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  • Aluminum Shaft?

    Hi, I recently got a request to make a shaft (Well, Multiple really) outta aluminum to replace a steel shaft. Never seen aluminum shaft in use so I thought I would ask here.

    Shaft is about 5" long, 5/8" OD (Shaft is solid), Sprockets held in place with cerclips and keyways on either end, Supported by two bearings about 1" away from the sprocket on the inside of the shaft (No outer support)

    HP specs are about 6HP outta a 2 stroke engine, Running into a 17 tooth sprocket on the left and a 10 tooth sprocket on the right, Estimating shaft RPM at 1200RPM.

    Some issues im wondering. Iv never seen aluminum shaft. Am I right in thinking under such stress it will fatigue and eventualy snap? Or the keyways will mushroom out? Im also suspecting it has to be DEAD on accurate OD or it will quickly deform/wear as it 'rolls' around inside the bearings and sprockets.
    Not sure if aluminum stock is accurate enough outta the box, Not really willing to do a run of turning larger stock to exact size due to precision required. Existing steel shaft is allready keyed and (ground?) exact size compaired to the sprocket bores, Like -0.0002 or something undersize, No notiable play. Any shaft marks stop the sprocket from sliding.

    And is $10 per part too much or too little to be charging in small batchs to put 2 keyways in and 2 cerclip grooves? (Allready have the cerclip groove tool ground), Assuming I don't need to turn the stock to size. Shop is equiped with manual Mill and Lathe.
    Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

  • #2
    Shaft

    Sometimes you have to learn to say NO.

    JRW

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    • #3
      If you were just being asked to key and groove the shaft to fit the specific parts, then the design would be your customer's responsibilty as to whether it worked, but since you have been given the power transmission requirements by the customer there is the appearance that there might be some expection on his part for you to have some liability for the design and future capabilty of the assembly performing up to his expectations.

      If you do this get him to pay first and make sure that everything you own is in your wife's name.
      "Patriotism is the last refuge of a scoundrel"

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      • #4
        $10 per part sounds good. Aluminum is easy to work with, and those parts sound simple enough. key each end = 5 minutes, groove each end = another 5 minutes. No problem.
        The only hassle might be getting a good fit into the bearings. Aluminum stock usually comes +/- .005, and isn't exactly round. .
        You might have to get 3/4 stock and turn each end.
        Just asking, but why is the customer requesting Aluminum for a shaft? 1018 is just as cheap, but stronger for a shaft. My 2 cents...

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        • #5
          Yeah I make parts for a guy that makes drive thru car washes, the shaft I do is 2"dia though and they must work fine since I have only had to make new ones for new car washes. If they didn't work fine it really wouldn't matter to me, the engineer/designer gave me a print of what he wanted.


          I know you're in Canada and Mcmastercarr doesnt ship there, so Im not sure what you can use for metal suppliers, but for example for 5/8 DIA X 12" piece of 7075 aluminum that is ground to plus zero minus .0005" it is $15.14 mcmaster #9063k171

          same thing in 6061 aluminum would be about half that, but 7075 would be a better choice(I think, but I'm not an engineer)

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          • #6
            Pretty far fetched: Maybe your customer wants a one-time torque limiter - sort of a mechanical "fuse".
            Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
            ~Practitioner of the Electromechanical Arts~

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            • #7
              Customer wants to replace steel shaft with aluminum shaft to go with this new aluminum (hard chrome coated?) sprocket he got. I believe its for lack of rusting (part is exposed to elements on a motorbicycle), for looks (Shiny aluminum, Matchs new chromed sprocket) And to a lesser extent weight.

              I wasent given transmission specs, this is based off my knowage of the parts usage. I would just rather inform my customer that I don't think the part is going to work well before taking his money to make a lot of them, If he still wants the part, thats up to him.

              How well do aluminum hard chromed sprockets hold up compaired to unhardened steel ones (That are currently wearing a little, Hardened steel sprockets in similar applications show absolutely no visable wear signs)?

              My biggest fear is fatigue, If the shaft is continiously torqued, Won't it weaken over time due to aluminums very low fatigue?
              My other fear is the keyways being distorted over time, With just using cerclips, the keyway/shaft accuracy is the only thing that stops impact stresses
              Last edited by Black_Moons; 08-03-2011, 04:38 PM.
              Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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              • #8
                I ride/race dirtbikes and aluminum is used alot for sprockets, frame etc. but the axles are still steel. However the wheel hubs are aluminum and the sprocket actually attaches to the wheel hub. Had me curious and I found this:

                http://www.axle-exchange.com/

                They are using 6061 for drive shafts on Mustangs, gotta be some torque there.

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                • #9
                  I just re-read your description, are you talking about a jack shaft? An intermediate shaft with sprockets on each end?

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                  • #10
                    Hard chromed aluminum sprockets?

                    That's funny.
                    Gene

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                    • #11
                      Originally posted by charlz
                      I just re-read your description, are you talking about a jack shaft? An intermediate shaft with sprockets on each end?
                      Yes, I am.

                      Id wonder about that website.. They seem to be making parts for dragsters, Where the life of a part would not be such an issue compaired to weight. Also those are some DAMN huge tubes.. And no keyways to worry about.

                      Intresting information however, But yea, as a jack shaft it has some seriously unsupported pulling forces, as well as the torque forces.
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        I don't think a jack shaft failure would be that catastrophic given the use you have described. Depends on what the chains do when it fails. I would explain your wear concerns, maybe having this part made out of aluminum is 'cool enough' for it to be considered a wear part. Dirtbikes run aluminum rear sprockets, everyone knows they wear faster than steel but accept that as the price for the weight savings.

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                        • #13
                          Originally posted by charlz
                          I don't think a jack shaft failure would be that catastrophic given the use you have described. Depends on what the chains do when it fails. I would explain your wear concerns, maybe having this part made out of aluminum is 'cool enough' for it to be considered a wear part. Dirtbikes run aluminum rear sprockets, everyone knows they wear faster than steel but accept that as the price for the weight savings.
                          Do aluminum rear sprockets wear faster then unhardened steel? And do they wear faster in street bike applications too? (Less debrie, its a street application for this shaft)

                          Chain can't do... too much when it fails as theres a freewheel in the back wheel, But it could theorticaly jam in beween the back tire and the frame.. but somewhat unlikey.

                          Hmm intresting, Mcmaster has keywayed 'Aluminum Shafts—Made of Alloy 2024-T4 aluminum, these shafts are lightweight and have more corrosion resistance than steel shafts. Hardness is Brinell 120.'
                          Wiki says 2024 has high strength and fatigue resistance.

                          I wonder how this alloy stacks up to the mild steel shaft I made for myself? (Or the unknown alloy shaft thats included with the kit that I bent one day accidently)
                          Last edited by Black_Moons; 08-03-2011, 06:18 PM.
                          Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                          • #14
                            Originally posted by Black_Moons
                            Do aluminum rear sprockets wear faster then unhardened steel? And do they wear faster in street bike applications too? (Less debrie, its a street application for this shaft)
                            They do wear faster, how many times faster I don't know, you rarely find steel sprockets although they do make 'hybrid' sprockets these days where the outer ring/teeth is steel riveted to the rest which is aluminum.

                            I don't know about between street and dirt but my thought is dirt would wear much faster as you are on and off the throttle a lot all the time versus street. Maintenance of the correct chain tension also effects wear.

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                            • #15
                              Black_Moons, in the 1970's when I raced sprint gokarts with 12 hp 2cycle engines we used aluminum sprockets on the axle. They were blue anodized and lasted about half a season of hard use on asphalt tracks. I don't remember the sprockets wearing a lot but they did deform some from the torque. I replaced them and the chain as needed.

                              As to the aluminum jack shaft, I suspect the keyways would get beat out but since it's on a motorbicycle I doubt the torque will be high.
                              It's only ink and paper

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