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    Quote Originally Posted by drcoelho View Post
    I have looked very closely at the Sunderland approach....just trying really hard to avoid having yet another machine in the shop......
    I was not suggesting that you add a machine, but rather modify your approach to the problem. ( or desired result )

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    Quote Originally Posted by motion guru View Post
    . . . I recognize those gears . . .
    Haha! I knew you would, but wasn't going to blatantly name you guys.

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    Quote Originally Posted by drcoelho View Post
    I stated several times, looking to do spur gears only, and mostly in the 1-5" diameter size.
    The traditional first step is a 7A Fellows shaper ... or a 6-10 Barber-Colman. If you could live with 3" diameter, a #3 Fellows might be ideal. SMALL

    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.
    I would not say that. It's just that ...

    That being said, I am still intrigued ...
    I can tell

    I look at the older machines and conceptually they just seem to be quite simple in operation, maybe I'm missing something.
    Old machines, new machines, all same-same. The problem is you are not thinking of the entire process. All you are considering is how cool it is to make two shafts rotate together.

    But that is not the whole story !

    None of the work I'm doing is for production purposes.
    Then why are you in love with hobbing ? Marcus has described a better way to do prototypes. Considering the cost of cutting tools, I'm going to go against my preferences and say wire edm is best for what you want to do.

    The problem here is, you're focussed on making two shafts rotate in a timed relationship. It's not as bad as you are making it, by the way. For every tooth in the part the hob rotates once, but the work rotates a fraction. 20T gear, hob rotates 20 times, work rotates once. That helps a lot to even out any small discontinuities.

    But it doesn't help with the biggest problem, the cutters. We're tallking hundreds of $$$ each here, for standard hobs. One pitch, one pressure angle, one tooth depth per hob. Want to try a 22 1/2* PA ? (Supposedly they run smoother.) $$$ and 8-10 weeks. How about a radiuis root on this part ? $$$ and another 8-10 weeks. Shall we just order one of everythig you think you might ever need ? You could go through $20,000 and still not have the one you want.

    This is the weakest point of your plan.

    I'll skip the mechanical stuff for now, but people have put a lot of thought into reacting the cutting forces, optimizing the machine constant for the type of work you plan to do, choosing the best bearings for the job, all that bla bla.

    But let's bring up just one small feature you haven't thought of - what will you do about cutting oil ? Unless you plan to spend the REALLY big bucks for carbide hobs, you're going to be cutting wet. VERY wet. Deckels aren't made for pumping three gallons a minute around. Where will the chips go ? Little Barbers and Fellowses have this all figured out. Doesn't sound like you've even considered it.

    Considering the fact that a gear cutting machine is more than just two shafts rotating together, I'd for sure pick up an old clunker for a base and add your electronics to that. That way all your mechanical stuff is figured outo and proven. Then you can still have the fun of figuring out the electronics but at least when you're done, you should have a functional machine.

    But probably the sensible thing to do in your case (you like math. I hate it) is to wire edm your parts. Then you don't have to build anything, and you get what you want right away. And it's useful for other 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
    But you haven't, which makes this exercise meaningless. You are grossly underestimating the hassle of cutting tools in making gears. This is the fact that will make your projected attachment useless for the purposes you have described.

    Door Number One : Wire edm

    Door Number Two : rebuild and electronify a Fellows straight line generator

    Door Number Three : (second-to-pessimum choice, only one step better than your deckel idea) -- find some other clapped-out hobber to use as a base. Seriously, Koepfer, Mikron, Sykes, B-C, Hamilton, they've all gone through this stuff and there's more to it than you think.

    Door Number Four: Search for a little gear grinder. You CAN dress the wheel to whatever shape you want fairly easily. You won't be restricted to buying hobs or shaper cutters. They can grind from solid. I know of a 6" David Brown (same design as a Matrix) and there was a guy who was modifying Hoagland dressers to make little fine pitch grinders out of them.

    Or even create your own, but using an existing machine as the base. Do this same project but use a little surface grinder as a starting point. Then you bypass all that hob stuff.


    Quote Originally Posted by implmex
    I thought these were totally obsolete dogs by now and that nobody would want one even if it were given to him.
    We have sold Maag shapers for $400,000 - $500,000,- $800,000. Not entirely obsolete

    For certain types of work they are still the best. The newer ones (only 50 years old) can even do hard cutting. They look slow but they take a big bite Hobbing big parts is not exactly speedy either. We did have some success with gashers that wouold cut AGMA 10 teeth on a 2.5 meter part in two hours, but the cutting tools were over $10,000 apiece and only worked for one part. Definitely production work !

    As a Maag-lover, I'm not sure why ZK wants a Sunderland ... except that they can do herringbones in a single operation. That's kind of neat, if you need to do herringbones. There are newer versions of the Sunderland that don't looks so antique but they must be rare as hen's teeth, I've only ever seen one.

    But if you really want one, ZK, there's one I know of in Thailand that you could get for a song. Needs work. And it's maybe a 60" machine ?

    Quote Originally Posted by Milland
    1) Add mass to the hob spindle ...
    You're reinventing the wheel Commonly done, LOTS of hobbers have external flywheels.

    Seriously, people have been cutting teeth for a long time. Research what's been done first, you'll be surprised. We didn't invent engineering yesterday ...

    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.
    You can't match speeds unless you are cutting a one-tooth gear. (you can do this with a herringbone, if absolutely necessary ) Hob rotates one revolution per tooth, part rotates once per however many teeth you are trying to cut. Plus or minus whatever you need for the helix, in the case of a helical gear. Electronic differential time ?

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  6. #104
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    Quote Originally Posted by EmanuelGoldstein View Post

    You're reinventing the wheel Commonly done, LOTS of hobbers have external flywheels.

    Seriously, people have been cutting teeth for a long time. Research what's been done first, you'll be surprised. We didn't invent engineering yesterday ...
    Nyet! As a mechanical designer (faux-engineer) I like thought experiments, and finding out that it's been done before confirms I'm on the right path - much more gratifying than checking out what others have done first.

    Ignorance is strength, I always sez. Or at least creativity.

    You can't match speeds unless you are cutting a one-tooth gear. (you can do this with a herringbone, if absolutely necessary ) Hob rotates one revolution per tooth, part rotates once per however many teeth you are trying to cut. Plus or minus whatever you need for the helix, in the case of a helical gear. Electronic differential time ?
    Nein! Auxiliary servo is acting as a virtual flywheel, and while it could be timed to the gear blank shaft what I'm suggesting is it acts to modulate "dumb" motor output and lock it to a specific speed, without having to be big enough to fully replace the prime mover. Think smart little guy getting the dull brute to do his bidding...

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    EmanuelGoldstein: the information you have provided is exceedingly interesting and useful, THANKYOU!

    Soooooo.... a few responses to you:
    - I had considered coolant, I've got both flood coolant and MQL options on my FPS 300 M milling machine
    - swarf is no problem, my mill can accomodate
    - My thought for managing the cost of gear hobs was to make some strategic choices about the types of gears I'll be using for my various projects and buy a subset of hobs to match these choices
    - All the machines you mention look really cool, BUT I REALLY REALLY REALLY do not want to put yet another machine in my shop, it's so darn crowded as it is

    I know I'm annoyingly persistent here, but be patient with me, will the following work?
    - FPS 300 M milling machine (late model Deckel FP1 clone)
    - Very high quality rotary, very high quality servo motor
    - Assume I solve the PLC/synchronization issue between cutter speed and work piece speed
    - Assume I've got the money to buy all the gear hobs I'll need
    - Assume I have available flood coolant and/or MQL coolant

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    Quote Originally Posted by drcoelho View Post
    - Assume I have available flood coolant and/or MQL coolant
    Don't even consider soluble oil. We're talkin' dead pteranosaurs here, and little tiny chips that clog everything and get packed into crevices and take forever to drain. Recutting is something to consider, that's one reason vertical spindle hobbers are popular.

    Most machines use very accurate wormgears for the hob and work spindles. Your deckel spindle may have a problem with backlash, hobbing is a very interrupted-cut situation. The load is forever changing, it's not practical to even figure out a chipload because the amount of material changes so much as the cutter passes through the work. There's a good chance your hob spindle will rattle. Bolt on Milland's ten pound flywheel maybe.

    What you are insisting upon is probably the worst possible way to do this, so I dunno what else to say.

    ZK, have you considered an SH45 or SH75 ? Pretty nice and easier to find than a Sunderland ....

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    Hi

    For me the price of hobbs just eliminates them from consideration.

    If I was to make a non-production gear cutting machine I would use my FUS22 Deckel clone, which includes a slotting head.
    With this I would electronically gear the table motions to a horizontal rotary table.
    I would use a single tooth rack as the cutting tool.

    A single tooth rack would be an easy tool to accurately grind and very cheap. The tool cutting edges would be straight and flat.

    This type of gear cutter would be able to generate any involute gear form with any tooth count. It could cut to a shoulder and, unlike a hob, it could do internal gears.

    The major disadvantages would be:
    very slow to cut a gear
    the amount of work required to retrofit CNC to the motions, but useful for other work. A CNC retrofit would be a lot less effort than a pure mechanical solution.

    I have not seen a milling machine configured as described above. The closest I can find is here
    I know the technique has been applied on shaping machines (and here) but I haven't seen it done on a mill.

    The key differences between a Fellows and the concept above are:
    The cutter remains stationary in the x,y axis (reciprocates on the z axis),
    the gear blank would rotate around the z axis and translate past the cutter on the x axis.
    Depth of cut would be adjusted on the y axis.

    I won't call this my idea because it is so obvious, someone else must have done it already.

    Dazz

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    This is an interesting idea. I've already got a slotting head accessory for my Deckel. It hadn't occurred to me to use a single tooth rack, I would have thought that multi-tooth rack would be required to get things right. There are some challenges in synchronizing the slotting head motion with the horizontal rotary movement. Also, I believe the rack needs to move incrementally along the tangent of the work piece as it rotates to get the curve right, which would require some tricky mechanicals on the slotting head, or I guess you alternatively are suggesting moving the milling table simultaneous with rotary index rotation....that seems to me to be a difficult thing to pull off with accuracy.

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    Hi
    With electronic gearing and LinuxCNC which can do almost anything, it's only a math problem.
    A single tooth cutter would be slow but with CNC, just start the program and let it run til done.

    I have the slotter and a heavy duty Russian made rotary table. I don't have CNC.

    Dazz

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    Unfortunately, I'd don't have CNC control of my milling table so this approach won't work in my case.

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    FYI, this is a very interesting article Nasa Reference Publication 1406 which provides a solid mathematical theory for Involute Spur Gears (among others): NRP-1406 NASA REFERENCE PUBLICATION DEVELOPMENT GEAR

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    I have thought about trying to convert one of my Barber Colman hobbers to CNC. I just don't know enough about controls and electronics to know where to start. Most of my gear cutting machines are WW 2 era machines.

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    Quote Originally Posted by gear cutter View Post
    I have thought about trying to convert one of my Barber Colman hobbers to CNC. I just don't know enough about controls and electronics to know where to start. Most of my gear cutting machines are WW 2 era machines.
    Shh! You can't talk about CNC conversion of manual machines here! Someone will come along and declare you a "home shoppe machinist" and banish you...

    /S

    Yeah, me too. I have a giant Monarch (15ft CC) that I want to convert, but figure I'll start with a smaller machine first. The idea is seductive, even if the reality is it's usually a time sink with less return than you'd like. But if you learn something, it's all good.

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    Used hobs go for peanuts. Back in the day I bought PILE at auction of a gear cutting place going out of business.

    I see they are on eBay
    https://www.ebay.com/sch/12576/i.htm...LH_TitleDesc=0

    They are fairly easy to re sharp on a tool and cutter grinder. just grind the leading edge back a bit.

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    "They are fairly easy to re sharp on a tool and cutter grinder. just grind the leading edge back a bit. "

    Nothing could be farther from the truth. I'm certain that you know the involute form produced by an improperly sharpened hob can greatly affect the final product. There is a reason that hob checking fixtures are just one more little detail that most folks not well versed in the overall process tend to not know about. Hobs for accurate gears are sharpened on hob grinders- not tool and cutter grinders. If you are very very carefull and know what you are doing, you might be able to sharpen a straight fluted hob on a T&C grinder without screwing it up, but no gear shop is going to do it that way.

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    Hi Dazz:
    You wrote:
    "For me the price of hobbs just eliminates them from consideration.

    If I was to make a non-production gear cutting machine I would use my
    FUS22 Deckel clone, which includes a slotting head.
    With this I would electronically gear the table motions to a horizontal rotary table.
    I would use a single tooth rack as the cutting tool.

    A single tooth rack would be an easy tool to accurately grind and very cheap. The tool cutting edges would be straight and flat.

    This type of gear cutter would be able to generate any involute gear form with any tooth count. It could cut to a shoulder and, unlike a hob, it could do internal gears."

    So here's a snip from my post #65 in which I describe something similar:
    When I have cluster gears or plastic gears to cut, my GO TO machine is my Haas Minimill with a custom G code writing program done for me by a buddy years ago that allows me to make a single tooth rack profile shaper cutter, and use spindle orient to generate an involute gear using the same strategy as the now ancient and long obsolete Sunderland gear shaping process uses.

    The only mods to the mill are a toolholder modified to allow me to position my single tooth shaper cutter in the proper relationship to my gear blank and lock it in place.
    In 45 years of doing this for a living, I've used the setup maybe 10 times, but when I NEED it, it's been a bacon saver and it's totally frickin cool to watch it dancing around the blank.
    For the simple price of a custom ground (by me) rack tooth with rake and relief, I can get any DP, or pressure angle or anything else I want...a cutter is under an hour to grind on the tool and cutter grinder and it consumes a buck or so in HSS.

    My process is like what you describe but with one big difference.
    I have no rotary table at all; the blank is mounted in a vee block in the vise or a 3 jaw chuck bolted to the table and cannot rotate.
    Instead, I simply rotate my cutter with spindle orient and then re-position it in X and Y before I do another shaper stroke in Z.
    This eliminates a good bit of screwing around to get set up and I don't have to care about all the stuff the OP was having to deal with using his approach.
    I just clock in my blank, grind and orient my custom single tooth rack, run my code writing generator, post it, and push the green button

    Of course the limitation is that my precision is limited by the accuracy of my spindle orient and my ability to interpolate the cutter position around my blank, so I know I'm nowhere even close to an accurate gear, but for prototyping a rude and dirty cluster gear it's still a very useful tool and remains a helluva lot better than a 3D printed abomination.

    When I need REAL gears, I will simply email Zahnrad Kopf with my specs and ask price and delivery, then refer my customer to him to do his magic, knowing my customer will get what they need to be successful.

    The real benefit of using these multiple prototyping approaches I've described is that I can get pretty much whatever I want for my prototype for cheap...my concerns are often about crowding a gear set into a place where there is not a lot of space, so I find it useful to be able to make non-standard diametral pitch gears or partial gears with other weird bits hanging off the end or little worm drives or little bevels...I've made all kinds of crazy stuff.

    Like all prototyping shops I also don't have time to dick around, and customers won't pay for it either.
    I've fucked around with a lot of different methods over the years to solve my prototyping problems...the ways I've described are the best ways forward that I have found.

    However the single most useful tool I've EVER found is to know when to farm the work out.
    That's why I always ask first what the gear set is going to be expected to do.
    Once I know the specs, I will also know whether I can successfully fake it or not.

    As I get older and have more painful fuckups under my belt, I've gotten better and better at making that evaluation.
    Now that I have less to prove, I'll ditch the tough ones in a heartbeat, to those who do it for a living and have the toys and the metrology to do it right.

    Cheers

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


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    Quote Originally Posted by Milland View Post
    Shh! You can't talk about CNC conversion of manual machines here! Someone will come along and declare you a "home shoppe machinist" and banish you...

    /S

    Yeah, me too. I have a giant Monarch (15ft CC) that I want to convert, but figure I'll start with a smaller machine first. The idea is seductive, even if the reality is it's usually a time sink with less return than you'd like. But if you learn something, it's all good.
    We have a Cleveland Planer retrofitted with ballscrew on the Y-Axis, Bridgeport Head, and 840D sl w/ HT8 pendant . . . it is one of the most used machines in our shop.

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    Quote Originally Posted by drcoelho View Post
    Unfortunately, I'd don't have CNC control of my milling table so this approach won't work in my case.
    If you have a slotting head you don't need nc for any of this. You could do it with tapes and base circle disks, like a Maag SD series grinder. You'd still have to index between teeth but hey now, easier than all these other plans.

    Cut to the chase. Wire edm.

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    Quote Originally Posted by EmanuelGoldstein View Post
    If you have a slotting head you don't need nc for any of this. You could do it with tapes and base circle disks, like a Maag SD series grinder. You'd still have to index between teeth but hey now, easier than all these other plans.

    Cut to the chase. Wire edm.
    Interesting, I'll give it some thought.

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    Quote Originally Posted by Milland View Post
    Shh! You can't talk about CNC conversion of manual machines here! Someone will come along and declare you a "home shoppe machinist" and banish you...
    .....
    I'd hate to think that this is the way it is here.
    Most of my cnc grinders started out life as basic manual machines.
    I built my first in 1979 from a Harig 612 and a expanded COSMAC ELF. A few years later it would get a upgrade to a ZX81.
    I knew nothing at the time about interrupt latency, servo loops, Z-transforms, rotary inertia and system response times. All greek to me.
    I just thought I could make it work somehow.
    The best way to learn this is to go do it and have it not quite come out the way you hoped for. As machinists we do this all the time on DOC, federates, tool geometry, path types.
    I still have the machine undergoing it's umpteenth upgrade and now it will be a 5 axis running on Galil and windows.

    The OP should not get too worried about it all being right on the first build. It won't be.
    Build it, find the bad things things, fix them.
    Most people who build such custom or one-offs go through a debug process.
    All good and great to ask for opinions as food for thought but you know what they say about stinky opinions.
    Gather as much data as you can digest and then run with your gut.
    Bob


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