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Timing belt confusion

Discussion in 'General Talk' started by beazleybub, Apr 1, 2018.

  1. beazleybub

    beazleybub Well-Known
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    I have noticed vendors listing timing belts as both 3GT and others as GT3. Is there a difference or are they just being represented wrong? I have never seen both style names sold in the same place. I have asked google five hundred ways and can't find a definitive answer.

    Thanks!
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    Actually there is misrepresentation on multiple levels. But to get a better idea of where things got off track let's start with GT2 belts. GT2 belts have been used in the hobbyist world for quite some time in 3D printers. The 2mm tooth module of the belts was ideal as there was rarely any significant opposition force in the pulleys and tooth slippage was not a problem. But when these belts started being used in hobby grade CNC router systems the oppositional forces were causing the belts to slip on the pulleys. As GT2 belts are available in 2mm, 3mm, and 5mm tooth spacings the slippage issue was easily resolved by upgrading to the 3mm tooth spacing. The problem however arose from what to call these belts as 3mm was not only a possible tooth spacing but also a fairly common width of the GT2 belts which came in 3mm, 6mm, 9mm and in the case of OpenBuilds, 5mm widths. So to simplify, people just started referring to these 3mm module GT2 belts as GT3 belts which was fine until Gates (the originator of the belts) decided to move on to the 3rd generation of the GT belt series which they named appropriately enough, GT3 belts. These belts reportedly have 30% better grip than the GT2 belts use the same tooth profile and come in the same 2, 3, and 5mm tooth spacings.

    So how does this answer your question? The answer truly lies with who is selling the belts or more specifically the knowledge level of those selling the belts. Most aren't smart enough to know the difference and thus whatever they are selling as a GT3 or 3GT is really nothing more than a 3mm module GT2 belt or pulley. And those distributors who are smart enough to know the difference will be providing information at a level which shows they know what they are selling. You will see multiple tooth spacing options for both GT2 and GT3 belts.

    Further reference: https://ww2.gates.com/europe/downlo...T_45-46.pdf&folder=brochure&location_id=19466
     
  3. beazleybub

    beazleybub Well-Known
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    Thank you for your reply. Currently I am designing a 3:1 ratio speed reduction gearbox and found my desired pulleys at two reputable manufacturers.

    SDP/SI carries Product | Designatronics Store | Stock Drive Products/Sterling Instrument and Product | Designatronics Store | Stock Drive Products/Sterling Instrument.
    These are desirable because they use the Fairloc Hub. However, they are listed as "3 mm (GT2)". If you look at it's profile (Pink) in the image below, it is obviously the wrong choice.

    B&B Manufacturing carries 60-3P09-6A4 - A 6A53-060NF0910 3MR-60S-09 78436078 TP3A3H9-60 | B&B Manufacturing and 20-3P09-6FA3 - A 6A53-020DF0908 3MR-20S-09 78436005 TP3A3W9-20 | B&B Manufacturing. These pulleys are listed as "GT 3mm" and are very similar in profile to the openbuilds pulley.

    Openbuilds only carries the twenty tooth pulley and even there it's called "3GT (GT2-3M)".
    3GT (GT2-3M) Timing Pulley - 20 Tooth - .250" Bore - 9mm Belt

    I have downloaded the cad files and compared the 20 tooth profiles. The first image includes all three profiles layered from smallest to largest.

    Pink: SDP/SI A6D53-020DF0908 (3 mm GT2)
    Green: B&B Manufacturing 20-3P09-6FA3 (GT 3mm)
    Blue: Openbuilds (3GT (GT2-3M)) Timing Pulley - 20 Tooth - .250" Bore - 9mm Belt

    [​IMG]

    (The Pink profile is obviously way different and most likely not a 3GT profile.)

    In the second image I have removed the Pink profile to compare Openbuilds to B&B. They are very similar although it appears the pitch diameter differs slightly.

    [​IMG]

    What are your thoughts? I don't think there will be an issue by using the B&B pulley as they are so close.
    There is only 0.009791" difference in the pitch diameter and the tooth radius is exactly the same. I'd buy both pulleys from openbuilds if they were available.
     
    #3 beazleybub, Apr 1, 2018
    Last edited: Apr 1, 2018
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You are grossly over analyzing this. Anything from SDP/SI or B&B will be dead on perfect (even if their publicly available cad representations are not). They are both high end ISO certified facilities.
     
  5. beazleybub

    beazleybub Well-Known
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    When it comes to developing my own parts, I don't have an issue with over analyzing my drafts. If manufacturers are "high end" then, I expect their CAD files to be high end as well. Better for me to over analyze than to waste time and money on what if scenarios. Thanks for your response.
     

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