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Power tapping 1/2" mild steel plate

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  • Power tapping 1/2" mild steel plate

    I have ~85 holes drilled and ready to be tapped 3/8-16. This is 1/2 hot rolled plate. I have a variety of 3/8" taps and want to know if I can safely tap the under power. My drill press has a lowest speed of 300 rpm.

    Can this be done without breaking the tap? At 300 rpm? I'd be using tapping fluid and new sharp taps but have some used as well.

    Thanks for the help.
    Last edited by PT Doc; 01-12-2014, 04:49 PM. Reason: Corrected thread specs

  • #2
    spiral point / gun taps ? 300 seems kinda fast to me, I have a vfd on my drill press,and therefore crank the rpm's down -- usually bout 75-150 depending. got a piece of scrap you could make a test hole ??
    bmw

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    • #3
      Use a spiral point tap. 300rpm seems pretty high to me unless you have a tapping head. I'd want to use a mill in backgear (60-80rpm).

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      • #4
        Get a reversible tapping head. That and sharp spiral point taps will walk right through it. The chips will come out the bottom of the hole, so have someplace for them to go. Of course you will need some type of cutting fluid too.

        The tapping head is made so you can control the speed just by how hard you pull on the drill press handle. Raising the handle a little makes it stop and raising it more makes it reverse. If you have never used one of these find a youtube vid. This is the safe, easy way to tap holes.
        Last edited by Toolguy; 01-12-2014, 02:29 PM.
        Kansas City area

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        • #5
          Sounds like a tapping head is in order.

          Ridgid Drill press has an 8 amp motor so who really knows the hp. With proper feed and speeds I have not had problems drilling up to 3/4 before. This drill press is not reversible. Maybe I'll do these by hand and look into getting a vfd and 3 phase motor and solve the reversibility problem and be able to lower the rpm.

          Chucking up the tap and unchucking every hole would get old. But so will hand tapping. Seems like a good time to find an apprentice?

          thanks for the help

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          • #6
            Do you have a variable speed 1/2" drill motor, reversible and with some type of torque setting for driving screws? Maybe even a 3/8 drill would work? I've tapped smaller holes like 1/4-20 without a problem using those 2 flute gun taps mentioned. I use that dark thread cutting oil on steel.
            Retired - Journeyman Refrigeration Pipefitter - Master Electrician

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            • #7
              Check this out. Tom has many fantastic video's online on many machining subjects.

              He does aluminum and steel (after 8 min) in a Bridgeport and hand drill.

              http://www.youtube.com/watch?v=I95YrmVUL18
              Last edited by Richard King; 01-12-2014, 06:42 PM.

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              • #8
                This should take around 1 hp to tap.
                300 rpm is ok if you tap on a cnc or with a head. Tapping directly on drillpress you have to stop the spindle really fast
                FSWizard - Free Online Speed and Feed Calculator

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                • #9
                  I saw this method of tapping using a cordless drill and wondered if one could be taken apart and modified to use in a drill press using the adjustable torque limiting feature as a clutch.

                  http://www.youtube.com/watch?v=0MyzdVGQXkg

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                  • #10
                    With a good spiral point tap and a quality tapping paste or fluid it shouldn't require 1HP. I've power tapped up to 5/8-11 on my now extant 1HP step pulley Bridgeport with no trouble, and did it at 325rpm. No need for a tapping head or CNC in my case.

                    On most drill presses, you wouldn't have the back gear that a Bridgeport has, just a few more pulley choices and probably power loss. And yes, you would need a reversing tapping head to be able stop quickly and back the tap out. Here's mine doing a 1/2-13 in 1117 steel. (though I'd posted it before and not too long ago.)

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                    • #11
                      I have a small DeWalt impact driver that I use for tapping. Irwin/Hanson makes a tap socket adapter http://www.amazon.com/Irwin-Adjustab.../dp/B000TGM7HY and I use that with a 3/8" socket extension bit. I have mostly done 1/4" 20 and smaller but it works quite well for me.

                      bob

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                      • #12
                        Cordless drill, tapping oil, spiral fluted machine tap and clamp your plate to a workbench, takes all of 10 seconds per hole or so.
                        Amount of experience is in direct proportion to the value of broken equipment.

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                        • #13
                          Originally posted by PT Doc View Post
                          I have ~85 holes drilled and ready to be tapped 3/8-16. This is 1/2 hot rolled plate. I have a variety of 3/8" taps and want to know if I can safely tap the under power. My drill press has a lowest speed of 300 rpm.

                          Can this be done without breaking the tap? At 300 rpm? I'd be using tapping fluid and new sharp taps but have some used as well.

                          Thanks for the help.
                          You didn't state your drill size. If you are in the low %'s, which I would be for 1/2" material, you can use a gun tap and a cordless drill/impact driver with loose juice.

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                          • #14
                            I drilled 5/16 for all of them for the 3/8-16 end thread. Tapping head seems like the best option. Another option that was recommended was a cordless drill. I just might try that since it has a clutch and can reverse and will save me all the hand tapping. Thanks for the help.

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                            • #15
                              Tapping heads reverse with internal gearing when you let go of the handle.

                              I would go with a tapping head over a cordless drill, especially if you want to have threads that are straight.

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