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Hobbing worms

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  • Hobbing worms

    Managed to get an hour today to have a further look at worm wheels.
    I can't see any reason why the electronic hobber can't do these quickly and easily but I have a cutter problem that covers small hobs.
    Using the horizontal mill presents a problem using small Mikron type cutters and also using taps, acme or otherwise, as hobs.
    I have arbours to cover 5/8", 3/4", 7/8", 1" and 1 1/4" but a lot of the smaller sizes are 5/16", 8mm, 3/8", 10mm and other odd socks, Taps are even worse being non standard shank sizes.
    Terry Sexton addressed this problem of small hobs in one of his articles where he made a new arbor and bearing support and mounted these outboard.
    I didn't facy this arangement as there is no outer support, it's very close to the overarm and it doesn't address the tap problem.

    Easiest way that I can see is scrap the arbor as such and use an ER32 collet chuck direct into the spindle and carry the hob on it's own unique arbor held in the chuck and supported by the overarm.
    This way with an ER32 you can go from 3/32" up to just over 3/4" with no gaps, ideal for tap shanks.

    So today I measured the overarm suport up on the Victoria as being 1 7/8" and turned a piece of material down to this size and 4" long. I also bored a No 2 Morse hole in it at the same setting.
    I then screwcut a l" length of 16tpi thread on each end and made two slotted nuts to fit each end.
    I used 16 tpi as on an english lathe you can engage anywhere and don't have to bother with a thread dial. This way you can thread at 250 rpm with no worries about crossed threads. Did I mention it was a rush job

    A No 2 Morse revolving centre off the lathe was fitted to this and the threaded bung fitted to the overarm bearing. The two nuts are just a quick adjustment method to bring the revolving centre to support the end of the tap / arbor.

    No picture as it's late here but if I get the chance tomorrow I'll get an 8 tpi Acme tap setup and run a 40 tooth wheel off and hopefully pics to follow.

    John S.

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

  • #2
    We're waiting for the pics John
    Free software for calculating bolt circles and similar: Click Here


    • #3
      Managed to create a bit of time this morning and got set up for doing a 40T wheel with a 8tpi Acme tap.
      The tap is a piece of unused Myford leadscrew that has been tapered, fluted and a bit if backing off done, not much.
      This has then been hardened with a 10 thou deep cyanide case. To say it's only mild steel case hardened it cuts well.
      Worked out the OD and depth of cut and away I went, disaster, all ripped teeth.
      Smack on forehead, note to self, reverse stepper for LH threads.
      Seeing as that was knackered I just kept feeding in on a 34 tooth setting until it cleaned and the results were OK but I had no ised if I was correct with diameters etc but as it's hobbed it has to run with an 8 tpi worm.

      Strike 2.
      New blank for 40T, stepper going right way [ or should that be left way ] and fed upwards into the blank for the stated depth, left it to do a rev revs to run out and it came out well.
      Time taken to cut this was just under 3 minutes, that's just cutting on a prepared blank.
      Had a look in the scrap draw and found a piece of 3" brass, this will just do a 72T worm wheel. Obviously with being larger it takes a propotionate time long to cut but due to the slower pulse rate I was able to go up a speed on the mill so the cutting time was roughly the same, just over 3 minutes.
      To save space I have posted the other pics on my web space.
      The above picture is:-

      There are 6 more, just keep changing the last number from 20 to 21 thru to 26.

      John S.

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


      • #4
        John S.

        sounds like you are on to something there.

        i have hobbed worms with an acme tap in my lathe. i wonder about maybe some small 3 jaw chuck at the driving end [that's what i used]. it made nice worm gears. i have some er collets and didn't think about using them as they are metric and i don't speak metric.

        what i did was set blank [gashed with a dovetail cutter] in my milling attachment with proper shims, etc. very much like what you are suggesting. i was cutting a 90 tooth gear to fit a 1/2" acme rod. used a cheap acme tap so if i broke it i wouldn't go ballistic.

        i want to see the pictures too.

        i am about to order bronze blanks for gears for my dividing head. i may be calling on you for guidance when i get blanks and ready to cut them.

        have a good day over there in 'jolly olde'.

        ........i dremel. therefore i am..........................


        • #5
          Seems to work just fine. So I guess the main advantage is that there is no need to gash the blank in advance. Why do I have the feeling that may be my Mark III hobbing and indexing fixture?
          Free software for calculating bolt circles and similar: Click Here


          • #6
            Something that is lacking in my 30 plus year educcation as a machinist is gear cutting. I never did it, never had the need. Hence to me it is pure wizardry. I have great respect for you who cut gears, hobs, worms, salamanders or whatever else they may be called.

            Paul G.
            Paul G.


            • #7
              If I show up at your door in a huge basinet and a truck load of tools do you think you can convince Gert to keep me as a shop pet? I hardly ever piddle on the floor except when I see new tools or get excited...