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  • Acme Tap, help required ***Warning machining content

    I am trying to make an Acme Tap to make some Delrin nuts. Yes I have read about the alternate methods. But I want to try this one out for comparison.

    Using some leadscrew material. 1/2" Acme. I have a 10 degree taper on the lead-in


    I have made it into 3 flutes using a 1/8? Ball nosed mill


    When I try to tap it will not feed into the material. It will go for a bit then will not feed. I am tapping by hand in lathe with tap in tailstock and winding by hand. Some firm pressure to start.

    I assume the issue is that I need to make the grooves bigger as I think there is too much material left on the tap.

    I would have made the grooves bigger but could not find a larger Ball nosed mill handy.

    Or I guess I could put some relief on the tap with a grinder.

    I have tried a couple of different diameter holes and and at 0.401" and still no better

    Thanks
    Dave

  • #2
    You need to relieve behind the cutting edges.

    As it is, all you're doing is rubbing.

    Take a very close look at a commercially made tap and you'll see what needs to be done.

    Comment


    • #3
      Yes, the flutes need to be bigger in relation to the size of the tap - be worth buying a cheap ball nose to do the job. This is an M8 tap I did

      http://richontools.com/index.php?mai...ex&cPath=15_59





      Last edited by Tel; 10-16-2011, 06:57 PM.
      Tel

      Comment


      • #4
        OK,I do need to find or buy a bigger Ball mill. None of my tooling suppliers are open today. :-(

        How many flutes is yours?
        Did you have to grind any relief?
        What material did you tap?

        Thanks
        Dave

        Comment


        • #5
          Dave,

          take a look at this picture and see how you need to position your cutter.



          Please not this is for a Left Hand tap so you need the cutter to the right of centre.
          .

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



          Comment


          • #6
            Thanks John,
            That make sense.
            Mark 2 coming up soon.
            Dave

            Comment


            • #7
              Also even in plastic you may find out as I did that it is possible to twist a homemade Acme tap trying to tap more than a couple thread diameters.

              You might consider making your first tap into a roughing tap,and the new one the finishing tap.
              I just need one more tool,just one!

              Comment


              • #8
                OK,
                I will bite.
                What do you propose in geometry to make a roughing and finishing tap?

                Thanks
                Dave

                Comment


                • #9
                  I made this tap to cut threads in a new compound feed nut for my metric Southbend 10k lathe. If I remember correctly I used 3 degrees for the taper. I should have made the flutes wider because it rubbed hard enough to twist the tap cutting in brass. It is 10mm x 2mm made from drill rod and hardened and tempered.

                  Terry

                  Comment


                  • #10
                    When I built mine I turned the acme threads down to more of a pointed thread. It helped the tap dig in easier and pull itself into the nut being tapped.







                    Andy

                    Comment


                    • #11
                      Originally posted by DFMiller
                      OK,
                      I will bite.
                      What do you propose in geometry to make a roughing and finishing tap?

                      Thanks
                      Dave
                      Redo the flutes and turn the OD down so the tap is only cutting maybe 60% of the full profile for the roughing pass.
                      I just need one more tool,just one!

                      Comment


                      • #12
                        Originally posted by John Stevenson
                        Dave,

                        take a look at this picture and see how you need to position your cutter.
                        John thanks very much for posting that. I have saved the image as I have a similar job coming up to go and that was simply gold!

                        Comment


                        • #13
                          Google on something like "tap sharpening relieving fixture". Note all the references to axial and radial relief in the results of the Googling. It's too difficult to explain without detailed pictures which I don't have.

                          You NEED relief behind the cutting edges, otherwise it won't cut easily if at all. There is absolutely no doubt about the need for relief. Even what John S showed is not right since it has no relief. But, using the largest possible ball end mill without relief will help some.

                          For proper tap making/sharpening the relief must be ground in a precision fixture so each flute is ground the exact same amount. For the type of results (accuracy) that can be expected with a homemade tap the reliefs could be done carefully by hand on a bench grinder.

                          Now stop all this nonsense, do some research, and do it right.

                          Comment


                          • #14
                            Originally posted by DR
                            Google on something like "tap sharpening relieving fixture". Note all the references to axial and radial relief in the results of the Googling. It's too difficult to explain without detailed pictures which I don't have.

                            You NEED relief behind the cutting edges, otherwise it won't cut easily if at all. There is absolutely no doubt about the need for relief. Even what John S showed is not right since it has no relief. But, using the largest possible ball end mill without relief will help some.

                            For proper tap making/sharpening the relief must be ground in a precision fixture so each flute is ground the exact same amount. For the type of results (accuracy) that can be expected with a homemade tap the reliefs could be done carefully by hand on a bench grinder.

                            Now stop all this nonsense, do some research, and do it right.
                            I've measured several acme taps here, and near as I can tell to tenths, there isn't any actual relief on them...... not on OD, anyhow, and apparently not on width.

                            Since a tap is totally un-guided otherwise, it actually makes sense that there isn't relief. With much relief the tap might not cut a good thread.

                            Yah.. and for this application, asking the OP to do the work of $10 grand worth of equipment on the tap is unrealistic....

                            The MOST LIKELY reason for problems here is that the "hook" is not present, as JS showed, and in consequence the plastic material is not cutting clean. Plastic does that.... it gets "plowed" a bit, instead of clean-cut, and then springs back to grab.

                            Also swarf room is minimal on the tap as shown...... Plastic swarf you'd swear expanded.... it gets jammed in and you can't go forward, (sometimes hardly backward either)

                            Even relief is not very helpful in that case.

                            best thing is likely to be a rough and finish cut, AND backing out to clear swarf more than you;d expect.
                            Last edited by J Tiers; 10-17-2011, 09:57 AM.
                            1601 2137 5683 1002 1437

                            Keep eye on ball.
                            Hashim Khan

                            If you look closely at a digital signal, you find out it is really analog......

                            Comment


                            • #15
                              Originally posted by J Tiers
                              I've measured several acme taps here, and near as I can tell to tenths, there isn't any actual relief on them...... not on OD, anyhow, and apparently not on width.

                              .................................................. .................................................. ....

                              I just checked the only ACME tap I had readily available to measure. Keeping in mind it's difficult to measure relief without a fixture and an indicator. I used a dial caliper.

                              The relief at the cutting end (taps only cut at the end, except maybe taper pipe taps) appears to be about .050" across two flutes of a four flute 3/4-8 Acme tap. So, that would mean each of the four flutes is relieved approx .025" behind the cutting edge.

                              I also checked a 1/2-20 conventional thread tap. It's relief across two of the the four flutes is approx .025".

                              Verify this yourself. Measure the diameter across the cutting edges at the smallest part of the end chamfer. Then rotate tap CCW and measure the diameter (right hand tap looking at the cutting end).


                              Again, why would the sharpening fixtures found by Googling as I suggested have so much mention of relief if taps were not relieved?

                              Comment

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