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  • contact wheel.

    I made a kmg knife grinder . These wheels in darkest africa cost a bomb.How difficult would it be to cast or machine an aluminium wheel and bond some polyurethane on it.
    I am concerned as to how to bond the urethane to the wheel securely so it doesnt delaminate.
    Also how would one make those tyre grooves that run at an angle.How would one machine that.?
    https://guide.alibaba.com/shop/250-5...l_5830549.html

  • #2
    Usa-nased knife maker here, good to see a like mind! Making a contact wheel is a bit of a challenge, as you stumbled on. Going with aluminium, nothing is particularly difficult to machine, all you really need are 2 bearing seats and the rim to concentric with the bearing seats. The biggest problem there is having a machine large enough to turn the diameter of contact wheel you want, a 2 or 3 inch wheel is doable on most hobby mahcines, a 4 or 5 inch one is possible, but an 8 or 10 inch wheel is likely out of reach to most home-shop guys. If you have a machine that can swing it though, nothing too challenging there .

    The hard part is the coating. Most commercial wheels, that i know of anyway, are made by machining an aluminium core, then using a mold to cast the rubber around it. You might be able to do this in a home-shop by constructing a mold and getting your hands on some castable urethane rubber, but youd want to make very sure the aluminium core is well centered in the rubber for fear of vibration.

    The grooves in the rubber are a contentious subject. The advertised reason for the serrations (proper name for the grooves) is that the grooves allow the belt to cut more aggressively and run cooler. Personally, im not sure i buy it. Id just as soon leave the surface smooth and avoid the complications. My personal views though, im not saying that they dont work, just that if i were making my own contact wheels i wouldnt bother because i have no real reason to.

    Depending on the size of the wheel you want, its worth looking around. A lot of people use longboard wheels or the rollers from pallet jacks for smaller wheels, larger wheels ive seen people use large casters like those in big work carts in the like. Theres also no reason your contact wheel HAS to be aluminium or other metal. Ive used MDF wheels for a number of years to good results. If i wanted a 10 inch contact wheel, what id be very likely to do is cut 4 10 inch rounds from some 1/2" MDF, sandwich them together, drill a recess the right size for some cheap bearings and maybe take some 1/8 80 durometer rubber and contact cement it around the rim. Will this be as durable as a commercial 10 inch contact wheel? God no, but it will be dirt cheap, do the job well and last long enough to get your moneys worth

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    • #3
      Hi Plunger, I am sorry I do not have answers to your questions but I think there are polyurethane pipes and fittings available for the air intake systems of motor vehicles so that might be a source for a polyurethane 'band' to put around your wheel.

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      • #4
        You might drop these folks a line,

        http://www.eagerplastics.com/cast.htm

        I don't know about overseas shipping and such, but they are very helpful.
        I have not made wheels, but I did cast a hard urethane plug for another project and they helped me select a suitable material. Mine is Task 4, 83 durometer, and was selected for the 1:1 mixing ratio in addition to the hardness.
        paul
        ARS W9PCS

        Esto Vigilans

        Remember, just because you can doesn't mean you should...
        but you may have to

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        • #5
          aluminum hub with a section of tire inner tube stretched over it for a skin?
          Just guessing here.

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          • #6
            Originally posted by 1-800miner View Post
            aluminum hub with a section of tire inner tube stretched over it for a skin?
            Just guessing here.
            Probably going to fly away when the 200mm wheel is running 6000rpm...
            Location: Helsinki, Finland, Europe

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            • #7
              Originally posted by plunger View Post
              I made a kmg knife grinder . These wheels in darkest africa cost a bomb.How difficult would it be to cast or machine an aluminium wheel and bond some polyurethane on it.
              I am concerned as to how to bond the urethane to the wheel securely so it doesnt delaminate.
              Also how would one make those tyre grooves that run at an angle.How would one machine that.?
              https://guide.alibaba.com/shop/250-5...l_5830549.html

              Don't know if this helps but Ive had a lot of success bonding polyurethane to cog pulleys. Just clean with acetone first.

              Comment


              • #8
                See if you have "Urethane Windshield Adhesive" there. It comes in a caulking gun tube. It's been used to hold front and rear glass in cars for at least the last 30+ years. Any auto-glass shop should have cases of it on hand. It's a little pricey at around $20 a tube but it could be applied to a machined wheel, cured then machined with a course rasp wheel on a grinder or knife edge tool bit. When fully cured, it's at or slightly harder than a car tire.

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                • #9
                  Search "grinder contact wheel" on YouTube
                  I have not tried any of these

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                  • #10
                    Why does your co tact wheel need to be covered? I made mine out of steel and knurled the contact area slightly. That gives the belt some traction.
                    Location: The Black Forest in Germany

                    How to become a millionaire: Start out with 10 million and take up machining as a hobby!

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                    • #11
                      Depending on specific needs, skateboard wheels, caster wheels, etc etc.

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                      • #12
                        Cast a machine a whgeel..easy to do in your backyard.
                        Cast a wheel that is safe at 3000 rpm, not so easy..
                        I have seen the film of the skull reconstruction from a grinding wheel that let go.. grim.
                        Cast is tricky for do it yourself..
                        What is wrong with billet ? Or just buying something that works?

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                        • #13
                          DennisCA built himself a grinder. It's mostly wood, including a pulley and some wheels:



                          Images were lifted from here:
                          http://bbs.homeshopmachinist.net/thr...92#post1168892
                          Location: Long Island, N.Y.

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                          • #14
                            I will either get a piece cut off a solid round bar or get a piece plasma cut from a sheet of 50mm thick.I am referring to casting some urethane on a machined wheel. How do you make sure its bonded well and the urethane doesnt delaminate.
                            I also am wondering how the mold with a tread would be machined. Could you machine this on a flat surface using flexible polystyrene or plastic and then just bend it to form a closed circle..

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                            • #15
                              Originally posted by plunger View Post
                              I will either get a piece cut off a solid round bar or get a piece plasma cut from a sheet of 50mm thick.I am referring to casting some urethane on a machined wheel. How do you make sure its bonded well and the urethane doesnt delaminate.
                              I also am wondering how the mold with a tread would be machined. Could you machine this on a flat surface using flexible polystyrene or plastic and then just bend it to form a closed circle..
                              Sandblast the surfaces and make a test casting to some scrap pieces to see how well it attaches. Polyurethane is probably going to adhere like a crazy and wont peel off even if you want.
                              Location: Helsinki, Finland, Europe

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