cutting spur gears on a mill

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cutting spur gears on a mill

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  • #563802
    brian jones 11
    Participant
      @brianjones11

      Who invented the helicoil insert – life saver for my Lambretta with a stripped spark plug hole?

      Obviously someone thinking out of the boxlaugh

      Now this rack thing needs more work

      I could tilt Doreens pretty little head thru 90deg but this would mean a 1 ft diameter cutting tool – NOT

      Does anyone know of a horizontal mill that rotates on the X axis rather than the normal Y axis?

      I have joined the Gearheads corner with the gearotic 3 installed – lovely little app free but you have to pay $129 one time for a manufacturing licence – which is probably reasonable if that floats your boat and you need CAM files

      You will be pleased to know I have already found faults with their Low PA forms but they welcome eccentric gear designs

      You probably know about them already

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      #563805
      brian jones 11
      Participant
        @brianjones11

        Now here's a silly question from SBP

        How are gear teeth made with an undercut root?

        The SCR CNC wallahs need not stir from comfy chairs

        This is strictly old school

        AFAIK it could only be done by shaping after roughing out?dont know

        OMG you gotta see this

        Edited By brian jones 11 on 21/09/2021 23:50:13

        #563812
        Michael Gilligan
        Participant
          @michaelgilligan61133
          Posted by brian jones 11 on 21/09/2021 23:16:34:

          .

          How are gear teeth made with an undercut root?

          .

          See here for various options: **LINK**

          Undercut of gears

          MichaelG.

          [ currently in bed ]

          #563814
          brian jones 11
          Participant
            @brianjones11

            Thats fantastic MG

            those animations are what I have been looking for. explains it all

            This should be a sticky for all young shavers to understand gears

            profile shifting has really done my head in

            #563817
            JasonB
            Moderator
              @jasonb
              Posted by brian jones 11 on 21/09/2021 23:16:34:

              Now here's a silly question from SBP

              How are gear teeth made with an undercut root?

              Already answered by Andrew yesterday:

              " In theory it should be able to cut small numbers of teeth as well. The undercut arises automatically. In some of the 1930s books I've got on gear cutting there are formulae for calculating whether a hob will undercut or not, even when not needed"

              This is how the Sunderland machines do it and what is suggested for the CNC method being discussed except a round rack form cutter will be used instead of a flat shaper type cutter as it is easier for a hobby user to make.

              Not sure what you are trying to do with your head on it's side and a large dia cutter? Can't you tilt the work

              #563818
              Dave S
              Participant
                @daves59043

                The undercut is an unfortunate artefact of the process of making an involute gear. It limits the strength of the root of the tooth, which can be a bit of an issue. Profile shifting just uses a different part of the involute curve, and so can avoid the undercut. It’s trivial to do in practice – using the same rack form cutter you just move it out a bit (simplification but essentially the process)

                I have made some 12 tooth pinions without undercutting by doing just that and they roll against the 144,96 and 90 tooth gears made with the exact same cutter perfectly.

                Dave

                #563823
                brian jones 11
                Participant
                  @brianjones11

                  Not sure what you are trying to do with your head on it's side and a large dia cutter? Can't you tilt the work

                  Think of it as a metal saw

                  goto 10.00 to see action

                  Dave S

                  Is profile shifting  the same as changing the PA? ie

                   

                  Edited By brian jones 11 on 22/09/2021 08:00:03

                  Edited By brian jones 11 on 22/09/2021 08:00:46

                  #563826
                  Dave S
                  Participant
                    @daves59043

                    Not really. Design pressure angle stays the same – hence the gear can be cut wit the same cutter, and mesh with gears cut with that same cutter. I believe the actual pressure angle where the teeth meet changes, as a result of being at a different point in the curve.

                    Read here: Gear Profile Shift | KHK Gears for an explanation of profile shifting. It is fairly common in industry to match the tooth form to the required result.

                    Edit to add: Introduction to Gears | KHK Gears is a fairly good primer on all things gear related.

                    Dave

                    Edited By Dave S on 22/09/2021 08:10:33

                    #563829
                    Martin Connelly
                    Participant
                      @martinconnelly55370

                      I think trying to use free hobbing for a quick way of making gears is going to be a case of more haste less speed because of the crap it will produce trying to get a usable end result with desirable features. You will soon get to the point where value for money (and time) makes it a waste of time. There is a reason that after the centuries of people making gears it has never been a major method of production. this thread is a reflection of this and should be closed as trying to explain the problems to the OP is best described as flogging a dead horse.

                      Martin C

                      #563837
                      John Haine
                      Participant
                        @johnhaine32865

                        On the PA / undercut question, Mike Cox has published tables for the button method of making involute cutters, and can supply the background spreadsheet. One can insert the pressure angle as a parameter in these. For clocks in the motion work (driving the hands) one can use involute just as well as cycloidal gears (in the train too probably) but it is nice to be able to use small pinion tooth counts (8 or fewer). One can use the spreadsheet to explore how the pressure angle affects the undercut, and use goal-seek to find a PA which gives no undercut. If you are making both gears, and where there is minimal torque, this can be quite a good option.

                        #563839
                        brian jones 11
                        Participant
                          @brianjones11

                          Kind of missing the point here MC

                          this thread has opened up a treasure chest of valuable insights from experienced members sharing their knowledge

                          The noob to this complex sphere has to battle through all manner of rubbish from google and YT

                          For example there is the self style expert on Gears sponsored by AGMA

                          Browse the Fundamental Laws of gearing at the beginning and you will get the picture

                          I do appreciate the Japanese link from Dave S

                          https://khkgears.net/new/gear_knowledge/introduction_to_gears/

                          OBTW

                          I did produce a perfectly serviceable plastic gear for modellers with light duty use in mind. Might work even better in Delrin. If it helps some modeller knock something up quickly then maybe it has a use despite the sceptics

                          img_0760.jpg

                          OBTW its a pity we cant rate these posts because some of them really are 5* solid gold

                          You cant make an omlette without breaking eggsdevil 

                          Edited By brian jones 11 on 22/09/2021 09:30:39

                          #563841
                          Martin Kyte
                          Participant
                            @martinkyte99762
                            Posted by Dave S on 22/09/2021 07:20:18:

                            The undercut is an unfortunate artefact of the process of making an involute gear.

                            I have made some 12 tooth pinions without undercutting by doing just that and they roll against the 144,96 and 90 tooth gears made with the exact same cutter perfectly.

                            Dave

                            Are you sure about that.? With low pinion counts undercutting provides clearance for the tip of the mating gear on the tooth exiting engagement. 12 tooth pinions and wheel counts of 90 96 and 144 sounds like clock wheels to me. I'm sure they can be made to work as you say but only by decreasing the engagemant. When a rack (or a hob) is used to generate an involute form it must of neccessity create the clearence it requires and with low tooth counts teeth are undercut.

                            regards Martin

                            #563849
                            Dave S
                            Participant
                              @daves59043

                              Yes it’s a clock, and no I’m not sure.

                              These are the first gears I’ve ever cut, and I suspect that I should have profile shifted the wheels the opposite way to thin the teeth.

                              Still it’s all learning, and if they are depthed ok then they mesh ok – even if it’s not quite correct…

                              Will do better next time

                              Dave

                              #563850
                              brian jones 11
                              Participant
                                @brianjones11
                                #563854
                                Martin Kyte
                                Participant
                                  @martinkyte99762
                                  Posted by Dave S on 22/09/2021 11:00:41:

                                  Yes it’s a clock, and no I’m not sure.

                                  These are the first gears I’ve ever cut, and I suspect that I should have profile shifted the wheels the opposite way to thin the teeth.

                                  Still it’s all learning, and if they are depthed ok then they mesh ok – even if it’s not quite correct…

                                  Will do better next time

                                  Dave

                                  No need to appologise, for many clock making situations tooth form will not matter a jot. Personally I like to use Thornton cutters and do use pinion cutters for pinions. Firstly because its easy and secondly I like the traditional cycloid tooth shape and flat bottom. I remember Alec Price lecturing on making clockwheel cutters and pointing out that old clocks had a variety of tooth profiles all made with shop made cutters and they all worked for many years successfully. If you are doing challenging horology like making watches or year going clocks then optimisation of friction really starts to matter otherwise so ling as you depth properly which basically means gettin each pair to run sweetly then you won't have too many issues. Swiss standards are more about allowing mass manufacture to function with interchangeble parts than anything else.

                                  regards Martin

                                  #563861
                                  Dave S
                                  Participant
                                    @daves59043

                                    I’ve gone involute for the clock because I wanted to explore the use of the “rotary Sunderland rack method” as a way to make gears.
                                    That plus many naysayers telling me that a clock couldn’t possibly work with involute gearing as it’s not possible to gear up with involutes… I’m not sure how the gear knows

                                    Dave

                                    #563866
                                    Martin Kyte
                                    Participant
                                      @martinkyte99762
                                      Posted by Dave S on 22/09/2021 12:18:27:

                                      I’ve gone involute for the clock because I wanted to explore the use of the “rotary Sunderland rack method” as a way to make gears.
                                      That plus many naysayers telling me that a clock couldn’t possibly work with involute gearing as it’s not possible to gear up with involutes… I’m not sure how the gear knows

                                      Dave

                                      Fair enough. but as far as "how the gear knows" the system will see whatever frictional forces and wedging actions are inhearent in the design. Involutes work fine on large clocks especially where there is heaps of power. Cast Iron gearing is happy in tower clocks especially at the opposite end to the escapement and you don't immidiately think of cast iron beaing a clockmaking material. No ideal for chronometers though ;O)

                                      regards Martin

                                      #563903
                                      duncan webster 1
                                      Participant
                                        @duncanwebster1

                                        I think this shows that involute is perfectly good for clocks, in fact better fuse. After all, a fuse is a clock that goes bang at the end of its set time

                                        #563940
                                        brian jones 11
                                        Participant
                                          @brianjones11
                                          #563947
                                          Michael Gilligan
                                          Participant
                                            @michaelgilligan61133

                                            That’s a good link **LINK** well found, Brian

                                            Have you considered the three ‘conditions’ listed at 175 on p119 ?

                                            Surely the spur gears you are producing would fail on all counts dont know

                                            MichaelG.

                                            #563950
                                            Martin Connelly
                                            Participant
                                              @martinconnelly55370

                                              The ancient Egyptians had armchairs.

                                              Martin C

                                              #563969
                                              SillyOldDuffer
                                              Moderator
                                                @sillyoldduffer
                                                Posted by brian jones 11 on 23/09/2021 04:08:55:

                                                In 1890 they knew a thing or two and armchairs hadnt been invented

                                                https://books.google.co.uk/books?id=dyYJAAAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

                                                I see not having an Armchair has let Brian down again. Having found a copy of the most excellent Grossman's Lessons in Horogogy, he hasn't read it! The Grossmans, father and son, were scientists. They say:

                                                grossmanquote.jpg

                                                Note the bit about the practical workman faithfully following 'the principles' in the execution of his work!

                                                Armchairs as tools are valuable at the design stage and when things go wrong. Not necessary for repetitive work or following instructions. Interpreting a good drawing is quite easy; bad drawings stretch the poor old brain, which might need help from strong coffee or this forum!

                                                Actually, the armchair isn't the best thinking tool available. I prefer a comfy office chair in front of a well-lit desk equipped with a computer, notebooks and pencils. At first the computer is used as a support tool rather than a thinking aid: they're good for reference; calculations; formal write-ups, and exchangeing ideas with friends etc. I learn best on paper taking notes from printed textbooks and start designs with rough pencil drawings rather than going straight to CAD. The computer is good later on at formalising and validating ideas, often exposing mistakes and allowing them to be corrected without too much aggravation.

                                                Some problems are best thought out whilst walking, and I occasionally wake up with answers, presumably having processed them subconsciously overnight whilst asleep or doing something else entirely: like free-hobbing the 'not thinking about it' method can't be relied on though!

                                                Going back to free-hobbing, a single gear, no matter how good looking, is useless. The acid test is making two or more gears that mesh together between designed centres. Free-hobbing struggles to do this and understanding why free-hobbing fails is an armchair job. No need to read Grossman, most shortcomings have been covered in this thread.

                                                While free-hobbing isn't good engineering, Brian is congratulated for flushing out other methods of making gears. A thread that gets over 240 replies and 12000+ reads can't be all bad!

                                                smiley

                                                Dave

                                                 

                                                Edited By SillyOldDuffer on 23/09/2021 10:52:30

                                                #563970
                                                brian jones 11
                                                Participant
                                                  @brianjones11

                                                  The full credit must go to Duncan Webster above for his "Fuse" link and his fascinating tale of bigotry by AGMA (my instincts were right about the mafia)

                                                  Its a book for the armchair Kobo, you can down load EPUB

                                                  Horologists OMG have they got their own closet on this board somewhere? I cant imagine their x30 world and desktop lathes and they wouldnt countenance free hobbing

                                                  I need a man's lathe

                                                  notice elf n safety – he should be in a boiler suit, not a flappy shop coat.

                                                  OBTW SOD

                                                  sometimes I feel its whack-a-mole time

                                                  12000 views have we gone viral – like Covid?

                                                  Certainly given the fustian Mew Board a throgging

                                                  Edited By brian jones 11 on 23/09/2021 11:07:30

                                                  Edited By brian jones 11 on 23/09/2021 11:11:38

                                                  #563975
                                                  Anonymous
                                                    Posted by SillyOldDuffer on 23/09/2021 10:50:07:
                                                    A thread that gets over 240 replies and 12000+ reads can't be all bad!

                                                    Don't confuse quantity with quality. smile

                                                    Andrew

                                                    #563978
                                                    Howard Lewis
                                                    Participant
                                                      @howardlewis46836

                                                      If involute gears cannot be used to increase speeds, someone ought to tell the manufacturers of gearboxes with overdrive top gears! And probably of Norton gearboxes for lathes

                                                      They have been getting wrong for YEARS!

                                                      Howard

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