A print turned out 2mm longer than the virtual model - is it warpage? how to solve?

Hello,

I ordered 2 prints of the same model that has a long thin part (the 194mm one) that turned out 2mm longer than the actual model in one of the prints while the other was fine. I am attaching a picture of the long part, and if someone needs it, I can also upload a photo of the difference.


Could someone help me with the following questions:
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[*] Is the inaccurate length (+2mm) of the long part due to warpage or a one-off printer error?
[*] Is the model too thin? Shapeways recommends a 10 to 1 ratio for height vs thickness to avoid warpage, so, a 193mm long wall, should be 19mm thick?
[*] Would a hollowed rectangle (eg: 3x3mm hollowed for 1mm thick walls) instead of a T shaped rib solve such issues? Or it must be thicker? I want to keep the price down, so if another shape works that has similar thickness would be fab.
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Which material did you print in?

WSF unpolished

If you go into Edit Model and then take the 'Edit Model' Tab (yes, I know...) what are the Original Bounds dimensions? Do they tie up with your expected values?

Edit: If I read your pictures correctly the longest dimension of your Model is 199.371 mm

One of the print ties up exactly with my model, while the second one is longer by nearly 2mm-s.
I suspect the issue could be related to warpage, so I wonder if a thicker (but more expensive) model would solve it? Or instead, the T shaped rib, I could do a rectangle shape that is hollowed and its walls are 1mm?
While I researched this issue, I came across a customer comment on this unrelated model of another designer:
https://www.shapeways.com/model/207226/4-4-case-for-iphone-4 -gsm-cdma-verizon.html?li=curatedproductGroup&materialId =25
: "This case isn't worth it. The first one (red) I brought was good and I gave it to my mom when she got an iPhone. I brought three black ones for myself and my dad and not one of them fitted! They were maybe 1 mm too long and wide so the iPhone just jiggles around. I asked for replacements, got three new ones, and only one case was acceptable. So out of five black cases I received, ONLY ONE had the right fit. I am very disappointed. "

The accuracy of WSF is stated as ± 0.15mm, then ± 0.15% of longest axis. By my math that's ±.4425mm so still wouldn't explain your 2mm. Warping shouldn't cause it to be longer, if anything should cause it to be shorter. I'd request a reprint.

Thx for the tip. I am still wondering if the model can be altered to avoid such an sls inaccuracy issue? I am worried that if I offer it for sale, and the customer buys one and does not see another working version in hand, the customer will dismiss the product and leave bad reviews. Should I warn users that in case if the model is not a perfect fit, they should request a reprint and occasional inaccuracies can happen with 3d printing?

By informing service, and making them aware of the issue, it makes us better at spotting these things before they go out the door. Mishaps are very rare, and we aim to eliminate them as much as possible. I wouldn't warn customers, but if they come to you with an issue, be sure to let them know to contact us to correct it.