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  • #16
    Did you perform this check in the same area of the screw where the half nut will be while cutting your thread? If there is local wear, the pitch can change between the worn and non-worn sections of the screw.



    Originally posted by Johannes Frank View Post
    RC Rider The action is a Borden Rimrock they all have 18 tpi. in one of the images in the first post Im holding a thread gauge against the cut threads from the lathe. I have other barrels from 3 different gunsmith all are 18tpi. I will check for the run out. I have counted the threads on the lead screw over 2 inches and they come out 20 tpi over 2 inchClick image for larger version

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    Paul A.
    SE Texas

    And if you look REAL close at an analog signal,
    You will find that it has discrete steps.

    Comment


    • #17
      Are these the charts for the OP's lathe? He gave the gear sequence as 50-85-60-60. But these charts seem to indicate that the sequence would be 55-60-50-60.

      It is hard to know which sequence would be correct since there obviously is another, unknown gear ratio designated by the letters A, B, and C which is probably chosen via a selector lever of some sort. Since he appears to have more than one thread pitch that is incorrect, that hidden gear ratio may be where the error actually is.

      It may be helpful to see the entire gearing setup rather then just a part of it. That would include any provision for metric threads too.



      Originally posted by The Artful Bodger View Post
      I have seen this situation a few times in the past where a Chinese or other lathe seems to have inbuilt thread pitch errors. However more than once we have found that the change diagrams are the problem.

      On this machine just what does 'H' mean?


      Meanwhile, have a look at this https://www.precisionmatthews.com/wp...v5-2021-09.pdf

      that seems to be the same machine. Have a look at page 15....
      Click image for larger version

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      Paul A.
      SE Texas

      And if you look REAL close at an analog signal,
      You will find that it has discrete steps.

      Comment


      • #18
        Originally posted by Paul Alciatore View Post
        Are these the charts for the OP's lathe? He gave the gear sequence as 50-85-60-60. But these charts seem to indicate that the sequence would be 55-60-50-60.

        It is hard to know which sequence would be correct since there obviously is another, unknown gear ratio designated by the letters A, B, and C which is probably chosen via a selector lever of some sort. Since he appears to have more than one thread pitch that is incorrect, that hidden gear ratio may be where the error actually is.

        It may be helpful to see the entire gearing setup rather then just a part of it. That would include any provision for metric threads too.




        The Precision Matthews in the PDF has a 8 inch lead screw, min is sad to have 10 inch so there will be a different gears.Right? Im going to double check everything. If i find the fault I will post it here

        Comment


        • #19
          Originally posted by Doozer View Post
          Put your thread pitch gauge on the lathe leadscrew and see how close to 10 tpi it actually is.
          On a China lathe, assume nothing.

          ---Doozer
          It came out 10 inch. Im going to do a more precise test on it.

          Comment


          • #20
            Originally posted by 754 View Post
            Whe you start the threading , do a scratch cut, then check against pitch guage.. what is it telling you ? If it dont match , cutting further wont fix it.
            should always do a scratch and check for first thread..
            I also do the test cut and check against a thread gauge. That is what matters, not the angle of the compound or the tpi of the leadscrew.

            Comment


            • #21
              Originally posted by Johannes Frank View Post

              It came out 10 inch. Im going to do a more precise test on it.
              So, how did you determine that the pitch was wrong originally?

              Could the problem you have be caused by anything else?

              One often overlooked problem is using the area on the leadscrew that crosses from a worn area to an unworn area. In that length, there is a change in the pitch of the threads, because of the wear. On both sides it is proper, but where the wear ends there has to be a transition.

              Threading is usually done near the headstock, and that area is usually the most worn. So it could be that your tests just happened to use that transition area. If you thread with the carriage in a different area, you may find that the problem goes away.
              2730

              Keep eye on ball.
              Hashim Khan

              Everything not impossible is compulsory

              Comment


              • #22
                The gear chart is wrong by the looks on it. The chart on the machine has a 60T on the leadscrew but the chart in the manual has a 65T.

                Click image for larger version

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                Attached Files
                Peter - novice home machinist, modern motorcycle enthusiast.

                Denford Viceroy 280 Synchro (11 x 24)
                Herbert 0V adapted to R8 by 'Sir John'.
                Monarch 10EE 1942

                Comment


                • #23
                  Originally posted by Johannes Frank View Post
                  I have counted the threads on the lead screw over 2 inches and they come out 20 tpi over 2 inchClick image for larger version

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                  It may just be my eyes or the angle of the pic, but from looking at the upper jaw of the caliper it appears that the pitch may be slightly less than 10 tpi.
                  It's all mind over matter.
                  If you don't mind, it don't matter.

                  Comment


                  • #24
                    It is possible that you have it set to do power feed instead of threading. The lever to the right of t he ABC lever is power feed when rotated to the right ( ^^^^^ mode ) and threading when it is to the left (the picture of the screw)

                    Click image for larger version

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                    At the end of the project, there is a profound difference between spare parts and left over parts.

                    Location: SF East Bay.

                    Comment


                    • #25
                      Going back to your post showing the calipers used to count the teeth. Did you actually measure the distance for the 20 teeth or just use the 2.00 on the gauge as a guide to count the number of teeth? You're looking for a very small difference which might be present between 10TPI and the possible alternative 2.5mm pitch. As in over 10 inches worth just 0.4mm or .016". Or a little more than that if it turns out that it is in fact 2.6mm pitch instead of the 10TPI.

                      Looking for this small a difference is where I'd be wedging round pins between the crests of the threads and measure across the span of the round pins then subtract one diameter of the pins to find the true spacing of the thread pitch. You'll need pins for this that are big enough that they don't quite fit below middle so you can get the proper span across the diameter of the pins. But they should rest pretty low so they are firmly in position. And a helper to hold them would be nice since you'll have your hands full with the calipers. A pair of same size drill shanks would do the job if you don't have suitable size pins. I'd test this by putting one pin into the gap and measure with the calipers and confirm that you are able to read the proper diameter of the pin or drill shank. That'll confirm that the size is not dropping too far into the gap and that you can then safely subtract the one full pin diameter from the test reading over a 5" span.

                      As you posted shortly after that post with the calipers it is best to assume nothing is as it says and measure to confirm everything. After all you're pretty clearly chasing down a small factor on this. I'd even count the teeth on your gears behind the end cover. One of them might be mis-stamped. It would be part of that "assume nothing is as it says" attitude that you need for tracking down something this small.

                      Have you tried a dial gauge lined up with the carriage travel and with the thread lever engaged manually turn the chuck through 18 revolutions yet? A small level on one of the jaws can be used to get exactly 18 turns on the chuck. And obviously at that point the dial gauge would want to show 1.000" of travel. I suspect it won't though. Which is the source of the problem. And from the way the trial thread you cut fit against the threads on the barrel I'm suspecting that you're getting closer to 19TPI. To me that would suggest that your 10TPI screw might in fact be 2.6mm and that is what is "stretching out" the thread as seen in the comparison picture in the opening post.

                      BTW, in all the hub bub about possible issues no one has yet mentioned that you're clearly an experienced photographer. Your camera work in this thread is amazingly good. It's making out job as the peanut gallery a lot easier...

                      And I have to close by mentioning that this is a nasty and perplexing problem you have. I, for one, will enjoy it when you post that you found the final source of the issue. Not as pleased as YOU will be of course....

                      Chilliwack BC, Canada

                      Comment


                      • #26
                        Originally posted by Peter. View Post
                        The gear chart is wrong by the looks on it. The chart on the machine has a 60T on the leadscrew but the chart in the manual has a 65T.

                        Click image for larger version

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                        Yes I know this and have tried, the manual say 65 t but that did not work. it is for a lathe with a 8tpi lead screw mine is 10tpi. Tey sema to have one manual for different lathes ?

                        Comment


                        • #27
                          Originally posted by BCRider View Post
                          Going back to your post showing the calipers used to count the teeth. Did you actually measure the distance for the 20 teeth or just use the 2.00 on the gauge as a guide to count the number of teeth? You're looking for a very small difference which might be present between 10TPI and the possible alternative 2.5mm pitch. As in over 10 inches worth just 0.4mm or .016". Or a little more than that if it turns out that it is in fact 2.6mm pitch instead of the 10TPI.

                          Looking for this small a difference is where I'd be wedging round pins between the crests of the threads and measure across the span of the round pins then subtract one diameter of the pins to find the true spacing of the thread pitch. You'll need pins for this that are big enough that they don't quite fit below middle so you can get the proper span across the diameter of the pins. But they should rest pretty low so they are firmly in position. And a helper to hold them would be nice since you'll have your hands full with the calipers. A pair of same size drill shanks would do the job if you don't have suitable size pins. I'd test this by putting one pin into the gap and measure with the calipers and confirm that you are able to read the proper diameter of the pin or drill shank. That'll confirm that the size is not dropping too far into the gap and that you can then safely subtract the one full pin diameter from the test reading over a 5" span.

                          As you posted shortly after that post with the calipers it is best to assume nothing is as it says and measure to confirm everything. After all you're pretty clearly chasing down a small factor on this. I'd even count the teeth on your gears behind the end cover. One of them might be mis-stamped. It would be part of that "assume nothing is as it says" attitude that you need for tracking down something this small.

                          Have you tried a dial gauge lined up with the carriage travel and with the thread lever engaged manually turn the chuck through 18 revolutions yet? A small level on one of the jaws can be used to get exactly 18 turns on the chuck. And obviously at that point the dial gauge would want to show 1.000" of travel. I suspect it won't though. Which is the source of the problem. And from the way the trial thread you cut fit against the threads on the barrel I'm suspecting that you're getting closer to 19TPI. To me that would suggest that your 10TPI screw might in fact be 2.6mm and that is what is "stretching out" the thread as seen in the comparison picture in the opening post.

                          BTW, in all the hub bub about possible issues no one has yet mentioned that you're clearly an experienced photographer. Your camera work in this thread is amazingly good. It's making out job as the peanut gallery a lot easier...

                          And I have to close by mentioning that this is a nasty and perplexing problem you have. I, for one, will enjoy it when you post that you found the final source of the issue. Not as pleased as YOU will be of course....
                          Thank you for your nice coment about my photo :-) if you like more then look at www.johannesfrank.com
                          Im going over everything again tonight to try to find the fault, nasty problem it is but then problem often is ;-) thank you

                          Comment


                          • #28
                            Sorry folks about the wrong manual, that was pretty dumb even for me.

                            Comment


                            • #29
                              I think this is a metric leadscrew. This lathe is sold in Germany, right? Since when did Germans make anything with inches?

                              Comment


                              • #30
                                Originally posted by danlb View Post
                                It is possible that you have it set to do power feed instead of threading. The lever to the right of t he ABC lever is power feed when rotated to the right ( ^^^^^ mode ) and threading when it is to the left (the picture of the screw)

                                Click image for larger version

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                                No it is set at treading, if I set it to the right the lead screw will not turn.

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