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?
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.
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.Quote:
Originally Posted by Marm
I have attached a picture of the device sitting in the holder.Quote:
Originally Posted by ServiceXp
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.
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.
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.Quote:
Originally Posted by ServiceXp
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.
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.
Also remember, this is a layered manufacturing process. I know on my printer, that stresses work differently in the various axis (axis's?, axi?, axis?), ahem, directions. If you are putting a lateral stress across the layers, it may tend to delaminate (words are failing me tonight, that's poorly described). It really depends on the orientation of how you print it and how it is used and designed. The identical same design might fail catastrophically with minimal loads, but print it 90 degrees the other way, it can be a beast. Also, what may be rigid in one direction, might be flexible in another, and brittle in another, all relative to print orientation.
But it doesn't sound like you're putting a lot of stress on this frame (I've learned this through trial and error of supporting a 5kg load with 20kg lateral stresses on my racing boat parts), so I wouldn't worry too much about stresses. Because, if there are no other design considerations for the parts in question, again, why go with the smallest tolerance you can? Add a little redundancy to the design. Of course, if adding the 2mm to this part, makes you compromise another part, then it becomes an issue of priority.
If you're reaalllly concerned, run your design through a stress simulator. http://scan-and-solve.herokuapp.com/ was a thread here a while ago, and I use it whenever I have concerns about design strengths. It's kinda intuitive, but it does take some getting used to, especially if you've never run a sim like this before. Just remember, red doesn't mean bad, just the highest level of stress.
Great advice Marm!
I have finally finished my design. Have a look at it and see if there are any issues Attachment 8686. However, the weight has ended up being a whole lot more than I expected. Really, it's only 1.2 ounces more so I guess I could live with that. I still intend to refine it a little more.
At this point, I have a concern that I never thought about until today. I didn't really think much about the fact that most printers build up an object layer by layer. So, that leaves me wondering about sections that are suspended in midair. There is one area in my design where I have a section spanning a 30 mm gap, supported on either side by the two central wedges. I don't know if this is a problem or not. I also don't know if it depends on which type of machine is being used. At this point, I don't know which printer will be used by the service I found on 3d hubs.
It shouldn't be a problem, they will use a support structure. The surface that needs the support will not be as smooth.
it should bridge 30mm without any problem. the first layer will be a bit droopy. you can sand it flat.
Hmm, looking at the model - you've actually got one small suspended part - in the middle - and two very long parts either side.
you will need to use support.
But nothing complicated, so just use about 15% automatic support and it shoild be pretty easy to remove.
What slicer are you using ?
And what settings are you using for walls infill etc.
with 3 shells/layers and 25% infill AND the support it comes in at around 61gms. - 3 gms being the support.
And that would be pretty damn strong.