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  • #31
    Yes, The Leadscrew must be Metric and they try to use gears for compliance , without using the 127 conversion ratio.
    Note that most all the numbers are even integers OR use 5 ( ie 55 or 85) and no prime numbers
    So I have note seen this lathe before , but did a quick search and found this photo
    Note they have a 55-60 ratio !

    https://web5.streamhoster.com/hvp/DROPROS/3Y6A3823e.JPG

    It looks like the same lathe, but the ratios are different.. can someone explain that
    Rich
    Green Bay, WI

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    • #32
      Originally posted by RB211 View Post
      I think this is a metric leadscrew. This lathe is sold in Germany, right? Since when did Germans make anything with inches?
      My old Biernatzki milling machine was made in Germany and is fully imperial from the fasteners, gears, leadscrews everything.

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      • #33
        Originally posted by RB211 View Post
        I think this is a metric leadscrew. This lathe is sold in Germany, right? Since when did Germans make anything with inches?
        Bought this direct from Weiss Machinery in China weiss.com.cn Asked specially for inch lead screw They have not bee able to see the problem, jet? This machines are sold in USA thru https://www.dropros.com/

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        • #34
          Originally posted by Rich Carlstedt View Post
          Yes, The Leadscrew must be Metric and they try to use gears for compliance , without using the 127 conversion ratio.
          Note that most all the numbers are even integers OR use 5 ( ie 55 or 85) and no prime numbers
          So I have note seen this lathe before , but did a quick search and found this photo
          Note they have a 55-60 ratio !

          https://web5.streamhoster.com/hvp/DROPROS/3Y6A3823e.JPG

          It looks like the same lathe, but the ratios are different.. can someone explain that
          Rich
          This is a Weiss WBL250 a smaller lathe. I do not know way it is different in gears, maybe it got 8 tpi lead screw? My Lathe is WBL290F The factory has looked at the image of my lead screw and say it it inch?!

          Comment


          • #35
            Yes, you have a metric leadscrew. Look at the changewheels for 2.5mm and you have a simple ratio of 5to8 (there will be a fixed 8 to 5 somewhere to compensate). Now look at the 10 tpi. There's a 9 to 17 ratio. You don't throw in a big prime like that unless you are trying to move between metric and imperial or visa versa.
            Did anyone notice the top of the OP's picture of the threadplate? It says leadscrew t= 1/10 and cross screw t=1/13. Like anyone is going to choose to make a dial on that screw with multiples of 13. It's a 2mm pitch screw. Check it with your DTI.

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            • #36
              When cutting inch threads with a metric leadscrew or vice versa there has to be a 127 tooth gear to make the thread pitch come out exact. Any combination of gears lacking the 127 tooth gear will give an approximation of the desired pitch.

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              • #37
                Metric 2mm leadscrew? Counting the threads, he has 20 threads showing. that would, if the thread was actually 2mm, be 40mm, which is NOT 2". The caliper is showing 2.00".

                It could be a 2.5mm leadscrew. Then that would be 50mm. but that would not be quite 2", where the 20 threads show up as MORE than 2".

                It looks as if the makers DID TRY to make it inch, but that they used the wrong numbers.

                The makers would have had to make the leadscrew 2.54mm to get a 10 TPI (obviously). If they screwed up (!) and made the leadscrew at 2.55mm pitch, it would end up at 51 mm instead of 50.8mm.

                The difference looks to be of that order. 0.2mm is about 0.008", and I could believe that of the picture. Could be close to that.

                2730

                Keep eye on ball.
                Hashim Khan

                Everything not impossible is compulsory

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                • #38
                  Rich, the needed gear ratio is dependent ONLY on the pitch of the lead screw and on the pitch of the desired thread being cut. Absolutely nothing else comes into this. Not the brand, not the model, not the country it is made in, nothing else.

                  But you MUST take into account ALL the gears, not just the visible ones and this lathe apparently has another, somewhat hidden set of gears as indicated by the A, B, C selector lever. And there could even be others in addition to that.

                  His photos are photographically good, but I am not satisfied by the one showing the two caliper jaws resting on the threads because there is an angle of view problem there. One caliper jaw seems to be dead center on the crest of a thread, but the other jaw appears to be more toward the bottom of the crest it rests on. For this measurement to be accurate, both caliper jaws (points) should be at exactly the same point on these two thread crests. This may be the case and only the angle of view is making it look wrong. But, on the other hand, it may be that they are not at the same point on those thread crests.

                  But then, a metric pitch of 2.5 mm would make the threads too short, not too long. And 2.6 mm would be an awfully odd metric pitch for the lead screw. I need to look at his photos more closely.



                  Originally posted by Rich Carlstedt View Post
                  Yes, The Leadscrew must be Metric and they try to use gears for compliance , without using the 127 conversion ratio.
                  Note that most all the numbers are even integers OR use 5 ( ie 55 or 85) and no prime numbers
                  So I have note seen this lathe before , but did a quick search and found this photo
                  Note they have a 55-60 ratio !

                  https://web5.streamhoster.com/hvp/DROPROS/3Y6A3823e.JPG

                  It looks like the same lathe, but the ratios are different.. can someone explain that
                  Rich
                  Paul A.
                  SE Texas

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

                  Comment


                  • #39
                    I hate to say it, but of all the possible explanations so far, this seems to be the most plausible. I also calculate about a 0.0055" to 0.007" error over about 8 to 10 threads in his photos. This is from an estimate of about 1/4 of the 0.0555" pitch in those photos.

                    I think a more accurate measurement of the lead screw pitch is certainly in order. I would favor using the actual travel of the carriage when the screw is rotated 50 (about 5") or even 100 (about 10") times. I do not like the idea of just holding the calipers next to it. And while the idea of using wires or drill rod in the threads seems OK, any damage at the area where the wire rests will throw the measure off by a number of thousandths. The movement of the carriage is what it is designed to do anyway and that is the best way to check how well it is doing what it is designed to do.

                    Another rough calculation shows that with an error of about 0.006" in 8 or 10 threads, there would be about 0.012" of error in a full inch. 0.012" = 0.3048 MM so I am going to guess that if the screw is actually metric, it is about 2.75 mm pitch. This is a far more likely (less oddball) number than 2.6 mm.

                    In support of my statement above, I checked my long spreadsheet of the thread pitches I can cut on my SB-9 with the manual change gears and a 127::100 compound. 2.5 mm is certainly one of them and the next round number after that is 2.75 mm. This is not any kind of proof, but just shows that the 2.6 mm number would be difficult to cut while the 2.75 mm would be a lot easier. My SB-9 is equipped with an 8 TPI lead screw.



                    Originally posted by J Tiers View Post
                    Metric 2mm leadscrew? Counting the threads, he has 20 threads showing. that would, if the thread was actually 2mm, be 40mm, which is NOT 2". The caliper is showing 2.00".





                    It could be a 2.5mm leadscrew. Then that would be 50mm. but that would not be quite 2", where the 20 threads show up as MORE than 2".

                    It looks as if the makers DID TRY to make it inch, but that they used the wrong numbers.

                    The makers would have had to make the leadscrew 2.54mm to get a 10 TPI (obviously). If they screwed up (!) and made the leadscrew at 2.55mm pitch, it would end up at 51 mm instead of 50.8mm.

                    The difference looks to be of that order. 0.2mm is about 0.008", and I could believe that of the picture. Could be close to that.
                    Last edited by Paul Alciatore; 09-28-2021, 10:08 PM.
                    Paul A.
                    SE Texas

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

                    Comment


                    • #40
                      Have we got an explanation yet?

                      Comment


                      • #41
                        Once again from post # 12

                        Originally posted by Rich Carlstedt View Post
                        .................................................. .................................................. ...
                        But I have run into similar issues with foreign made machines where "Metric" is their base measurement system
                        and they either make a mistake OR actually try to fudge the parts to fit Imperial requirements. And this was with Large Industrial Machines.
                        .................................................. .......................
                        I blew up your picture to show you
                        The red lines are centered on your caliper POINTS . note the slight difference in the tooth crests.
                        .................................................. ........

                        ‚Äč...........................
                        Johannes -I suggested you try a 6 inch span as that would give you almost one whole tooth difference between 2.5 mm and 10- TPI.
                        Measure the Leadscrew and count the threads over a longer distance is the simple way to determine "If" the leadscrew is Imperial or not.

                        We know that there is no 127 conversion ratio. It can't be hidden as there is also Metric chart numbers for the gears
                        Rich
                        Green Bay, WI

                        Comment


                        • #42
                          When cutting inch threads with a metric leadscrew or vice versa there has to be a 127 tooth gear to make the thread pitch come out exact. Any combination of gears lacking the 127 tooth gear will give an approximation of the desired pitch.
                          The 127 conversion ratio is very common but it is by no means the only one. For example:-

                          ..not all perfect but some are and the others too close for me to notice the difference.
                          This if for an 8TPI leadscrew but I am confident there will be a similar table for a 10TPI leadscrew.

                          In this case however we are looking for 18TPI cut with 10TPI leadscrew, no metrics involved.
                          Last edited by The Artful Bodger; 09-29-2021, 02:16 AM.

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                          • #43
                            I've got 2 old lathes with a 10 thread leadscrew, one uses 26/66 for the metric conversion set and the other uses 25/63.
                            Last edited by Richard P Wilson; 09-29-2021, 08:16 AM.
                            'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                            • #44
                              Well I have not found the problem jet, but I cut this threads on this lathe when making spider on the back of the spindle. 1,5 mm threads fit perfect. So I think I can not cut inch threads on this lathe.? Im now cutting more mm threads to see if they are ok?


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                              • #45
                                What gears did you use for the 1.5mm thread? Sounds very much as if , whatever they say, the factory has supplied a metric leadscrew. Yes you will be able to cut imperial threads, you will just have to use a suitable conversion gear in the gear train, and you will have to cut them without opening the half nuts at the end of each cut.
                                'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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