also I found a very easy way to get small broken taps out is by hole punching it about 20 times. It just flies right out.
  20. May 4, 2016 #19


    User Avatar
    Science Advisor

    Different stainless steels work harden differently. If you “work” the tap you may harden the material, then break the tap when it hits the previously hardened wall. If you continuously turn the tap the chips will be hardened but the material being cut will be fresh and normal hardness. The speed of cutting is important because the hardening process is a chemical phase change. In some materials, if you back off torque momentarily you may hit a hardening wall.

    Avoid machining old, salvaged or unidentified stainless steel. You will probably need carbide tooling.

    There are different flute profile taps, spiral flute taps are designed to cut continuously while straight flute are designed to be reversed to break the chips. Don' be mislead by “spiral point”, in hard materials they are often as bad or worse than straight flute because they clog with chips, especially in blind holes. The spiral path of the flute decides the curl of the chip and the quality of the thread finish.

    There are many different stainless steels. What grade material are you threading ?
    How long or deep is the thread you are cutting? Blind or through hole?
    Is your material new or aged? Has the material been subjected to cold temperatures? for what periods?
  21. May 4, 2016 #20
    Could you explain the material hardening? I still don't fully understand it. The stainless type is 420
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Threads for Best stainless steel
How steel fails?
Stainless steel friction / galling