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Need suggestions to minimize deflection on long gantry

Discussion in '3D printers' started by bacree85, Apr 4, 2018.

  1. bacree85

    bacree85 New
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    Hey Guys,

    With all the tool change work that the E3D guys have done, I'm really interested in doing something like that for my printer which would mean that I can make my gantry MUCH lighter than it is now since I won't have to plan for carrying multiple tool heads at once. The problem I'm running into is that I want to use the lightest linear rails I can for my longest axis (X axis on the Y gantry), such as 20x40 but with a span of 1755mm and an estimated load of about 670g (1kg max), even with 20x60 rails I'm still looking at roughly .1mm or so of deflection in the center and I'm not nuts about that.

    I think it would solve the problem if I used a 20x80 but then the weight is getting back up there and I might need to beef up the Z gantry the Y gantry rides on.

    In any case, my actual question is: Does anyone know of a way to make a 1755mm length of 20x40 or 20x60 stiffer so there is less deflection and if not, what light weight material could I substitute that is stiffer and can support 1kg with a minimal deflection <.05?

    Apologies if there is not enough info or if what I wrote is confusing, I'm on a super short lunch and that time just ran out but I wanted to get it out there!
     
    #1 bacree85, Apr 4, 2018
    Last edited: Apr 4, 2018
  2. bacree85

    bacree85 New
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    Hmm, after looking at the spreadsheet again it looks like I remembered incorrectly. The deflection should only be .07, not .1mm which is still not ideal, but it's better. If I can keep the weight under .5kg then it would only be .05mm which still not idea but should only have a minor effect.

    I'm still curious to know if anyone has any ideas how to make a 20x60x1755 rail stiffer. I thought about taking a continuous strip of carbon fiber of some height and thickness and affixing it to one or both sides to see if that might help? Or maybe even just a tensioning rod down the middle? I'm not an engineer so I'm not sure how to figure out if either of these will have an effect or how much without just buying a bunch of stuff and testing it.

    https://openbuilds.com/projectresources/how-to-calculate-v-slot®-deflection.175/
     
  3. Scotty Orr

    Scotty Orr Master
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    Have you considered going with a bowden setup to reduce weight even more? E3D's Titan extruder fitted with the grooved bowden adapter works great for me. (I'm not pushing filament as far as you would be, but it's worth considering.)
     
  4. bacree85

    bacree85 New
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    Hi Scotty, I had thought about a straight up Bowden but between the Y and Z being roughly the same length it's likely to a bit more of an issue. I just ordered two 18ncm short steppers and I'm going to test out a setup with one on the X carriage and one mounted a not far away with a bowden tube between. They will both be wired the same and use the same geared extruder and I'm hoping between the two it would be enough to to drive 3mm filament but I'm not sure. So if does work, the stepper itself is less than half the weight of my current stepper so it's not as light as a proper Bowden, but I'm hoping it will be enough. I'll see though :)
     
    #4 bacree85, Apr 5, 2018
    Last edited: Apr 5, 2018
  5. Kevon Ritter

    Kevon Ritter Master
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    The only way to really fight deflection is to have as much surface area away from the center of the beam. If the objective is to keep the vslot/wheel setup, then maybe you can use a 2060 on the bottom with a carbon tube on top. Connect the two using a group of print clamps spacing along the length. I can draw something up.
     
  6. bacree85

    bacree85 New
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    Hi Kevon,

    Thanks for the reply! I might need to see a drawing to know what you mean exactly. I do indeed intend to use the top and bottom grooves for bearing tracks so I'm not sure how I would use a tube on top.

    What I was thinking would be to take a strip of carbon fiber and attach that to the front and/or back and use the strength of it when it's oriented vertically but I wasn't sure how much that would help, if at all. I've attached an image below to show what I mean. I'm not sure about what fastener pattern or spacing but I'll experiment with that unless there is a good way to find that out.
     

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  7. Kevon Ritter

    Kevon Ritter Master
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    I'll be home in about 30min. I'll get straight to it.
     
  8. Kevon Ritter

    Kevon Ritter Master
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    It's essentially using the principle of an i-beam, while keeping weight and use in mind. By use, I'm guessing you still want to use wheels. If so, you would have to have everything "hanging", but that's not an issue. In the pic below, that's a 25mm OD tube. The center of the tube to the center of the v-slot is 50mm. I just pulled it out of my head, but it should at least give you idea. The tube brackets would need to be clamps of course.

    Here is a really good video on how i-beams work.


    In the RC community, the regular beaters will often use packing tape on the wings to act as a skin. Same principle, different application.
     

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