Gear Shaping Cutter Design
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    Default Gear Shaping Cutter Design

    I know this is a long shot, but what are the chances that someone here has a background or actual knowledge** of the design of Gear Shaping cutters? **- no real interest in conjecture.

    We need a Gear Shaping cutter and it is a custom cutter. So far, every normal outlet is unable to satisfy the required date, regardless of expedite fees. We're being told 16 weeks by most places, and that simply won't work for the customer. So I got to thinking...

    I've been making custom cutters for milling, turning, and even normal shaping for years. So why not a
    Gear Shaping cutter? For the moment, forget about the mechanics of it. What about the theory of the design and construction? I've searched high and low and have not found much about it. It's seemingly more obscure than the design of Hobbing cutters. Yet, there are companies doing so...

    So where is this trove of knowledge being stored? I've tried the usual suspects and combed through the countless books and whitepapers that I've accumulated over the years. Dudley treats it better than most ( no surprise there ), but is still largely sparse and leaves the potential student wanting. On the surface, it's little more than the opposite gear, in conjugate motion, reciprocating with sharpened edges... But there HAS to be more. Clearances and considerations that I'm simply completely ignorant of.

    So where is it? Where are the guidelines and equations? Where are the dos and don'ts?

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    Well, EG seems quite knowledgeable about the subject, if you want try PM'ing him.

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    EG has made one cutter that I'm familiar with- it was a straight sided internal clutch hub that he made the cutter for. I'm sure he will be along shortly. I'm thinking the approach is two rolling cylinders- one the finished form of your part and you map discrete points from that to your cutter has they roll together. YA probably could do a pretty good job mapping the two together in Solidworks or other solid modeling program. The trick being your tool profile needs to be some multiple of your part circular pitch.

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    You rang ?

    ITW did have at least one pamphlet on the design of shaper cutters. They gave them out at their gear school. From memory, they did the design manually on drawing boards, odontographically You could do that in a cad program now more easily.

    Besides the 5* face angle, you're right, there was information about the form change as the cutter was resharpened and the side clearance. They were roughed on shapers with a tilt table. They also made a big point about the heat treat - as I remember, they got the cutters within 50* of melting before quench. Something like 2100* ? You need an accurate thermostat for that !

    Then they ground them on what looked like a Kolb single-wheel grinder but the cutter axis was at an angle. Also the wheel was over the work instead of the opposite, but the same principle. Definitely special machines. If you look at Fellows-made shaper cutters, they must have been ground on something similar to Pratt & Whitney gear grinders, with big stationary wheels that the cutter generated through but no fore-and-aft motion.

    There's a good chance we could beat 16 weeks if you can tolerate China. And the price would be half. The accuracy is fine but the steel less so. Still, for the price if you don't mind resharpening more often, it's an option.

    Making your own is .... interesting Kind of a worthwhile experience tho ...

    If you can find someone who has that old Illinois Tool literature, that'd be great. Mine went the way of all flesh when I inadvisedly gave custody to some slimebags

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    Quote Originally Posted by Dan from Oakland View Post
    EG has made one cutter that I'm familiar with- it was a straight sided internal clutch hub that he made the cutter for. I'm sure he will be along shortly. I'm thinking the approach is two rolling cylinders- one the finished form of your part and you map discrete points from that to your cutter has they roll together. YA probably could do a pretty good job mapping the two together in Solidworks or other solid modeling program. The trick being your tool profile needs to be some multiple of your part circular pitch.
    Dathan made cutters like that for me, a hub type shaper cutter that makes 12 straight sided slots in a 6.5" bore. I went through Ash to get it made. It's really interesting to watch the paths the edges of the cutter makes in relation to the finished part as the machine rotates the cutter in the part, and there are no straight edges anywhere on the cutter. The 2 cutters are slightly different diameters but both work the same in the cut. Was pretty challenging to get it to run correctly on a 6A also, and Ash was no help there at all, no one there seemed to have much hands-on shop experience with the machinery, at least 20+ years ago . I'm sure you've already called Ash but Dathan offer design consulting on their site, perhaps they could give you the geometry to wire the cutter you need yourself?

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    Quote Originally Posted by EmanuelGoldstein View Post
    You rang ?

    ITW did have at least one pamphlet on the design of shaper cutters. They gave them out at their gear school. From memory, they did the design manually on drawing boards, odontographically You could do that in a cad program now more easily.
    That's exactly my plan, right now. Thanks for the reminder on ITW. I should have known that off the top of me head. Have countless normal cutter stuff from them.


    Quote Originally Posted by EmanuelGoldstein View Post
    Besides the 5* face angle, you're right, there was information about the form change as the cutter was resharpened and the side clearance. They were roughed on shapers with a tilt table. They also made a big point about the heat treat - as I remember, they got the cutters within 50* of melting before quench. Something like 2100* ? You need an accurate thermostat for that !
    Dudley cites 1.5° - 3.5° side relief and various top reliefs depending on pressure angle, but in honestly it read like it was dated, and relevant more to the material and processes of the era, than this one. Still, invaluable for the bread crumbs...

    Still, conspicuously absent is any discussion of tooth clearances, tip and root. Hobs and Rack tools incorporate it. I discovered this when I was forced to make a few Hobs. ( another story, for another time ) And the reasoning makes perfect sense, so I'm thinking that a Shaper cutter shouldn't be any different, here. After all, something has to install that Root Clearance into the gear. It won't magically appear on its own... But how much? The same, typical value as Hobs? It sure seems a simple question, but then I'm completely ignorant, here. I don't know what I don't know.


    Quote Originally Posted by EmanuelGoldstein View Post
    Then they ground them on what looked like a Kolb single-wheel grinder but the cutter axis was at an angle. Also the wheel was over the work instead of the opposite, but the same principle. Definitely special machines. If you look at Fellows-made shaper cutters, they must have been ground on something similar to Pratt & Whitney gear grinders, with big stationary wheels that the cutter generated through but no fore-and-aft motion.
    Interesting. Thanks.


    Quote Originally Posted by EmanuelGoldstein View Post
    There's a good chance we could beat 16 weeks if you can tolerate China. And the price would be half. The accuracy is fine but the steel less so. Still, for the price if you don't mind resharpening more often, it's an option.
    I've never bought chinese gear tools*. We always purchase quality tooling and Class AA or A. ( unless the only option is B, as in Timing Pulley Hobs. This might well be an emergency, though... Send me an email through the site or PM me your contact info and I'll shoot you over the details of what we need.

    *- Once used a chinese hob that came in a shop closing purchase. It blew up, on the second pass.

    Quote Originally Posted by EmanuelGoldstein View Post
    Making your own is .... interesting Kind of a worthwhile experience tho ...

    If you can find someone who has that old Illinois Tool literature, that'd be great. Mine went the way of all flesh when I inadvisedly gave custody to some slimebags
    I honestly do not want to. Maybe some other time. But right now, we are too busy for me to be fiddle farting around with making cutting tools. I'd MUCH rather find someone to make it. Will likely need two for the size of the order. There is another custom cutter for the OD Spline, so maybe more to make.


    Quote Originally Posted by Mud View Post
    Dathan made cutters like that for me, a hub type shaper cutter that makes 12 straight sided slots in a 6.5" bore. I went through Ash to get it made. It's really interesting to watch the paths the edges of the cutter makes in relation to the finished part as the machine rotates the cutter in the part, and there are no straight edges anywhere on the cutter. The 2 cutters are slightly different diameters but both work the same in the cut. Was pretty challenging to get it to run correctly on a 6A also, and Ash was no help there at all, no one there seemed to have much hands-on shop experience with the machinery, at least 20+ years ago . I'm sure you've already called Ash but Dathan offer design consulting on their site, perhaps they could give you the geometry to wire the cutter you need yourself?
    That was my thinking. I'd buy some M2 or similar and machine the holes and features I want, then heat treat, and then WireEDM. Finally, sharpen and go to town. Of course, this is in ID Spline, so I'll need to make some manner of shank rigid enough to hold a small button cutter, too.

    Thanks all.

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    I forgot to add in my response, that another question regarding Form is nagging at me, as well.

    We know that the grinding of form cutting tools can alter the form imparted upon the work by incorrectly sharpening/grinding their faces**. And it occurs to me that this is very much to be at least considered when dealing with the 5°(+/-) Face Angle used on Shaper cutters. So, it seems prudent to construct the Involute Profile on a plane that resides at 5° from normal, and then project that profile onto the normal plane for the consideration of wiring the tool. Am I thinking of this correctly? Or is this of minor concern?

    ** - we need only look to the importance of the sharpening Hobs or even Involute Form Mills to see how changing the rake angle even slightly impacts the resulting Involute's accuracy of form.

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    I'm thinking something along these lines... It's a 0.7083 Major Diameter...


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    Duh! Did you contact Broachmasters? They make shaper cutters. The Broach Masters

    Dan

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    .700 major? So a shaper cutter would need to be .450 or so dia? If you'fre not considering wiring it that means it's in a blind hole or working to a shoulder, right? And I'm guessing the slots need to be timed to the part too? Could it be done with a series of button broaches?
    Forgive me for drifting from the original question, the small size just makes it look like a PITA to shape.

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    Quote Originally Posted by Dan from Oakland View Post
    Duh! Did you contact Broachmasters? They make shaper cutters. The Broach Masters
    Dan
    Yes, Sir. One of the first ones. They have the longest lead times, and most expensive prices. (3-4 weeks longer, and 33% more expensive ) I'd still buy them if I could get them in time.

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    Quote Originally Posted by Mud View Post
    .700 major? So a shaper cutter would need to be .450 or so dia? If you'fre not considering wiring it that means it's in a blind hole or working to a shoulder, right? And I'm guessing the slots need to be timed to the part too? Could it be done with a series of button broaches?
    Forgive me for drifting from the original question, the small size just makes it look like a PITA to shape.
    I was not clear. Apologies. The cutter OD of the required custom is 0.7083". Obviously, custom due to the Skip Space configuration.

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    Zahnrad,

    Sent you an email with some info... we can go from there.


    PM

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    Hi Zahnrad Kopf:
    I have a Solidworks protocol that I use whenever I have a form cutter to make that has rake on it.
    As you point out, of course the rake grinding operation will distort the form unless it's compensated.

    So my modeling protocol is to blow my form through the blank without draft in Solidworks, add the rake and then add the draft as a parting line draft instead of a neutral plane draft.
    That way I get the proper form at the cutting edge and I can just wire cut that shape.

    Attached is a sequence of quick and dirty pictures.
    Forgive the faked crappy involute profile...obviously it's a bodge but it does illustrate the modeling method.

    Of course you would still have to set the blank up on the wire and burn it which you've stated you're not eager to do but if you can't find any other way, this will get you there.

    On another note; I'd go get a big rectangular lathe blank of HSS or even better, a thick HSS slitting saw for this.
    It's just WAY easier than trying to harden a soft HSS slug properly...I've always had piss poor luck every time I've tried it.

    So here is my method...let me know if it is an option for you.
    Cheers

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

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    PM didn't let me attach files...trying again

    on edit...it put them in the wrong order...sorry guys!

    MC
    Attached Thumbnails Attached Thumbnails cutter-5.jpg   cutter-1.jpg   cutter-3.jpg   cutter-4.jpg   cutter-2.jpg  


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    Hi again all:
    On a last note; if you model one the "correct" way (rake first then parting line draft) and model one the "wrong " way (simple taper on profile, then rake) you can do a compare in Solidworks and save the results as a file you can measure.
    The form error with 5 degrees of rake and two degrees of draft is MINISCULE....something of the order of 2 tenths skinnier at the root of the tooth for the profile modeled "wrong".
    I don't know the application you're making these for Zahnrad Kopf, but is this even going to matter?

    Having said that, of course it's no hardship to model it correctly, so I'd just do it that way.

    Cheers

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

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    Quote Originally Posted by EmanuelGoldstein View Post
    You rang ?

    ITW did have at least one pamphlet on the design of shaper cutters. They gave them out at their gear school. From memory, they did the design manually on drawing boards, odontographically You could do that in a cad program now more easily.

    If you can find someone who has that old Illinois Tool literature, that'd be great. Mine went the way of all flesh when I inadvisedly gave custody to some slimebags
    I well remember ITW's Bob Modarrow's class from '81 when I worked for Lees Bradner. We had fun bantering over lead chart interpretation of shaping vs. hobbing. I've managed to accumulate quite a gear library over the years. Just today, a Fellows engineer's widow dropped off all his text books, notes and manuals. Shame no one coming along to groom for a rewarding trade. Agree about not loaning reference materials.

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    Quote Originally Posted by 10 fingers View Post
    I well remember ITW's Bob Modarrow's class from '81 when I worked for Lees Bradner. We had fun bantering over lead chart interpretation of shaping vs. hobbing.
    That _is_ actually interesting to look at. So are the Form Charts. I also am taken by the surface finish difference between Hobbing & Shaping. Each are generative, but very different.

    Quote Originally Posted by 10 fingers View Post
    I've managed to accumulate quite a gear library over the years. Just today, a Fellows engineer's widow dropped off all his text books, notes and manuals. Shame no one coming along to groom for a rewarding trade. Agree about not loaning reference materials.
    D, if you ever want to unload some of that, I'd be honored to have it so I could use it with the Apprentice. He is really enjoying the gear work and has the right head for it. He has been right in the depths of everything going on right now and has been eating it up. He's looking forward to running the Shaper and I've asked our mutual friend about staying a few extra days in the effort of having him impart some of that wisdom to us both.

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    Quote Originally Posted by implmex View Post
    I have a Solidworks protocol that I use whenever I have a form cutter to make that has rake on it.
    One correction - shaper cutters are not a cylinder, they are a truncated cone. And you can't use them all the way back. As ZK mentions, what the cutter cuts changes over its life. The tooth part stays the same as long as you stay in the good part, but the root clearance does change, as well as the fillet shape (a little bit.)

    Those little bastards are trickier than they look. They aren't form cutters, btw. You probably know that but thought I'd make it clear to others.

    Quote Originally Posted by 10 fingers View Post
    I well remember ITW's Bob Modarrow's class
    He spelled it Moderow if you want to search, he did give some AGMA classes I think after ITW folded up shop, but as far as I can find now he is gone. But that really is the book you want, zahnrad. Goes into detail about the design of shaper cutters. There's got to be some people who still have all their stuff.

    The really great thing about the ITW school was those guys made everything themselves. They were a real factory and supplier. Seeing how it was done was so much better than AGMA having a one-week class in some machinery dealer's showroom

    AGMA is a sad ghost of its past

    ... from '81 when I worked for Lees Bradner.
    Clevelands kick ass. I have witnesses

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    Not my field, but just for kicks asked Abe Books about books on gear machining. They found Illinois Tool Works stuff at Illinois Tool Works - AbeBooks
    as well as curious results such as Gear School Volume 1, (which looks like manga), The Girlfriends' Guide to Baby Gear (self explanatory), Heaven in High Gear (who knows) and other excursions of the search engine. Who knew gears could command such interest?


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