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10" Atlas back gear

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  • 10" Atlas back gear

    I have found that on the head stock of my 10" Atlas the index pin cannot be engaged with the large gear. They do not line up. About half a hole off. The gear has 10-241 cast in it so seems to be correct. Also the back gear does not engage right, it meshes with the big gear before the smaller gear. I can shim it back but it then will not mesh fully with the small gear. I have looked at many times trying to understand what I should do. I feel stupid asking but don't know where to go from here. I have been a millwright in a saw mill and worked with quite a few lathes but this has me stumped.

  • #2
    Atlas spindle

    What type of bearings does the headstock have, sleeve or roller? If they are sleeve, they MIGHT be worn enough to give the problems you see. It would take a lot of wear to give the problem you have. Simple test! With the belt loose can you wiggle the spindle?


    • #3
      The 'large gear' on the spindle is the 'bull gear' I believe. There is a pin that pins it to the cone pulley. (There is also an "index pin" that sets the bull gear into one of 60 possible positions. I'll assume you don't mean this, because the back gears would never be engaged, nor would the lathe be turned on, if the index pin was set.)

      You will never engage the back gears AND push the bull gear's pin at the same time. The reason is that the purpose of the back gear is to change the ratio of the pulley to the bull gear to 6:1. But the purpose of the pushing the pin in is to accept the normal 1:1 ratio. One or the other.

      So if the pin is in, there is a 1:1 ratio between the pulley and the bull gear/spindle.

      If the pin is out, the bull gear (and spindle) will not turn; the pulley will just spin.

      If the pin is out and the back gears are engaged, the pulley (and small gear) spin, the small gear spins the back gear, the other end of the back gear spins the bull gear/spindle.


      Now if the pin is out so the bull gear is not connected to the cone pulley, the bull gear should spin as needed for the back gear to engage. If you're saying that the back gear engages the bull gear materially before it engages the small gear on the spindle, then it sounds like something is assembled wrong or you have the wrong parts on the lathe. If one gear is engaged before the other by a fraction, then it could be you need to adjust the shims.


      • #4
        Oh, are you saying the 60 holes in the bull gear are on a circle that is too large, and the index pin is half a hole to the inside?

        That would be an enormous amount. It would be possible that the hole for the pin was mis-drilled at the factory. IMO this is unlikely. Does the pin and its mounting hole pass a visual inspection?

        Now, if you're saying that the bull gear also engages the back gear before the gears on the other end engage, then it sound likes that's the wrong bull gear.

        If the part number on the bull gear is correct, then you may have 2 problems.

        Do all the parts in the spindle fit good and tight? No rattling?


        • #5
          Probably someone has broken the bull gear by using it whilst trying to remove the chuck, and found a replacement off another model.
          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


          • #6
            Originally posted by bytewise
            What type of bearings does the headstock have, sleeve or roller? If they are sleeve, they MIGHT be worn enough to give the problems you see. It would take a lot of wear to give the problem you have. Simple test! With the belt loose can you wiggle the spindle?

            This is what I was thinking right away. If it is a roller headstock I would look more at the bull gear being changed or something. Might be from the same size lathe but from a different year where they changed the size a bit for some reason.


            • #7
              the index pin is just for indexing. Period. Never any purpose trying to index with back gears. The coupling pin is what couples the bull gear to the cone pulley and allows the gear reduction to 28 rpm or the normal operating ranges.

              The index pin is on the outside of the headstock casting whild the coupling pin is inside the headstock casting in the recess of the bull gear.


              • #8
                10" Atlas lathe Bull gear

                It is a roller bearing head stock and yes the index pin looks good but will not engage the 60 index holes. I have set up differentials so feel the bearing preload is good. also when trying to cam the back-gears into engagement the bull gear is engaged first. I did think of possibly a different gear but my bull gear is cast with 10-241 as is identified on Atlas's parts breakdown sheet.
                With the problem of the index pin not lining up correctly and the back gear assembly meshing first with the bull gear and not meshing completely with the smaller gear on the head stock spindle it just seems that the "bull" gear is from a different lathe even though it has 10-241 cast into it Is the "bull" gear from a 12" Atlas lathe a different size?


                • #9
                  The bull-gear for a very old Craftsman 12" has a part number of 10-241 according to this parts diagram.

                  Doesn't mean your bull gear should not be.

                  Check the brackets holding the back gears on, look for shims. Perhaps the left end has a ton of shims.

                  On my old lathe, the left-side bracket (10-245L) is considerably thinner than the bracket on the right side (10-245R.) The reason is because part L3-108 is inserted between 10-245L and the headstock, effectively thickening the part. If the brackets are reversed on your lathe (assuming this construct is the same, of course) it would give the behavior you describe.

                  Look here, 3rd picture down. On the left, see the rod with the ball on it - this lifts the motor. Note the fork the rod sits in - this is L3-108.

                  If I was correct, however, the index pin would still not fit. Frankly, I would not sweat the index pin - I never think of using it for anything. Anything you do to make the back gears mesh correctly will carry the day.


                  • #10
                    Atlas back gear mystery?

                    I am not worried about the index pin. If I really needed that feature I could make an offset pin. The engagement of the back gears does concern me. After I got the lathe I had to replace the small arbor gear as it came with the lathe in four (4) pieces. I would appreciate it if someone would measure the O.D. of both gears so that I could compare mine. I have had the cam part of the back gear off but will take it off again and measure to center to see if one bracket is different. I do appreciate all of the input from everyone


                    • #11
                      OD of the gears probably doesn't much matter as long as your bullgear is the same diameter as the large gear on the back gear shaft. The two small gears should also be the same diameter. Either yours aren't, or the back gear shaft isn't parallel to the spindle. Or, something is whacked in the cam and the left end isn't being advanced.

                      Just the same, I'll measure mine tomorrow when I get home from work.
                      Last edited by Tony Ennis; 02-06-2012, 12:22 AM.


                      • #12
                        It might help to know what model you have and a view of your headstock. Perhaps some of the parts were replaced with whatever was available at the time. The index pin on my 12" goes through the headstock casting and into the same 10-241 gear. I don't see how it could be off-set. Unless maybe the headstock casting is from a different model.


                        • #13
                          i had one that someone apparently used the index pin as a spindle lock to remove a stuck chuck and bent the tip enough it didn`t want to go in the holes anymore- if one of the holes in the bull gear is "smeared" that may be your culprit. if so make a new pin.


                          • #14
                            Atlas back gear mystery?

                            Hi folks. well I measured the mounts for the eccentric shaft on the lathe and they are identical from mounting face to shaft center-line (no extra shims either). It all seems to come back to an oversize large "bull" gear on the headstock arbor. It seems crazy but I don't know what else to think. Can anyone suggest someone who might be an expert on Atlas Lathes? With all the knowledgeable people on this website I can't believe I am the only one who has run into this kind of a problem. Thanks for your time. Maybe I can find someone close with an Atlas 10" that I can measure. I am in Humboldt County in Northern California.


                            • #15
                              Atlas back gear mystery?

                              I need to add that the eccentric can't be fully rolled because it fully engages the large "bull" gear too soon but the smaller gear is only half engaged at the same point.