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  • Gearcutting 101...

    Hi all,

    i need to cut some large gears in cast iron, max dia is 495.30mm with 76 teeth in 4DP, the rings are all about 25mm thick.

    Rather than send them out, i want to do them myself. I have now equipeed the shop with an Adcock & Shipley 2E horizontal mill onto which i can mount my 12" rotary table. I have some cutters coming in the correct ranges for each teeth set.

    I know about bracing the wheel under the cut and centering the cutter on the table axis, also keeping the arbor support as close as possible to the action, obviously the cut will be made by lifting the knee.

    What i need to know is, how do i work out how many passes to take for each tooth and what speed to use - is it the same as ordinary milling?

    I'll also have to make or find some dividing plates to fit this table, it currently only has a direct degree scale plus a vernier scale reading to minutes and seconds.

    Any help is much appreciated as always.
    Dave
    If it does'nt fit, hit it.
    https://ddmetalproducts.co.uk
    http://www.davekearley.co.uk

  • #2
    I'm no gear cutting expert ..
    but just thinking about the 76 teeth and winding the knee up and down ,..probably four times 76

    makes me break out in a sweat

    spinach anmd popeye come to mind .


    all the best.markj
    Last edited by aboard_epsilon; 07-11-2009, 08:52 AM.

    Comment


    • #3
      Originally posted by Davek0974
      Hi all,

      i need to cut some large gears in cast iron, max dia is 495.30mm with 76 teeth in 4DP, the rings are all about 25mm thick.

      Rather than send them out, i want to do them myself. I have now equipeed the shop with an Adcock & Shipley 2E horizontal mill onto which i can mount my 12" rotary table. I have some cutters coming in the correct ranges for each teeth set.

      I know about bracing the wheel under the cut and centering the cutter on the table axis, also keeping the arbor support as close as possible to the action, obviously the cut will be made by lifting the knee.

      What i need to know is, how do i work out how many passes to take for each tooth and what speed to use - is it the same as ordinary milling?

      I'll also have to make or find some dividing plates to fit this table, it currently only has a direct degree scale plus a vernier scale reading to minutes and seconds.

      Any help is much appreciated as always.
      Dave
      When doing that big flywheel ring gear I did it with one pass per tooth, not a problem at 8DP. I'd guess that at 4dp you would be better with at least two passes, maybe making the first with a slot cutter. I did make a first run round taking off a few thou just to check the division setup was OK (I was using a stepper driven rotary table). Unless you have power feed to the knee, you'll have some good muscles in your arm by the time you finish!

      Tim

      Comment


      • #4
        I agree with the guys about the setup...... If u really have to use the rotary table build yourself an agle plate and mount the RT at 90 deg so u can use the table feed. I did a few 56 t gears recently and it was a long process even with the power feed!
        Is this a metric gear or imperial? if it's metric u need a mod gear cutter not a DP although if it's a slow run gear with adjustable clearance it will likely work fine. The formula for depth of cut escapes at the moment but when I bought my cutters it had the wd right on them.
        BTW what # cutter did you order I'm guessing a DP 4 #7?


        al
        Last edited by The Fixer; 07-11-2009, 10:02 AM.
        I spent most of my money on women and booze, the rest I just wasted.

        Comment


        • #5
          i never cut gear teeth before and i'm not understanding something in this setup. don't you just set the knee so the cutter makes the correct depth of cut and then run the table horizontally into the cutter for each tooth? i'm talking for a horizontal mill here. why would you need to raise the knee into the cut, and several times at that?

          andy b.
          The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

          Comment


          • #6
            Andy, he wants to use a rotary table not an indexing/dividing head....
            al
            I spent most of my money on women and booze, the rest I just wasted.

            Comment


            • #7
              Thanks all so far,

              Its a 4DP job, but i work in metric so the diameter is 495.30mm or 19.5". This ring with it's 76 teeth will require a No.2 cutter. The whole job will require No's 2, 3, 4 & 7 with teeth counts ranging from 15 to 76.

              Yes, i'm using a rotary table, i cant see any setup being more stable than a rotary table laying flat on the bed with a 19.5" ring on top, i would never want to attempt a peripheral cut on that ring with it standing up.

              BUT, now that you've mentioned it, i can see the merit of gashing the ring with a plain side / face cutter smaller than the tooth root and almost to depth first. This cut can be done using the table traverse, feeding into the cutter on center.

              The final cuts must be made by the knee or i will end up with concave teeth.

              So, presuming i have removed a fair chunk of iron from each tooth, would the shaping cut be possible in one pass?

              Thanks

              Dave
              If it does'nt fit, hit it.
              https://ddmetalproducts.co.uk
              http://www.davekearley.co.uk

              Comment


              • #8
                Originally posted by Davek0974
                Thanks all so far,

                Its a 4DP job, but i work in metric so the diameter is 495.30mm or 19.5". This ring with it's 76 teeth will require a No.2 cutter. The whole job will require No's 2, 3, 4 & 7 with teeth counts ranging from 15 to 76.

                Yes, i'm using a rotary table, i cant see any setup being more stable than a rotary table laying flat on the bed with a 19.5" ring on top, i would never want to attempt a peripheral cut on that ring with it standing up.

                BUT, now that you've mentioned it, i can see the merit of gashing the ring with a plain side / face cutter smaller than the tooth root and almost to depth first. This cut can be done using the table traverse, feeding into the cutter on center.

                The final cuts must be made by the knee or i will end up with concave teeth.

                So, presuming i have removed a fair chunk of iron from each tooth, would the shaping cut be possible in one pass?

                Thanks

                Dave
                If your wheel overhangs the edge of the rt, try to arrange a packing block between wheel and mill table. I used a block af Ali, with a shim to complete the gap which I slid in before each cut and out before turning the RT.

                I don't see why you shouldn't finish in one pass if the centre has been removed first, you'll have to suck it & see with the feed rate for a decent result without too much stress & strain.

                Tim

                Comment


                • #9
                  Yes, i'll definately give it some under-support near the cut.

                  I think the cutters are about 4-1/2" dia so i'm guessing about 100rpm?

                  Dave
                  If it does'nt fit, hit it.
                  https://ddmetalproducts.co.uk
                  http://www.davekearley.co.uk

                  Comment


                  • #10
                    can't most rotary tables be mounted vertically? wouldn't the force of cutting on the gear be the same moving the knee up and down as moving the mill table left and right? like i said, i never cut gears and i'm no machining expert.

                    if it was me, i'd somehow find a way to mount the gear vertically, but i'm stubborn (and sometimes lacking in common sense).

                    andy b.
                    The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

                    Comment


                    • #11
                      can't most rotary tables be mounted vertically? wouldn't the force of cutting on the gear be the same moving the knee up and down as moving the mill table left and right? like i said, i never cut gears and i'm no machining expert.

                      if it was me, i'd somehow find a way to mount the gear vertically, but i'm stubborn (and sometimes lacking in common sense).

                      andy b.

                      its the force required to lift the knee without cutting ..this is hard work in itself

                      you try it ..wind your knee up and down ..probably 5 inches or so that is required to take it in and out of the cut, then think about doing this 74 times ..that's just for the first cut, then you got the same for each and every tooth.

                      it will require perhaps one or two more passes after that .......so you could be winding it up 222 times ..and winding it down 222 times.

                      so you'd be lathered sweaty.......all this whilst trying to work out the sequence of dividing.

                      time to buy Tony's division master i think ..

                      all the best.markj

                      Comment


                      • #12
                        Vertical mounting is the weakest method of using a rotary, the problem will be worsened when you take a 12" table, stand it up and mount a 19-1/2" wheel on it

                        Cutting with the table horizontal sends all the forces straight into the knee.

                        The time taken is irrelevant, it won't matter if i only manage two or three teeth per evening, what matters is being able to say "I cut the gears" at the end.

                        Dave
                        If it does'nt fit, hit it.
                        https://ddmetalproducts.co.uk
                        http://www.davekearley.co.uk

                        Comment


                        • #13
                          Dave,
                          Instead of pre-gashing the teeth and wearing your arms out, what about pre-drilling on the Bridgy before transferring to the horizontal ?



                          Two holes, 6mm and 10mm will remove most of the meat for a final pass with the gear cutter.

                          .
                          .

                          Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



                          Comment


                          • #14
                            Originally posted by Davek0974
                            Vertical mounting is the weakest method of using a rotary, the problem will be worsened when you take a 12" table, stand it up and mount a 19-1/2" wheel on it


                            Dave
                            i missed that key part. yeah, i guess by the time you come up with a stack of metal to bolt the table and 20" gear to, that might be a bit unsteady. at least the gears aren't 4" thick so you don't have to move the knee up and down 6" per cut.

                            andy b.
                            The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

                            Comment


                            • #15
                              Thanks John, Andy, all,

                              i guess any method of pre-removal of waste is a good thing but i hadnt thought of drilling.

                              I'll choose which method when i get the mill cleaned up and installed, found most of the cutters i need, just one to get now.

                              Having finally realeased the last owners cutter from the long arbor, i find the key missing I guess it is just standard key material 1/4" x 1/4" in this case but should it be as long as the shaft or just a short bit?

                              The missing key explains why i had to use a 30" breaker bar on the arbor nut

                              Dave
                              If it does'nt fit, hit it.
                              https://ddmetalproducts.co.uk
                              http://www.davekearley.co.uk

                              Comment

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