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  • _ Idea: Off center arbor for making a gear cutter (drawing inside).

    Just recently i made a gear cutter and ground the relief for the trailing lands of the cutters with a dermal. While searching the net before making the cutter i seen a couple of different ways to create the relief along with having a couple ways suggested to me, but none of them seamed like an easy (set up for later use) and long term solution. Well... now an idea popped into my head and heres the start...

    An arbor with a straight shank which will be held in a three jaw chuck or a collet. The end of the arbor which the gear cutter blank will be locked to for turning and shaping will be offset. The face of the arbor will have a pin sticking out of it (green in drawing) and a cap (the cap will lock the gear blank to the arbor) that will have 'x' number of holes in it (for this i picked ten) which will correspond with the number of cutting edges the gear cutter will have. The cap will also have a square broached hole in it which a key (blue in drawing) will set it (fastened to the cap some how) which will lock/align the cutter blank.

    On the shank end of the arbor mill a small flat then make a sleeve with an off center bore (same off-set as the arbor) so you can use the same arbor in a dividing head to cut the cutting edges. Instead of using the dividing head to rotate the cutter blank, you would use the cap to rotate the blank just as done in the lathe.

    On paper im pretty sure this set-up could be used over and over again and there will be no need in using a four jaw chuck or drilling the cutter blank with holes or any other method except for making new caps for the different number of cutting edges you want. Just need to broach the cutter blank first and you could use this for any gear cutter blank you want.

    Any thoughts on if this will work, good idea, bad idea (gonna look for some scraps this week and see what i can come up with )???

    The off set here is a 1/16, i did not look into this yet, just concept right now.






    _
    ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
    http://site.thisisjusthowidoit.com
    https://www.youtube.com/user/thisisjusthowidoit

  • #2
    if i`m following you correctly -

    isn`t this pretty much(in concept) what sir John drew up for relieving cutters in his "making involute cutters" document?
    just trying to get my thick head around it.

    anyway, nice job on the gear you made.
    have you tried out the single tooth cutter on an offset arbor approach yet? it eliminates the need for releif entirely and is easily sharpened an infinate number of times just by touching up the face of the cutter.

    single tooth cutters on an offset arbor absolutely slay delrin and aluminum, works on steel and cast iron too but may take multiple passes per tooth.
    i love delrin gears- the idlers on both my lathes are delrin and they have stood up to everything while running smooth and almost silent.
    Last edited by 1200rpm; 06-10-2013, 02:14 PM. Reason: clarity

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    • #3
      An offset arbor works very well for grinding with relief. Any of the tool nd cutter grinder manuals will have info on how to set up with offset and a tooth stop to get a particular amount of clearance.

      I even had one application where the cutter was single flute and circular. The machine it ran on was a high speed router that had an offset mounting hole in the spindle and a tooth alignment guide to set up the cutter.

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      • #4
        Originally posted by 1200rpm View Post
        isn`t this pretty much(in concept) what sir John drew up for relieving cutters in his "making involute cutters" document?
        Not sure... while searching the net before making the current cutter i came across a site which seam to be aimed at a smaller lathe (it starts with a 'T', has a bit of a "cult" following, sorry im drawing a blank on the name right now) which had something simular (if that is his site, then yes ). The arbor used to cut the gear was off-set in the lathes chuck (four jaw or a "spacer" under a single jaw of a three jaw chuck) and a pin in the face of it, then the person would bore out the cutter blank and then drill three holes (i think, cant rember right now) in a circle and used them three holes to index the cutter blank.

        What i want to do is eliminate the need to drill the extra holes in the cuter blank (by drilling the indexing holes in the cap) and also eliminate the need to off-set the arbor each time its used (by cutting an off-set seat/hub on the face of the cutter (so when the arbor is used later, there is no need to off-set it, just pop it in a three jaw or collet and go)). It seams as long as the indexing pin is placed correctly (at the "high" of the off-center face) when you go to cut a new gear cutter later down the line there will be "next to no" set up, just bore and broach the cutter blank, toss the arbor in the chuck and your ready to form.

        Ill have to work on the drawing alittle more... what i posted here is mainly to get the idea on paper so i dont forget.



        Originally posted by 1200rpm View Post
        have you tried out the single tooth cutter on an offset arbor approach yet?
        No, ive only cut two gears, the current one posted here and another one a few years back which was pretty much a simple spur gear where the teeth where set at a small angle to match the helix angle of the thread on the lead screw of my little 3-in-1 machine (the gear was used for a thread dial i made). Right now i do not have a real mill and don't ever see that happening (at least not a full size knee mill, a larger bench top mill/drill more then likely) so for now the gear cutter will be used in the 3-in-1 machine and that thing is not too power-full or ridged so the more cutters the easier things go



        Thanks for the heads up on checking a Tool and Grinding manual, Jpfalt, there might be one laying around the place i work at.

        _
        ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
        http://site.thisisjusthowidoit.com
        https://www.youtube.com/user/thisisjusthowidoit

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        • #5
          The offset idea works. I've seen similar ideas in old books. You just need all the teeth cut on identical circular reliefs, so that when you grind the faces, the edges stay in the same relationship to one another. The fixture needs to be made very accurately to hold that.

          I've cut gears with single tooth cutters, shop made, and I've cut gears with multi tooth cutters. I know which one is faster and less nerve wracking, not to mention less likely to knock the setup out of alignment.
          Last edited by J Tiers; 06-11-2013, 09:24 AM.
          1601

          Keep eye on ball.
          Hashim Khan

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          • #6
            Originally posted by J Tiers View Post
            .... You just need all the teeth cut on identical circular reliefs, so that when you grind the faces, the edges stay in the same relationship to one another.....
            Is what im thinking... after making the arbor is to make an off-center sleeve (same off-set as the arbor), Mill a flat on the arbors shank which will be used to lock the sleeve on to (now the off-center sleeve and the off-center face/hub are concentric with each other), then chuck on the sleeve (with the arbor locked inside of it) and mill two flats on the arbor, one on the top and one on the side, these two flats will be used for future alignment (to get the chucking rotation correctly for the relationship you mentioned). Since the gear cutter blank will be broached before hand, the blank will be consistently mounted on the arbor via the 'key' in the arbors cap, so remounting later down the line to resharpen should not be a big deal. What im hoping/trying to do is invest all the accurately and tedious time and work into the arbor so down the line its easy and fast to use. You would just grab the thing out of your box, pop it in the lathe and your done... move it over to a mill, quick and easy aliment with an indicator on the flats of the arbor and your done.
            ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
            http://site.thisisjusthowidoit.com
            https://www.youtube.com/user/thisisjusthowidoit

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            • #7
              my cutters have all been the single tooth on offset arbor type- which is great for delrin but can be time consuming on steels and such.

              I`d like to try making a multi-tooth cutter sometime and your plan seems like a great way to go about it.
              if you go through with it, please post!

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              • #8
                If you examine the action of an actual cutter relief unit for a lathe, you will find that the offset is exactly what it does. To that basic concept it adds indexing from one tooth to another, and automatic action, but in essence it is doing an offset cut just as you say.
                1601

                Keep eye on ball.
                Hashim Khan

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                • #9
                  yes, i want to say Marv Klotz?? has on his site the formula for setting the proper ammount of offset to achieve the correct relief.

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                  • #10
                    I sent this link to someone's website last night in reference to this. Don't remember who though.
                    This was posted a while ago and is not my idea.
                    It is picture heavy, but that is a very good thing.
                    http://www.deansphotographica.com/ma...ultipoint.html

                    I believe it is the same idea and allows you to regrind the teeth with the same tool so you do not lose the relief.
                    Last edited by mc_n_g; 06-12-2013, 10:33 PM. Reason: add more

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                    • #11
                      I played with this idea a bit using my CAD program. One of my questions was just how many teeth could you produce on a cutter using this technique. I read John's writeup and in it he did just three teeth. That seemed to work easily. So I first tried four. Here is my CAD study showing the various steps involved and some considerations:



                      This study shows several things. First, it follows a generalized procedure that will work for any number of teeth. I choose four teeth for this study so I first divided the circle into four equal segments with two diagonal lines. In step 1 I add an arc of larger radius. I placed the ends of this arc on the ends or two adjacent diagonals so it subtends 90 degrees or 1/4 of the original circle. The center of this arc is shown by the small cross in the lower, left quadrant. The diameter of the arc and therefore the clearance angle can be adjusted by moving this center.

                      In step 2 I have copied that single arc to all four quadrants. This gives us a near circular figure with four lobes.

                      In step 3 I drew a second arc that has the same center as the original circle so it is on the axis of rotation of the final cutter. This arc intersects the 45 degree diagonal where it meets the arc drawn in step 1. It should be obvious that these two arcs are tangent at this point and that means that if a tooth were ground at that point, it would have zero clearance angle. In fact, it would have a negative effective clearance because the step 1 arc goes up from the cutter's center from that point onward. This, in theory, is the last point where you could resharpen the cutter and in fact, you would have to stop well short of there in actual practice.

                      In step 4 I have filled in the flutes with a shape that would be fairly easy to cut with a milling cutter (with a rounded edge). So far the steps show turning operations in the lathe and milling operations.

                      In step 5 I show the sharpening of each tooth with an abrasive wheel. A cup wheel would be best to reach the bottom of the face of the teeth. In it I add the rake angle of 5 degrees. This can be accomplished with standard grinding techniques.

                      And that completes the creation of a four tooth milling cutter with clearance on each tooth. It can be sharpened by grinding only the face of each tooth so whatever profile (like a gear tooth) that is given to it in steps 1 and 2 will be preserved for it's entire life.

                      At step 6 I have added two short lines to allow me to measure the clearance angle on the drawing. My dimensions were:

                      Cutter OD = 2"
                      Offset of center of larger arc = 0.283"

                      With those numbers I got about a 10 degree clearance angle. I am sure that with a little work I can develop a formula that will give me the necessary offset for any desired clearance angle. Or at least, for any reasonable one.

                      If you look further at step 3 you can see that the clearance angle rapidly reduces from the original point of the tooth as it is resharpened towards the bisector. On each resharpening the clearance angle is reduced. In fact, due to the rapidity of this reduction, a rather large initial clearance, like 10 degrees, may be desirable. For practical reasons, I would estimate that resharpening would stop about half way through the original tooth depth. This may vary for different designs and numbers of teeth, but it seems to be a common feature for cutters of this design.

                      I said that I wanted to know if this procedure could produce a cutter with any number of teeth. From the above and John's work, it is obvious that three and four teeth are easily possible. Mathematically/theoretically the method will work for any number of teeth. Each of the above steps can be generalized for any number of teeth. However, at some point when you add more teeth, it will become difficult to get any real clearance with a larger arc of a practical radius. If you are making a gear cutter, this radius would presumably be cut on a lathe and every lathe has a limited swing. Substituting a straight line (an arc of infinite radius) for that arc could extend this number of teeth somewhat, but even that will rapidly fall short as the number of teeth increases. And, with a straight line, you will loose the ability to turn the desired profile in a lathe. Perhaps it could be cut in a scraper. I suspect that 8 to 12 teeth may be the practical limit. And the more teeth you make, the fewer the number of times you will be able to resharpen it.

                      All in all, this appears to be an excellent way to make a milling cutter in a small or home shop.
                      Last edited by Paul Alciatore; 10-16-2019, 06:08 PM.
                      Paul A.

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

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                      • #12
                        Originally posted by mc_n_g View Post
                        I sent this link to someone's website last night in reference to this. Don't remember who though.
                        This was posted a while ago and is not my idea.
                        It is picture heavy, but that is a very good thing.
                        http://www.deansphotographica.com/ma...ultipoint.html

                        I believe it is the same idea and allows you to regrind the teeth with the same tool so you do not lose the relief.
                        That was me, thank you.
                        The site you sent is the one i tried to mention earyler in the post, i couldnt find or remember it (Taig was the name of the lathe...). Thanks.
                        I would like to make something so there is no need in drilling the holes in the cutter blank (or having a second fixture to mill the flats or resharpen (which im pretty sure he did not need..))

                        Thanks alot Paul for your step by step with CAD... last night i tried drawing it up and just confused myself. I was trying a 10 tooth cutter, drew a 2" circle then played around with drawing 10 point polygons using the points as reference like you did in your step 2, but i was drawing full circles which those points being the center and it just look like a bunch of circle on paper... very hard to distinguish cutting tips and relief..
                        Guess i need to work on my basic CAD skills a whole lot more.

                        Today i tried to "wing it" on the lathe (trying to find the "right" off-set for an eight tooth cutter) and did the following.

                        1) Grabbed a piece of 2" stock and roughly scribed 8 lines on it (looking to test an 8 tooth cutter).
                        2) Chuck it up in a four jaw chuck, off-setting both jaws one and two by .175 on the indicator.
                        3) "Leveled" out the chuck and then aligned a scribed line with the tip of the tool cutter.
                        4) Spun it and brought the tool in till it just kissed the "highest" OD of the part
                        5) Took a .025 DOC (.05 off the diameter) cut
                        6) Magic markered the part
                        7) Indexed the stock, repeated step 3 and took another cut, did that 7 times

                        In the end there is about .625 between each high point on the stock and i have no idea what degree the relief is.

                        This is all really really rough... i just needed to see something tangible.
                        By this test, i would think if you where to off-set it any more you would loose more distance between the high points (using 2" stock) and with less of an off-set you would be loosing more relief. Even if you where to cut the teeth with a 1/4" end mill (horizontally (like Paul's step 5) not vertically your not leaving much to resharpen later or strength to the cutters tooth). Gonna try different size stock (bigger) and maybe a 6 tooth cutter along with offsetting it farther in one direction then the other (EG: jaw one .175 and jaw two .225).

                        Aligning - indexing (always putting the protractor on the same jaw)



                        Magic markering stock (on the top) before a cut:



                        Took a cut and now marking a line on the face where the marker was cut off



                        Test done
                        ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
                        http://site.thisisjusthowidoit.com
                        https://www.youtube.com/user/thisisjusthowidoit

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                        • #13
                          .
                          Starting to give it a shot... the sleeve is complete and the arbor is just about done. Only thing left for the arbor is to drill/ream a .187 hole in the face of the hub for an indexing pin. After that a cap will need to be made with a hole for a piece of key stock along with a hole pattern to index the cutter blank.

                          Heres alittle more info on whats been done so far...






                          The sleeve and the arbors shank are both threaded. Slide the sleeve on and then thread the bolt into both to pin them together.









                          Last edited by iMisspell; 06-23-2013, 12:27 AM. Reason: edited link back to my site
                          ~ What was once an Opinion, became a Fact, to be later proven Wrong ~
                          http://site.thisisjusthowidoit.com
                          https://www.youtube.com/user/thisisjusthowidoit

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                          • #15
                            And for the truly ambitious:

                            http://www.youtube.com/watch?v=kJ8kyC_bpHs

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