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Question about belts and pulleys.

Discussion in 'General Talk' started by DarkAlchemist, Sep 3, 2015.

  1. DarkAlchemist

    DarkAlchemist Veteran
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    I have been playing in SW for a few weeks and something is really bothering me and that is that I can't find a way to make the GT2 belt line up straight with any plate using 20mm x 20mm V-Rail. We have the pulley and we have the Nema 17 with a toothed gear and the nema plate and what I don't like is the idea of the belt (either under or over) going at an angle to the V-Slot 20mm Gantry plate. The closer the plate gets to the pulling side the more the plate will try and follow the belt so if the belt is at an angle to the plate the more the forces will try to pull that plate down, or up depending on the belt going over or under the pulley/gear to the V-Slot 20mm Gantry plate. Wheels preventing it or not the forces are still there and is a bad design to allow it to happen.

    Hard to explain but I want the belt to line up horizontally straight to the plate from the pulley and the gear but how? With the pre drilled set of holes it makes it nigh impossible and pulling a plate where the GT2 belt is not flat is just not a good thing.

    So, I am trying to figure out how others managed to make that belt completely parallel with the 20mm extrusion pulling the gantry plate along? One of the last two pieces I need to figure out before I start buying the stuff.
     
  2. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    You're probably not going to be able to get it completely parallel. But you should be able to get it fairly close by adjusting up the hole centers and by looping the free end back under as shown below to suppress the top of the belt.

    IMG_7259.JPG
     
  3. DarkAlchemist

    DarkAlchemist Veteran
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    That is a lot closer than what I was coming up with BUT the Gt2 timing pulley is 12.2mm diameter and the smooth idler is 17.5mm diameter so how is that going to work? Easy enough with the 12.2mm one but 17.5mm one? Could you show a picture of that?

    Thanks.

    edit: Doing the belt like that also means you can't really attach the beam to anything on 3 sides leaving the only way to attach it to another is via the black angled corner connectors, right?
     
    #3 DarkAlchemist, Sep 4, 2015
    Last edited: Sep 4, 2015
  4. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    I don't have any idler pulleys to work with but it should be far less of a problem than the 20T pulley. The larger diameter puts the belt closer to the natural position it wants to be in. You could also probably use just a typical belt connection on that side of the slider.
    I don't quite understand the question. Can you show a model of what you are trying to do?
     
  5. DarkAlchemist

    DarkAlchemist Veteran
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    In your situation the motor would face the opposite way than in the picture but can't attach anything on top as that is where the belt, and plate are. Can't attach anything on the side with the motor mount plate. Can't attach the beam to the other plate on the bottom because there will be a belt (on yours) going under it so that kills 3 sides for any way to attach that beam.[​IMG]
     
  6. Ronald van Arkel

    Staff Member Resident Builder Builder

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  7. DarkAlchemist

    DarkAlchemist Veteran
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    I finally figured it out and it was a complete redesign but to answer your question a 30T would be a horrible resolution imo. I use a 16t myself (another thing openbuilds doesn't have) due to the nice round, and whole, number you get for steps.

    In response to the matter above I was correct his way with the belt in the above scenario would mean only that one side is usable and no way would a belt work with t-nuts and screws going into the middle of the 20x20 extrusion.
     

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