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  1. #1
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    Jan 2009
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    HTD Timing belt and backlash

    I am building a CNC router using two 48" long Tolomatic belt drive actuators for the x axis. The actuators currently are using 1" wide 5M HTD rubber/fiberglass timing belts. After my initial tests I would really unpleased with the stretch in the belts. I am considering upgrading to a rubber/steel belt which should reduce stretch. The more I read about HTD belts the more that I learning that they are good for torque but not for positioning accuracy. I am considering switching to modified curvilinear (GT2) style belt but this would require I change my pulleys. Can anyone comment on the accuracy of timing belts and the different tooth styles (ie HTD, XL, GT2, etc).

    Thanks!

  2. #2
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    You may also consider GT2 carbon fiber belts. After initial installation, re-tensioned belt has near zero stretch.

    Dick Z
    DZASTR

  3. #3
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    Quote Originally Posted by RICHARD ZASTROW View Post
    You may also consider GT2 carbon fiber belts. After initial installation, re-tensioned belt has near zero stretch.

    Dick Z
    I was looking at the GT2 with Carbon fiber and my biggest problem is that I need to change my pulleys to use the GT2 belts. What I am trying to figure out is worth the effort since my pulleys are custom to my linear actuators and would be rather involved to change.

  4. #4
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    Hi, I have been studying belt drive setups for a while. My personal opinion is that the best tooth form for a conventional belt drive is the AT style, and for even more precision, the ATL style. You can also buy precison shaped timing pulley teeth to reduce backlash even further.

    All of that being said, tooth shape, tooth strength, and engagement accuracy is most likely not your current limiting effect, it is belt width, and there is nothing much you can do about that with those actuators. That leaves you with only the tension members to work with.

    Steel tension members, IMHO, are a must. Further, not all tension member construction is the same, and Brecoflex is one of the best for this, regardless of the tooth style. edit - I did some more reading on the carbon fiber members that R. Zastrow discussed - also a viable option if you are happy with the belt style.

    If you are wanting to do this on a tight budget, then just change out the belt for a better one, but I would go the full route and go for an AT style chance out if you can. AT-10 25mm wide. Just keep in mind that there will be some stretch under high loads / high acceleration no matter what you do. When I ran the numbers, the main challenge was acceleration of the gantry.

    What are your build goals for results ?

    Harry

  5. #5
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    Quote Originally Posted by harryn View Post
    Hi, I have been studying belt drive setups for a while. My personal opinion is that the best tooth form for a conventional belt drive is the AT style, and for even more precision, the ATL style. You can also buy precison shaped timing pulley teeth to reduce backlash even further.

    All of that being said, tooth shape, tooth strength, and engagement accuracy is most likely not your current limiting effect, it is belt width, and there is nothing much you can do about that with those actuators. That leaves you with only the tension members to work with.

    Steel tension members, IMHO, are a must. Further, not all tension member construction is the same, and Brecoflex is one of the best for this, regardless of the tooth style. edit - I did some more reading on the carbon fiber members that R. Zastrow discussed - also a viable option if you are happy with the belt style.

    If you are wanting to do this on a tight budget, then just change out the belt for a better one, but I would go the full route and go for an AT style chance out if you can. AT-10 25mm wide. Just keep in mind that there will be some stretch under high loads / high acceleration no matter what you do. When I ran the numbers, the main challenge was acceleration of the gantry.

    What are your build goals for results ?

    Harry
    Harry,
    Thanks for the post regarding your research with timing belts. My goal with this project is to improve accuracy as much as possible. However, this being said, I realize that there are some limitations based on the design of the system and probably if I get within .005 accuracy I am doing fine. I am not too concerned with rapids. Since my post this morning I decided to order order the Poly/steel HTD belts and see how they perform. If I am still having problems then I will need to consider changing my belts and pulleys (to the AT or GT type) order replace the belt drives with a ball screws. After everything I have read about belt drives I don't see why the belts won't perform well if I get the right style belt and set it up correctly (ie tension).

    Do you have any good pointers with how much tention I should put on the belts once installed?

  6. #6
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    Sep 2016
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    Re: HTD Timing belt and backlash

    Realise this is an old thread but I am in the process of designing and building my own belt driven router and had the idea to use two belts on each side of the X axis. Actually it would be a dual belt in belt drive on each side with the belt offset a little or two pulleys offset like a split pinion. I am going to try it with a gt2 (PU, steelwire) belt but want to use HDT5m 15mm steel reinforced PU belts on my machine.
    What do you think?

  7. #7

    Re: HTD Timing belt and backlash

    Quote Originally Posted by heavyweather View Post
    Realise this is an old thread but I am in the process of designing and building my own belt driven router and had the idea to use two belts on each side of the X axis. Actually it would be a dual belt in belt drive on each side with the belt offset a little or two pulleys offset like a split pinion. I am going to try it with a gt2 (PU, steelwire) belt but want to use HDT5m 15mm steel reinforced PU belts on my machine.
    What do you think?
    I work on a new power tranmission project, purchased HTD 5M and GT2 from https://www.zzr-parts.com . Available in PU and rubber belt body

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