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Aluminum as a bearing material?

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  • Aluminum as a bearing material?

    Ok, I'm thinking of a shortcut here and thought I'd see what others suggest.
    I've finally worn the teeth on a 20 tooth tumbler gear on my Atlas/Craftsman 12 inch. It gets a lot of use in power feeding and is now worn to the point that the noise it is making is objectionable.
    I could just buy a replacement, or, of course, make one.

    Aluminum is what I am thinking about for a replacement gear. It should be as durable as the zamak gear it will replace. I just happen to have the right tooth cutter and an index head, so, I really just need to make an arbor and go to work. However, the gear has a 3/4 inch hole with two opposed keyways in the center. It fits over a keyed bushing with a smooth bore to free spin on the stud. The bushing appears to be steel and the stud is of the shoulder variety. If I reproduce the gear, I will have to employ the shaper to cut the keyways (or abuse the carriage on my lathe a bit) and that makes more work. The arbor would probably just use a woodruff key on one side.

    All that seems a lot of trouble. I have an arbor already for a smooth bore the size I need to fit the stud. If I just made the whole gear of aluminum, the teeth would end up perfectly concentric with the bore and I wouldn't need to cut keyways. I could machine an inch and half or so up and just slice off completed gears. That way if the aluminum bearing surface on the ground stud begins to wear out, I have spares to throw on.

    If this were an oil bath environment I wouldn't hesitate. The gear will spin at nearly lathe rpm when I am using the leadscrew and is an open gear. The only lubrication it will have is what it can hold. Would I likely be happy or unhappy that I used such a dodge?

    If I do go the keyway route, I'm thinking of cutting the gear from acetal. If it held up, it would be nice and quiet. I can't imagine getting away with a delrin bearing at 2000 rpm, though, even with a bit of oil.
    And, of course, I could probably use an Oilite bearing in either blank, but that complicates my arbor.

  • #2
    I'd probably make a larger hole in the gear and press in an oilite bushing with the correct ID.

    Mike

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    • #3
      I think that could be OK, given a little grease. (straight alum) Depends on alloy though.
      But I don't understand why the OEM had the double key?
      Cutting the keyways on the lathe if you don't have the broach is N.B.D.
      Yer just in for the labor right?

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      • #4
        Originally posted by Carm View Post
        I think that could be OK, given a little grease. (straight alum) Depends on alloy though.
        But I don't understand why the OEM had the double key?
        Cutting the keyways on the lathe if you don't have the broach is N.B.D.
        Yer just in for the labor right?
        Thanks for the input. The double key allows the gear to be one of their standard change gears which need the keyed bush to hold them in pairs. I tried a magnet on the keyed bushing and it doesn't attract. It looks cast, so it is probably zamak as well and not steel. I suppose if zamak will work as a bushing, aluminum would. The bore doesn't appear worn much, just the teeth. Sound right?

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        • #5
          Aluminum running on steel, especially with oil, should be OK. Again, alloy might make a difference, and longevity could be a consideration. I like the idea of a press fitted bronze bushing. Otherwise, aluminum as a gear should be at least as good as Zamack. Bob.

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          • #6
            Hope your alooneyum is a high number series (6xxx) and not soft.
            Had to look up Zamak.
            Zinc, aluminum,magnesium and copper (und kopfer for those who know dwarf fart)
            Not much to lose if you make sausage and cut a slice when you need it.

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            • #7
              You probably want 2024 or 7075 for that. One of those in a T-4 to T-6 temper would probably run for quite a while.
              Kansas City area

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              • #8
                Thanks for the input guys. I used 7075 aluminum. I reamed the hole to a close fit with the stud, turned and bored a blank, and cut the teeth. It's installed and working fine. My visions of a sausage went by the wayside when I discovered I didn't have a bar of 1 1/2 inch aluminum, so I just chucked a scrap and made one off.
                I've been turning a lot of steel lately and had almost forgotten the joy of machining aluminum. Start to finish about 3 hours including time out for dinner. It looks good, works fine, and is quieter. I'm happy.

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                • #9
                  The gear is used as either an idler or as a drive gear depending on where you use it. The 20-T is used often. That's why all the gears may or may not use the bushing.

                  I set up several banjos so it would make changing the gears easier for threading. That lasted a few times then I put my feed set up on and it's been there ever since. I switched to dies and never looked back.
                  Last edited by CCWKen; 03-02-2015, 09:12 PM.

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                  • #10
                    aluminum is not ideal for this. Too soft. Likes to friction weld to surfaces.

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                    • #11
                      Lay the open gear lube to it. Been running 7075 for years. Works fine.
                      Wayne

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                      • #12
                        Originally posted by peekaboobus View Post
                        aluminum is not ideal for this. Too soft. Likes to friction weld to surfaces.
                        Agreed, likes to gall and make aluminum oxide everywhere, a wonderful abrasive.
                        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                        • #13
                          Originally posted by peekaboobus View Post
                          aluminum is not ideal for this. Too soft. Likes to friction weld to surfaces.
                          Originally posted by Black_Moons View Post
                          Agreed, likes to gall and make aluminum oxide everywhere, a wonderful abrasive.

                          It all depends on the alloy, look at all the sliding action going on within a steel/iron cylinder mated to an aluminum piston.
                          Piston to cylinder surface speeds up to 4,000 ft./min. Billions of examples doing very well.
                          Also most overhead camshafts run directly in aluminum heads for hundreds of thousands of miles with no issue.
                          Too many other examples to mention.
                          Home, down in the valley behind the Red Angus
                          Bad Decisions Make Good Stories​

                          Location: British Columbia

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                          • #14
                            Acetal is a great material for gears and probably ok for the bore as a bearing material too. Cut one from acetal or perhaps use the friction melting technique to form teeth.

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                            • #15
                              In addition to the uses Willy posted, aluminum main bearings have become more common in vehicles and small engines such as Briggs and Stratton have used just the aluminum housing as a bearing in their non industrial series engines for years.
                              I came across this site which speaks to materials used for aluminum bearings.
                              http://www.keytometals.com/Article106.htm

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