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  • Coupling, How would you build it?

    A friend needed two couplings out of steel. The couplings join an electric motor to a hydraulic motor. OUtside diameter of the coupling is 40mm. Overall length 60mm. One bore is 25mm diameter 40mm long with a 8mm keyway. The other end is a 20mm diameter bore 20mm long with a 6mm keyway.

    I made one. The difficult part was cutting the 8mm keyway in the 25mm bore that butts up to the 20mm bore. So a shoulder 2.5mm to deal with. I milled a slot 10mm wide 13mm long at the shoulder for the shaper tool relief.

    My problem was the stick out of the HSS cutter 7.5mm for the 8mm slot. I broke two cutters. If I had too much positive relief on the face of the cutter it would dig in if I took anything over a few thousandths of a depth of cut. With no relief I got lots of chatter. The shaft holding the cutter was 18mm diameter. The clapp box was locked down.

    I thought about trying to cut the second one backwards, meaning start the cut in the slot and push out the back end. Or cut the slot backwards with the cut on the return stroke.

    How would you all make this part and how would you grind your cutter? My shaper is quite heavy duty with 24" travel on the ram and it weighs 800 Kilos I think. Not sure about the weight. In the 3D model I don't have the slot modeled.

    Last edited by Black Forest; 03-16-2016, 11:54 AM.
    Location: The Black Forest in Germany

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

  • #2
    Personally I would look for Love joy brand couplers, either proper size or modify to fit.

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    • #3
      Originally posted by metalbender View Post
      Personally I would look for Love joy brand couplers, either proper size or modify to fit.
      There is no room for a LoveJoy type coupler.
      Location: The Black Forest in Germany

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

      Comment


      • #4
        I'd be tempted to try making the smaller diameter coupling a separate piece that is pressed (or otherwise fastened) into the larger outer coupling. That would at least allow to you to cut keyways completely through both parts, so that keyway cutting is no longer your headache. Depending on the tooling at your disposal, it seems like machining that outside profile of the inner coupling would be less of a headache.
        Max
        http://joyofprecision.com/

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        • #5
          B F,

          Back rake 15 - 20 Deg. Front rake or clearance 1 - 3 deg. Side clearance 3 deg. Cut the 6mm slot first all the way through the coupling then widen the 8 mm slot. Depth of cut .01 to .02 mm

          Bob

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          • #6
            Rotate the 6mm keyway 90 degrees and then you can cut both all the way through.

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            • #7
              I like elf's idea!

              If, for some reason, you need the keyways to be aligned like your drawing shows, then I thought of a variation of my idea that doesn't involve trying to machine a difficult outer profile on the inner piece. Rather than try to use words, here's a quick sketchup I did:

              Max
              http://joyofprecision.com/

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              • #8
                Originally posted by elf View Post
                Rotate the 6mm keyway 90 degrees and then you can cut both all the way through.
                Yes that would be my preferred method. If absolutely necessary you could then loctite a bit of key in the smaller bore and turn it down if cosmetics are important.

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                • #9
                  My first thought is your bore sizes tell me we are talking about multi-HP motors. 3HP? 5HP? That makes me wonder about the square edges between the two diameters. A tapered section, with a round fillet would be much better. At least add a fillet to that internal, square angle.

                  I like the idea of offsetting the keyways, that would make the overall part stronger. But I would not cut the 8mm one all the way through. That will weaken the coupling. I would go a bit into the smaller end but not all the way through. A hole drilled at the end of that keyway would provide a place for the chips to go while cutting and would not weaken it as much as a full length keyway will.

                  I hope your customer realizes that this non-flexible coupling will be hard on the motors' bearings unless they are aligned almost perfectly. I would use some kind of flexible coupling. And any misalignment will produce a cyclic, once per revolution, stress on that middle point of the coupling which will tend to produce stress cracks at that sharp edge between the two bores. I would not be at all surprised to see this coupling come apart at that point. This part needs to be beefy (large OD).
                  Paul A.
                  SE Texas

                  Make it fit.
                  You can't win and there IS a penalty for trying!

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                  • #10
                    Mr.Alciatore raises very good points.
                    I would make two parts, each with their respective keys, and threaded holes for setscrews.
                    The interface of each would have two projections @ 180 and two notches 180 apart but 90 from the projections.
                    Leave clearance between the tang/slot. Assemble w/ high durometer urethane caulk.

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                    • #11
                      Originally posted by Black Forest View Post
                      A friend needed two couplings out of steel. The couplings join an electric motor to a hydraulic motor. OUtside diameter of the coupling is 40mm. Overall length 60mm. One bore is 25mm diameter 40mm long with a 8mm keyway. The other end is a 20mm diameter bore 20mm long with a 6mm keyway.

                      I made one. The difficult part was cutting the 8mm keyway in the 25mm bore that butts up to the 20mm bore. So a shoulder 2.5mm to deal with. I milled a slot 10mm wide 13mm long at the shoulder for the shaper tool relief.

                      My problem was the stick out of the HSS cutter 7.5mm for the 8mm slot. I broke two cutters. If I had too much positive relief on the face of the cutter it would dig in if I took anything over a few thousandths of a depth of cut. With no relief I got lots of chatter. The shaft holding the cutter was 18mm diameter. The clapp box was locked down.
                      Relief or rake?

                      You ALWAYS need relief or you can't cut anything, the tool just rubs. Rake is the angle that commonly causes dig in.

                      I would consider finding rectangular HSS to provide more tool rigidity for the same width.

                      Also make sure its sharp, and consider that lots of carbide tooling goes through steel just fine with *negative* rake. So don't worry if positive rake is not working for you. (Although that suggests a great lack of rigidity somewhere that it digs in so badly), you still have more options.

                      Yes, negative rake can still be sharp.

                      Also, How much does it matter if there is chatter? Yea its not great for the machine or tool, but I have done a number of jobs where the machine/work just sings (Sometimes fixable by applying weights, or pressing a rag or something.. Wrapping lead around the tool is an old timer trick to dampen vibrations)

                      Iv heard thin wall aluminum tubing just RING so loud I needed ear protection.. or to touch the tube with my finger ever so lightly while cutting it.

                      Sometimes, you need a good finish, Other times its a keyway that is going to be hidden by a key from every ones eyes and could easily be filed out to +- 0.01" with a poor surface finish and not matter. (Though most people can file a keyway much more accurate then that with a little test fitting!)

                      Also, You could consider using a narrower tool and side steping to reduce load on machine (less likely to chatter)

                      Large amounts of tool cutting edge in contact with the work basically guarantees chatter.
                      Last edited by Black_Moons; 03-16-2016, 03:35 PM.
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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                      • #12
                        Like Paul suggested, drill a hole at the end of of the 25mm bore, to give the tool somewhere to start. Then lock down the clapper box and cut on the draw stroke. That would work just fine on my little 24" planer, so your 24" shaper should have no trouble at all.
                        'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

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                        • #13
                          A bit of a hack, but could you mill a slot where the large keyway is supposed to go and then braze a bushing over it to get the original diameter back?

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                          • #14
                            Black Forest: I had a similar job a few years ago. I needed to cut a key in a blind hole. I drilled two small holes where the key would clean up the holes and the holes were just about a 1/16th deeper than the key needed to be. I also tilted the angle of the holes slightly so that where the key ended, there wasn't hardly any metal . This key was cut in the shaper . I hope this makes a bit of sense. It worked well.

                            Sarge

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                            • #15
                              The drawing shows the key ways meeting, I would rotate them 180 degrees apart and run them right through.
                              Easier as you can then broach them or shape them as clear cuts instead of blind keys, much more difficult
                              Mark

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