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What's the largest sized tap I can power-tap with a 1 HP motor?

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  • What's the largest sized tap I can power-tap with a 1 HP motor?

    I have a 1-HP motor on my mill.
    What's the largest sized tap I can safely drive, without the motor stalling?
    1/2 (12MM) maybe?
    I think 5/8 might be pushing the envelope a bit.

  • #2
    my quick reaction is, 1/2" maybe in 10 ga sheetmetal. . . it sounds like a good trial and error thing. . . I tied 5/16" in a block of aluminum with my Bridgeport. . . first one snapped the tap off, got to the point where I was running out of suitable taps, I finished the project with a hand lever and tap. . .
    I suppose you could get into measuring how much torque your machine puts out with a bot, nut and torque wrench, then measure how much torque it takes doing it by hand with a torque wrench.
    it sounds like a lot of figuring toget the real technical answer. . . . . just a first thought. . .

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    • #3
      Depends on the tpi and thread %, so yeah, likely a trial and error sort of thing.

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      • #4
        I recently tried a OSG Fast Spiral Fluted Tap an was amazed at how easily it cut.
        Byron Boucher
        Burnet, TX

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        • #5
          I've done 5/8-11 in mild steel @ 70% with a spiral point gun tap with the tap held in a collet.That was a 1hp pancake motor J-head B-port.There was more than enough power running in back gear to drive the tap.Anything bigger would be approaching the driving limit of the R-8 spindle IMO.
          I just need one more tool,just one!

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          • #6
            Originally posted by Boucher View Post
            I recently tried a OSG Fast Spiral Fluted Tap an was amazed at how easily it cut.
            did you eventually beak it or you still have it?

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            • #7
              You can make a rough estimation of the available torque at the headstock.

              Torque = 5252 * Power / RPM

              So for a 1725 RPM, 1HP motor, you are looking at about 3 foot pounds of torque.

              You will most likely be running in back gear and typically that is about 6:1 so you are looking at about 18 foot pounds of torque at about 287 RPM.

              Of course that does not take into account gearbox losses so factor in a loss of 15% and you end up with about 15 foot pounds at the spindle for a WAG.

              Now you just need to figure out how much torque your tap needs :-)

              Joe
              https://www.youtube.com/channel/UCIF...7S66kX1s8rd0qA

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              • #8
                Originally posted by dian View Post
                did you eventually beak it or you still have it?
                Still have it. The part that I was threading was a little over 1" thick 416 stainless with a through hole. This was started under power in the lathe and completed turning by hand. My supply of regular gun taps were getting somewhat dull but The new fast spiral fluted tap cut like butter by comparison.
                Byron Boucher
                Burnet, TX

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                • #9
                  I would think it would mostly depend on the gearing or belt arrangement and the final speed of rotation as the torque is what you measure when turning a tap and the more you gear down or otherwise MECHANICALLY reduce the speed of the motor, the more torque you will have.

                  Tap Torque = Motor Torque X Motor RPM / Tap RPM

                  Electronic (VFD, chopped DC, etc) means of slowing a motor may not reduce the torque, but they do not usually multiply the torque so they don't count: just gears and pulleys and the like.

                  Using a ground tap will require less torque than a cut tap. And a taper tap will need less than a plug tap if the material is thin (less than the length of the taper). Fine thread less than a coarse thread. A cutting fluid with good lubrication properties will also help: in fact, lubrication is more important than cooling here. Many factors at work here.
                  Paul A.
                  SE Texas

                  Make it fit.
                  You can't win and there IS a penalty for trying!

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                  • #10
                    It's more a function of the gripping power of whatever you choose to drive the tap, i.e. drill chuck, collet, etc. That's usually the limiting factor.

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                    • #11
                      I had no problem at all with a 1/2-13UNC-2B in 1117 steel using a spiral point tap under power, held in a regular Jacobs drill chuck.

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                      • #12
                        If it's on a Bridgeport then 6-32 is about the limit
                        .

                        Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                        • #13
                          Originally posted by John Stevenson View Post
                          If it's on a Bridgeport then 6-32 is about the limit
                          Wot? My machine that I used for the 22 second video was (and still is for the new owner) a gen-u-whine 1HP Bridgeport. The hole wasn't oversized, the tap wasn't new. Ok, so there's a chance I didn't send the tap through the 1" thick steel. I may have drilled the backside of the hole open to 5/8" to within 1/8" of the top surface, but it looked good didn't it?

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                          • #14
                            Originally posted by PixMan View Post
                            Wot? My machine that I used for the 22 second video was (and still is for the new owner) a gen-u-whine 1HP Bridgeport. The hole wasn't oversized, the tap wasn't new. Ok, so there's a chance I didn't send the tap through the 1" thick steel. I may have drilled the backside of the hole open to 5/8" to within 1/8" of the top surface, but it looked good didn't it?
                            It's just John and his ABB (Anti-Bridgeport Biggotry) showing up Obviously he needs sensitivity training
                            I just need one more tool,just one!

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