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  1. #1

    need a little advice on ABS wall thickness for my first project.

    I'm getting ready to send off my first design to a printing service in a day or two, but I need to refine it a little. It seems a little thick, but that's because I'm not sure yet on how thin I can make weight bearing sections when using ABS. I have attached my design, and you can see that the thinnest sections are 4 mm. It needs to be able to hold an eye-tracking camera weighing about 200 g. Can I get away with reducing it to 3 or even 2 mm?
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  2. #2
    Engineer-in-Training ServiceXp's Avatar
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    Do you have a picture of the device? If I'm looking at the orientation correctly and how the device might sits in it. I would at the very least Chamfer the rear inside corners. I think you might be able to reduce the "front" walls dims down to 2.5. BUT it would be helpful to see how the device would sit in the 'cradle' to give more help.

  3. #3
    Engineer Marm's Avatar
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    From personal experience, learned the hard way, you don't want to minimize your design. If 2.5mm thick is the lightest you think you can get away with, then 4mm should be just fine, and will hold up to any expected abuse. Especially since you're sending this out to be printed, you'd much rather find you spent a little bit more for materials, than find you have to redesign and buy a second one when the first breaks.

  4. #4
    Quote Originally Posted by Marm View Post
    From personal experience, learned the hard way, you don't want to minimize your design. If 2.5mm thick is the lightest you think you can get away with, then 4mm should be just fine, and will hold up to any expected abuse. Especially since you're sending this out to be printed, you'd much rather find you spent a little bit more for materials, than find you have to redesign and buy a second one when the first breaks.
    I don't know what the minimum thickness is that I could get away with. I did find this tablet holder for a galaxy tablet: http://www.thingiverse.com/thing:395373 and the main bottom section is only 1.5 mm. That makes me think that 2 mm would be just fine for my device. I just don't know how strong ABS is, not having done this before.

  5. #5
    Quote Originally Posted by ServiceXp View Post
    Do you have a picture of the device? If I'm looking at the orientation correctly and how the device might sits in it. I would at the very least Chamfer the rear inside corners. I think you might be able to reduce the "front" walls dims down to 2.5. BUT it would be helpful to see how the device would sit in the 'cradle' to give more help.
    I have attached a picture of the device sitting in the holder.
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  6. #6
    Engineer-in-Training ServiceXp's Avatar
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    So the device sits in the cradle without any leaning, and the entire cradle sits flat on a table??? (Need to understand what forces will be placed on the cradle and the single view doesn't really show much) If so, I think you could reduce the entire design down to 3-4mm using ABS which should provide some wiggle room.

  7. #7
    Sorry, I haven't gotten to the rest of the design yet. The eye tracker camera will sit completely flat in the cradle. However, it needs to have a 17° angle. To achieve that angle, the whole cradle will be sitting on 4 wedges (same material). Finally, the wedges will be sitting on a rectangular plate that will be velcro-ed down to a plastic tray that I already have. The cradle, wedges, and rectangular plate will all be one piece. For the most part, the tray will be rotated up by 90° at a vertical orientation. I might also need to completely flip the tray to an upside down horizontal orientation with the cradle facing downward (I am also going to add a Velcro strap to the front of the cradle to hold the tracker in.) I'll try to make another image if I have not explained this well enough.

  8. #8
    Engineer-in-Training ServiceXp's Avatar
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    Maybe you can point to where you think the most stresses will be placed against the cradle structure? I'm still thinking 4mm ABS with the inside corners chamfered should work well

  9. #9
    Quote Originally Posted by ServiceXp View Post
    Maybe you can point to where you think the most stresses will be placed against the cradle structure? I'm still thinking 4mm ABS with the inside corners chamfered should work well
    I'm most concerned about the main bottom section that my device will be sitting on. Most of that section is already 4 mm thick. On either side are sections that are raised up a bit, to fit the shape of the eye tracking device, and they are 7 mm thick. I was hoping I could maybe get down to 3 mm. Most of the time, the whole thing will be flipped up to a vertical orientation. That means that those two bottom ledge supports will be bearing most of the weight. If I kept those supports thick enough then maybe I could reduce the bottom section.


    By the way, I found a printer on 3D hubs who has offered to give me a second free printing if the first one is not sturdy enough. I can try 3 mm and see if that holds up.

  10. #10
    I have done some rough calculations to estimate the potential stresses on my holder. Assuming that the internal structure of my eye tracking camera is relatively even, I would say that the density is approximately 1.7 g per cubic centimeter or 1 oz per cubic inch. If you noticed an earlier comment I made in this thread, I posted a link to a tablet holder on thingiverse. The main weight-bearing support sections of the tablet holder are only 1.5 mm thick and the distributed weight of the tablet is significantly greater than my eye tracker. That leads me to think that 2 mm would be enough for much of the cradle.
    Last edited by dmehling; 02-11-2016 at 06:52 PM.

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