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Turning sprockets -- cermets ?

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  • Turning sprockets -- cermets ?

    Evan posted a while back about turning a sprocket with cermets.
    Originally posted by Evan
    This particular insert is pretty tough. A lot of carbide inserts won't do what it will. I used it to turn down a hardened bike sprocket on my moped and it did just fine without damage even with the interrupted cut.

    .........Bicycle sprockets and related parts are some of the hardest things I have ever machined. I tried some carbide on the sprocket and all it did was rub. In the past I have usually ground the parts instead of trying to turn them. I was rather surprised when the insert cut the sprocket with ease.
    I may have a similar application. I've been fooling around with chainsaw sprockets, trying to modify a 404 rim sprocket to fit lo-pro chain (the only alternative is a spur sprocket that costs $50 and is only available from one source).

    The mod is pretty simple -- just take a 404 rim with a 1.521" OD, and turn it down to 1.435". Problem is, like Evan's bike sprocket, chainsaw sprockets are harder than heck, and there's an interrupted cut.

    The rim spins on the saw at upwards of 13,000 rpm, so the mod does have to be done with some precision, held tightly on a snug fitting mandrel as it is machined.

    End view of rim mounted on lathe mandrel.


    Side view, you can glimpse the spokes of the sprocket that result in an interrupted cut.


    On the right is a 404 rim that I turned down from 1.521" OD to 1.435" to fit lo-pro chain. I used a carbide TNMG bit and it did the job, but ...... it didn't like it. It was VERY difficult to cut, especially the interrupted cut. The whole lathe shook and I was afraid something was going to break. The bit was chewed up a little. Diameter control is hit and miss because of the degrading bit, plus the lathe itself flexing due to the extremely tough cut.

    Despite the machining problem, the rim itself seems to do the job on the chainsaw. The 404 rims can be bought for $5 vs. $50 for the special spur sprocket.


    One rim will typically last me a year, so if I were only making these for myself, I wouldn't mind burning up a TNMG bit on every rim -- assuming my lathe doesn't get destroyed in the process. However, some of my chainsaw buddies have expressed an interest, and I'd like to oblige them if I can do so without spending a lot of money. For example, I'd be willing to try a few cermet bits, which would be handy to have on hand, anyway.

    Before we start talking about alternative methods like grinding, any suggestions on a particular cermet to try? I've got a CNMG toolholder, but might be willing to spring for another style of holder.

    Alternative methods -- this job might be better done on a tool and cutter grinder, but I don't have one, and it's not a paying job, so outsourcing isn't an option.

    A tool post grinder would also work, but it would be very slow, and no one likes to use a tool post grinder on their pet lathe. Nor do I have a "real" tool post grinder. Occasionally I have used a die grinder clamped to the lathe toolpost. It worked, as long as I took very light passes.

    I've tried annealing a rim before machining, but so far I've only been able to partially anneal it. I only went up to 1680 degrees F -- I'll try one more time at around 1800. Even if I succeed in annealing the rim, then I still have to figure out how to harden and temper it after machining, and I have no idea what the material is or what the temper should be.
    Last edited by MTNGUN; 05-12-2010, 12:05 AM.

  • #2
    In case it helps... chainsaw rim sprockets are made by metal injection molding (MIM).

    Comment


    • #3
      MIM, huh ? No experience with it, but I'll google and see what I can learn.

      Thanks, Lakeside.

      Comment


      • #4
        Evan was using a TC30 grade of Kyocera cermet.

        Here's how Kyocera ranks TC30 compared to their other cermet grades -- hard, but not very tough. Still, it was tough enough for his sprocket.

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        • #5
          Basically compressed metal power. If you're turning Stihl sprockets, they are made by Oregon (for Stihl).


          For some reason, I can't see your pictures.

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          • #6
            cermet is nice, try Boron.
            Last edited by Carld; 05-12-2010, 12:39 AM.
            It's only ink and paper

            Comment


            • #7
              Your info did help, Lakeside, because Wikipedia says MIM is a type of sintered powdered metal.

              In other words, all bets are off regarding the metal composition and "temper." The material may be something that cannot be annealed like a conventional tool steel.

              Comment


              • #8
                I'll upload the pics to photobucket (instead of "borrowing" them from the AS forum) and try again in a few.

                Comment


                • #9
                  Refused access

                  Originally posted by lakeside53

                  .................................................. ..

                  For some reason, I can't see your pictures.
                  Same here. Access is refused at the arborsite.com site as registration and logging on are required.

                  It would be easier if the OP were to up-load to PhotoBucket and then provide the links.

                  The first link was to Evan's site/server and it worked OK.

                  [Edit]

                  Oops.

                  Sorry MTNGUN.

                  I didn't see your post until I had finished typing and posting mine.

                  [End edit]
                  Last edited by oldtiffie; 05-12-2010, 12:07 AM.

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                  • #10
                    Many sprockets and small clutch items are made with sintered metal.
                    Cermets are a good approch as carbide is of little value on this hard material.
                    heat treating will do nothing, as the part was pressed at several million pounds per square inch and then fired at about 2400 F (as I recall)
                    There is lots of Chrome and other hard metal in the particles.
                    Grinding is a more effective approach, or EDM .
                    Rich

                    Comment


                    • #11
                      Originally posted by Rich Carlstedt
                      Many sprockets and small clutch items are made with sintered metal.
                      Cermets are a good approch as carbide is of little value on this hard material.
                      heat treating will do nothing, as the part was pressed at several million pounds per square inch and then fired at about 2400 F (as I recall)
                      There is lots of Chrome and other hard metal in the particles.
                      Grinding is a more effective approach, or EDM .
                      Rich
                      That makes sense to me.

                      I'm shopping for cermets now -- I'll probably buy a few cheap cermets from ebay and make a toolholder for them, just like Evan did. Even if the cermets don't work on the sprocket project, they'll probably find a use somewhere down the road.

                      Comment


                      • #12
                        I ordered some Kyocera TN6020 bits for my CNMG toolholder.

                        CN6020 seems to be what Kyocera is pushing these days. Even if they don't work out on this hobby project, I'll probably find a use for them on a paying job.

                        If they do work well, I'll post an update.

                        Comment


                        • #13
                          I routinely machine parts made by the powder metallurgy molding process. There are different grades of material. The really hard grades are light in colour, usually with a light brown tint. They can be machined even with carbide but you need to use the really tough C1 or C2 grades to avoid rapid destruction of the edge.

                          PM me your address and I will send you a couple of sticks of solid C1 carbide to try. You will need at the least a silicon carbide wheel to grind the cutting edge to shape. They are already preformed so not much grinding is required.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            That's a generous offer, Evan, but I can pick up some C2 or C1 bits if you really think that would work better than the Cermet ?

                            I have no idea about the composition of these rims, but a file barely scuffs the rim material, so they are nearly file-hard.

                            As Rich suggested, it would make sense that some sort of wear resistant material has been added to the mix.

                            I was seriously afraid that my cross slide was going to break while turning the rim with a standard bit (it was an unmarked TiN coated bit that came with the toolholder, probably C5 or C6). The whole lathe was shaking and it sounded like a jackhammer. I don't want to do that again.

                            The partially annealed rim didn't shake the lathe badly, but it still dulled the bit (that time a Kenametal KC810). And I'm not going to mess around with annealing anymore, now that I know that the rims are sintered metal.

                            Comment


                            • #15
                              C1 carbide won't work better in terms of cutting abillty but it will last a lot longer with that kind of abuse. C1 carbide is used for log peeling teeth and is able to withstand hitting embedded rocks. It's also used on stump grinders.
                              Free software for calculating bolt circles and similar: Click Here

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