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  • Nylon milling machine gears

    I have a little story to tell. I have a CX601 milling machine from Busy Bee Tools and I love it. This milling machine does everything I want, except drill 1" holes in aluminum. I don't do that very often, but when I do, it's mostly ornamental holes thru flywheel webs. And this is the point where my mill lets me down. There is a nylon compound gear in the gear-head, and it lets you put the mill into the equivalent of "back-gear" on a lathe. About every two or three years, this compound nylon gear manages to strip all the teeth of one side. It costs around $70 for a new gear, and it's a royal pain to take the mill apart and replace the bad gear. It doesn't happen all at once. When it first decides to eat that gear, it jumps out of gear into neutral. If you can spare a hand to hold it in gear, it works just fine, but sometimes I run out of hands to do that. It doesn't take much force to hold it in gear, and I'm sure that if it was held firmly in gear so that it couldn't jump out, then it wouldn't wreck the gear. So, today I'm designing a third hand to hold the mill in "back gear" while I drill large holes. In the pictures, you will see a side view of my mill where the gear selector knob is, another picture that shows my "third hand" in position, and in the third picture you can see a bad nylon gear and it's replacement good nylon gear.


    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

  • #2
    And here you can see a 3D model of my milling machine with the knew "third hand" installed and a detail of the 3/4" thick third hand. The 1/2" diameter knurled steel pin screws thru the arm and is captured behind the sheet metal enclosure that houses the motor. This sheet metal housing is quite "beefy" and should easily be able to counteract any forces that try to shift the gear selector out of gear. To put the machine into it's normal gear, you just unscrew the threaded pin enough that it no longer is held captive behind the steel motor housing.

    Brian Rupnow
    Design engineer
    Barrie, Ontario, Canada

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    • #3
      I have a G0759 (G0704) Griz which looks to be the same machine. I can't use big drills because the spindle gets slightly wobbly or I stall the motor.

      Did you need to do anything with the controller to get more grunt in low gear?
      -paul

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      • #4
        Did you model the whole machine? I have been slowly correcting and remodeling a lousy interpretation of the machine i found on grabcad, which was found to be waayyy off after some quick scale checks.

        Another thing that my head does is it will grind or stop when the quill is > 50% down, some of the time. I've been mulling over doing a swap to a polychain timing belt but it's fifty lines deep on my shop todo list...
        -paul

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        • #5
          Yes, I modeled the whole machine when I was adding DRO's to it. I don't have to do anything with the machine to get it into "low range" except slow it right down to almost a stop, turn the knob shown and then ramp the speed back up. If you want I can send you a .step file of it---I will need your real email address to do that.
          Brian Rupnow
          Design engineer
          Barrie, Ontario, Canada

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          • #6
            Of course one alternative would be to drill as large a hole as the mill is comfortable with, then increase the size with a boring head. Of course this will take much longer. I have not had the pleasure of using annular cutters, but it may be that they take less oomph than a comparable size drill. Those who know will chime in.
            "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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            • #7
              Originally posted by mickeyf View Post
              Of course one alternative would be to drill as large a hole as the mill is comfortable with, then increase the size with a boring head. Of course this will take much longer. I have not had the pleasure of using annular cutters, but it may be that they take less oomph than a comparable size drill. Those who know will chime in.
              I have the same machine and that is exactly what I do for larger holes. A 1" annular cutter would also be a very good way to go, much less power and drama needed.

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              • #8
                Originally posted by Stu View Post

                I have the same machine and that is exactly what I do for larger holes. A 1" annular cutter would also be a very good way to go, much less power and drama needed.
                X2 on the Annular Cutter,if want to run a little higher RPM use the Carbide Tipped ones,Accusize has holder to R8 $66 cdn.

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                • #9
                  Does it have to be a plastic gear?

                  I'd think that an aluminum on would be easy enough, and would hold up better. If the plastic meshes with other plastic gears, then I suppose it would be more work. I am not a big fan of plastic gears used as a "mechanical fuse", but a lot of manufacturers seem to be, or else they have discovered that plastic is cheap.
                  4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                  Keep eye on ball.
                  Hashim Khan

                  Everything not impossible is compulsory

                  "There's no pleasing these serpents"......Lewis Carroll

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                  • #10
                    Originally posted by J Tiers View Post
                    Does it have to be a plastic gear?

                    I'd think that an aluminum on would be easy enough, and would hold up better. If the plastic meshes with other plastic gears, then I suppose it would be more work. I am not a big fan of plastic gears used as a "mechanical fuse", but a lot of manufacturers seem to be, or else they have discovered that plastic is cheap.

                    The real question is what breaks next if the gear doesn’t fail?

                    Its a $70 gear that lasts 2-3 years of I am guessing pretty regular use. That’s under $2.50 a month of “maintenance” costs to own the mill. I would just keep a spare on the shelf and change it when needed.

                    And mentioned above there are better cutting methods that will prolong this.

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                    • #11
                      Brian: I would be tempted to fab a shop-made annular cutter for aluminum. This would put less strain on the machine as a whole. I have used store-bought annular cutters that were 2" in dia. and cutting 2" deep in aluminum The cutting went easy in a Bridgeport. I used cutting oil and frequently cleared chips Most small flywheel webs should be do-able with shop made tool.

                      Sarge41

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                      • #12
                        Originally posted by oxford View Post


                        The real question is what breaks next if the gear doesn’t fail?

                        .................
                        Of course. And whether the gear fails as a "fuse" for BR. Sounds as if it does not, that the issue is due to another problem entirely.
                        4357 2773 5150 9120 9135 8645 1007 1190 2133 9120 5942

                        Keep eye on ball.
                        Hashim Khan

                        Everything not impossible is compulsory

                        "There's no pleasing these serpents"......Lewis Carroll

                        Comment


                        • #13
                          It should be possible to add a spring to the end of that handle such that it will hold tension on the gears in both positions.
                          http://pauleschoen.com/pix/PM08_P76_P54.png
                          Paul , P S Technology, Inc. and MrTibbs
                          USA Maryland 21030

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                          • #14
                            I too have the same machine.
                            Once the gear stripped out the first time I converted the machine to belt drive with a 3HP three phase motor and VFD.
                            No problems since then.

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                            • #15
                              Makes one wonder why there is axial thrust displayed on a straight cut spur gear, there should not be any if the gear sets are aligned properly.
                              Are thrust washers or thrust bearings installed to counteract any unwanted play?
                              Rather than forcing the gears to say in place by pinning it in place, perhaps a look at why the issue is there in the first place.

                              It may be a simple fix, if it requires a total re-engineering of the drive, than yeah annular cutters or better yet, the VFD and belt drive is the one that I like best.
                              Home, down in the valley behind the Red Angus
                              Bad Decisions Make Good Stories​

                              Location: British Columbia

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