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Thread: Material for hardened gears

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    9100's Avatar
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    Default Material for hardened gears

    I need to make some hardened gears. These are small spur gears, 2 - 3 inch diameter with keyways in their bores. I don't have a spec on hardness or alloy, just something with good wear properties. I will cut them on a 4th axis on a CNC mill. Current thinking is to make them slightly over thickness and slightly under bores and finish grind, but I have no way to grind the teeth, so it needs to be a steel with good machining properties and minimal growth, shrink, or distortion.

    I have heard of hones that will work with a keway but have no experience with them. I have a Sunnen MBB 1600 hone, so that is a possibility for the bores.

    Suggestions?

    Bill

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    Heavey Metal is offline Titanium
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    Martin gear and sprocket

    If you just want to make some 4140ph works real good and the face will work harden.

    To hone a keyed bore build a pressfit key bore the key and than hone remove the key and save it for later if it is too short on the next one shim it.

    I know i am not much help on materal selection.

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    Zahnrad Kopf's Avatar
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    Really depends on what they need to do, in what environment, and for how long you expect them to.
    Are you doing the heat treating or sending it out? Makes a difference in material choices and ease.
    4140 is okay. 4140 Pre Hard is good if you don't have heat treating in-house, too.
    8620 is very nice if you are sending them out to be case hardened. (also works well in home style casening)
    Hone the bore before cutting the keyway. Need more info to give you hardness ranges.

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    Superior hones will hone keyed bores.

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    9100's Avatar
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    To answer a few questions, these are lathe change gears run in the open with grease. Martin doesn't make the ones I need. We are talking professional quality here, as accurate as I can make them. The heat treat probably will be done by Paulo. I checked the Superior site but didn't find anything about keyways. Since I have a Sunnen machine and the factory is within walking distance of my shop, They will be the first ones to contact. In the mid 1960s I had some 64 pitch gears that ran in a glass dust atmosphere. We ate brass Bostons in days. A local gear maker made some steel ones of an alloy that had a very controllable case depth. The small teeth still had enough unhardened core that they didn't snap off. Years later, they were still going. Unfortunately, the gearmaker is long gone and I do not recollect the alloy. A similar case would be good here.

    Bill

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    Mark Rand is offline Titanium
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    I've had good results making gears with 4340 (EN24 over here) up to 4" dia. Cuts nicely in the PH state. A bit gummy, but not too bad in the annealed state. Hardens nicely and suffers little, if any, distortion (I couldn't measure any change in dimension in the 1" dia test pieces that I made for the purpose).

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    I had a bunch of gears made to replace old one's in the headstock of my lathe years ago. They were made of 4140/42 and the teeth were flame harden and the bores ground to size. Still running good as the day they were installed.

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    Zahnrad Kopf's Avatar
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    Quote Originally Posted by 9100 View Post
    To answer a few questions, these are lathe change gears run in the open with grease.
    If that's all they're doing, you can get by just fine with 4140 Pre Hard.
    But, if you want them to be what I call "cookie gears" (crispity crunchity outside/soft, chewy inside)
    then by all means, 8620 Case Carb'd .015"-.02" deep will do you just fine.

    Best of luck.
    4GSR and jdj like this.

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    Heavey Metal is offline Titanium
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    Martin will make you any pitch or tooth # gear that you want they will also make expanded pitch ones.

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    Quote Originally Posted by 9100 View Post
    We are talking professional quality here, as accurate as I can make them.
    Not trying to throw sand in here but I would think you'd be better off generating the gears (as in hobbing them) instead of 4- axis milling to make a much smoother running gear instead of many profile-milled steps. You did mention having them finish ground which would render that point moot. I would personally make them out of cast grey iron durabar, classic wear material for 100+ years, unless you have specific reason not to (IMHO that would be strength). If you have too much wear in actual existing service then increase the thickness to reduce the contact pressure or use a better "open gear/wire rope" lube. I don't have all the info here so perhaps this isn't appropriate but thinking over the 7 or 8 lathes I've owned in my life the above would fit the bill.

    I have also made modified compound gears to "adapt" to a standard Boston Gear pitch that I didn't have in the original pitch. Luckily the banjo was flexible enough to allow such machine transgressions, however I could not close the end cover.

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    Bradley Simmonds is offline Aluminum
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    I work for a large gear manufacturing company in Melbourne Australia

    Either EN36A of 8620 are the two best case hardening materials used for this type of gear....I would choose the latter.
    We use our sunnen hone on our keywayed bores no problems theree
    If you intend to grind the gear teeth milling the teeth on a four axis should be fine, if not I would be hobbing the gear of at worst I would be using an involute gear cutter

    Good Luck :-D
    ADFToolmaker, 9100 and thermite like this.

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    9100's Avatar
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    OK, more clarification. I am not generating the involutes with the 4th axis. I will buy involute cutters. I need at least 3. The 4th axis is for automatic indexing. I will only be finish grinding the faces and bores, not the actual teeth. Martin Gear showed no interest in making these as specials and told me where to get cutters. I suppose that if I was sufficiently adventurous, I could dress a grinding wheel to the pressure angle and grind the teeth, but that would be a long process. Actually, just getting the 4th axis going has been enough of an adventure. Someone gave it to me because no one knew what to do with it. The techs at the factory told me that it was a special made for Tree mills and run by their system. They said that when they got one in for repair they put one of their own motors on it and switched back when they returned it. The motor turned out to be a fairly standard Baldor brush type DC servo with tach generator and encoder. I made a servo amplifier interfaced to an Aerotech motion control card that I have controlling the old Boston Digital mill, replacing the original computer that had a row of lights blinking in binary code and was programmed with punch tape. The whole kluge works surprisingly well.

    8620 sounds like the answer I was looking for.

    I have never tried to hone a bore with a keyway, but the stones and mandrel pads are much wider than it is, so maybe I am all right.

    Thanks for the advice,

    Bill

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    thermite is offline Diamond
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    Quote Originally Posted by 9100 View Post
    OK, more clarification. I am not generating the involutes with the 4th axis. I will buy involute cutters. I need at least 3. The 4th axis is for automatic indexing.
    Pitching in with another recommendation for 8620 and case-hardening.

    And with only one of each to make? I'd suggest a shaper and HSS bit ground as needed for the cutting if you have access to one.
    I just can't see the price of 3 or 4 each involute milling cutters for onesie non-stock gears, less'n a paying client is footing the cost and/or there is a serious time constraint.

    Bill

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    Mean while in the real world of actually applied thread cutting gears there's a hell of a lot of us running cast iron and nylon - tufnol based gears that are showing no sign of wearing out any time soon. Hardened steel on hardened steel need a oil bath to run well. Polymer and steel or polymer and iron combinations last darn near forever in a minimal lube application like this. Hardened gear on hardened gear especialy cut on a mill not a proper gear hob will eat one another for breakfast. Whats more a metal to polymer gear train is a lot quieter. Hardened gears ring.

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    9100's Avatar
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    Quote Originally Posted by thermite View Post
    Pitching in with another recommendation for 8620 and case-hardening.

    And with only one of each to make? I'd suggest a shaper and HSS bit ground as needed for the cutting if you have access to one.
    I just can't see the price of 3 or 4 each involute milling cutters for onesie non-stock gears, less'n a paying client is footing the cost and/or there is a serious time constraint.

    Bill
    These are several sets for a client, strictly business, not a home shop project. Just to keep the record straight, my shop has been my only employment for 34 years except for a few part time and consulting jobs. Admittedly the old saw that it was not intended to be a non-profit organization applies here, but this isn't a hobby shop. I don't have a material spec, although I may be able to get a sample to Rockwell. He wants hardened steel and I don't have any latitude in that area beyond choosing the best alloy. Finding a custom shop to make them and making the rest of the assembly myself is still a possibility, but the cost of 3 cutters is trivial in the overall scheme.

    Bill

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    shs_cm is offline Plastic
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    Chk. price of having them wire cut after heat treat, & forget the grinding?
    Stan

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    thermite is offline Diamond
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    Quote Originally Posted by 9100 View Post
    Finding a custom shop to make them and making the rest of the assembly myself is still a possibility, but the cost of 3 cutters is trivial in the overall scheme.

    Bill
    .. in which case I'd go for a proper specialist that does little else but make - and heat-treat - and certify - gears every day of the week, and concentrate on the more unique/specalized part of the task.

    'Usual suspects' aside, Google still finds a few of 'em about that do not restrict themselves to 'vanilla' items (which are all too often simply imported these days).

    Bill
    Last edited by thermite; 05-13-2012 at 11:59 PM.

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    gappmast is offline Aluminum
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    Honing a hole with a key way is no problem on a Sunnen hone if you use the correct tool. For that application you will need a key way hone, it has a wide stone that will bridge across the gap.

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