Design tips for standard resin - wall thickness?

#1

I’ve been trying to design enclosures for my electronic products and wonder if there is a resource (a Form blog posting perhaps?) that talks about recommended box wall thicknesses for dimensional stability and what not (using standard resin).

I’ve found that 1/16" walls are too flexible and prone to warping or deforming. I’m trying a run with 1/8" walls now, but that seems awful chunky to me. I guess I could split the difference and try 3/32"… but I’m using a lot of resin reinventing the wheel box.

#2

maybe try the thicker material with pockets modeled into it. To give you stiffness in the best areas and save material in other areas.

#3

Well, there’s this design guide: https://archive-media.formlabs.com/upload/formlabs-design-guide.pdf

…But it’s talking more about just printing the features (in Clear v4, 100 microns, on Form 2) than making functional prototypes. And the stiffness of a box really depends on the whole geometry, not just the wall thickness. Depending on how much warping you can tolerate, or how stiff you want your part to feel, or how stiffly you want it to enclose your electronics, 0.1" or 3/32" or 2mm might be reasonable dimensions, similar to what you might end up with in an injection-molded ABS part.

…but in the end it still depends on the size and shape and corners and ribs and bosses and holes and how it’s all being loaded in use, et cetera.

There is probably not an existing guide, but hopefully other designers will chime in here.

In the event that they don’t, you may be able to save resin in the long run by coming up with a simple test case involving printing just part of your design, dialing in the thickness that seems right there, and then going back to printing full parts.

Do you happen to be going more for looks-like or works-like prototypes here?

#4

I am an Industrial Designer, not a mechanical designer, but have some experience in the design of plastic injection molded parts due to working closely with mechanical engineers and mechanical designers since 1998. I recommend thinner walls for small objects, ie a key FOB or earbud and smaller (1.0-1.5mm). Inversely, much thicker for larger objects, ie a laptop enclosure (2.5-5mm wall thickness). When designing plastic parts I also consider where to locate features such as ribs and stand-offs. Lastly, the wall thickness might need to be designed thicker/thinner depending on the parts function and performance requirements. I am assuming you have very little exposure to designing plastic parts. I have 3d printed about 300 parts in total with the Form1 and Form2 using the basic resins (black, white, clear) and a few of the more expensive resins. Through all this I have found that using Plastic part design guidelines is very useful in mitigating warping and optimizing material use required to print a part.

#5

Thanks. That guide is very helpful.

My test at 1/8" walls finished, and things didn’t really get that much better. I also got today a copy of an earlier version of the design from Shapeways - with the 1/16" walls.

Now, I don’t suppose I can expect a printer in my garage to do as good a job as they do, but I’m not sure I’m getting the results I ought to.

What I’m trying to get done is a roughly 6" x 2 1/2" x 2" box - it’s a GPS Clock. The design is open - an earlier revision is on Thingiverse: https://www.thingiverse.com/thing:3895904

Jumping ahead to a reply that came in while I was starting this reply… I not only have very little plastic modeling experience, I’m fairly new to 3D design entirely, and the first thing I did was buy a Form 3. My own little joke is, “Congratulations! Here’s your 3D learner’s permit.” “Thanks. I’ll have that Ferrari over there.”

I took some pictures. First, the Shapeways box. There’s a little bit of a mismatch in the fit, but I am fairly sure that’s because I have friction-fit a piece of acrylic in the front (the design has four stiles to hold the acrylic in place and the intent is to secure it with some glue) that’s a wee bit tight.

The next pictures are out of the Form 3. These pieces were run through the Form Wash and Form Cure with recommended cycles and then were removed from their supports.

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#6

Newer versions (not yet on thingiverse) have the 1/8" walls instead of 1/16th and have been redesigned to secure with self-tapping screws, so the receiving boss is now much, much thicker with a smaller hole. Also, the boss in the back now has a full “pocket” so that the two sides can be secured with a 3/8" screw instead of a 3/4".

But I don’t have any ribs or other structure for stiffening. There’s not really going to be any stress on anything once it’s assembled, it’s just going to sit on a shelf. The issue is that the pieces I print just aren’t fitting together properly and I’m wondering what I’ve done wrong.

#7

Number one- Use Rigid Resin- not regular resin.

You will find it much better at printing larger thin walled parts. It also has a better feel and finish than the white resin.

Number 2- create a network of “ribs”- that is, Imagine your bezel wall is going to be 0.1" thick. Regularly spaced on the Inside of that wall you want some 0.1" thick walls that are perpendicular to the exterior wall surface, and stick inwards about 0.2" this will add stiffness to the thin walls and help minimize warping. A good designer places these ribs to support bosses or other features that support the internal hardware.image2

#8

I think I may have gotten past the immediate issue. I think perhaps the issue may be a quirk of the printer, but I’m not sure.

If I orient the case so that it stands more or less vertically in the printer, it comes out perfectly. I probably don’t need to keep the case at 1/8" thickness now, but I kind of like it that thick, it turns out. It feels more substantial, if that makes any sense.

If I’m right, then the issue is dimensional inconsistency across the build area. I’m not quite sure I fully believe that.

#9

Orientation affects how much shrinkage based warpage you get and in which areas and direction you get shrinkage.
So definitely orientation can help minimize warpage.

But do yourself a favor and try the Rigid Resin- if I am producing a finished part like a bezel- that’s what I use.
Its heavier- stiffer- warps less with thin walled prints- and it has the best appearance and feel of all the resins.

#10

Alas, Rigid won’t work on the 3 for now.