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  • broke a gear in my headstock, got some questions

    Hi all, I have a HF combo mill/lathe (44142) and recently broke some teeth of a gear inside the head stock. Specifically, the gear is 3rd inline on the gear train, that is, it runs off a compound gear that is driven by the gear on the spindle. HF no longer supports this unit in any way, the grizzly 9729 is identical & supported, but the part is out of stock until mid sept.

    here is the gear:




    my questions:

    1. why is it made in this manor (steel bore, plastic teeth)?
    is it because its cheaper to cut teeth in plastic? Is it an intended failure point to prevent other damage? Is it to quiet the gear train?

    2. what type of plastic might this be? I know nylon is common, this is pretty hard, maybe derlin? If I were to make one, what material would you recommend?

    3. I have never cut a gear before, but what better time to learn than when you are in a bind? I dont have any gear cutting tools, but I do have a rotary table and or my lathe spindle. I was thinking I could grind a tool and use my lathe as a makeshift shaper to cut the teeth. I do not have proper indexing plates, but I'm thinking I might be able to make something to index off the old gear, perhaps spanning several teeth to get past the broken ones. Thoughts on this method?

    thanks in advance for your help!

    ps. if anyone is curious how it broke, I was attempting to cut a 1tpi tapered auger thread, driving the lathe manually by the leadscrew.
    "it is no measure of mental health to be well adjusted to a profoundly sick society." -- krishnamurti
    "look deep into nature, and then you will understand everything better." -- albert einstien
    "any intelligent fool can make things bigger and more complex...It takes a touch of genius - and a lot of courage to move in the opposite direction."

  • #2
    The nylon gear has 2 purposes. It is the weak link. If it fails it does not tear out something more costly. A Nylon gear, and a straight cut one at that, will run much quieter than a metal gear. They probably used it more for to protect the gearbox than for the quiet.

    You can lookup the Grizzly equivalent for your machine and get parts from them. Gear cutting will require a special cutter, and a good indexing head. You also need to use some different techniques with plastic as some plasitcs like to degas after they are machined and they shrink in cross section. Bores get bigger and the ODs get smaller...

    You could also look for a metal gear, just take care not to over;load the whole machine...

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    • #3
      Does the mill portion still work ?? Or did this gear kill it

      Comment


      • #4
        Originally posted by kf2qd View Post

        You can lookup the Grizzly equivalent for your machine and get parts from them. Gear cutting will require a special cutter, and a good indexing head. You also need to use some different techniques with plastic as some plasitcs like to degas after they are machined and they shrink in cross section. Bores get bigger and the ODs get smaller...

        You could also look for a metal gear, just take care not to over;load the whole machine...
        as stated in the original post, grizzly cant get me the gear for at least a month, having my lathe out of service for a month is just not acceptable. I will prob get one from them, but I need something to get me through to there.

        as for the special gear cutter, I realize that I don't have the ideal tools, what is your opinion on the makeshift shaper method I described? still leaves me with an indexing problem to solve, but I have a few ideas brewing on that front.


        " Does the mill portion still work ?? Or did this gear kill it "

        gear kills the power feeds for both the lathe & mill, but both work in a manual capacity.
        "it is no measure of mental health to be well adjusted to a profoundly sick society." -- krishnamurti
        "look deep into nature, and then you will understand everything better." -- albert einstien
        "any intelligent fool can make things bigger and more complex...It takes a touch of genius - and a lot of courage to move in the opposite direction."

        Comment


        • #5
          I have to Hob some 1.5Mod gears here shortly. If you can have all the other work DONE and READY, I might be able to help you out. You would need to have your blank completed and make an arbor for it as well. I would do ONLY the Hobbing.

          Comment


          • #6
            Originally posted by mtraven View Post
            as stated in the original post, grizzly cant get me the gear for at least a month, having my lathe out of service for a month is just not acceptable. I will prob get one from them, but I need something to get me through to there.

            as for the special gear cutter, I realize that I don't have the ideal tools, what is your opinion on the makeshift shaper method I described? still leaves me with an indexing problem to solve, but I have a few ideas brewing on that front.


            " Does the mill portion still work ?? Or did this gear kill it "

            gear kills the power feeds for both the lathe & mill, but both work in a manual capacity.

            Well if your rotary table accepts plates I would just order one and go to town with a hand ground profile tool. Way back before I bought my indexing head I was in a similar position. I ended up grinding a profile tool by hand and used a makeshift doohicky to index off the old gear.

            I think you can knock this out

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            • #7
              I have the same machine and I also crashed it and blew the "fuse" that plastic gear. That's why you need spares. So make a few . I would take advantage of zahrands offer

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              • #8
                Originally posted by Axkiker View Post
                Well if your rotary table accepts plates I would just order one and go to town with a hand ground profile tool. Way back before I bought my indexing head I was in a similar position. I ended up grinding a profile tool by hand and used a makeshift doohicky to index off the old gear.

                I think you can knock this out
                I think you will find that few if any "standard" "A", "B" or "C" plates have 127 holes so a plate for 127 holes would need to have 127 holes - but that would be "crowding it" if you wanted to stay within the limits of a standard set of sector arms.

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                • #9
                  It looks like this gear has 56 teeth. My lathe has an 80 tooth plastic gear that I stripped a while ago, but fortunately it came with a spare:



                  I found some for sale on eBay, but I didn't need any. Here are some ABS gears that might work:
                  http://www.ebay.com/itm/65T-65Tooth-...-/151235863094 (65 tooth)
                  http://www.ebay.com/itm/57T-57Tooth-...y/151235707592 (57 tooth)
                  http://www.ebay.com/itm/55T-55Tooth-ABS-Change-Gear-7x10-7x12-Mini-Lathe-Harbor-Freight-Grizzly-/161228264524 (55 tooth)

                  The number of teeth may not matter much because it is just a "tumbler" or idler between the spindle gear and the small gear on the banjo.



                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

                  Comment


                  • #10
                    Originally posted by PStechPaul View Post
                    It looks like this gear has 56 teeth. My lathe has an 80 tooth plastic gear that I stripped a while ago, but fortunately it came with a spare:

                    The number of teeth may not matter much because it is just a "tumbler" or idler between the spindle gear and the small gear on the banjo.
                    thanks for the suggestions, but mine is not a tumbler, its keyed to that shaft & outputs through 1 of 3 gears pinned to that shaft dependent on the position of the gear selector. so its got to be a direct match, 56t gear.

                    as for indexing plates, that's a no go, my table does not accept them, just quick indexing plates that are only good to about 32 divisions.

                    Zahnrad:
                    that is a very generous offer & I may end up taking you up on that. I'm working on a setup to try to do them on my own, Ill post at the end of the night & let you all know where I am at (or ask for more help).

                    Thank you all so much for your suggestions, its great to have this forum as a resource.
                    "it is no measure of mental health to be well adjusted to a profoundly sick society." -- krishnamurti
                    "look deep into nature, and then you will understand everything better." -- albert einstien
                    "any intelligent fool can make things bigger and more complex...It takes a touch of genius - and a lot of courage to move in the opposite direction."

                    Comment


                    • #11
                      I can't remember where i saw this.
                      There is a way of making light duty non precision gears, by running a strip of heavy brass foil or thin sheet between any 2 gears of the correct
                      pitch. The strip will get corrugated, I believe that model outfits even sell this strip ready made in small sizes .
                      You cut off the amount of teeth you need and wrap it around a blank wheel and then pour in some alloy that then fills in the space between them.
                      Then center and bore the hole, keyway etc.

                      I've never done it, and don't know how much torque those teeth can transmit, but it shouldn't take too long to try.
                      If I was doing it I would drill some holes in the periphery of the blank to key in the molten alloy, no need for precise spacing.

                      Comment


                      • #12
                        Originally posted by oldtiffie View Post
                        I think you will find that few if any "standard" "A", "B" or "C" plates have 127 holes so a plate for 127 holes would need to have 127 holes - but that would be "crowding it" if you wanted to stay within the limits of a standard set of sector arms.
                        I guess then im missing something here. Why would you need to have 127 holes? If the table has a 40:1 ratio you wouldnt need nearly 127 holes.

                        Maybe im just under the wrong impression that rotary tables have a 40:1 ratio????

                        Comment


                        • #13
                          So, you need a 56 tooth gear. Is it Mod 1 as are the 7x lathe change gears?

                          I ask, because I have built a digital indexer based on an Arduino which runs a driver/stepper connected to my 4" vertex RT. I have made straight hobbs for Mod 1 and 16 DP gears. Over the winter months I cut a set of change gears for a 12" Atlas lathe. I have not yet cut Mod 1 gears, but could.

                          Chuck

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                          • #14
                            Originally posted by chucketn View Post
                            So, you need a 56 tooth gear. Is it Mod 1 as are the 7x lathe change gears?
                            Originally posted by Zahnrad Kopf View Post
                            I have to Hob some 1.5Mod gears here shortly. If you can have all the other work DONE and READY, I might be able to help you out.



                            Originally posted by chucketn View Post
                            I ask, because I have built a digital indexer based on an Arduino which runs a driver/stepper connected to my 4" vertex RT. I have made straight hobbs for Mod 1 and 16 DP gears. Over the winter months I cut a set of change gears for a 12" Atlas lathe. I have not yet cut Mod 1 gears, but could. Chuck
                            Well there's something one doesn't see every day. Hobs being made in a home shop environ. It happens. It's just not too common. How are you making your Hobs? Material? Heat Treat? Grinding? How are you relieving them? I am interested because it's a subject close to my heart due to the fact that I make a LOT of Non Standard Gears, bearing completely custom Pitches and Pressure Angles. Or are you actually making Form Mills, and not Hobs?

                            Comment


                            • #15
                              I first ground a HSS lathe tool to a precise fit in the gear tooth profile of the Mod or DP gear. I did this for both a 16 DPgear for the Atlas and a mod 1 gear for my own mini lathe.
                              Next I turned a 1/2" dia piece of drill rod to have 5 rings, spaced the same as a screw thread of the pitch of the gear. Like profiling a rack except the teeth were rings, not helical like a screw. I made one with each lathe tool, for each type of gear. I then gashed the rings into teeth with my mill, holding the drill rod with the RT in horizontal mode. Adjusting the RT to cut the gash and then relief. I don't have the resulting tool in front of me, but I think I cut 5 gashes, and relieved the backside of each tooth made. I also turned a relief(smaller dia for 1/4" between the 5th tooth and the shank on each tool.
                              I hardened the drill rod tools, but did not temper as I was cutting aluminum, and quenched in used motor oil.
                              I put the hardened tool in the mill, and mounted the gear blank on a mandrel in the RT, with the center ring of teeth set on the center axis of the blank. I used the Arduino based stepper setup on the RT to index the blank, made 2 passes to cut the gear profile to depth. The 1st, 2nd, 4th, and 5th ring of cutters each cut a partial profile, and the center or 3d ring of teeth cut to depth on one tooth at a time. As the RT was indexed, each ring of teeth on the cutter cut a little more of the involute profile. Obiously the complete gear was cut in 1 complete revolution, plus 3 teeth from the starting point.
                              As I cut a total of 8 gears for the atlas, I experimented with various depths of cut per pass, and making multiple passes at the same depth for a complete revolution of the blank. I settled on 2 passes per tooth, increment, 2 passes, as the quickest method for me.
                              I used WM Berg's Gear Spec program to calculate the gear blank diameter, and used formulas on the web to determine cut depth.

                              Chuck

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