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  • metric threading gears

    I have an old Monarch lathe....love it but am often called on (sometimes by myself) to cut metric threads. Does anyone know if / where you can get change gears for metric threading on an American lathe?

  • #2
    Can you cut gears? That's the best, get any gear you want.

    A number of "very close" ratios are do-able with standard gears and give errors of tenths over a few turns
    CNC machines only go through the motions.

    Ideas expressed may be mine, or from anyone else in the universe.
    Not responsible for clerical errors. Or those made by lay people either.
    Number formats and units may be chosen at random depending on what day it is.
    I reserve the right to use a number system with any integer base without prior notice.
    Generalizations are understood to be "often" true, but not true in every case.

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    • #3
      You can cut your own gear
      Typically 127 and a 100 tooth gear or 37 and a 47 tooth gear (this can be cut with most indexing head or table)

      If you lucky some mm threads will be very close inch this works too

      I have used all three and they all work

      Dave


      Originally posted by mudnducs View Post
      I have an old Monarch lathe....love it but am often called on (sometimes by myself) to cut metric threads. Does anyone know if / where you can get change gears for metric threading on an American lathe?

      Comment


      • #4
        Boston Gear should have them, but be prepared for a bit of sticker shock. After all, virtually ALL American lathes used standard gear designs, perhaps different pressure angles and diametric pitches, but not from another planet!
        Duffy, Gatineau, Quebec

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        • #5
          Another option would be to measure the shaft size of your lathe and the diametric pitch and pressure angle for your Monarch and see if anyone here has a machine with gearing that is at least the proper diametrical pitch. The hole you can bush or bore out to suit. That way you could conceivably buy a 100/127 and the other gears for a currently made import or the like.
          Chilliwack BC, Canada

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          • #6
            Thank you gents. I read an article yesterday on the gearing used for an 8TPI lead screw (100/ 127 and 37/47 gears). My lathe has 4 TPI so those should still work.
            I'll check with Boston gear and read up on cutting my own (never done it).

            cheers.

            Comment


            • #7
              Not all lathes out there have the 100:127 ratio double gear. Mine, for example, uses an 86:91 double gear in the middle of the train. Then a couple of swappable smaller gears on the input shaft to the QCGB to pick up the "metric" side of the center double gear.

              Likely as not your lathe has some sort of larger gear in the middle of the train. Perhaps check to be sure that it does not have the stacked on extra to make it metric. You may be surprised. And even if it does not have a double gear noting what is there might lead to finding a suitable mating gear to mount coaxially with something you have which provides the 1:1.27 ratio needed.
              Last edited by BCRider; 10-17-2018, 03:48 PM.
              Chilliwack BC, Canada

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              • #8
                I used a 125/127 gear bought on ebay. It was for one of the Chinese lathes and fortunately, the seller included the diameter. It was close enough to the original Smart & Brown gears of similar tooth number to be viable. The teeth were MOD1 and I bought a number of part machined MOD1 gears from a UK supplier at less than £8 each and totally replaced the original imperial dp gears (only three, 48, 48 and 120) which the lathe had. Now I have about eight metric pitches, and also can double or halve the original range of tpi. This came in handy when I wanted to make a new leadscrew nut of 6 tpi acme when the lathe only went to 8 tpi before. The old gears have been kept as they were perfectly good.

                Comment


                • #9
                  Originally posted by BCRider View Post
                  Mine, for example, uses an 86:91 double gear in the middle of the train. .
                  I'm intrigued. Which lathe is that? Is there another high prime in the train?
                  The 37/47 is used by Logan.

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                  • #10
                    Another option, slightly better than 37/47 is 63/80. This is a particularly good option for South Bend lathes, as the existing idler is 80 tooth.

                    If you let us know what the end gears are on your monarch, what pitches the existing box will cut, and what metric pitches you are interested in. we can certainly help you figure out your options. Please note, however- that my experience has been that the end covers on monarchs often preclude the use of large diameter gears. This may require you to change the pitch of the gears.

                    allan

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                    • #11
                      As for the pressure angle, Most older ones will be 14 1/2 degree, through the 1950s anyhow.. But for some machines, you may have to look out for "stub form" teeth and the like. Lots of makers had their own private little "better ideas", often better for their parts departments......
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.

                      Comment


                      • #12
                        Originally posted by kitno455 View Post
                        Please note, however- that my experience has been that the end covers on monarchs often preclude the use of large diameter gears. This may require you to change the pitch of the gears.

                        allan
                        I found the same thing (cover prevented large gears) with my 9x20. I wanted to have super fine longitudinal power feed, so I opened up the bottom of the gear cover so that I could use a 100 tooth gear on there.
                        At the end of the project, there is a profound difference between spare parts and left over parts.

                        Location: SF East Bay.

                        Comment


                        • #13
                          I'm not trying to hijack this thread but it brings up a question that could be used here also.

                          I have a harbor freight 44142 combo lathe/mill. It has nameplates on it so I can cut English and metric threads. I have to manually change gears that's no big deal.

                          Now if I cut an English thread I use what the name plate says and a nameplate on the power feed lever has numbers 1 thru 6 on it. So I can engage power feed using the appropriate number and when I get to the end of the thread that im cutting , I can disengage and move the table back to the right where I started and dial in a few thousandths more and wait for that number to come around and engage again and cut the thread deeper. I can do this until the thread depth is correct.

                          When I try to cut a metric thread as per the nameplates on the machine, there is no mention of which number to use on the thread dial. So because of that I cannot disengage the power feed . I must stop the motor , back out the cutter, reverse the motor , wait until carriage is back to the right side , turn off motor , crank in more depth of cut, turn on motor in forward direction. Never disengaging the power feed. That works.

                          If I reengage using the same or any other number on the thread dial the next pass is messing up the threads.

                          So which number should I use? Does it matter? Can I disengage while cutting metric threads?

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                          • #14
                            That looks good using 63 tooth gear
                            But the BS 0 does not have 63 index
                            This why the 37 / 47 works for most as you cut with BS-0
                            You can use compound indexing using a BS-0 head

                            Dave


                            Originally posted by kitno455 View Post
                            Another option, slightly better than 37/47 is 63/80. This is a particularly good option for South Bend lathes, as the existing idler is 80 tooth.

                            If you let us know what the end gears are on your monarch, what pitches the existing box will cut, and what metric pitches you are interested in. we can certainly help you figure out your options. Please note, however- that my experience has been that the end covers on monarchs often preclude the use of large diameter gears. This may require you to change the pitch of the gears.

                            allan

                            Comment


                            • #15
                              Originally posted by ahidley View Post
                              So which number should I use? Does it matter? Can I disengage while cutting metric threads?
                              It does not matter as long as you do not disengage the feed.

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

                              Location: SF East Bay.

                              Comment

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