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  1. #141
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    "How did they do that back before the days of CNC dressers?"
    "A dresser built something like a miniature Excello thread miller?"

    I can't say with certainty. I know Mr. Goldstein would know, but I'd bet you're right.

    vid:

    The grinding wheel turns slowly as a form dresser does its thing. That could have been done in the old days with mechanical gearing, a lead screw and a powered form diamond wheel.

    Then the grinding wheel turns at about 3000 rpms (?) acting as a single tooth worm with the gear turning 1/number of teeth slower as the gear is ground.

    --david

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    Thanks for posting the video Marcus. I am working on a planetary gearbox with plastic planets for a riding mower, I know I won't have time to screw around making my own gears for the prototype but wish I did. I am close to being able to cut metal gears on my $5000 wire edm.

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    Hi again drcoelho:
    I just noticed you wrote this back in a previous post (post #137):
    " rack form cutters can be easily constructed and can cut a variety of gearswhereas gear hobs are specific to a particular gear"

    That's actually not quite true; the hob will also cut every tooth count of a gear of the same diametral pitch and pressure angle, just like the rack will.
    There are actually only two substantial points of difference between them:
    1) the rack can cut very close to a shoulder
    2) the hob cuts continuously

    Yes, there are other differences of course, but in terms of what you can make with either approach, these are probably the biggest ones (gearmakers: dope slap me if I've overlooked something important).
    But since both GENERATE the involute faces and flanks, both will cut 12 teeth or 100 teeth and everything in between too.

    Cheers

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


  4. #144
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    YIKES!
    I feel like Roger Rabbit listening to "Shave and a Haircut" with steam shooting out his ears....

    ONLY the seasoned professionals are allowed to talk about gears.
    But I can't hold back any more.


    YouTube
    Thanks for that!
    But I cannot help but asking..
    If I had the part in a 4th axis, to rotate it, and further defined the "Rack" motion as at an angle in the Y/Z plane, That angle in the Y/Z plane could be used as the pressure angle as you calculate multiple passes to generate the tooth.

    IF that was correct, then you could simply use a straight disk cutter in the spindle to cut any tooth count at at any pressure angle, at any DP or module.
    Cut the front of the teeth on one side of the 4th axis, and back of the teeth on the other side of the 4th axis.
    NOT well enough for production, NOT for fine instruments, but maybe Red Green or cement mixer grade gears...

    Index the 4th axis, and calculate the path for maybe three teeth front side on one side of the 4th, and three teeth back side on the 4th.
    Index and repeat, generating multiple paths for each tooth profile.

    Almost one tool for almost any (straight) gear.

    Possible? But not practical?

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    Hi 3t3d:
    Interesting and super good idea!
    I can't see any theoretical reason why it wouldn't work.
    The only practical problem is the skinniness of the saw and the amount of meat it has to remove, most of which is going to engage the saw only on one side.
    But with a stubby enough saw (small diameter, big hub) you could probably make it work just fine on forgiving materials like 360 brass and Delrin.

    The nice thing by contrast, about a saw that has a rack tooth cross section, is that it is relatively stout.
    The downside, as you imply is that you still need a different saw for each PA and DP. and you can't just buy it off the shelf.

    It is a very clever idea though...someone has got to try it!
    Are you willing?

    Cheers

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

  6. #146
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    Actually, if the saw is flat, then it can be used for ANY DP or pressure angle..

    My thinking is that:
    > a rack tooth has a straight side.
    > a single tooth rack could cut any DP,since there is not an adjacent tooth.. it is just a matter of depth to cut any DP.
    > if you had rack cutter of the exact PA, then it's relative motion to a gear in the 4th axis would be straight up and down.
    > but, if you had a single, single sided tooth on a rack cutter, then you could move the rack past the gear at a non tangent angle, to match ANY PA

    >actually, since we can use any imaginary tangent angle to match the angle of our "Rack" and the required PA.


    Bottom line, ANY flat sided cutter could be used to generate ANY PA, and ANY DP as long is it is small enough to fit into a gear tooth space.
    Even a double angle cutter, ad single angle cutter, or a flat disk.

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    Yes you are exactly right.
    I wasn't clear when I wrote back to you; my apologies!
    I also limited my thinking to a parallel side saw vs a rack XS shaped saw, and as you correctly point out, there's no requirement at all for anything other than a flat profile, angled or not, and a skinny enough tip to fit in the tooth space.

    Cheers

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

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    I decided to delete what I wrote until I have more time to think about it...
    Last edited by David_M; 06-18-2019 at 09:34 PM.

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    Hi David M:
    You wrote:
    " the next step would be using a wire edm with a rotary 4th c "

    Naaahh!
    , if you're going t o use a wire EDM, you may just as well lay down a piece of plate with some start holes in it and walk around the profile a few times.
    Your way would be cooler, but also a lot harder.

    Cheers

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

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    Quote Originally Posted by 3t3d View Post
    YIKES!
    I feel like Roger Rabbit listening to "Shave and a Haircut" with steam shooting out his ears....

    ONLY the seasoned professionals are allowed to talk about gears.
    But I can't hold back any more.


    YouTube
    Thanks for that!
    But I cannot help but asking..
    If I had the part in a 4th axis, to rotate it, and further defined the "Rack" motion as at an angle in the Y/Z plane, That angle in the Y/Z plane could be used as the pressure angle as you calculate multiple passes to generate the tooth.

    IF that was correct, then you could simply use a straight disk cutter in the spindle to cut any tooth count at at any pressure angle, at any DP or module.
    Cut the front of the teeth on one side of the 4th axis, and back of the teeth on the other side of the 4th axis.
    NOT well enough for production, NOT for fine instruments, but maybe Red Green or cement mixer grade gears...

    Index the 4th axis, and calculate the path for maybe three teeth front side on one side of the 4th, and three teeth back side on the 4th.
    Index and repeat, generating multiple paths for each tooth profile.

    Almost one tool for almost any (straight) gear.

    Possible? But not practical?
    Are you guys unaware that you can already get 14 and 20 degree insert tooling to do this? It was in an issue of Tool Engineering magazine.

  11. #151
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    Quote Originally Posted by implmex View Post
    So the challenge would be to make a dresser that could put basically an Acme threadform onto the periphery of a grinding wheel.
    Reishauer

    This was the competition back before cnc = form grinding vs generating grinding. Then in the generated grinding camp you had the rack wheel type like Maag and Kolb and Pratt & Whitney and the threaded wheel type like Reishauer. A Reishauer is just like a hobber except with a grinding wheel. The little 6" machine I was thinking of is a threaded wheel type. The advantage there is that you can dress any shape you like into the wheel, much easier than ordering and paying for a hob. They even make off-the-machine dressers for Reishauers so you can prepare different grinding wheels ahead of time.

    One interesting feature was that the gears for the original batch of Reishauers was made on Maag grinders The Maag was actually more accurate but the Reishauer type (Matrix in England built some too) is WAY faster. And you can grind up to AGMA 14 or 15 on them, so probly good enough for most people ...

    In the 70's the form grinder people (Red Ring, Michigan Tool) did use diaform dressers and templates. Mostly they were used for shapes not amenable to generated grinding, such as straight-sided splines or internal gears or non-invoute shapes. Some normal external gear grinding but most people went for the Reishauer or Maags instead.

    But nowadays the generated grinders have lost their most interesting maker - Maag has been gone for many years - and the form grinders with cnc dressers are the popular ones, at least in the bigger sizes. Machines like the Hoflers can grind bearing journals, faces, and teeth all in one setup and their accuracy is the same as the old generated wheel rack-type machines. And they are much faster.

    I was thinking that for drcoelho's thing, a 4th axis rotary would be the hot ticket. He basically wants to build that anyway but instead of trying to drive a hob and sync them, he should put the work into the 4th, a straight-sided cutter on the horizontal spindle, and rotate the part while traversing in Y through the cutter.

    Oh wait. Is this an nc Deckel or a manual one ? If it's not even nc, sheesh. I give up There's a way to do it with base circle disks and pitch bands but forget it, don't even wanna go there, he's too stubborn

    How did they do that back before the days of CNC dressers?
    A dresser built something like a miniature Excello thread miller?
    A v-shaped diamond would traverse the wheel in time, making a thread. Yeah, kind of like a thread mill.

    Of course this video shows spline grinding and the machine is a tool grinder, not a dedicated gear grinder, so I don't actually know if this method is ever used to make gears, but I can't see why it wouldn't work rather well.
    They did. There were at least two makers that I can think of, Red Ring and Michigan Tool. They had their marketing lit saying theirs was the best way but most people went for generated, unless the job had some special requirements. All those templates was a killer and also they only do one tooth at a time so pretty slow compared to a Reishauer. Faster than a Maag but the Maags were very intricate and capable - they could control every portion of the wheels' path, do tip and root relief and crowning, whatever you wanted, just learn to run the machine. Really nice machines, if you like that sort of thing. See if you can scrounge up a manual for an SD 32X, you'll like it a lot.

    @ 3t3d - yup, you could do that. But it's so easy to make the two or three normal v-shaped cutters, keep them n the shelf, and they are more rigid and faster - only have to make one pass - that probably no one would do it with slitting saws. But you could, if you were in a corner on a Friday night ...

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    I mentioned using a wire and a fourth axis (this applies to a straight sided end mill too) :

    This has the timing setup to cut a gear space that is the same width as the "wire" (drawn as 0.01") exactly at the pitch diameter:


    And this includes a dwell for tooth thickness and a timing adjustment to get a 20 degree pressure angle (you can see a properly drawn gear overlaid in the last frame):


    The "wire's" path is just a straight line, so this is generating.

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    Quote Originally Posted by David_M View Post
    This has the timing setup to cut a gear space that is the same width as the wire exactly at the pitch diameter:
    Are you rotating that from the base circle ? The involute is derived from the base circle, not the pitch diameter. Just wondering ...

    But one of the neat things about using a wire edm is that you can avoid undercut in small numbers of teeth like you get by generating. So, umm ... this is not the method I would use, if'n I had a wire edm

    Just for fun, run a 12 tooth pinion through your animation and see what you get ...

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    Yes, the involute base circle mathematically.

    You are really making me think when you mentioned undercutting by the hobb. I guess that larger diameter hobbs undercut less?

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    Quote Originally Posted by David_M View Post
    Yes, the involute base circle mathematically.
    Cool ...

    You are really making me think when you mentioned undercutting by the hobb. I guess that larger diameter hobbs undercut less?
    No, it's a function of the number of teeth, the base circle diameter and the height of the teeth. Just try running your other animation - the one that used a rack tooth - on 11 or 12 teeth and you will see it ... use something like an 8 pitch and it is obvious. It's even worse with shaper cutters.

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    Stupid me. That rack is a pretty large diameter.


    11_tooth.png photo - David photos at pbase.com

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    Quote Originally Posted by EmanuelGoldstein View Post
    Reishauer

    I was thinking that for drcoelho's thing, a 4th axis rotary would be the hot ticket. He basically wants to build that anyway but instead of trying to drive a hob and sync them, he should put the work into the 4th, a straight-sided cutter on the horizontal spindle, and rotate the part while traversing in Y through the cutter.

    Oh wait. Is this an nc Deckel or a manual one ? If it's not even nc, sheesh. I give up There's a way to do it with base circle disks and pitch bands but forget it, don't even wanna go there, he's too stubborn
    EmanuelGoldstein: OK, I'll throw you a bone (or get a little less stubborn....)....yes, my Deckel is manual and not NC, sorry.....BUT WAIT....I do have a Brother Speedio with rotary/simultaneous 4th axis.....what would you suggest as best strategy if I abandon the Deckel and go with Brother ?

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    This is "cutting" a 12t, 20dp, 20pa with a flat-sided cutter:


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    Quote Originally Posted by drcoelho View Post
    I do have a Brother Speedio with rotary/simultaneous 4th axis.....what would you suggest as best strategy if I abandon the Deckel and go with Brother ?
    Oh jeeze. You're set ! Just make a fixture for the 4th to hold your blanks and get a couple of v-shaped cutters and away ya go ! Nothing to do but cut teeth !

    If you put the 4th on a sine plate you could even cut helicals

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  24. #160
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    Hi again drcoelho:
    You wrote:
    "BUT WAIT....I do have a Brother Speedio with rotary/simultaneous 4th axis.....what would you suggest as best strategy if I abandon the Deckel and go with Brother ?"

    WOOOHOOOHOOO, it has sunk in at last!

    Man that was some kind of convincing process!
    By my count, it took ten posts from me and others to get you to break the hobbing mindset.
    I first recommended a rotating rack cutter and your Speedio way back in post #98...I even posted pictures.

    But it's DONE...the old mold is broken.

    Look forward to making good gears easily and cheaply once you figure out the very simple relationship between a rotary index and a cutter translation in Z

    AND REMEMBER THEY DON'T HAPPEN TOGETHER.
    Rotate
    Drop in Z
    Make a cutter pass.

    Keep us posted on your progress.

    Cheers

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

    Oh yeah...while I'm at it: resist the urge to try to make this work like a Maag gear grinder.(link below)
    You can probably do it if you must but you'll drive us nuts in the process.

    YouTube

    MC




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