Differences between HTD, GT, AT and T pulleys?


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Thread: Differences between HTD, GT, AT and T pulleys?

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    Question Differences between HTD, GT, AT and T pulleys?

    Anyone care to give me a bit of noob education on the differences between common pulley/belt profiles? From what I've found, the GT and AT profiles are better for linear positioning than the HTD and T profiles respectively, but otherwise I'm struggling find more info on "what" the different profiles are good for.

    Ultimately, I'm looking at creating a slow/high torque 4th axis for a CNC machine.

    My current plan is to drive a 60 Tooth AT5 Pulley from a 20 Tooth AT5; using a 25mm wide belt. The input (on the 20 tooth) would be anything up to 120rpm and 10Nm of torque (so approx 40rpm and 30Nm on the 60 tooth output).

    I'm not needing to hold metalworking levels of tolerance (it's a woodworking machine), but obviously I don't want it slipping or snapping belts.

    Am I being realistic with the above, should I be looking at a different profile and/or thinner or thicker belt?

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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Hi Sploo - GT and HTD profiles were developed for power transmission and are not ideal for positioning applications. T and AT were developed later. I recommend you use an ATL belt profile which is stiffer then the AT for the same size (uses AT pulleys) and its teeth are more accurate. ATL belts are designed for positioning applications and are compensated for the extra preload a positioning application requires. The size you discuss should be OK without dong the math if your up to the math see attached.. . Cheers Peter S

    Attached Files Attached Files


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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Quote Originally Posted by peteeng View Post
    Hi Sploo - GT and HTD profiles were developed for power transmission and are not ideal for positioning applications. T and AT were developed later. I recommend you use an ATL belt profile which is stiffer then the AT for the same size (uses AT pulleys) and its teeth are more accurate. ATL belts are designed for positioning applications and are compensated for the extra preload a positioning application requires. The size you discuss should be OK without dong the math if your up to the math see attached.. . Cheers Peter S
    That looks very useful; many thanks. From a quick scan through it also appears to discuss the number of belt teeth engaged on a pulley; which was a concern I had with my design of a 3:1 pulley ratio at fairly close centre-to-centre distances. Plenty for me to read!



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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Hi Sploo - 3:1 will work fine. Higher then that and teeth count can be a issue. All explained in the docs...Peter



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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Quote Originally Posted by peteeng View Post
    Hi Sploo - GT and HTD profiles were developed for power transmission and are not ideal for positioning applications. T and AT were developed later. I recommend you use an ATL belt profile which is stiffer then the AT for the same size (uses AT pulleys) and its teeth are more accurate. ATL belts are designed for positioning applications and are compensated for the extra preload a positioning application requires. The size you discuss should be OK without dong the math if your up to the math see attached.. . Cheers Peter S
    GT series is the closest tolerance Timing pulleys and belts that are made and are used where you need accurate positioning

    AT profile will work fine for what he wants to do but are not as accurate as the GT series

    Mactec54


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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Hi Mactec - You have put forward the GT in other threads as the best choice and that it has the least backlash. But none of the manufacturers recommend GT as a linear drive solution only power drives (although it is used by many for the application) . So is there a manual or data you can provide to explain this? The ATL belt is the only belt profile specific to positioning drives...as far as I can find. Peter



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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Quote Originally Posted by peteeng View Post
    Hi Mactec - You have put forward the GT in other threads as the best choice and that it has the least backlash. But none of the manufacturers recommend GT as a linear drive solution only power drives (although it is used by many for the application) . So is there a manual or data you can provide to explain this? The ATL belt is the only belt profile specific to positioning drives...as far as I can find. Peter
    Simple:

    https://assets.gates.com/content/dam...17195_2014.pdf



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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Hi 109J - Thanks, but that doc does not discuss positional applications or how to design a GT for a positional application. Although at the end it has a few diagrams showing belts being used in this sort of application the doc does not cover it. It does mention linear drives but in applications that are not positional critical. GT belts use fiberglass as the reinforcement which is great for strength, fatigue & small pulleys etc but means they are not as stiff as steel belted AT or ATL belts of the same size. I looked around for the specific stiffness of the GT belts but couldn't find it. Also the specific strength of the belt is not discussed in the doc as it covers power transmission apps. For positional apps the preload of the belt is much higher and has to be calculated differently to a power app as well. So I'll stick with AT's or ATL's Peter

    fibreglass E=70GPa
    steel E=200Gpa approx 3x stiffer for same cross area.



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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Very useful info all - many thanks.

    I haven't had chance to go through the docs Peter posted yet - so a question in case it's not mentioned; the AT5 pulleys I've been looking at have flanges up to the 42 tooth option, then the 44, 48 and 60 do not have flanges (though the vendor can add them).

    If I were using a 25mm belt between a 20 tooth and 60 tooth pulley (diameters roughly 32mm and 95mm respectively, with a centre-to-centre distance of maybe 100mm) would I be needing flanges on the 60 tooth pulley, or would it likely be unnecessary? The additional cost of the flanges is tiny, and I have space, so there's nothing stopping me doing it.



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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Hi Sploo - I've always used flanges both sides, but with the short span, not having a flange on the big one should not matter. But you will need to have the shafts parallel and pulleys true for it to work correctly. Avid don't have a flange on the big side...see attached. Peter

    Attached Thumbnails Attached Thumbnails Differences between HTD, GT, AT and T pulleys?-drive-jpg  


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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Quote Originally Posted by peteeng View Post
    Hi 109J - Thanks, but that doc does not discuss positional applications or how to design a GT for a positional application. Although at the end it has a few diagrams showing belts being used in this sort of application the doc does not cover it. It does mention linear drives but in applications that are not positional critical. GT belts use fiberglass as the reinforcement which is great for strength, fatigue & small pulleys etc but means they are not as stiff as steel belted AT or ATL belts of the same size. I looked around for the specific stiffness of the GT belts but couldn't find it. Also the specific strength of the belt is not discussed in the doc as it covers power transmission apps. For positional apps the preload of the belt is much higher and has to be calculated differently to a power app as well. So I'll stick with AT's or ATL's Peter

    fibreglass E=70GPa
    steel E=200Gpa approx 3x stiffer for same cross area.
    You are good at posting numbers but have no real experience with these belt here is a PDF and I have many of then on this subject your AT belt profile is old hat, and out dated, yes it is still used but does not compare to the GT series Belts in any way take a look at the numbers in this PDF

    You can get any type of Timing Belt profile with different cord designs and materials, you chose the material and cord for the job you are doing, you are not stuck with one cord type saying the ATL steel is better is total BS you can have steel cords in any profile if there was a need

    Attached Thumbnails Attached Thumbnails Differences between HTD, GT, AT and T pulleys?-the_world_of_timing_belts-pdf  
    Mactec54


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    Default Re: Differences between HTD, GT, AT and T pulleys?

    Quote Originally Posted by sploo View Post
    Very useful info all - many thanks.

    I haven't had chance to go through the docs Peter posted yet - so a question in case it's not mentioned; the AT5 pulleys I've been looking at have flanges up to the 42 tooth option, then the 44, 48 and 60 do not have flanges (though the vendor can add them).

    If I were using a 25mm belt between a 20 tooth and 60 tooth pulley (diameters roughly 32mm and 95mm respectively, with a centre-to-centre distance of maybe 100mm) would I be needing flanges on the 60 tooth pulley, or would it likely be unnecessary? The additional cost of the flanges is tiny, and I have space, so there's nothing stopping me doing it.
    If the cost is not much then go with the flanges they are also easy to fit flanges at any time if you have access to a lathe

    Mactec54


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Differences between HTD, GT, AT and T pulleys?

Differences between HTD, GT, AT and T pulleys?