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Replacement Change Gears for Atlas / Craftsman Metal Lathes

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  • Replacement Change Gears for Atlas / Craftsman Metal Lathes

    The popular 10" and 12" Atlas and Craftsman metal lathes were equipped with change gears made of cast "ZAMAC". These gears are much softer than steel or cast iron gears, and not nearly as durable.
    Better quality change gears are available, but the information as to exactly what to buy, and where to buy seems a bit scarce. Here is my attempt to help.

    Browning, Union Gear, and Boston Gear make a range of change gears that will fit these lathes. These gears often show up on eBay, but of course you can't expect the size you need to be available when you need it. Boston Gear products are sold by A number of other industrial or specialty suppliers carry Boston and/or Browning and/or Union, and some time spent with a search engine will help to find these, but at the time of this writing (January, 2014) I've found Amazon to have the best prices.

    When purchasing change gears, or any spur gears, for that matter, you need to know:

    1. Pressure Angle. Either 14.5 degrees or 20 degrees.

    2. Diametral Pitch. (DP) This is the number of teeth per inch of diameter at
    the "pitch line". You can determine the DP of an existing gear by dividing the number of
    teeth plus 2 by the outside diameter. *(see example at bottom)

    3. Bore diameter and configuration (smooth bore, keyways, splined, etc.)

    4. Gear face width and hub thickness

    5. Number of teeth

    Fortunately, there's a bit of standardization here:

    1. Change gears for the lathes in question all have 14.5 degree pressure angle. You
    don't have to worry about that.

    2. The Atlas / Craftsman 10" and 12" lathes all use 16 DP gears.

    3. All of the 16 DP change gears from Union, Boston or Browning have a 3/4"
    bore with two keyways. This is the configuration that fits your Atlas / Craftsman lathes.

    4. Likewise the hub and face thickness are standardized. The 16 DP gears are 1/2" thick.

    With this in mind, all you really need to know is the numbering system used by the manufacturers. It's not very complicated, either.

    Boston Gear:

    "GBxx" The two letters, "GB" denote a 16 pitch gear with 14.5 degree pressure angle, 3/4" bore, two keyways, and 1/2" thick. This is followed by the number of teeth and sometimes a letter suffix. You can forget about the suffix when searching. So a 30 tooth gear would be "GB30." A 127 tooth gear would be "GB127A". Boston lists these gears in tooth counts from 20 to 128.


    "NCG16xx" The letters "NCG denote 14.5 degree change gear. 16 is the diametral pitch and xx is the number of teeth. So your 30 tooth change gear would be "NCG1630" And a 127 tooth gear would be "NCG16127". Browning lists these gears in tooth counts from 20 to 129.


    "CG-16xx Style K". The letters "CG denote 14.5 degree change gear. 16 is the diametral pitch and xx is the number of teeth. Style K denotes the 3/4" bore with two keyways. Your 30 tooth change gear would be "CG-1630 Style K" And a 127 tooth gear would be "CG-16127 Style K". Union lists these gears in tooth counts from 20 to 129.

    Now, knowing these numbering systems, you can search eBay or your favorite industrial parts supplier for high quality gears to fit your old lathe. These gears will be interchangeable with the old ZAMAC gears.

    The part numbers for steel keyed bushings for these gears are:

    Browning, CGB16

    Boston, GGB16A

    Unfortunately for the owners of 6" Atlas / Craftsman / AA / Dunlap lathes, your gears are 24 pitch, and neither of these manufacturers make change gears to match.

    *Calculating Diametral Pitch. Example: Your gear has 64 teeth, and measures 4-1/8" outside diameter. Divide the diameter into the tooth count + 2, thus: 66 divided by 4.125 is 16, and your gear is a 16 pitch.

    One final note: the ZAMAC gears have 1/2" thick hubs and 3/8" wide faces. The steel and cast iron gears I've discussed have full 1/2" wide faces. This can cause some slight interference and noise in the gear train. The easy remedy is to put a thin, .010" or so shim washer behind the stud bushing of whichever gear pair has the larger gear in the "Front" position (away from the headstock.)

  • #2
    That's a great bunch of information. Thanks for putting it together and sharing it.
    "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill


    • #3
      Yes, thanks! My winter project is reconditioning an Atlas 10".

      More tools than sense.


      • #4
        Great bunch of information you have posted, thanks for taking the time to do this.


        • #5
          When upgrading my atlas 10in I looked at 127 tooth 16dp gears which are over 8in Dia. Kind of difficult to fit into the change gear setup. I found by using 32dp gears I was back in the ballpark. Two gears are all that are needed to cut most of the metric pitches needed. One 127 tooth and one 40 tooth gear in 32dp.
          My article in HSM Mag Nov/Dec 2007 shows the various setups.
          I also added a reverse switch to the motor to make metric thread chasing more enjoyable.


          • #6
            Thanks for posting this information. Very valuable for us atlas owners.

            My youtube:


            • #7

              Thanks for the well written information on change gears. I have been trying to develop some understanding on this subject. This has been most helpful.

              Kevin B.


              • #8
                Owners of atlas/craftsman lathes have bean looking fo change gears for years so far i have not fund or known of anyone that
                was successfull in finding steel gears. There are 2 options 1 make your own 2 stay with what clausing has to offer
                800-323-0972 one can find gears on e-bay at premiumum


                • #9
                  My ZAMAC change gears are 70 years old and doing fine. Clearly they do not get used every day. Be advised that there are two different styles of change gears for Atlas/Craftsman 10" and 12" lathes. The difference is the hub thickness. If you buy gears from different generations of lathe, you'll have to deal with this. Not a big deal, but something you should know.

                  A full set of new gears will probably cost 2-3x more than the lathe is worth.
                  Last edited by Tony Ennis; 01-22-2014, 07:46 AM.


                  • #10
                    The alternate source of gears is a good reference. The Atlas gears are standard change gears and any 14-1/4 degree pressure angle 16 pitch gear can be adapted.

                    If the original Zamac gears have lasted this long, they will continue to give good service for many years to come. Zamac in and of itself is actually a very good material for this application and the fact that there are so many useable gears available after decades of use is proof of that.

                    A recent entry into the Atlas parts market is MyMachineShop.Net. They advertize in the Village Press magazines and offer most replacement parts for Atlas machines. They are manufacturing new parts, such as the half nuts and the prices seem reasonable.

                    Jim H.


                    • #11
                      Great post Jim, thanks for that.


                      • #12
                        mymachineshop is just a bit south of me. He mostly buys atlas/chraftsman machines and parts them out. He is also a big seller on e-bay He will ship all over the world


                        • #13
                          I am a happy happy happy customer of MyMachine Shop.
                          price was reasonable, packing was great. Plan on future purchases

                          As Phil Robertson says Happy Happy Happy
                          George from Conyers Ga.
                          The early bird gets the worm, BUT it's the second mouse that gets the cheese.


                          • #14
                            I know this is an old thread, but my question fits in with the info here.
                            Does anyone have a complete list of the change gears that came with a 1936 Atlas 12" lathe? A friend has one, and he lost/had stolen, all the change gears that were not on the lathe at the time. I'm setting up to make him a replacement set out of aluminum. Also any nice to have extras?



                            • #15

                              The auction has all the gear tooth counts shown.