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ah bugger it - weird azz internal thread required :(

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  • #16
    I had to do a similar size internal thread and if I remember I ran the lathe backwards and threaded from the bottom of the hole to the open end. that way, if you return the carriage to the same spot, a stop, and advance the tool, then engage the half nuts. Saves having to stop before you break something. Even with a screw on chuck threading isn't a high stress thing and the chuck will probably stay on if it is snug.

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    • #17
      good tips TGTool and wdtom, I'll definitely keep those in mind. I'll try first with the reverse threading and use the carriage stop to get me back in the relief groove each pass. Great idea that.

      Haven't done anything on it yet, making good progress with the paper so wanted to role with that.

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      • #18
        Matthemuppet: Another trick handy for small internal threads is to leave a short bit of stock on the entry end that has been bored to just .005" smaller than the desired major dia. of the thread. This short collar is just long enough for two or three threads. This will allow you to know when you are getting to within a few thousandths of being at the major dia. After the thread is completed, then face off this collar. Hope this makes sense. Good luck.
        Sarge41

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        • #19
          good point, thanks for the tip. I need to do that anyway as there's a seal at the base of the piston that seats on the major OD of the thread plus a bit. I have a nice little bokum boring bar that's a bit like a V shape (almost like a threading tool) that I'll use to cut that land, zero the DRO/ dial then cut the relief groove on the other side of the thread to the same depth. The V shape will provide a nice start to the thread too.

          Going to get started on the test run, need to figure out the change gears for 28tpi first, that's always a bit of a chore.

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          • #20
            The tactic of running backwards and threading on the way out is good in some situations. I don't think you can do that using a tap as as a threading tool. Running backwards, the tool needs to be upside down if it's towards the operator or right side up threading on the back side of the hole. The tap is ground to cut in the forward direction so you'd be using the back side of the flutes which may have a slight relief. And in any case it isn't ground for rake on that side. I do conventional threading sometimes on the back side of the hole just so I can watch it more easily. This is turning in the normal direction and threading towards the headstock but in this case the tool is upside down.
            .
            "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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            • #21
              I am really sorry if I step on anyone. I only read the OP's usually.

              I saw my Cannondale and my Mom came to mind. She had a Cannondale road bike. Top of the line at the time.

              Love your photos and let me know if you need any specific turning or milling? (smallish footprint lol) It varies. JR
              My old yahoo group. Bridgeport Mill Group

              https://groups.yahoo.com/neo/groups/...port_mill/info

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              • #22
                Originally posted by LKeithR View Post
                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...
                Havent seen you in a bit, nice to see you up and about or semi-vert? Really, been more than a year no? JR

                My old yahoo group. Bridgeport Mill Group

                https://groups.yahoo.com/neo/groups/...port_mill/info

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                • #23
                  thanks for all the tips everyone. Gave it a shot last night. Theory was sound, execution not so much. I don't think I got the tool height and angle right (it's bloody hard to see inside a 7/16" hole!), which I know how to fix in future. Then I struggled to touch off to zero my cross slide so I ended up taking too big of a bite and fracturing the top of my tool. Then it just went downhill from there.

                  But, I did cut some partial threads and they were RH too, so that's promising. I think I'll grind a HSS bit to fit and try the reverse threading again, seems like a good trick to have up my sleeve.

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                  • #24
                    alright, I discovered something today - that I'm an idiot.

                    Why was my carbide or HSS threading tool not cutting, when running the lathe in reverse and threading away from the headstock? Because I used (or ground) a RH threading bit! No wonder it wouldn't cut, it was like trying to drill a hole in reverse (slaps head).

                    Turned the HSS threading tool right way up, cut of the last attempt, drilled and bored a new hole and cut the thread in about 20min.
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                    I cut these towards the headstock and used the carriage stop (set with the tool in the middle of the relief groove) to judge when to open the half nuts. Worked really well and the piston threads on nicely.

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                    • #25
                      Originally posted by mattthemuppet View Post
                      alright, I discovered something today - that I'm an idiot.

                      I cut these towards the headstock and used the carriage stop (set with the tool in the middle of the relief groove) to judge when to open the half nuts. Worked really well and the piston threads on nicely.
                      Thank you sir, good education.

                      I like your lathe, never saw it before.

                      Mine are already posted up here I believe.

                      I like that one cause it looks approachable.

                      For example? I am some one off the street, pops in to a used machine store (love that place) what is a Metal Working Lathe?

                      I am supposed to know this? I know Zero about metal machining. Still had to transition from the drill press though. So I would visit my Friend's store when I could.

                      Van Nuys. Had to go to court there some times. This guy and his help was needed. JR
                      My old yahoo group. Bridgeport Mill Group

                      https://groups.yahoo.com/neo/groups/...port_mill/info

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                      • #26
                        thanks, I like my lathe too, though I think I'll like my new SB9 alot more

                        got the ID threads cut and through hole drilled last night. Target length was 95.11mm +/-0.05 and it ended up at 95.07mm so I'm pretty happy with that. Part of the bore looks terrible, but it's just a clearance hole thankfully. Threads came out nicely though.
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                        cobbled together set up in case the 2ft of bar hanging out the back decided to move around. I doubt it would have held for long but at least it would have given me time to turn the lathe off
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                        • #27
                          Originally posted by mattthemuppet View Post
                          alright, I discovered something today - that I'm an idiot.
                          .
                          Let he who has not sinned cast the first stone.

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                          • #28
                            A bar hanging out the back end doesn't have much force until it gets a ways off the centerline. So that setup looks plenty adequate for the job. Bend the end of the bar a foot off center and watch out. It can be pretty impressive if you ever encounter it.
                            .
                            "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                            • #29
                              Originally posted by tlfamm View Post

                              Let he who has not sinned cast the first stone.
                              very true, very true

                              Originally posted by TGTool View Post
                              A bar hanging out the back end doesn't have much force until it gets a ways off the centerline. So that setup looks plenty adequate for the job. Bend the end of the bar a foot off center and watch out. It can be pretty impressive if you ever encounter it.
                              i figured it was worthwhile insurance - I was running fairly slow, but I've seen videos of bars bending that that would not be a good end to my day!

                              Anyway, finished up the machining part of the project, just have to reassemble the damper and get everything back together again.

                              Threading the top nut in white delrin
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                              checking for it with the damper housing
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                              hole bored and cup seal grooves cut. Made a grooving bar out of O1 by turning some 1/2" rod down a smidge, then offsetting it ~1.75mm in the 4 jaw and cutting the relief. Milled the top down flat and then ground the side relief. Didn't bother hardening it.
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                              silly tool holding method - 3/4" chuck in a tool holder as I forget that my larger holders are 12mm NOT 1/2"! Doh!
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                              finished parts, with beat up old top nut for reference
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                              Last edited by mattthemuppet; 10-21-2020, 12:27 PM.

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                              • #30
                                finished everything, put it back together and had a short test ride. Seems a little tight, maybe the new piston seal needs to bed in a bit, but it works, the lockout locks out and the bike is back on the wall so I have some space back!

                                assembled damper shaft
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                                assembled damper and air chamber piston
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                                installed
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