Announcement

Collapse
No announcement yet.

Gear Hobber

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Gear Hobber

    Since gears are always a popular topic of polite conversation around here, I thought I might mention something I just stumbled across.
    Some of you may keep better tabs on this then I do, but it looks like Martin Models is working on a the plans/castings for a gear hobber.

    Check out the bottom of this page:
    http://www.martinmodel.com/MMPtools-...tools-sub.html

    You can click through the picture for some more interesting images and tantalizing clues.

    Josh

  • #2
    Somewhere in the basement is a set of the Helix castings, looks like I will soon be one version behind. Thanks for posting the link. Regards, Earl

    Comment


    • #3
      Oh nice! That's the College Engineering Jacob's hobber castings.

      By coincidence, Model Engineering Workshop has had a series of articles in the last three months about modifying the CES hobber to cut spiral gears.

      The only issue I see with it is that it uses tiny little hobs, so you'd have to be able to cut your own. Not many hobby-class QCGB lathes can cut diametral-pitch threads...
      "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

      Comment


      • #4
        Pi

        I think that it should be said that if cutting a hob for straight (ie spur) gears the hob will be a spiral (ie like a thread or a worm).

        The lead of the hobbing cutter will need to be the circular pitch of the required (DP?) gear adjusted for the helix angle of the hobbing cutter.

        The lead of thread used to cut the hobbing cutter will therefore have a "pi" component in it.

        Pi ~ 3.1416 or in gear ratio terms: 22⁄7, 333⁄106, 355⁄113.

        Comment


        • #5
          That kit is made by Gary Martin who I used to work with at TechShop. All the kits have nice castings made locally, especially the dinky deere engine.

          Comment


          • #6
            Originally posted by oldtiffie
            The lead of thread used to cut the hobbing cutter will therefore have a "pi" component in it.

            Pi ~ 3.1416 or in gear ratio terms: 22⁄7, 333⁄106, 355⁄113.
            Or, more practically, a fraction of pi, and then taking this into account when positioning the QCGB. On my Colchester, the ratio is pi/4 and the H lever (vs the normal L) is engaged to add a x4 multiplier:



            So, it should be possible to change the end gears on most any lathe with a QCGB to make it cut dp pitches....
            TexasTurnado

            Comment


            • #7
              All nice 'n' curvy

              Thanks TT.

              My no-QCGB lathe (3mm lead-screw) has a "pi" (22/7) function.

              For those that don't have it, it is easy enough to work our the required pitch to cut the worm on the lathe and the, seek out the nearest tpi/lead from the tpi (inch) and lead (mm) tables and set that ratio on the lathe. It is surprising just how accurate you can get.

              There is another matter of the tooth form and the positioning/tilt (or not) of the lathe tool.

              In an ideal case the teeth of the hob will need to be relieved - not an easy task as the greater the number of teeth on the hobbing cutter the closer the "faceted cuts" (one per tooth) will be to a smooth involute curve on the gear teeth.

              Comment


              • #8
                Nope, Sorry, Wrong info as that machine will use the smaller commercial hobbs. I have both the castings and the drawings from CES in the uk but am a few yrs. from building it. And to be truthfull that hobbing machine could be built using steel plate and some larger structual steel angle iron sections. With maybe some bolted on cast iron or bronze for the dovetail slides. It is a pretty complicated build tho. But commercial hobbs generly run about half the price of a full set of gear cutters to cut one D.P. plus for those that don't know, Hobbing is really fast and it's the most accurate way to cut gears. (using CNC? I don't know)

                Pete
                Last edited by uncle pete; 12-18-2010, 07:08 AM.

                Comment


                • #9
                  Originally posted by uncle pete
                  Nope, Sorry, Wrong info as that machine will use the smaller commercial hobbs.
                  Are you sure? The smallest commercial hob that I've ever seen is 2" long, with a 1 1/4" arbor.

                  Eyeballing the dimensions on the CES kit, that hob looks a lot smaller than that? Have you found a source for tiny hobs, or is that a 2" hob in the Gary Martin's picture?
                  "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                  Comment


                  • #10
                    The hobs on that machine are actually pretty small, maybe 3/4" OD. You can get them from Ash Gear.

                    The guy that actually built the patters is part of the Portland Model Engineer group. He has spent years working on it. I have a closer, bigger, picture of the unit at home. I will post it later.

                    Comment


                    • #11
                      Lazlo,
                      Not 100% but 99%, I've been reading a few articals about this machine over the years and do recall some pictures in M.E. or M.E.W.? magazine showing a completed machine with some gears it had made along with both commercial and home built hobs. WHAT issue of that magazine it was in sure doesn't ring any bells, But maybe some of the uk readers here can either confirm or say I'm out too lunch on that 1%.

                      Pete
                      Last edited by uncle pete; 12-17-2010, 08:12 PM.

                      Comment


                      • #12
                        Arceuro does the smaller hobs but only in MOD form, they do the commercial ones in DP with a standard 1" bore.
                        .

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



                        Comment


                        • #13
                          Thanks john, I was racking my brains trying to remember who in the UK had fairly reasonable priced hobs that would fit this equipment. Edited to add, I'm almost positive this hobber was designed to use Myford lathe gears to provide both the drive and the proper gear ratio for each different hob.

                          Pete
                          Last edited by uncle pete; 12-17-2010, 08:20 PM.

                          Comment


                          • #14
                            Here are the hobbs. http://www.arceurotrade.co.uk/Catalo...ools/Gear-Hobs

                            Comment


                            • #15
                              Originally posted by Robin R
                              I'm really confused. Based on Robin's link, I'm guessing the Jacobs uses 8mm hobs?? So there are no DP (Imperial) hobs available for the Jacobs kit?
                              The DP hobs on that link are 22 mm (??).

                              I've got about a dozen commercial gear hobs of various sizes, and they all use a 1 1/4" arbor.

                              I dropped Gary an email asking him about availability of the hobs...
                              "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

                              Comment

                              Working...
                              X