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  • Mechanical Clutch

    My brain never stops!!! Not all of my ideas are good ones, but I never run out of mechanical things to think about. Playing about with my model sawmill has got me thinking about simple mechanical clutches. Not something that tightens or loosens a drive belt, and not something that creates "drag" when disengaged. Rather some device that totally and completely disengages the driveshaft from whatever it is driving, and can be engaged softly like the clutch on an automobile, not with a sudden "grab and lurch". It would have to be simple, cheap, small, and a minimum of moving parts. I have many small, single race ball bearings from disassembling various "things" over the years, and they will take a lot of axial as well as radial pressure without failing. I was doodling on a piece of paper, and where the levers are in the sketch, think about a Destaco style clamp. Not the ones with the swinging lever, but the push/pull type. I see the friction material as being oak or maple, glued into a brass or aluminum housing. Not sure if I will build something like this or not, but it is intriguing!!!

    Brian Rupnow

  • #2
    My friend , you are a deep thinker!! Lol-- Looks logical to me.

    Are those coffee stains!!?

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    • #3
      The mechanism of an Ettco-Emrich tapping head is just like that. It's called a cone clutch. The way I understand it is that it has a thin layer of leather between the cones. There are 2 cones for forward and reverse. It is very tractable - the more pressure you apply to push the cones together, the more torque it puts out. The tapping head I have is a real pleasure to use. Just an up or down motion of the drill press handle gives you forward and reverse, neutral is in the middle and easily controllable. You can tap an #0-80 hole as easily as a 3/8-16.
      Your version should work very nicely. You may want to make the tension spring loaded or screw adjustable.
      I have enjoyed following your builds, very interesting and nice work too! Thanks for sharing with the rest of us!
      Best Regards - Warren
      Last edited by Toolguy; 12-19-2012, 08:09 PM.

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      • #4
        Brian first if your brain stops we will all miss you, that said the clutch that you drew is just like the one on my old round tube Cub Cadet,

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        • #5
          Your drawing is similar to how the brass synchronizer rings work in a manual transmission. AS the shifter is moved the syncronizer ring is pressed against a cone shaped area on the end if a shaft with an integral gear getting it spinning at the same speed as the shaft of the gear being shifted into. The only difference is that the outside of the syncronizer ring has teeth that mesh with splines in the syncronizer assembly.

          http://www.youtube.com/embed/L3j6HaAieEU?rel=0

          http://automobiles-hariadhikari.blog...ar-system.html

          The point of what I have said is that given that syncronizers are small enough to fit inside manual transmissions for cars you might be able to adapt some internal parts of a junk manual transmission to your application instead of starting from scratch.

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          • #6
            Centripetal clutch yields full disengagement when revs are low.

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            • #7
              Originally posted by bob_s View Post
              Centripetal clutch yields full disengagement when revs are low.
              Yes, you are correct. If I was running my models with a high winding chainsaw or weedeater motor, that would be just the ticket. I used to run go-carts during part of my miss-spent youth, and although we called them centrifugal clutches, I think we're talking about the same thing. However, all of the model machinery I would run with a clutch are quite low rpm devices.
              Brian Rupnow

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              • #8
                That looks very similar to the power feed clutch on my lathe. (Rockwell 10")
                but on mine the cone is driven by gear teeth on the od. and engages the
                female to drive a gear. The shaft does not rotate and is used only to engage &
                disengage the clutch. and of course, I don't think I can get away with using
                oak for the cone.

                edit: maybe ironwood?
                Last edited by Scottike; 12-19-2012, 08:53 PM.
                I cut it twice, and it's still too short!
                Scott

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                • #9
                  Cone clutches. Back in the good old days (before hydralics and VS drives), variations of these were very common. They were used in a wide variety of devices from old american lathes to heavy earth moving machinery. Cat, for one used them with a band brake on their exterior surface for winch drive clutches. (Worked on/with them while in uncles employ.) If you are are considering building one for heavy service look in some of the older (60 + years) engineering handbooks for design details.

                  Another type of smooth clutch/drive mechanism used by some of the "poorboy" loggers and "peckerwood" sawmills here in the deep south and maybe elsewhere might also fill someones needs. These utilize a rear end (from a lawn mower size to a truck size) as a winch or clutch. These utilize the property of a differential whereby the braking of one axle while rotating the differential assembly causes the other axle to rotate. Usually a winch drum is bolted to one axle and the other end is braked/controlled with the original brake mechanism. Often one and sometimes both axles are shortened.

                  My appologies if the later portion of my reply highjacked your topic. This was not my intention.

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                  • #10
                    I've had several old Case tractors with hand clutches & loved them. You could be off the tractor while it was in gear & nudge the clutch to move as little as you like without climbing back on. Get a drawing of that & I think you'll like it! JMHO
                    "Let me recommend the best medicine in the
                    world: a long journey, at a mild season, through a pleasant
                    country, in easy stages."
                    ~ James Madison

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                    • #11
                      Looks very similar to the clutch on my JD 312 lawn tractor. As I recall, the friction facings look like custom facings of typical material.

                      Cone clutches are also found on some older small drilling rigs from GEFCO. The cone is activated by an air cylinder.
                      Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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                      • #12
                        Here is another clutch.



                        This one uses a bullet shaped cam to spread two spring steel friction shoes against the inside of the driven pulley. It is part of the drive set up for my old line shaft lathe.
                        Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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                        • #13
                          It may not meet all your requirements, but one of the cheapest "clutches" that has a soft start is an automotive differential with one working brake.

                          Not only can this arrangement achieve the entire range of soft-hard starts, prolonged slipping usually has no detrimental effect.

                          Dave

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                          • #14
                            Hi Brian, the clutch that you have sketched up should work faithfully. In my younger years we had a gas powered tugger that had a 3000# line pull with a cone clutch that was activated with about a 3'-0 lever and cam. You could ease the drum into motion so slowly that the cable would just inch along,but the motor would stall before the clutch slipped. The motor was a four cylinder Wisconsin, not sure what the horsepower was, but it was quite large. The clutch was simply made of wood with a material like a brake shoe making contact with a steel cone. Should be very easy to make for a man with your capabilities. Jim

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                            • #15
                              Brian, if you intend to try this with local hardwood, see if you can get either dry sugar, (not red,) maple or hop hornbeam, aka "ironwood." Most of our hardwoods are not really suitable for these kinds of compression and friction loads. You might also try persimmon, (look for an old driver.) If you opt for exotics, a lot of them are oily, (ebony, most rosewoods, blackwood, lignum vitea,) and may tend to crack. I have some East African olive which would work well. It is dense, fine grain, not oily, but the postage will kill you!
                              Duffy, Gatineau, Quebec

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