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  1. #13
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    Quote Originally Posted by blowlamp View Post
    1/ Why is the standard form not suitable?
    Among the many dozens I've seen, what is a 'standard' profile?
    Quote Originally Posted by blowlamp View Post
    2/ Is the CAD drawing just a representation or is it to be used for manufacture?
    Not sure what you mean. While Gates seems to offer the exterior dimensions in CAD drawings, I'm not convinced the drawings accurately represent the profile. But I could easily be mistaken.
    Quote Originally Posted by blowlamp View Post
    3/ If the design is patented, would it be legal to make your own anyway if done commercially?
    Cutting one or two prototypes for an experimental project wouldn't likely be an issue. But I certainly wouldn't mass produce any or try to market any.

    Quote Originally Posted by RICHARD ZASTROW View Post
    Looking at the date of the patent raises a question; Is this the CURRENT form?
    Dunno. That's the reason for seeking a CAD program which may have the profile included in it's library.

    Quote Originally Posted by RICHARD ZASTROW View Post
    One other thing, if you can buy the sprockets, why go through all the effort to draw and make your own?
    Therein lays the problem, Gates doesn't make the sprocket I need - specifically, the mounting is completely different, and I'd prefer 7075 aluminum. Yes, Gates offers "made to order" customs, but I'm guessing the costs would be beyond my budget. I also have access to local CNC should I need different ratios (a strong possibility).

  2. #14
    Ghost
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    Quote Originally Posted by blowlamp View Post
    In your second drawing there are a couple of corners (that look important) in the root of the tooth, that can't be taken out cleanly by normal endmilling because of the cutting tool radius. That probably leaves form tools or possibly laser cutting, although I'm not sure how suitable a laser-cut surface would be for running a belt on.
    Martin.
    The flat is a true flat, so a simple index on a rotary should cut it.

  3. #15
    Ghost
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    Dec 2008
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    Still looking for a sprocket expert that can confirm the model as "true" or not. If true, no need any software as the models are available. I dont know enough about them to say if it is just a "toy model".

    Anyone?

    Beuller.....Beuller??????

  4. #16
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    May 2008
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    MVHPV.

    The reason I posted the file produced by CamBam is because I believe it will allow you to easily produce pulleys for use with timing belts that are commonly available.

    If the CAD drawing was only intended to represent the basic form of the pulleys I was going to suggest that you don't go to too much trouble in getting an exact shape. Conversely, if the drawing were to be sent to a CAM system for manufacture, it would need to be accurate.

    BurrMan

    That would remove some but not all of the material in that area, a little would remain on each curved section near the root.

    Martin.

  5. #17
    Ghost
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    That would remove some but not all of the material in that area, a little would remain on each curved section near the root.
    I am assuming that the sides come off of the assembly. A straight pass over the top.

  6. #18
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    Quote Originally Posted by blowlamp View Post
    The reason I posted the file produced by CamBam is because I believe it will allow you to easily produce pulleys for use with timing belts that are commonly available..
    The Poly Chain GT is available in over 29 different belt lengths spanning 4 different widths - that equates to 116 individual sizes. Bare-in-mind, that's counting only 8mm pitch. Doesn't seem too uncommon or unpopular to me. http://www.vbeltsupply.com/8mmpolychainseries9274.html

    Also...

    The Poly chain exhibits the highest efficiency of any currently available belt drive, short of roller chain. Crap!... now i'm beginning to sound like a salesman.

    Question Blowlamp,

    Does CamBam specify manufacture's profiles, or just one or two generics?

  7. #19
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    Quote Originally Posted by MVHPV View Post
    The Poly Chain GT is available in over 29 different belt lengths spanning 4 different widths - that equates to 116 individual sizes. Bare-in-mind, that's counting only 8mm pitch. Doesn't seem too uncommon or unpopular to me. http://www.vbeltsupply.com/8mmpolychainseries9274.html

    Also...

    The Poly chain exhibits the highest efficiency of any currently available belt drive, short of roller chain. Crap!... now i'm beginning to sound like a salesman.

    Question Blowlamp,

    Does CamBam specify manufacture's profiles, or just one or two generics?
    Well I never did doubt that there would be a selection of available products, but the fact remains that the The Poly Chain GT tooth profile is not as common and is going to be harder to machine than the HTD tooth form because of its shape.

    I've just checked the CamBam documentation which says the pulleys are made to the HTD5 form. See here: http://www.cambam.co.uk/docs/tutorials/profile-new.html

    This might be of some help See here: http://www.roymech.co.uk/Useful_Tabl...ing_belts.html

    Martin.

  8. #20
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    Quote Originally Posted by MVHPV View Post

    Therein lays the problem, Gates doesn't make the sprocket I need - specifically, the mounting is completely different, and I'd prefer 7075 aluminum. Yes, Gates offers "made to order" customs, but I'm guessing the costs would be beyond my budget. I also have access to local CNC should I need different ratios (a strong possibility).
    Assuming you can buy an existing sprocket of the correct diameter and pitch, any competent machinist or toolmaker with an optical comparator can document the profile by sectioning the sample.

    Gene

  9. #21
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    Sep 2006
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    36

    Post It is a generated form

    Quote Originally Posted by MVHPV View Post
    Thanks guys. Been there, and when clicking through the "Partview" feature for both specs & cad files, I stumbled across this:



    Not all samples displayed the above, but both the 30 and 71 grove (among others) in the 8mm pitch x 12mm width, did. Needless to say, because of the critical nature of the profile, I'm a little dubious because of the warnings.
    The GT2 Polychain did not exist when I last cut cogs, I downloaded the design data & Patent data, the [x~y] co-ordinate equations are listed, and one could crunch the numbers to get the form, tolerances are given in the spec.

    As posted the form is a kind of involute so each tooth count is different in form, I expect they are normally hobbed or shaped, Ash Gear has tools for most of the older types, but one has to enquire for this form, [proprietary].

    In the Gates PDF downloads is an interchange doc showing the differences.

    So, in my opinion the CAMBAM form is not correct.

    Gates drawings are representative, not actual form, as each tooth space is different for each number of teeth, apparently they can not display the true form in a cost effective manner, because then we could just download, make a form tool and mill it that way.

    As this is for yourself, not for resale you could crunch the numbers to get the profiles you want and make form tools to mill them.

    Cheers,

  10. #22
    slvrsky07
    Guest

    Re: Tooth profile for designing synchronous drive sprocket?

    Did you ever find the belt profile for an 8mm pitch GT2 pulley? I am in search of the same thing. I would like to make some aluminum pulleys for a boat out drive to try different belt ratios. I emailed gates directly and they sent me some of the drawings. I am trying to get them entered in fusion 360 to eventually output to the CNC mill.

    Here are somethings I found so far:
    https://capolight.wordpress.com/2018.../#comment-5093

    https://build-its-inprogress.blogspo...68354574899572

  11. #23
    slvrsky07
    Guest

    Re: Tooth profile for designing synchronous drive sprocket?

    Here is the progress I made using Fusion 360 and the data Gates sent me for a 34 tooth GT2 tooth profile. I took the x,y values to make the circles in the first drawing. Then extruded one tooth and then did a circle mirror to get the full 34 teeth. I am going to try on the cnc soon. My only question if anyone is following this at all would be, changing the number of teeth need more than just a diameter change? I received a few tooth profile sheets and the main x,y values stay constant but there are some other values that change per size. Wondering a way to streamline this so it would be easy to change my cam model to try different sizes without having to do the trig each time. Also if you use the values of the tooth profile sheet and compare them to the ones of the downloadable 3d cad files on Gates website, they appear to be accurate. Most of the cad files will only show 1 tooth though so you will need to probably make your own cad drawing.

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