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Tapping Stainless Steel

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  • Tapping Stainless Steel

    I need to tap a regular (course) M3 thread into 303 Stainless Steel (18-8 gauge) but it is proving to be the most difficult step in my electronic system chassis design. Can anyone give me a heads up as to what kind of hand tap I would use to cut M3 metric threads (through hole) into my 5/16 inch (8mm) SS keystock?

    It is a very hard metal indeed and has destroyed three M3 taps in less than 12 minutes.

    I have found the homeshopmachinist bbs has been a great deal of help to me in this rather complicated project.


    Oh yes, did I mention I have 52 tap holes?
    Last edited by chris2a2; 12-02-2009, 09:23 AM.

  • #2
    At that size consider dropping to 50% thread engagement and use a larger tapping drill.
    Paul Compton


    • #3
      I was afraid of that. I am tempted to upsize to M4 since I have the clearance for it. Which brings me back to the original question. What kind of tap would I use. I have seen solid carbide from M4 and above available over the internet.


      • #4
        For stainless I go for a Tin coated two fluke tap. make sure it is new and use plenty of lubricant. When the tap starts to go dull trade for a new one. And Like EV says 50% threads are acceptable in stainless.


        • #5
          ? Are the taps you are using made for tapping SS, i wore out a few master craft ones and when i get into tapping SS its usualy 2 to 3 inches down, anyhow i bought some really nice taps made specificly for SS and harder metals and i have never had and issue sence nore have i worne out even one tap yet , there not the cheapest or the most expensve but they work

          use lots of cutting fluid as well keep the hole clean SS is a bugger for sure just dont force the pressure into the cuts either if you see or feel the tap twisiting then back it out and gently back in again


          • #6
            Unfortunately I live in Athens, Greece. This is the land of poor quality, counterfeit products, and unbalanced equations. I bought the taps as Praktiker which is a general hardware and home improvement multichain store.

            If you have a line on any suppliers of quality cutting tools in the UK that ship to the continent it would be greatly appreciated.

            My cutting techniques are decent though I am not proficient. However, I have managed to cut very clean taps into cast iron and I did hang around the tool & die makers at work for many years before I retired. Yes, 18-8 does feel like you are chipping glass when I tap so I back out frequently and use a lot of cutting oil. Hmmm, this SS must be as hard as cast and much more fickle.

            Thanks again, Chris

            P.S. I did find solid carbide direct from the US at M3.5 but you don't even want to know how expensive it is. OK I will tell you anyway; about 90 dollars US.


            • #7
              Forget Praktiker, it doesn't get any worse.

              For top-quality tools, go here:


              If you click on the "Hoffmann Group" tab, and then click "Partners", you'll see they are represented in Greece by "Pangakis".

              To look for products, go to the eShop and click "Guest access" (which means full info except prices).
              You'll find taps in product group 1.
              You can also try ordering a catalogue.

              Best Regards,

              Last edited by Benta; 12-02-2009, 11:17 AM.


              • #8
                Thanks Benta. Moving here from the US is what the first astronauts on Mars would feel like; no TV except for the Alien Cable Network, and no hamburgers except for 5 day old souvlaki.


                • #9
                  Use Paul's advice in post #2 of this thread. He means to use a slightly larger tap drill than is usually specified for the M3 thread.

                  Secondly, get a tap made specifically for stainless, OSG Exo-taps are one brand that comes to mind.


                  • #10
                    There is a green tapping fluid for stainless that works really well. I do not remember the name but someone on line may. I tapped a lot of threads in stainless as plant engineer in an ice cream plant.


                    • #11
                      Originally posted by Jim Hubbell
                      There is a green tapping fluid for stainless that works really well. I do not remember the name but someone on line may. I tapped a lot of threads in stainless as plant engineer in an ice cream plant.
                      You may be thinking of AnchorLube G771, Anchor Chemical Co, Enco stocks it. Label is messed up on my bottle, so I can't quote the address but the phone is 440-871-1660. I bored some mystery stainless that was tougher than bird beaks with this and it worked pretty well. // video_man


                      • #12
                        A 3 or 4 flute reasonable quality High Speed Steel tap should be ok.


                        • #13
                          OK in Europe Dormer is good, so in English RS component M3 Dormer Blue ring for stainless here

                          in Greece use RS Greece


                          same thing but I cant read it

                          Steve Larner


                          • #14
                            Possible Alternative


                            Have you considered installin Riv-Nuts or something similar. Just drill
                            the proper sized hole and install.

                            There a multitude of manufactures. Here is one for an idea. Don't know
                            what might be available over there.


                            Can't copy the photos sorry. Just an idea. They are know my lots of
                            different names.

                            Good luck.


                            • #15

                              I wanted to thank all who responded to this thread. Suggestions and recommendations of everyone were more than helpful.

                              I tried to contact OSG in Belgium and made no progress. I contacted OSG in Ohio USA and found their technical consultants well informed. So I found a distributor of OSG in New Jersey since I have a mailing address there. The prices were not that bad and the drill bits and taps are specifically for stainless steel. I know it is a round about way to get things done but I wanted to get the right tools for good results.

                              As far as the tapping fluid, I found the company that makes it. It is CRC Industries based in Belgium. It is called Super Tapping Fluid and is a mixture of natural oils and synthetic additives for drilling and tapping tough materials like stainless. I did manage to find a distributor here in Athens and am waiting for a price quote. It is a green, viscous fluid.

                              I did consider riv-nuts but it may prove to be quite difficult to use since I am using 5/16 SS keystock. It is basically like working with a square block of metal.

                              Thanks also to Steve Larner for the rs website here in Greece. I will bookmark them for future reference.

                              I realize now that being a good machinist, just as any technical profession, is as much a part of practical experience as it is book learning. We remember our mistakes much more than our successes and it is invaluable experience.

                              Thanks again to all.
                              Last edited by chris2a2; 12-05-2009, 04:33 AM.