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  • Tapping question

    Hey guys, need some advice here. I have a piece where I have to tap numerous holes in a piece of 1018 steel, .750" thick. they are 5/16 x 18 through holes. I have always hand tapped, mainly cause that is all I have. In this case I would like to power tap, if possible. I do not have a tapping head, but have seen people tap directly in spindle.

    First off equipment I have:
    Jet JTM-2 mill (bridgeport clone)
    2HP single phase motor
    Slowest rpm is 80rpm.

    Now the questions:

    1. Is it possible to power tap this thick, or is it pushing it to much?

    2. I know I need a spiral point tap. Can you recommend brand, type, coating etc. Preferably from MSC.

    3. Do you recommend using tap in drill chuck or collet. My thinking is that if I use drill chuck, the tap would slip rather than break the tap, if it binds. Thoughts?

    4. Do I tap a bit then reverse direction until through, or just run straight through?

    Thanks in advance, any tips or tricks would be great.

  • #2
    You can easily tap with the mill. Though unless you are on three phase or VFD it will not be a whole lot of fun since you have to wait for the motor to stop every time. That's where a tapping head comes in.

    Dont back taps off. Thats one way to break them. Gun taps push right on through.

    Use a good cutting fluid. Tapmatic works fine, so does high sulfur cutting oil. Cutting waxes also work well.

    Comment


    • #3
      Tapping

      You can tap in the drill chuck. DO NOT use a keyless one for that - use a 1/2" or bigger keyed chuck and tighten it snug to begin with. If it slips too much, tighten a little more. Repeat as needed. Make sure the shank of the tap will not bind up in the hole when you get all the way in. You may need to make part of the shank smaller for a hole that deep. OSG, Greenfield, Kennametal, Hertel, basically any of the well known name brands will do. For the coating, I prefer AlTiN.

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      • #4
        I would wonder the order of operations you'll be using. The reason I mention it is more than likely you will drill all in one shot and follow up with a tap. That means repositioning over the already drilled hole. A floating holder might help you out there in that it self-aligns to a certain extent. All the textbooks tell me that should help avoid broken taps for you, but I will admit to never owning a floating holder. I wonder if you could get away with a drill/tap combined tool. The hole is pretty deep, though, so it might put some bad mojo in action having the hole not be finished when the tap section engages the work (thread then provides the thrust for the drill section). I don't know, but I wanted to throw these ideas out there so perhaps someone with more experience in this area can chase out the good from the bad in my suggestions.

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        • #5
          It's going to be touchy without a tapping head or a VFD. Make sure you establish the proper timing in scrap material before working on the good stuff.

          A tap chuck will not slip as it drives the tap shank on the square, making a broken tap a good possibility if you screw up.

          An ordinary keyed drill chuck will slip since the tap shank is hardened, but you should be able to back out the tap under power. A keyless drill chuck might loosen if you try to back out the tap under power.

          You probably don't have a regular R8 collet to fit the tap shank, but it will work and you might be able to roughly adjust the driving torque by adjusting the drawbolt torque.

          RWO

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          • #6
            If you may be making multiples of these ...Id get a tappping head.

            You dont have to break many decent taps before you'd cover the best part of the cost of a head..(and tapping with cheap taps is no fun at all).

            Comment


            • #7
              Take a look at the taps on pg 302 of the MSC catalog and I think you'll find what you need. They are pricey, but without a tapping head you'll need to go with the best taps you can get.

              BTW, I 2nd the recommendation on a tapping head. You may be in a time crunch, but I'd certainly get one if you're doing a lot of threaded holes. the time savings & tooling savings will pay for the tapping head in short order. Check EBay & use a Craig's List search engine (I use Tempest) and you may find a good deal.

              Oh yes as others have said, use a good tapping fluid.

              Comment


              • #8
                1. Is it possible to power tap this thick, or is it pushing it to much?
                5/16-18 won't be tough to do. Check to make sure you have enough threads on the tap to make it all the way through. Spiral point (gun taps) work great for through holes. 100 to 200 rpm and PLENTY of cutting oil.

                2. I know I need a spiral point tap. Can you recommend brand, type, coating etc. Preferably from MSC.
                DON'T CHEAP OUT ON TAPS!!! Hertel, Butterfield, etc.

                3. Do you recommend using tap in drill chuck or collet. My thinking is that if I use drill chuck, the tap would slip rather than break the tap, if it binds. Thoughts?
                Unless you spring for a tapping head, a drill chuck works good. Tap shanks are often a bastard size.

                4. Do I tap a bit then reverse direction until through, or just run straight through?
                Straight through is best although I have been known to reverse the spindle if the tap slips in the chuck. If it still slips I tighten the chuck or finish by hand.

                Though unless you are on three phase or VFD it will not be a whole lot of fun since you have to wait for the motor to stop every time.
                Nah, just use the brake lever as soon as you turn off the spindle, then reverse the tap out of the hole. It takes a bit of practice and hand to eye coordination.
                "The truth is incontrovertible, malice may attack it, ignorance may deride it, but in the end; there it is." Winston Churchill

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                • #9
                  Cut a square hole in a rod to slip the end of the tap into. Chuck your new holder. Hold the tap, lower the quill, hit start, feed. The tap will fall out when it is done. Pick it up, repeat.

                  bob

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                  • #10
                    Unless this is a critical job consider using an oversize tapping drill so that you are not forming full depth threads. This greatly reduces the torque requirement and the possibility for jamming without sacrificing much strength.
                    Mike

                    Comment


                    • #11
                      1) you don't need 3/4" tapped for a 5/16 hole from a strength perspective, clearance drill up to half of that if the design permits it

                      2) your mill will work fine, you don't need 3P, a brake or VFD. At lowest rpm, just turn the motor off and it will slow fairly quickly. You have to watch it obviously and develop a bit of a sense of how much momentum is there, but its not too hard to do.

                      3) Don't use your best Rohm keyless, use an older chuck as you may well spin a tap. Doesn't much matter though, I'm never found the hardened shafts of taps chew or get chewed up...still don't use the new Rohm

                      4) Use the spiral points, you have to with machine tapping, and go straight through. a regular tap will jam if you're not reversing to break the chip but you don't want to try and do that, cripes might even burn out a motor trying

                      5) use some cutting fluid, I usually use dark cutting oil I keep in an oil can so its always handy

                      6) as has been said use quality taps
                      .

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                      • #12
                        As an earlier poster suggested, unless the threads have very high strength requirements, I'd go for less than the 75% thread depth that is what you get with the drill size recommended on most "standard" drill charts.

                        For a 5/16"-18 thread, an F drill give you 75% thread depth. A H drill lowers the thread depth to 60% and makes the tapping a lot easier but the thread strength will still be around 90% as strong as the 75% depth threads.

                        If you can still get your hands on some sulfur based thread cutting oil (the EPA has made this very hard to find) I'd use that or if you can get some Moly-Dee and can stand the smell it would work well for this job.

                        Good luck-

                        Paul T.

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                        • #13
                          Along the lines of what Rowbare said, I have thought of a tapping tool that might work, but I haven't gotten around to building it yet, so...

                          In a length of bar larger than the size of a T-handle tap wrench, drill an axial hole deep enough to accept the tap wrench head + the max depth of tap. Now slot the bar parallel to and through the hole to the same depth. The idea is that you make a "holder" for the tap wrench that can go in a drill press or milling machine chuck. The hole will guide the tap wrench and the slots will drive it, but provide enough "float" so it will self align with the hole to be tapped. By setting the chuck at the proper height, the tap wrench will walk itself down the tool and out the end when it gets to the bottom.

                          As I said, it's a design concept: I haven't built one yet and perhaps the reason I haven't seen anything like this on the market is an indication that it won't work well, but who knows?

                          Comment


                          • #14
                            Good taps are fine providing they are sharp - and are replaced or sharpened (tool & cutter grinder) when not sharp - and are use properly and sensibly.

                            A close look at a tap will soon show that there are many real and potential "stress raiser points" even when new and even more if carelessly sharpened.

                            Any tap will snap if not sharp - smaller taps more then bigger ones.

                            Taps are consumable items and regular inspection, sharpening or replacement are standard cost items - no tap lasts for ever - length of life depends on type of use and sharpness.

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                            • #15
                              Originally posted by 3jaw
                              5/16-18 won't be tough to do. Check to make sure you have enough threads on the tap to make it all the way through.

                              X 2. The shanks on all the 5/16-18 taps I have are larger than the hole.

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