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Lathe Gear (re)calculation assistance (please)

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  • Lathe Gear (re)calculation assistance (please)

    Hi, I was after some help with calculating change gears as I have just bought as secondhand lathe that didn’t come with all the change gears. The change gears that are missing are less common sizes like 42, 52, etc. Most of the change gears for sale on eBay and Aliexpress are dividable by 5, like 40, 45, 50 etc so I wanted some help to do the calculations to substitute the specified gears with close enough base 5 gears.

    In terms of background, the lathe is a TopTech Turner 210 with speed change via belts, searching via google only shows the 210V model which is largely the same but has the additional feature of electronic variable speed. The gear change set specified for it is:
    25, 30, 33, 40, 42, 52, 60, 70, 75, 80, 90, 90

    I currently have the following gears that came with the lathe:
    25, 33, 80, 90, 90
    which leaves me missing:
    30, 40, 42, 52, 60, 75

    The metric thread pitch for the lead screw is 2mm, it has a 40 tooth drive and the gear change table for cutting metric threads looks like:

    Metric 0.4 0.5 0.6 0.7
    A B H 70 H 75 H 75 H 75
    C D 30 75 30 60 42 70 42 60
    E F 80 H 80 H 80 H 80 H
    Metric 0.75 0.8 1 1.25
    A B H 90 H 52 H 52 H 52
    C D 30 40 60 75 H 60 75 60
    E F 80 H 80 H H 80 80 H
    Metric 1.5 1.75 2 2.5
    A B H 70 H 75 H 70 H 70
    C D 60 40 70 40 H 80 75 30
    E F 80 H 80 H H 40 80 H
    Metric 3 3.5
    A B H 70 H 80
    C D 90 40 75 33
    E F 60 H 52 H

    My question is that given that I can’t easily find replacement 42 or 52 tooth gears, what gears should I buy (that are divisible by 5) and what would an alternate combination be to cut the metric threads that have a 42 or 52 specified. Thanks in advance for your replies.


  • #2
    I've had another thought about this if you saw my initial post.
    It isn't clear from the info but I think you mean that the 40 is a fixed gear on the mandrel that then drives the B position gear in the table. Then B drives D which is coupled to C which drives E. Where H is shown it is either a spacer or omitted so in some cases the gear shown is an Idler so can be any value that fits.
    Looking at 2mm since the leadscrew is 2mm we need 1:1 ratio. Therefore you have 40 driving 70 as an idler driving 80 as an idler driving 40 - so 1:1 overall.
    For 1mm we want half speed so 40 drives 52 as an idler driving 60 as idler driving 80 so 40:80 or 1:2 overall. So in this case you can use something else not 52.
    Since the factors of 52 are 13x4 unless you have another 13 factor eg 26 or 39 it is never gong to be needed for metric ratios. it looks like it is always being used as an idler.
    Last edited by Baz; 01-12-2020, 12:29 PM.

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    • #3
      For 3.5mm pitch, which might be a bit of a strain on the lathe anyway, you would need 40, 40, 70, 40 or 40, 20, 35, 40.
      For the 42 it is only used in the .6 and .7 pitches.
      For 0.6mm use 40, 75, 45,80
      For 0.7 mm use 40, 50, 35, 80

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      • #4
        Originally posted by Baz View Post
        I've had another thought about this if you saw my initial post.
        It isn't clear from the info but I think you mean that the 40 is a fixed gear on the mandrel that then drives the B position gear in the table. Then B drives D which is coupled to C which drives E. Where H is shown it is either a spacer or omitted so in some cases the gear shown is an Idler so can be any value that fits.
        Looking at 2mm since the leadscrew is 2mm we need 1:1 ratio. Therefore you have 40 driving 70 as an idler driving 80 as an idler driving 40 - so 1:1 overall.
        For 1mm we want half speed so 40 drives 52 as an idler driving 60 as idler driving 80 so 40:80 or 1:2 overall. So in this case you can use something else not 52.
        Since the factors of 52 are 13x4 unless you have another 13 factor eg 26 or 39 it is never gong to be needed for metric ratios. it looks like it is always being used as an idler.
        Hi Baz, Thanks for your answer and yes, the 40 tooth is the fixed gear on the mandrel that is coupled to the chuck with F (or E if a spacer is used on F) being the drive of the lead screw. Gear Change Table
        Last edited by Ricco; 01-12-2020, 09:24 PM.

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        • #5
          42 prime factors are : 2, 3, 7
          52 prime factors are : 2, 13

          to replace them the alternative(s) would need to be divisible by the same set but not necessarily at the same time (within the same gear)
          --
          Tom C
          ... nice weather eh?

          Comment


          • #6
            Originally posted by Ricco View Post
            Hi, I was after some help with calculating change gears as I have just bought as secondhand lathe that didn’t come with all the change gears. The change gears that are missing are less common sizes like 42, 52, etc. Most of the change gears for sale on eBay and Aliexpress are dividable by 5, like 40, 45, 50 etc so I wanted some help to do the calculations to substitute the specified gears with close enough base 5 gears.

            In terms of background, the lathe is a TopTech Turner 210 with speed change via belts, searching via google only shows the 210V model which is largely the same but has the additional feature of electronic variable speed. The gear change set specified for it is:
            25, 30, 33, 40, 42, 52, 60, 70, 75, 80, 90, 90

            I currently have the following gears that came with the lathe:
            25, 33, 80, 90, 90
            which leaves me missing:
            30, 40, 42, 52, 60, 75

            The metric thread pitch for the lead screw is 2mm, it has a 40 tooth drive and the gear change table for cutting metric threads looks like:

            Metric 0.4 0.5 0.6 0.7
            A B H 70 H 75 H 75 H 75
            C D 30 75 30 60 42 70 42 60
            E F 80 H 80 H 80 H 80 H
            Metric 0.75 0.8 1 1.25
            A B H 90 H 52 H 52 H 52
            C D 30 40 60 75 H 60 75 60
            E F 80 H 80 H H 80 80 H
            Metric 1.5 1.75 2 2.5
            A B H 70 H 75 H 70 H 70
            C D 60 40 70 40 H 80 75 30
            E F 80 H 80 H H 40 80 H
            Metric 3 3.5
            A B H 70 H 80
            C D 90 40 75 33
            E F 60 H 52 H

            My question is that given that I can’t easily find replacement 42 or 52 tooth gears, what gears should I buy (that are divisible by 5) and what would an alternate combination be to cut the metric threads that have a 42 or 52 specified. Thanks in advance for your replies.
            Purchasing a 3d printer would be the least expensive way to acquire the gears.

            Comment


            • #7
              Yes, change gear sets are all about prime numbers and how many primes that are needed in the calculation. Yes, they can be on different gears than the ones the table specifies, but you must also consider the fact that the gears must physically fit into a train on your lathe.

              Any gear that is used only as a idler can, in theory, be replaces with a gear with any tooth count. This is only limited by the physical fit that I mentioned above. And, of course, small tooth counts gears are not practical (1 to about 12 teeth).

              A 3D printer is, of course, one possibility. But if you are in a commercial shop where there is frequent or constant usage, I would keep at least two spares on the shelf. Another thing you can do is keep an eye on E-Bay. I have purchased several change gears for my SB that way. You may not be able to just get the single gears that you want. But you can buy groups of gears that contain that one sometimes and then just sell off the others.



              Originally posted by Astronowanabe View Post
              42 prime factors are : 2, 3, 7
              52 prime factors are : 2, 13

              to replace them the alternative(s) would need to be divisible by the same set but not necessarily at the same time (within the same gear)
              Paul A.
              SE Texas

              Make it fit.
              You can't win and there IS a penalty for trying!

              Comment


              • #8
                Here in the UK we have "HPC Gears" who have a range of off-the-shelf gears in DP or module pitches, not too expensive and I'm pretty sure they'll ship overseas to the Rebel Colonies - there are options for steel, heavy-duty steel, Delrin, Tufnol etc.
                I've built gear trains with PLA 3D printed gears, they're good, but not that durable?

                Dave H. (the other one)
                Rules are for the obedience of fools, and the guidance of wise men.

                Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

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