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Tapping 3" Deep in Mic-6

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  • Tapping 3" Deep in Mic-6

    I have this part to make. I have never tapped this long before in any material. I have Mic-6 cast aluminum on hand and will be using that.
    My current collection of taps is just common hand taps as I don't have to ability to power tap. I need a reasonably close thread fit.

    Thoughts on best tap (gun tap?), possible problems, etc?

    Last edited by polaraligned; 02-11-2018, 08:19 AM.

  • #2
    Originally posted by polaraligned View Post
    I have this part to make. I have never tapped this long before in any material. I have Mic-6 cast aluminum on hand and will be using that.
    My current collection of taps is just common hand taps as I don't have to ability to power tap. I need a reasonably close thread fit.

    Thoughts on best tap (gun tap?), possible problems, etc?

    Your biggest problem might be finding suitable tap. Silver brazing or TIG welding extension shaft could be your ticket..

    "nut taps" are typically enough long and thin shank but AFAIK do not come with gun point.

    One possible problem with loooong thread like that is pitch errors. Your material is reasonably nice aluminium alloy so I THINK you can get away with it.

    Comment


    • #3
      Completely another issue is that does it NEED to have this long thread?

      Kind of bad design but sometimes you gotta do what the customer wants...

      Comment


      • #4
        I'd go with the weld-on extension or make a tap myself. Other than the height, I like drawings that use all even numbers.

        Comment


        • #5
          The best tap for that is a 6" long with reduced shank and spiral point.
          https://www.mcmaster.com/#taps/=1biuv9j
          Click on screw thread taps, then long reach machine taps.
          Kansas City area

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          • #6
            I'm betting its your part not a customers? Can we talk about some changes to remove the issue?

            Otherwise, long taps and taps with brazed extensions are standard stuff for reaching into dies etc. Braze an extension on a gun point tap, squirt a little wd40 on it, and have at it, probably in the mill.
            in Toronto Ontario - where are you?

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            • #7
              Taps are available, but not cheap. This is MSC's offering, Victor lists up the 3/8"-16. You might want to contact them.

              https://www.mscdirect.com/product/details/64183288

              Look for pulley taps, nut taps or reduced shank taps.
              Jim H.

              Comment


              • #8
                I did not design this part. I am going to machine it as a favor for another fellow amateur astronomer.
                The original part is a narrow cylinder, about 1", that has a thru hole tapped in it. The problem is that original narrow block rocks too much on the threaded rod and creates a lot of backlash when fine adjusting the azimuth. There is a pin on the bottom of the Tee that rides in a slot, so the threaded rod/block interface is all that keeps it from rocking and creating excessive backlash.

                Design comes from here: http://www.gregpyros.com/html/superw..._adjuster.html

                Any other ideas are welcome.

                Here is a picture of it on the mount:

                Comment


                • #9
                  Bit more complex to make but avoids the ugly long thread:

                  Make threaded insert(s) and bore the hole to bigger size. Lock the inserts in place with set screws or retaining compound.
                  Inserts can be also made of better bearing material than aluminum.

                  Variation B of the above: make the other end insert axially floating(thight slip fit), ie mill a "keyway" to it where end of the setscrew/guide pin can ride.

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                  • #10
                    Well youre BIGGEST problem is going to hit those 4 decimal places tolerances. :-(
                    ...lew...

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                    • #11
                      I would say, if you want a tight long well fit thread, modify the part to use an evanut. Heck, why not go all the way, and change over to a leadscrew? https://www.ebay.com/itm/304014-3-1-...-/142078323768.

                      Perhaps you could change the top of the part to be a tube with a nut at each end and a spring in the center pushing them apart.

                      There's lots of room there to modify the top, so go for it!

                      Comment


                      • #12
                        Originally posted by achtanelion View Post

                        There's lots of room there to modify the top, so go for it!
                        Well heck, I might as well put in a precision ballscrew with preloaded angular contact bearings on the end.....Not.

                        I need reasonable as this is just a favor.

                        Comment


                        • #13
                          Originally posted by polaraligned View Post
                          Well heck, I might as well put in a precision ballscrew with preloaded angular contact bearings on the end.....Not.

                          I need reasonable as this is just a favor.
                          Threaded inserts save you from sweaty hands and 50 usd on buying the tap. About as easy to make as the original and you get added bonus of adjustable backslash.

                          Comment


                          • #14
                            Originally posted by MattiJ View Post
                            Bit more complex to make but avoids the ugly long thread:

                            Make threaded insert(s) and bore the hole to bigger size. Lock the inserts in place with set screws or retaining compound.
                            Inserts can be also made of better bearing material than aluminum.

                            Variation B of the above: make the other end insert axially floating(thight slip fit), ie mill a "keyway" to it where end of the setscrew/guide pin can ride.
                            I was thinking along the same lines as your first suggestion, but if I can tap 3" long reasonably well, then that would be my first choice.

                            Comment


                            • #15
                              To make it with the option of adjusting backlash out thread one end of the part as you planned and make a threaded bushing with the matching 1/2" thread on the inside. Provide a method for locking the bushing in position, maybe a short section with no threads on the outside of the bushing and a set screw. This way you can adjust out the backlash as it wears, possibly provide a little "pre-load" even. It looks from the picture that you have plenty of room to make the part a little thicker if necessary to get material for a maybe 3/4" or even 7/8" thread on the outside of the bushing.

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