Finding best material for tablet holder, balancing strength and weight?

[dmehling]

I need some advice on my design for a tablet holder that I want to get 3-D printed using a printing service, not my own printer. I need to decide which material to use and how thin I can make it. I asked for advice already on a 3-D printing forum, but they could only tell to find out through trial and error, which is not practical for me without my own printer.

Basically, I have a 12" x 8" rectangular surface, with four smaller rectangular sections cut out, making a frame with a cross in the center. I have included an image file of my very rough design (this design doesn't yet include the side supports). I want to know how thin I can make the surface, and also how narrow I can make the sections. I have considered using nylon, which seems to be a very popular material for 3-D printing, but I'm not sure how strong it is. I might have to use something like aluminum instead. Actually, I would love to use carbon fiber, but I can't seem to find out if it can be 3-D printed. I would probably have to order the parts, and find a machine shop to cut the pieces to the right sizes, since I don't really want to mess with fragments of fiber.

I need to be able to support up to 2 pounds. I will be attaching this holder to an articulating camera arm with a tripod style connector. The connection will be made at the very center of the holder.

Any suggestions are greatly appreciated.

 

[billy_joule]

Specific strength is the term you're looking for:
https://en.wikipedia.org/wiki/Specific_strength

From you're image I don't see any reason you need to do any 3D printing, traditional methods will be cheaper, faster and stronger. An off the shelf solution will likely be cheaper and faster again. There's a huge range of tablet holders out there. I own a 3D printer but I still rely on traditional methods for most things - 3D printing is not the holy grail, it has significant limitations.

If you are set on 3D printing, then you must be using a CAD software? Many have built in FEA which can be used to develop your design to achieve sufficient strength.

 

[dmehling]

I only thought of 3-D printing because I thought it would be easier to make a design and send it off to a printing service.

I have only been using programs like Tinkercad and Sketchup, neither of which I like, and I don't think they have fea (what does that mean anyway?). I'm a novice here so I need a program that is free and not too complicated.

 

[Mech_Engineer]

Are there no tablet holders available for your model tablet?

 

[dmehling]

I need a special holder for both my tablet and an eye tracking camera. There is only one specifically made for that purpose that I know of, but the weight of the holder seems at least twice what is necessary, and it is quite expensive.

What might really help me at this point is knowing how to make use of the specific strength formula. I have no idea what the specific strength value of a material even means.

 

[Mech_Engineer]

My feeling is that if you're not sure how to make use of a material's specific strength (or specific modulus) you might not need to make use of it. An overview of each:

• Specific strength (a.k.a. strength-to-weight-ratio) is a ratio comparing a material's breaking strength (or sometimes yield strength) to its density. For a part being designed to have high breaking strength but not too heavy, this parameter helps compare different materials. For example brass (I assume Brass 360?) and Aluminum 7075-T6 have similar tensile strengths in the chart, but aluminum is 1/3 the density of brass. This is one main reason why airplanes use aluminum and not brass, because if they used Brass they would end up weighing nearly 3x as much!
• Specific modulus (a.k.a. stiffness-to-weight-ratio) is similar in its use, except the specific modulus might be used more commonly in structural design where deformation is a concern. A material with a high stiffness to weight ratio will deform less while keeping weight down. In my personal experience I use this parameter more than specific strength because I'm typically designing structures with very low deformation under load.

Honestly your easiest route is probably trial and error: put together a design that you think will work, get it fabricated, and see how it goes. Make revisions based on your prototype, and iterate as needed.

Regarding what material you need to use, practically speaking I think your most cost-effective option will be a thermoplastic like ABS or Nylon. For the purpose of a tablet case or mount thermoplastics are the standard. I seriously doubt you will need the strength of a metal like Aluminum, and will likely spend more to have it fabricated (especially true for a 3d printing process). If you decide to have something machined at a traditional machine shop also consider a plastic called Delrin, it is more machinable than most plastics but AFAIK is not available for most 3d printers.

 

[dmehling]

My challenge is I am trying to get my design perfected before submitting it to a machine shop or 3-D printing service, since I cannot do it myself. I know enough at this point that nylon or aluminum would probably work. The only thing I don't know is the minimum amount of material needed and how much empty space I can have in between the sections of holder (see earlier image I uploaded). A CAD program with finite element analysis sounded like the easiest way of knowing for sure, but the program I tried was way too complicated for me (they probably all are).

Nylon sounds like a good choice, which is what was recommended to me on a 3-D printing forum. I only mentioned aluminum because I have previously used an aluminum laptop tray that could be attached to an articulating arm. It seemed fairly lightweight to me, but if it costs more and is more difficult to get fabricated then it is certainly not worth it.

 

[Mech_Engineer]

Unfortunately a CAD program with FEA won't be a silver bullet, 1) because you need to know how to operate the software and what the results actually mean, and 2) because while FEA software can model well-defined problems it won't be very good at telling you things like "how much material is enough."

My feeling is aluminum won't be a good fit for this application because it's likely machining will be more expensive than a plastic 3d printed part (back to the prototypes thing).

I really do think your best bet is plastic and planning on at least 2 iterations of prototypes (or maybe more), taking your best bet in CAD using your judgement and maybe measurements from similar items, and then try it out and see what happens.