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ah bugger it - weird azz internal thread required :(

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  • ah bugger it - weird azz internal thread required :(

    bit of a rant, bit of a request for advice

    I'm in the process of repairing the damper for my Cannondale Headshox Fatty Ultra fork (I know, I didn't make up those names) which has a worn damper shaft and damaged top gland/ nut. Pisses all of it's oil out in short order, which then goes all over the fork, frame and front disk brake. Plus having no damper with an air spring fork is "interesting". I've put this off for 7 or 8 years so it's time..

    Finally got the piston off the damper shaft to find out that it was threaded in (doh!) and with a weird azz thread - 7/16-28. Major OD and pitch match perfectly, so I'm 100% sure that's what it is (metric would be M11x0.9?!). Obviously don't have a tap that pitch.

    I'm remaking the worn part of the damper shaft using a piece of 1/2" W2 TGP rod as I wanted something smoooooth against the seals and it was either that or stainless TGP. I need to drill it out to 5/16 for the lockout rod and drill/ thread one end to 7/16-28. I do have a small solid carbide threading bar I could use.

    Question - doing a small internal thread in W2 is kinda scary. Should I bunch up my man pants and have a stab at it or should I just buy a tap? External threading I'm not particularly fazed by, but I've never done an internal thread this small and I've not worked with W2 before (O1 yes, but no internal stuff).

    I'll be sitting on the couch drinking a beer while I await your response..

    top cap, top gland/nut and piston
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    piston hacksawed off shaft
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    Turned down to discover the threads (no wonder I couldn't press it off)
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    Bare piston
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  • #2
    KBC has 7/16-28 taps if that's what you're looking for. You could also make everything from scratch if
    you wanted to--choose your own thread...
    Keith
    __________________________
    Just one project too many--that's what finally got him...

    Comment


    • #3
      good point, I'll check them out. Don't really want to remake the piston as it has an ID seal and a couple of passageways that I wouldn't be able to make without a rotary table (that I haven't made yet ).

      I might have to check out that "threading away from the headstock" deal..

      Comment


      • #4
        Originally posted by mattthemuppet View Post
        I might have to check out that "threading away from the headstock" deal..
        Good technique to know. Just be careful. Some have done this and inadvertently generated a left hand thread!

        On something as small as 7/16 I would go with a tap if it's available and the design permits it.


        Comment


        • #5
          At this point in my life I'm a hobbyist and don't have the time constraints of a professional. Also, I can afford to waste a bit (not too much!!) material. My approach with something I have not done before is "just try it". Maybe on a test piece first until I'm comfortable if it looks especially tricky. There's a first time for everything, A chance to learn something new, push the envelope, extend my skill set, seek new horizons, express previously avoided cliches....
          "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

          Comment


          • #6
            McMaster also has the taps. It actually is a fairly standard thread, shows up in standard thread lists, taps etc are available.
            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


            • #7
              thanks all. I think I might try single pointing the thread, because a) I'm cheap, b) I want to finish this up so I get get my bike back up on the wall and c) I've already screwed up the first piece (it slipped in the chuck) so I now have a test piece

              Comment


              • #8
                A hand crank on the spindle makes it easier to do fine threads.

                Comment


                • #9
                  Victor Machinery at www.victornet.com has a huge selection of standard and oddball thread pitches in taps and dies at (I think) very low prices.
                  Kansas City area

                  Comment


                  • #10
                    I've sometimes used a smaller tap as a single point internal thread tool. In this case a 1/4-28 tap would give you enough room to back out (if you don't overdo it) and withdraw. I try to line the tap straight or just slightly canted towards the front end so with deflection I don't get a smaller thread further in the hole. You don't technically need the tap lead-in so could grind the end of an extra tap so you have full depth threads, particularly for a blind hole. I make a 3/8-20 nut that way recently so I could graduate it for 50 thousandths. I could have gotten the tap for $25 - 30 and would have if I thought I'd do this several times, but for a one-off, money saving, do it today job it worked.

                    Edit: I see Victor would have had an economical solution. hmm
                    Last edited by TGTool; 10-14-2020, 11:20 AM.
                    .
                    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

                    Comment


                    • #11
                      yeah, those prices aren't bad at all. Good back up plan to have. I have 3ft of this W1 rod and the shaft is only 3 1/2" long so I can screw it up plenty of times

                      Tap as a threading bar is interesting - did you use it as is (tip excepted) or grind away some of the threads to make it like a full form threading bar with just 3 or 4 cutting edges? I have a couple of 1/4-28 taps (no idea from where) so that's an option on the table.

                      Hand crank is a good idea, though my lathe can go down to a few rpm in back gear. I have a carriage stop and a DRO so I should be able to stop in the internal relief at the end of the thread reliably. It'll be neat to try out my Micro100 threading bar I got a cheap ages ago ($5 from Amazon?) for just this eventuality.

                      I've got some writing I need to get on with so I'll have a practice this afternoon.

                      Comment


                      • #12
                        Really , nothing like learning to single point.. it bumps you ahead a lot .
                        you gain confidence, in time it becomes easier. Good skill to have......when you can make a piece faster than driving across town to get it, or at midnight , or waiting days for it... that is the big payoff.. and fixing stuff you may have to otherwise toss..

                        Comment


                        • #13
                          Originally posted by mattthemuppet View Post
                          bit of a rant, bit of a request for advice

                          I'm in the process of repairing the damper for my Cannondale Headshox Fatty Ultra fork (I know, I didn't make up those names)….
                          It is a proven fact that forks make people fat.

                          -Doozer

                          DZER

                          Comment


                          • #14
                            Originally posted by mattthemuppet View Post
                            yeah, those prices aren't bad at all. Good back up plan to have. I have 3ft of this W1 rod and the shaft is only 3 1/2" long so I can screw it up plenty of times

                            Tap as a threading bar is interesting - did you use it as is (tip excepted) or grind away some of the threads to make it like a full form threading bar with just 3 or 4 cutting edges? I have a couple of 1/4-28 taps (no idea from where) so that's an option on the table.

                            Hand crank is a good idea, though my lathe can go down to a few rpm in back gear. I have a carriage stop and a DRO so I should be able to stop in the internal relief at the end of the thread reliably. It'll be neat to try out my Micro100 threading bar I got a cheap ages ago ($5 from Amazon?) for just this eventuality.

                            I've got some writing I need to get on with so I'll have a practice this afternoon.
                            If I've got a through hole I'll just use a regular tap and go past the tapered threads.

                            Setting tool height and clearance is important and I sometimes futz with a trial piece to make sure I'm cutting well. The smaller tap diameter provides an advantage for clearance but in these small sizes a few thousandths up or down or rotated can make a noticeable difference. With a two or four flute tap you can sort of hold your scale across the points and see where you are. A three flute is harder. The rake generated by the flutes of a tap usually means good cutting conditions. If it cuts in a tap-drilled hole it ought to cut here and you can cut a few thousandths at a time rather than all at once.
                            .
                            "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

                            Comment


                            • #15
                              Originally posted by elf View Post
                              A hand crank on the spindle makes it easier to do fine threads.
                              The smaller the thread lead the slower the tool moves, an 8 TPI thread has a lead of .125" so in 8 revolutions the tool will travel 1".
                              27 TPI has a lead of .0370" , 27 revolutions are required for the tool to travel 1 inch, this is much easier to control.

                              Comment

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