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Thread: One step closer...

  1. #1
    Craftsman
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    One step closer...

    One day I intend to make a watch.
    Iím still a long way off, but tonight I made a good step in the right direction :)

    A large part of a timepiece is of course the wheels and pinions. Iíve been contemplating how to cut them without bankrupting myself buying the cutters.

    The Sunderland gear planer uses a fairly simple cutter for racks, and generates the curves of the spur gears by coordinating the cutting and a rotation, so the gear blank rolls against the rack as though it already had th teeth.

    I have several old engineering texts with some of the relevant details in:



    Of course I donít have a gear planer, and generally they are for much larger gears, but I can use the technique with a little bit of lateral thinking.

    First make a rack form cutter, simple lathe work.



    Then wack it into an indexer on the mill



    And create some flutes for the cutting edges.



    Then handily I have recently bought a kiln (for enamel) which I can use to Heat treat. So much easier than a blowtorch.



    I decided to keep the tooth count smallish for my first gear - 30 teeth /12degrees each. That also means I can use the simple divider. To assist my little brain I wrote down all the teeth angles so I could tick them off as I go.



    Then itís a question of put on the right cut and index /cut / repeat...



    Once the first pass is done I rotated the indexer by 6 degrees, moved the cutter by an equivalent linear amount and cut it again. This generates the tooth curves.

    The end result is gear shaped:



    And meshes with another 48dp gear nicely.



    I got a beautiful pattern when parting the gear blank off the stub it was machined as part of.



    There is more work to do, but I think the method will work without too much effort.

    Dave

  2. #2
    Grand Master magirus's Avatar
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    Great work Dave! Look forward to future progress. Meanwhile, that Porsche . . . ;-)

  3. #3
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    Great work. Thanks for sharing....and keep us posted on the rest of your "journey".

    Sent from my G8441 using TZ-UK mobile app

  4. #4
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    Had to make another cutter as the first one is too short to make a 144 tooth gear.
    I printed out the 144 tooth gear to compare the lengths and clearance with:



    Then I milled some flutes and a bit more clearance on the shank.



    Bit of a heat treat and I knocked some steel into the shape of a pinion.



    Then I whacked the bar into the Lathe and proceeded to put a hole in the middle and part off a few pinions for closer examination.



    They need a good debur (I need to sort a better parting tool I think) but the tooth form is quite reasonable.


    Dave

  5. #5
    Grand Master magirus's Avatar
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    Good to see some some progress Dave, keep at it!

  6. #6
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    Dave - can't believe there havent been more comments on this... epic work! I'd love to see a few videos of the milling and lathe processes. If you ever get a chance to record them and upload them to YouTube it would be great! Looking forward to future updates!

  7. #7
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    Ive made some wheels.
    First trepan out some blanks, which avoids making loads of swarf just to get a roughly right sized blank.



    2 cut out without a hitch Happy face :)



    Because they are only roughly the right diameter I made a stack of Gage Blocks to allow me to size them to within a very small tolerance




    Turn to correct outer diameter in the lathe, whilst on the arbour they will get gear cut on.



    Cut some teeth


    And repeat x144. Took less time than you might think



    Now the blanks have teeth its time to give them some spokes.
    so I marked out 3 spokes:


    cutting a long thin slot is fraught, and usually ends up with a broken tiny endmill, so I went the easy route and chain drilled out the scrap.





    Then some filing to clean up the drill half holes



    And a pair of wheels is done enough to make the next bit.


    Ill do 'proper' finishing when the rest of the movement is more complete.

    I'm learning quite a lot about things that will help when I get to watch sizes, although I'm still not doing any work on the Porsche...

    Dave

  8. #8
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    Well I think you're bonkers Dave S !
    In an eccentric way of course.
    I think you have to be to make a watch by hand.
    I think of people like George Daniels, Kari Voutileinen, the late Derek Pratt and of course AL Breguet. I know how much work making even one part can be and wish you all success.

    Sent from my SM-G900F using Tapatalk

  9. #9
    Grand Master magirus's Avatar
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    Great stuff Dave! Now, about that Porsche . . . ;-)

  10. #10
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    Brendan, Iíll take that as a complement :)
    I have to make a couple of timepieces - one for each child...
    New book on gears on order - these are involute tooth form rather than the traditional cycloid form, but I havenít yet found a complete set of writings which have convinced the engineer in me that involute really is a no no.

    Dave

  11. #11
    Master Webwatchmaker's Avatar
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    Quote Originally Posted by Dave S View Post
    Brendan, Iíll take that as a complement :)
    I have to make a couple of timepieces - one for each child...
    New book on gears on order - these are involute tooth form rather than the traditional cycloid form, but I havenít yet found a complete set of writings which have convinced the engineer in me that involute really is a no no.

    Dave
    Of course it's a compliment !
    Such skill and patience is required.
    It's a while since I made a wheel !
    From what I remember the involute gear form is used by most heavy industries, gearboxes etc, and will work well in both directions but sometimes require lubrication.
    With cyclical gears there is less friction but depth is more critical and devices turn best in only one direction due to tooth contact interfaces.
    *You've got to make three ! I want one too.

    Sent from my SM-G900F using Tapatalk

  12. #12
    Great story with some lovely machining

    Well done that man

  13. #13
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    Bit more progress, so a quick update.
    I hacked out a couple of more wheel blanks, this time for 96 and 90 tooth wheels.



    Then bunged them in in the mill and cut some teeth in the same manner as for the 144 tooth wheels, of course cut one at a time, as they have different tooth counts...





    Now I have 4 wheels, the smaller 2 of which need crossing out for spokes:



    The layout for the hands will be in a classic Regulator style - Large central minutes, with smaller hours and seconds, similar to this picture stolen form the internet:



    So the wheels end up laid out something like this:



    The hours are on the lower large 144 wheel, the minutes on the middle wheel, and the seconds end up on the escape wheel shaft.

    The steel for the pinions and shafts has appeared, so I'll be cutting them shortly, along with escape wheel and then plates.

    I've also got some reading material, about 1/2 way through it so far. Lots of maths and formulas, so needs to be read with attention.



    Dave

  14. #14
    Grand Master magirus's Avatar
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    Love the technical jargon Dave, "hacked" and "bunged"! Good to see more progress.

  15. #15
    Soon you will be able to build one of these??


  16. #16
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    Following a lot of reading about aspects of gear manufacture I've started on the Pinions.

    When I get to Watch sized parts I think I might want to make a slightly smaller setup for cutting.
    (Anvil for scale ;) )



    Cutting is much as before



    Involute Pinions with low tooth counts suffer from undercutting, where the root of the tooth becomes thinner.
    This is often quoted as why you cant use involute gears in a time piece - cycloidal profiles dont suffer from this as the root flanks are radial.
    To counter the undercutting it is common in industial gearing to use a concept known as profile shift.
    This means that the involute tooth is still involute in shape, but a different part of the involute curve.
    'Form' gear cutters - as generally used in clock making - dont allow profile shifting.
    However with a rackform generation process (such as hobbing or planing) all you do is make the blank bigger, and move the cutter out a bit. (Danger - slight oversimplification)

    Doing this does mess with the actual pressure angle, but I have more thinking to do about the consequences of that.
    In the mean time here are some pinion teeth cut with a +0.25mm (approx) profile shift.
    I havent taken them out of the mill yet, as there are a few things I want to try whilst the setup is still in place.
    You can see the effect of the shift to give a "pointy" tooth shape with no undercutting.



    compared with the same pinion without profile shift



    Either pinion will roll correctly against the previously cut wheels, but the shifted one has a different center distance (as its physically larger).
    That matters if the gears have to fit into an existing plate, but as I'll depth the train anyway it will 'just' get accounted for.


    Dave

  17. #17
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    The cycloidal form is used in clockmaking/watchmaking.
    Out of curiosity why did you decide on involute?

  18. #18
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    There are a few reasons, but mostly it boils down to being bloody minded and wanting to try something that is not normal ;)
    Whilst traditionally the cycloid tooth form is used I have failed to find any actual evidence that it is really superior to the involute form - both tooth forms produce a rolling action, both are theoretically ďgoodĒ.
    I have found a lot of ďhearsayĒ about various aspects, including how involute gear trains donít work for gearing up ( how does the gear know?), and that you canít cut low tooth count pinions. There is some truth to the latter - with an off the shelf commercial form cutter you canít, but by profile shifting itís actually quite common in industrial practices.

    Another aspect is that I can make pretty much any tooling I need to - my shop is well equipped. I have wanted to try this method of a single (rack form) cutter for all gears for a while, and making that tool for involute gears is trivial. Being an engineer Iíll take the path of least resistance the solutions are generally more elegant :)

    As I said I intend to progress to watch sized timepieces, and being able to make my own tools, and know how to run the process are (IMO) useful bits of knowledge.

    Dave

  19. #19
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    Cycloid runs with lower friction in lower torque situations.

  20. #20
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    Do you have a source for that statement?
    Dave

  21. #21
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    Pretty sure it will be in Theory of Horology by WOSTEP, but it is also in my gears book but can't remember the title. Will look it up later when I get home and post it here, its not an expensive book and worth it.
    Have you read wheel and pinion cutting in horology? Well worth the money that book.

  22. #22
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    I have Wilds Wheel and Pinion cutting, though itís a few years since I read it. Iíll have another look, but IIRC it just makes a statement to the effect of gear trains for clocks are cycloidal, but involute is sometimes used in the winding works. I donít recall anything more scientific than that.
    Iím currently still working through WO Davis.
    Would like to find some actual data showing the comparison of friction / torque for involute and cycloid gear trains - not seen any proper data for that yet.

    Dave

  23. #23
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    I'm not one side or the other, I suggested the wheel and pinion book just because it's useful for this, rather than one profile or another being better.

    The book is A W Marshall - gear wheels simply explained. But by its title it's only a paragraph, no real data to back it up.
    Would be great to make two trains of both forms and test them for power reserve, see which lasts the longest.

  24. #24
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    Let me make one train first, then maybe I should make another and do the research directly...
    Of course that would mean buying the cutters which the whole point was to avoid....

    I'm not sure there is one right answer, inevitably there are a set of trade offs in almost any engineered thing.

    Dave

  25. #25
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    Indeed, involute is also easier to depth. I would like to be able to find more information on the other profiles used now like microgear. Very hard to find any information at all on that profile.

  26. #26
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    Fascinating post Dave, Thank you for sharing your work.

    I have the suspicion that this is the sort of thing I wanted to study while doing mechanical engineering, not attempting to get my head around La Place transforms.

    Looking forward to the next installment, don't worry about the Porsche, it can wait ;-)

  27. #27
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    Been busy laying a hedgerow, so this took a break for a bit, but now thatís done itís time to get on with it.

    I managed to mis-index the pinions whilst trying at few extra things, and as a result knackered them.
    So tonight I knocked out another ďstickĒ.





    I havenít made a depthing tool yet, and that would require finished wheel/pinion sets anyway, so I bunged the stick in my little unimat and found a bolt to act as the wheel shaft.

    The gears and pinion mesh nicely enough given the roughness of the jig.

    Not sure how to post a video here, so here is a link to a tweet with a couple of seconds in:
    https://twitter.com/solutionsbydave/...382662657?s=21

    Dave

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