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  1. #81
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    Hi All:
    Let's re-state the problem briefly and maybe that will help get clarity on what the OP needs to accomplish with his electronic gearing.
    A fine pitch AGMA class 10 gear may not have a tooth to tooth pitch error of more than 0.0005" and a total deviation for all teeth of more than 0.001" for pitch diameters up to 2"

    This ignores all of the other specifications for the gear, but since the principal vulnerability of electronic gearing in this application is fluctuation of the synchronicity between hob and work spindles, this is probably the most relevant single measure.

    Let's say our hob is 1.875" OD and made from HSS so we will run it at around 80 SFM so about 160 RPM. (You may obviously change these numbers at will if you're cutting say brass as opposed to 4140 HTSR )

    Recognizing that the hob spindle speed is uncontrolled and will vary as the load changes and also as the input current and voltage changes, and that the work spindle can only react after the hob spindle deviates from it's nominal speed, how fast does the work spindle have to respond to stay within the tolerance band for tooth spacing error allowed by the specification.

    If you can do that relatively easily and completely reliably when the hob spindle speed can fluctuate by +/-10 RPM (at a guess), you're golden, and you will be able to make very good gears provided you do everything else well.
    If you can't do that or something close to that, you may as well just get a really good indexer and a set of B&S involute cutters and just mill them, because you'll probably make better gears from the point of view of tooth spacing (but not tooth form).

    If you can hold the hob spindle speed very close to the nominal value, I assume the problem becomes correspondingly less difficult.
    I also assume that a big direct drive (or zero backlash drive) motor with clean incoming power is the simplest way to ensure fairly constant hob speed under real life conditions if you can't actually regulate it.
    (Of course I also assumed that a servo motor acting as a drive motor so you could command and regulate it's speed would be helpful in this regard, but motion guru has assured us that this is not the case, so I was wrong there.)

    So calculate what you have to accomplish based on those inputs and tell us how quickly you must be able to make a meaningful response to the hob speed changing in an uncontrolled way.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

    On Edit:
    While I'm at it we can think of the consequences of hob spindle speed variation and resulting lag of the workpiece rotation if the workhead can't keep up or overcompensates.
    Imagine the hob speed oscillating and the work not keeping up.
    The result will be that the profile of each tooth space will be wavy, not straight from one face of the gear to the other, and each gear flank will be gouged wherever the workhead goes out of synch.
    If the hob is large and the gear thin, the tooth thicknesses will be irregular so their effective spacing will also be irregular

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    Marcus,
    Keep in mind that your math solution only works out with a perfect cutting tool.
    Nobody makes "zero" cutting tools.
    This is a problem I have to explain over and over again to young process engineers and that includes simple turning, milling, boring, threading and you name it.
    You have a tolerance on your part, the cutting tool guy has a tolerance also. Why expect a perfect cutting edge location or geometry?
    People won't pay for "A" class carbide insets yet expect such performance.
    Given that the cutting tool has errors your class 10 become harder but few have the ability to check such other than being surprised at errors once the thing is put together.\

    The really weird part of this comes with the customer saying "Sometimes my cuts works out perfect, other times it makes scrap".
    Bob

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    Quote Originally Posted by drcoelho View Post
    My understanding is that Fellows machines mostly do gear copies, e.g. you need to have a master gear to start with...didn't want to have that limitation.
    Where in the hell did you get that idea ?

    This is what I am talking about. Before you design a machine, maybe you should know something.

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    Agreed CarbideBob!

    AGMA class 10 is hopelessly ambitious for a machine of this kind for a bunch of reasons but my point in dragging this particular spec out was to begin a conversation about roughly where he has to be, in order to make a better gear by hobbing than he can by indexing and milling.

    I've oversimplified the issues drastically so I could focus just on the electronic gearing and what has to happen in that regard.
    Of course, you're totally correct that the hobs will have tolerances too, and that the window within which you have to stay narrows rapidly as you add every new source of error.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    I'm gonna put a lot of money and time into working towards perfect synchronicity between the cutter spindle RPM and the rotary axis RPM. I'm also gonna put a lot of effort into very high quality tramming of the setup for low TIR, etc...Given that I see encoders with 1 million points per revolution resolution available, and given that I'm totally confident I can find a PLC that will have effectively zero latency at this 1 million resolution measurement, the area that I think needs most focus is how to keep the servo motor sync'd...the question in my mind is how much momentum the servo motor has and can one adjust its speed in a responsive enough manner to match any variations coming out of the cutter spindle.

    With respect to gear hob quality, I'm at the mercy of the commercial world...I'll certainly strive for buying quality, but whatever the market makes available will be my limit in this regard. I presume that high-end CNC gear machines also use these same gear hobs, so maybe there is hope of getting quality gear hobs?

    I don't need AGMA class 10 quality, my goal is to just match old school hobbing machine quality, and I doubt the older machines were holding that quality.

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    Quote Originally Posted by implmex View Post
    Agreed CarbideBob!

    AGMA class 10 is hopelessly ambitious for a machine of this kind for a bunch of reasons but my point in dragging this particular spec out was to begin a conversation about roughly where he has to be, in order to make a better gear by hobbing than he can by indexing and milling.

    I've oversimplified the issues drastically so I could focus just on the electronic gearing and what has to happen in that regard.
    Of course, you're totally correct that the hobs will have tolerances too, and that the window within which you have to stay narrows rapidly as you add every new source of error.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining
    Marcus, simple question: what AGMA class does an old school gear hobbing machine hold? Knowing that gives me my target spec for this project...

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    Quote Originally Posted by EmanuelGoldstein View Post
    Where in the hell did you get that idea ?

    This is what I am talking abuot. Before you design a machine, maybe you should know something.
    EmanuelGoldstein: second request, please be polite and don't insult folks for whom you know absolutely nothing about. I in turn will treat you with the same respect.

    Given your experience in this topic area, I would welcome any specific technical suggestions you might have to improve on my ideas.

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    Hi drcoelho:
    That is a question for those who run these machines every day and have to meet and certify to quality specs.
    That's certainly not me...I have no more than a casual acquaintance with gear making but I've adapted what little I know to the prototyping problems I knock up against just like the ones you are frustrated with.

    EmanuelGoldstein, Dan from Oakland, Zahnrad Kopf and others on this forum all do this for a living and know this turf a gazillion times better than I do, so they are the guys to ask.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Quote Originally Posted by drcoelho View Post
    EmanuelGoldstein: second request, please be polite and don't insult folks for whom you know absolutely nothing about. I in turn will treat you with the same respect.
    You are asking ignorant questions. That's all there is to it. You want to design a machine but your knowledge base is totally lacking. You haven't even told people what the requirements are, yet you say you want to experiement with non-involute shapes. Then you don't know what tolerance class you want, but wildly guess at what "old school hobbing machines" can do.

    Well, a fairly decent Barber-Colman 3 will do AGMA 10* if you are careful and have good tooling. 9 is pretty much a picnic. Mikrons and Koepfers and newer B-C's will easily do better than that. It's not real unusual for instrument gearing to be in the 12-ish range. Fine pitch is definitely a world of its own, measuring is about as hard as making. Some people make parts that are more accurate than master gears, which can lead to measurement difficulties

    You haven't even said whether you need helical or just spur is okay. Or if you need to make shafts or just gears. Those all have a bearing on what is the best way to cut the teeth. Basics first.

    The whole idea of hobs is counter to what you said you wanted. A rack is MUCH easier to make onesy-twosies and easier to make accurate than a hob. It's just straight sides evenly spaced at an angle. If'n I wuz going to start over with a non-production shop, I wouldn't even mess with disk type shapers, I'd go straight to the rack type.

    Class A and better hobs, btw, are EXPENSIVE. If you want something weird, you'll go through heck getting it, and expect to wait twelve weeks for one.

    @Marcus : commercial hobbing machines use a servo driving a wormgear for the work, and a servo driving the hob spindle. Some use a direct drive motor for the work spindle. Those occasionally have problems with cogging. A couple use two servoes with two wormgears, anti-backlashed against each other for the work spindle. There's a variety of choices

    *Rational AGMA, not the upside-down crap they changed to recently. Millenials will have a lot to answer for when St Peter meets them at the gate. With luck, they will go Below.

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    Quote Originally Posted by drcoelho View Post
    ... And mostly because I want to be able to create gears on the fly without having to order and wait, and also so I can experiment with unusual and exotic gear forms that might otherwise be unavailable.
    I'll leave the academic discussion for others with more time at hand. However, I am curious as to the above statement and how much it is TRULY the issue when there are at the very least a handful of us that do this quite regularly.

    We just delivered a handful of Prototype Gears in essentially two days from the placing the order to the sweaty palms of the customer assaulting the parts. Time is NOT an issue when you are willing to pay for it. Of course, this was a incredibly well known, global corporation that knew what they wanted. So they picked up the phone, told me what they wanted, and asked that we FedEx NDA the parts to them, ASAP.





    Then again, there are at least two other customers of ours contributing to this very thread that have asked us to make gears for them and deliver in very short order. So, it is not like it's uncommon...

    A recent order from another of them, here -

    I believe that these were into their hands in 4 days, if I recall correctly. Been a few weeks since. And that included Heat Treatment and WEDM.



    That leaves your statement of, "...experiment with unusual and exotic gear forms that might otherwise be unavailable."

    Are you also proposing to make the Hobs? I ask, because I have done so and can tell you right now that if you are already encountering this much trouble with the basics of the machines themselves, you are in for a wild ride and world of hurt when it comes to making custom Hobs. Even if you get your head around that, there is NOTHING fast about it. So, you once again return to your "want it right now" desire...

    I've just spent the last 6 weeks bunghole deep in math just trying to get to the point of making our own Gear Shaper Cutters and can report with enthusiasm that we will be actually trying our first one in the next 7 days. But it has been an ENORMOUS EFFORT that has relied on the knowledge and good will of SEVERAL others ( some of them members here ) just to get to this point.

    I completely understand the "want to do it" mentality and support it likely more than most any other, here. So, take this advice for being worth the amount of money you have paid for it -

    Do it because you want to do it.
    Do it because you want to learn something.
    Do it because you have money to burn and a hobby that will enable you to do so.

    Just don't for one second think anyone with the slightest amount of real knowledge or experience is going to buy that it's because you cannot get gears in quick fashion from a shop that can actually make them. It just doesn't hold water.

    I've been down this road. It wasn't worth it. But I had fun and learned quite a bit. However, I was not kidding anyone ( or myself ) about my motives. I sincerely wish you good luck with your efforts.

    Have fun and learn.

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    Quote Originally Posted by EmanuelGoldstein View Post
    You are asking ignorant questions. That's all there is to it. You want to design a machine but your knowledge base is totally lacking. You haven't even told people what the requirements are, yet you say you want to experiement with non-involute shapes. Then you don't know what tolerance class you want, but wildly guess at what "old school hobbing machines" can do.

    Well, a fairly decent Barber-Colman 3 will do AGMA 10* if you are careful and have good tooling. 9 is pretty much a picnic. Mikrons and Koepfers and newer B-C's will easily do better than that. It's not real unusual for instrument gearing to be in the 12-ish range. Fine pitch is definitely a world of its own, measuring is about as hard as making. Some people make parts that are more accurate than master gears, which can lead to measurement difficulties

    You haven't even said whether you need helical or just spur is okay. Or if you need to make shafts or just gears. Those all have a bearing on what is the best way to cut the teeth. Basics first.

    The whole idea of hobs is counter to what you said you wanted. A rack is MUCH easier to make onesy-twosies and easier to make accurate than a hob. It's just straight sides evenly spaced at an angle. If'n I wuz going to start over with a non-production shop, I wouldn't even mess with disk type shapers, I'd go straight to the rack type.

    Class A and better hobs, btw, are EXPENSIVE. If you want something weird, you'll go through heck getting it, and expect to wait twelve weeks for one.

    @Marcus : commercial hobbing machines use a servo driving a wormgear for the work, and a servo driving the hob spindle. Some use a direct drive motor for the work spindle. Those occasionally have problems with cogging. A couple use two servoes with two wormgears, anti-backlashed against each other for the work spindle. There's a variety of choices

    *Rational AGMA, not the upside-down crap they changed to recently. Millenials will have a lot to answer for when St Peter meets them at the gate. With luck, they will go Below.
    Thanks for all the useful and actionable information above, very helpful.

    I stated several times, looking to do spur gears only, and mostly in the 1-5" diameter size.

    I am learning a lot about this subject very quickly, and REALLY appreciate all of the comments. I will admit up-front that I am very green on the machining side of things, but I can guarantee I know a LOT more on the computer/PLC/electrical engineering side than most folks on this forum.

    It is possible that this project is totally ridiculous from a cost/return basis and that I should just out-source my gear production needs to others. That being said, I am still intrigued about whether it is possible to adapt a Deckel manual mill to replicate the capabilities of some of the older style gear hobbers....you might view this as an intellectual exercise on my part. I look at the older machines and conceptually they just seem to be quite simple in operation, maybe I'm missing something.

    None of the work I'm doing is for production purposes.

    At a minimum, I have learned a lot from you and the other experts on this forum and in this thread....very very interesting stuff.

    So, let me state the requirements of the project as follows:
    - assume I've already collected a number of commercial gear hobs and they are sitting on the shelf
    - I'm working late at night out in the middle of nowhere and decide I want a gear that evening
    - I whip out my little gear hobbing accessory for my Deckel mill, tram it, and create the gear
    - I STILL don't have the space for a dedicated gear hobbing machine in my shop....

    What would YOU do given these requirements?

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    Quote Originally Posted by Zahnrad Kopf View Post

    Are you also proposing to make the Hobs? I ask, because I have done so and can tell you right now that if you are already encountering this much trouble with the basics of the machines themselves, you are in for a wild ride and world of hurt when it comes to making custom Hobs. Even if you get your head around that, there is NOTHING fast about it. So, you once again return to your "want it right now" desire...

    I've just spent the last 6 weeks bunghole deep in math just trying to get to the point of making our own Gear Shaper Cutters and can report with enthusiasm that we will be actually trying our first one in the next 7 days. But it has been an ENORMOUS EFFORT that has relied on the knowledge and good will of SEVERAL others ( some of them members here ) just to get to this point.

    I completely understand the "want to do it" mentality and support it likely more than most any other, here. So, take this advice for being worth the amount of money you have paid for it -

    Do it because you want to do it.
    Do it because you want to learn something.
    Do it because you have money to burn and a hobby that will enable you to do so.

    Just don't for one second think anyone with the slightest amount of real knowledge or experience is going to buy that it's because you cannot get gears in quick fashion from a shop that can actually make them. It just doesn't hold water.

    I've been down this road. It wasn't worth it. But I had fun and learned quite a bit. However, I was not kidding anyone ( or myself ) about my motives. I sincerely wish you good luck with your efforts.

    Have fun and learn.
    Never planned on making my own gear hobs, always planned on buying those commercially.

    I'm doing this because it is an interesting project.

    OK, OK, I got it....much easier/cheaper/faster to just buy the gears.....

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    Quote Originally Posted by drcoelho View Post
    Never planned on making my own gear hobs, always planned on buying those commercially.
    I'm doing this because it is an interesting project.
    OK, OK, I got it....much easier/cheaper/faster to just buy the gears.....
    Okay. That was likely an error on my part. It was the logical extrapolation of your writing -

    Quote Originally Posted by drcoelho
    ... and also so I can experiment with unusual and exotic gear forms that might otherwise be unavailable.
    Since you are discussing a Gear Hobber ( or rather, a Gear Hobbing attachment ), want to do "unusual and exotic gear forms that might otherwise be unavailable", and also want them faster than you think someone else can supply them, I extrapolated that you would then make your own Hobs. Otherwise, I'm not clear on just how you would propose to make such gears. Ordering custom Hobs will delay your efforts by months, as typical turn arounds for customs is 8 - 16 weeks, usually.

    In my case, we were experimenting with Asymmetrical Tooth Forms as well as non standard Pressure Angles. Crazy, fun stuff.

    These days, I want to do similarly with Pinion Cutters, as well as Non-Involute forms additionally.

    Frankly, you'd be well advised to listen to Emanuel Goldstein's advice. Using a Rack Form tool will make your task IMMENSELY more simple and easily achieved. The relative motions are simpler, easy to calculate, and the tooling SO MUCH SIMPLER to make.

    In fact, we're looking for a Sunderland right now...

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    I have looked very closely at the Sunderland approach....just trying really hard to avoid having yet another machine in the shop......

    And the "unusual and exotic gear forms" requirement was probably more than I need at this stage...but I don't discount the idea of fiddling with that at some point in the future.

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    Hi Zahnrad Kopf:
    You wrote:
    "In fact, we're looking for a Sunderland right now... "

    I thought these were totally obsolete dogs by now and that nobody would want one even if it were given to him.

    Do you want it because you can make cutters for your experimental stuff so much more easily?
    Is there another reason I'm not thinking of?
    Are these machines even still produced and desired in gear shops around the country?

    The ones I've seen working just seem so damned SLOW to me... like machining flat plates with a shaper.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
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    Just to stir the pot a bit (people are being unreasonably civil), some thoughts on helping with sync of machine (hob) spindle to gear blank spindle:

    1) Add mass to the hob spindle. A removable flywheel of some size will cut down on fractional rotation errors by being, uhh, a mass that resists RPM variations due to motor output, cutter load, or other things that could cause variation. And given that it's removable, it would not interfere with normal machine use, while simplifying electronics requirements for syncing (?).

    2) A step beyond - a second (removable) servo motor attached to the hob spindle that would not only act as a flywheel on its own, but be actively driven to match speeds with the gear blank spindle. Therefore it would enhance sync (presuming drive electronics are up to snuff) through both mass and active RPM changes (at the cost of some tuning to counter torque ripple from original drive).

    I suspect whatever is done, adding the right incoming power filters to the machine and electronics (line/load reactors, etc.) would help with minimizing milling spindle output changes. As will mechanical optimization (hob TIR error minimization, ditto gear blank, all bearings in good nick, blah, blah).

    I do love spending (virtually) other people's money...

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    Well, a fairly decent Barber-Colman 3 will do AGMA 10* if you are careful and have good tooling. 9 is pretty much a picnic.
    BadaBOOM. That is all you need to know, right there. While building your own CNC is probably an irresistible concept to a person raised in the digital age, if your goal is to actually earn a living manufacturing your product you have to quit trying to reinvent technology that was perfected between 1920 and 1950. You are just not going to equal the results, nor the cutting rigidity, nor even the ease of use of an "old school" gear hobber even in a one-part application. Sorry, but it has to be pointed out (if making money doesn't matter, then, absolutely, go for it).

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    Hi drcoelho:
    You wrote:
    "I have looked very closely at the Sunderland approach....just trying really hard to avoid having yet another machine in the shop......"

    Were you aware you can "do the Sunderland process" on a mill without much difficulty?
    It helps if the machine is CNC but it's not hard to do and you've got a Speedio, so you're all set for toys..

    This is not like the process I described previously where I was specifically making (or should I say "faking") cluster gears and treated the machine like a vertical shaper.

    What you need to grasp conceptually, is that the Sunderland process generates gears by moving a blank across a rack shaped cutter to generate the involute profiles of the tooth flanks.
    There is no need for it to be a shaper, although that's how the machines were originally built.
    You can just as well gang a stack of saws each of which has the correct rack tooth geometry, and saw the tooth spaces of the gear rather than shaping them.
    By indexing the blank and raising and lowering the stack of saws, you will do exactly what a Sunderland machine does to generate involutes with all of the benefits and pains of this process.
    Fundamentally you will make flats that approximate the involute...it's characteristic of the process, but with enough passes spaced close enough together, it is a very close approximation indeed.

    So if you really want to make gears on your mill, it's an attractive option entirely because of the simplicity of the cutting tool.
    All you need is a single tooth flycutter, or (if you want), a flycutter that is like a ganged saw. but made of a rack shaped strip bolted onto an arbor

    Make up a flycutter, write yourself some code and go at it.
    Ditch the Deckel for this, run it on your Speedio and go to town.
    If you want the results to be decently accurate, you need a good fourth axis indexer capable of very small increments, but you no longer have to synch a rotating hob with a workhead...you're just indexing, making a small Z axis move, and then cutting a path along X, so it's really simple to implement and ideal to automate on a VMC.
    Write yourself a parametric program and you can make any weirdass gear you want...no fuss no pain.

    I've done it and I even still have some cutters I made up for it decades ago.
    Worked very well for the application and was cheap and quick to implement.
    Attached is a picture.
    Cheers

    Marcus
    www,.implant-mechanix.com
    Vancouver Wire EDM -- Wire EDM Machining
    Attached Thumbnails Attached Thumbnails fake-sunderland-cutters.jpg  

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    Quote Originally Posted by Zahnrad Kopf View Post
    A recent order from another of them, here -

    I believe that these were into their hands in 4 days, if I recall correctly. Been a few weeks since. And that included Heat Treatment and WEDM.
    . . . I recognize those gears . . .

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    Quote Originally Posted by implmex View Post

    I thought these were totally obsolete dogs by now and that nobody would want one even if it were given to him.

    Do you want it because you can make cutters for your experimental stuff so much more easily?
    Is there another reason I'm not thinking of?
    Are these machines even still produced and desired in gear shops around the country?

    The ones I've seen working just seem so damned SLOW to me... like machining flat plates with a shaper.
    Hi Marcus!

    Where to begin... Sunderlands are long obsolete. You are correct in that many ( if not most ) shops would not want one. However, they are fairly popular in other parts of the world and widely sought for rebuilding/remanufacturing and putting into use as they are slow, but venerable work horses. They get the job done. They are also able to make disproportionately larger gears than their size might lead one to assume. Not to mention Herringbone gears...

    However... you are correct about my main reason for wanting one ( right after the coolness factor ) is the simplicity of the tooling and the ability to make just about any of it, easily.


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