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  • Enlarging gear bore

    Hi, I have a 50t 1 modulus gear with 12mm bore that needs to be fitted over a 13mm shaft.

    I only have my round column mill drill to do it. I do have a 2inch boring head with craptacular boring bars that none seem to fit in that diameter anyway.

    I don't have any metric hole making tools...

    How should I go around doing that? What tools? What order? Drill and ream? Smaller boring bar?

    Thanks,
    S├ębastien

  • #2
    You can use a small size end mill in your boring head if the end mills have the right shank size. It simply turns the end mill into a single point cutter.

    Since it's a gear be SUPER careful in getting the spindle dialed in dead on to the gear bore. Gears are fussy that way.....
    Chilliwack BC, Canada

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    • #3
      You can bore it with a smaller boring bar and split bushing (or EM/BB with reduced end as BcRider mentions above), but why not just drill and ream?

      Consideration : Does it have a key way? Is it hardened?

      If you use an end mill, make sure you orient it correctly.
      Last edited by lakeside53; 03-17-2017, 09:24 PM.

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      • #4
        road trip to Mcgyvers shop?

        lol

        With what you've got, ream it If you had say a 12.5 or a 1/2" twist drill you had confidence in there accuracy you could drill first but its .039 so is reamable and sometimes unless the hole is small the bit can be a bit grabby when taking off a very small amount. If drill, slow speed and slow feed.

        as per Lakeside, that's assuming its soft and no keyway
        Last edited by Mcgyver; 03-17-2017, 10:03 PM.
        .

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        • #5
          Boring head of course. You will need a carbide tipped bar to fit the head that is small enough to enter the gear bore.





          Below is a Micro boring head for those tiny holes:

          Last edited by SilveradoHauler; 03-17-2017, 09:53 PM.

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          • #6
            You can use a small size end mill in your boring head if the end mills have the right shank size
            That sounds like a simple idea, now I just have to hunt an end-mill with 1/2 inch shank and 7/16 cut diameter! Should I look for special angle of flutes?

            If you use an end mill, make sure you orient it correctly.
            I've never used and endmill that way, my instincts tell me the tooth of the endmill should be on the tangential intersection with the radius, is that right?

            Consideration : Does it have a key way? Is it hardened?
            No keyway, 2 set screws, 20mm thick. Hardened? It's premium chinese grade, the teeth look to be hardened but the center not so much. I figured the bore was about the same hardness as parmesan cheese.

            road trip to Mcgyvers shop?
            Careful, if I don't succeed it might just happen! My wife has family in Toronto, don't need much of an excuse for a road trip

            If I was to ream it, where would I procure said reamer? Are ebay chinese grade ok for the 1 hole? Or might they not even make it through? I do have one 1/2" drills I do trust, it's HSS USA and so far has gone through anything like it was nothing.

            How would you guys hold the gear for the operation? Aluminium plates on the jaws of the vice or clamp it straight to the table of the mill?

            Thanks for the great answers so far.
            S├ębastien

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            • #7
              I'd just clamp it down making sure I have clearance beneath. You could go crazy (5 minutes) and make soft jaws for your vise with your Boring bar.. If you have a 12mm drill blank (or the drill with care) or make one, and use that to find "center", then bore away. Chinese reamers are fine for this purpose but do you need 13.01 or 12.99 or ??

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              • #8
                Originally posted by slamadeleine View Post
                Careful, if I don't succeed it might just happen! My wife has family in Toronto, don't need much of an excuse for a road trip
                n
                you'd be welcome. I didn't read our post carefully, was thinking you had the reamer for some reason. Don't know suppliers in Montreal, but there always KBC mail order. China reamer will be fine imo.... its not like everything from there is crap, its just probability thing.....but I've bought them from KBC and they were ok. Maybe its that a place like that, selling to industry, would have a little better quality stuff than bottom end consumer tool retailers?
                .

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                • #9
                  This would all be a dream to do if you had a lathe. I take it you don't have one? Or is this gear to go in the head of the lathe to get it running?

                  Since it's a boring head if you had a piece of 1/2" drill rod you could drill it out and split it with a hacksaw to take a 3/8" shank end mill. And a 3/8 two flute end mill would be a nice size for this boring job.

                  A reamer would work too but you'd need to buy one and wait for it to arrive.
                  Chilliwack BC, Canada

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                  • #10
                    A mill is a lathe in disguise. All you need is a chuck that fits on the spindle somehow.

                    Then you can hold the cutter with the vise, or other means on the table, and off you go. Someone here has no lathe and uses a mill as the lathe. AKBoomer,maybe?

                    Holding a gear is tricky, but you can do it with a piece of metal, perhaps 1.5mm aluminum, wrapped around the gear to give a round surface to the "spiky" gear OD.
                    Last edited by J Tiers; 03-18-2017, 12:18 AM.
                    1601

                    Keep eye on ball.
                    Hashim Khan

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                    • #11
                      I've​ used HSS endmills as boring bars numerous times when I had no other option, in both Mills and lathes. A two-flute works best you'll want to grind some side relief above the cutting edge so it don't rub on the bore and index or orientate it in the boring head as you would any other bar. If I had no other option going in to a 12mm hole with a 1/2" bar/endmill my new friend (for a few minutes) would be the bench grinder.

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                      • #12
                        Thanks for all the ideas!

                        Indeed, I don't have a lathe... I plan on getting one later but, like most things, budget first!

                        Now if my newbie butt can get in it's newbie gear and stop fretting it'll get done! I am going to the scrap yard to get a few 20mm thick pieces to try the various techniques on.

                        Thanks again!

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                        • #13
                          Clamp the gear to the table with spacers allowing enough clearance for the tool bit to exit the bore and not strike the table.

                          Dial the bore in true to the spindle with a dial indicator held in a chuck. You will need a bracket of sorts to hold the indicator in the chuck.

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                          • #14
                            Easy job in a lathe.

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                            • #15
                              I am not a home machinist, more like a home metal butcher so please don't laugh. How about a piloted counterbore 12mm pilot in a 13mm counterbore. It has nowhere to go but straight andyou don't have to worry about finding the center.


                              Sent from my SM-G900V using Tapatalk

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