How to make a large ring gear?

Advert

How to make a large ring gear?

Home Forums Workshop Techniques How to make a large ring gear?

Viewing 15 posts - 1 through 15 (of 15 total)
  • Author
    Posts
  • #332243
    Rainbows
    Participant
      @rainbows

      I want to add a gearbox within the flat belt pulley on the spindle of my Denbigh mill. At the moment the hang up is how to make a MOD 4 38 tooth ring gear.

      Im going to make a prototype on my 3D printer to check everything will work on the mill but with a worst case scenario of 1.5KW at 50 RPM I don't trust PLA much.

      Can anyone recommend a way to build the gear? Tools I have are a lathe, mill and 3d printer. My current thought is using the printer to make a mould for some sort of plastic or epoxy? Not sure what or how though. Wishing I had a shaper. Might try and out source it but feel like it could be too expensive.

      Advert
      #15980
      Rainbows
      Participant
        @rainbows
        #332247
        JasonB
        Moderator
          @jasonb

          External or Internal?

          #332251
          Rainbows
          Participant
            @rainbows

            Ah yeah, ring gear of a epicyclic gear so internal teeth

            #332253
            Ian P
            Participant
              @ianp

              Laser cut from steel?

              Ian P

              #332260
              JasonB
              Moderator
                @jasonb

                Well I have got to make a 24T 1.75Mod one for an engine I am working on at the moment and will be planing it on the lathe, with some pre drilling to get rid of the majority of the waste there won't be a massive amount of metal to remove on your 4MOD one. Even easier if cut from a slice of Oilon or sheet Tuffnol

                imag1524.jpg

                Edited By JasonB on 15/12/2017 20:48:08

                #332264
                Clive Foster
                Participant
                  @clivefoster55965

                  Rainbows

                  Have you verified the tooth shape for that ring gear and its associated pinions?

                  As I understand it there can be interference problems with physically large internal gear teeth, especially at relatively low tooth counts, and modifications to tooth shape et al may be needed for proper running.

                  Seems to be some detail on calculations here :- **LINK**.

                  Looks as if off the shelf ring gears start at around 50 teeth and go upwards. Usually significantly larger. Could interference issues with standard gears be the reason why?

                  Clive.

                  #332273
                  Neil Wyatt
                  Moderator
                    @neilwyatt

                    I think Andrew Johnston has been looking for information on internal gears for some time. That link may be useful to him.

                    Neil

                    #332275
                    Neil A
                    Participant
                      @neila

                      Gear Engineering by H.E.Merritt gives the following advice:

                      "A general-purpose rule, for the avoidance of tip interference at standard centres, is to make the difference between the tooth numbers not less than

                      (T-t)min =10 + t/5

                      By strict geometry, the minimum tooth number difference at which tip interference begins is approximately 8, for 20 degree full depth proportions, at standard centres. But this is a marginal condition."

                      Using this advice I designed a small reduction gear box for a governor drive in 10DP with a 21 tooth pinion and 36 tooth internal gear. Addendum modification was +0.25 for the pinion and -0.25 for the internal gear. This was about as close as I thought it prudent to go. The gear boxes have been in service on US Coast Guard vessels for over 30 years now, and I have not heard of any problems. So I would say it's a fairly good rule to follow.

                      As far as actually cutting the gear, personally I would follow JasonB's advice and use the lathe to plane the profile.

                      Neil

                      #332276
                      Carl Wilson 4
                      Participant
                        @carlwilson4

                        Friend of mine could possibly 3d print this for you using a Form Labs 2 SLA machine.

                        We have been using this to manufacture change wheels for mainly Harrison Lathes, with great success.

                        The gears are printed in a tough resin that is hard-wearing. Mechanical properties can be provided.

                        So far we’ve only tackled external gears but an internal one would be interesting. My friend uses Inventor to render the gears so calculation of allowance for the interferences should be straightforward.

                        Pm me if interested.

                        Carl.

                        #332278
                        Rainbows
                        Participant
                          @rainbows

                          Found a thread on practical machinist where they were arguing over laser cut gears. Couldn't tell if they were ok or trash from it though.

                          Might well end up broaching it on the lathe, will mean adding indexing to it but thats useful anyway

                          The reason for 3d printing it was so I would have a final check that I hadnt bodged any calculations before making it properly, think I fudged the gears though and the bowden tube went pop so thats gone well. Might have to actually do research on it now instead.

                          The 3d printing sounds interesting, will get in touch with you in a bit

                          #332282
                          John McNamara
                          Participant
                            @johnmcnamara74883

                            Hi Rainbows

                            A while back I made a few Epoxy timing gears….
                            **LINK**

                            Also made some for a clock….
                            **LINK**

                            If your application is slow speed they work fine

                            For this sort of application use more Epoxy maybe 25% by volume
                            And plenty of release agent (Wax) so you can get the belt off

                            Bore the mould and bearing bore in one setting as shown and the result will be very accurate.

                            Belts are available with hundreds of teeth so high ratios can be achieved with one pair of gears.
                            Small pinions are available quite cheaply ready made, its not really worth making them unless you want the exercise.

                            Regards
                            John

                            #332314
                            John McNamara
                            Participant
                              @johnmcnamara74883

                              Hi Rainbows
                              Hmm I missed that you want an internal ring gear, I was thinking an external gear train.
                              Regards
                              John

                              #332363
                              Ian P
                              Participant
                                @ianp
                                Posted by Rainbows on 15/12/2017 19:27:16:

                                I want to add a gearbox within the flat belt pulley on the spindle of my Denbigh mill. At the moment the hang up is how to make a MOD 4 38 tooth ring gear.

                                To recap, what you are looking to make is an internally toothed gear with 38 teeth and Module 4?

                                If this is for an epicylic gearset, unless I've got the wrong end of the stick I cannot see how you will have enough room for the sun and planet gears inside. A 38 tooth gear with external teeth is about 6" diameter, presumably an internal one would be a similar size.

                                Mod 4 has quite large teeth compared to gears which are common to typical small workshop machinery, even a 12" swing lathe changewheels are a lot smaller than mod 4.

                                Maybe I have misunderstood the application.

                                Ian P

                                #332393
                                Peter G. Shaw
                                Participant
                                  @peterg-shaw75338

                                  I have a note which says "Extracted from Dave Lammas' article in ME 20.09.91 page 338". This appears to be one of a series of articles on Gear Cutting by Lammas. My extract concerns a method of creating an internal gear. The basic idea (check with the original article(s)) is that a tool steel cutter is made identical to the corresponding pinion. The cutter is then hardened & tempered, followed by the removal of several teeth leaving one tooth at say 12 o'clock, and sufficient teeth to cover an arc of 120 degrees centered on 6 o'clock. The single tooth is first used to carve, or gash, out the internal gaps, followed by the arc of teeth which then trim the sides of the internal teeth.

                                  Apparently aluminium & brass cut quite readily, whilst cast iron & mild steel require more effort and some care.

                                  Peter G. Shaw

                                Viewing 15 posts - 1 through 15 (of 15 total)
                                • Please log in to reply to this topic. Registering is free and easy using the links on the menu at the top of this page.

                                Advert

                                Latest Replies

                                Home Forums Workshop Techniques Topics

                                Viewing 25 topics - 1 through 25 (of 25 total)
                                Viewing 25 topics - 1 through 25 (of 25 total)

                                View full reply list.

                                Advert

                                Newsletter Sign-up