What should I avoid when creating *.stl files?

[Jsk]

I just received the first batch of 3d printed parts that I designed for my current ship build. Most of the parts printed successfully, but others failed. I do NOT want my own 3d printer. That's a hobby unto itself and I have plenty of hobbies. However, I would like to know how to design *.stl files with a minimal chance of failed prints. Let's face it, since I'm not doing the printing I'm paying for someone else's time and material. I want to avoid wasting their time and my money.

 

My process has been this: I model the parts in Wings3d (my modeling application of choice for many years), which is a subdivision modeler. Wings will export *.stl which I open in the Prusa slicer to see if the slicer catches any errors in the file. Mostly, I think *.stl is a pretty basic file format so the program used to model the part shouldn't matter too much. I don't think there's much in the *.stl that can cause problems when printing but I'm not entirely certain. Occasionally, the slicer will identify an error which I can't find in the origin model so I'll open the *.stl in Blender, and then export it again as *.stl. After that, Prusa typically will not report any errors.

 

I have not added any supports. To me, that seems like something that would be more specific to the slicer program used in the actual printing process. Is that a correct assumption?

 

Also, the guy who printed these for me said that something in the files had 'blown up the printer and he had to clean the tank'. I'm not sure what that means. I've used him to print purchased *.stl files and he's been pretty reliable. A number of the parts I had designed came out very foreshortened as if they had collapsed in length. Is that something that could be caused by the *.stl file?

 

Another question I have is about warping. My understanding is that most warping is due to the curing process where the resin inside the casting cures at a different rate than the outside layers. As a modeler, is there anything I can do to alleviate this?

 

For example, in the picture below, would the 8 inch gun--which is mostly solid--have less of a tendency to warp if it was hollow? if there was a channel running down through the center almost the entire length?

 

The 6-pounder guns under the 8-incher suffer from being too thin in the barrels and shoulder rests. That's just me not knowing the parameters of the printer used and that lesson has been learned.

 

But the 6-inch barrel at the bottom of the picture suffers from something else. I also had a number of ventilators that somehow seem to have shifted during printing. Is there anything in the *.stl that could cause that or is it simply an error in the slicer used to print?

Any other advice for a 3d print noobie?

 

TIA!

[thibaultron]

Most of what I see seems to stem from a insufficient number of supports.

 

Here is an example of one of my typical cannons with supports, in 1/24th scale.

 

What scale are your prints in?

 

 

[Jsk]

These are for a 1/200th scale model. So the 8" gun (the big one) is 68mm in length. I'm not sure what slicer the guy printing the items is using and I'm assuming his program allows him to add the supports. This particular part came without supports attached but it looks like there were 10 in-line running along the bottom. The 6" gun did have a number of supports attached similarly. Other pieces do seem to be adequately supported.

[thibaultron]

That's a very small scale! The only thing I can think of is to print them vertically with the barrels farthest from the build plate, and the widest part toward the bottom. There is not enough of the smaller guns to tell me what they are supposed to look like.

 

Also have him cut back on the cure time, long cure times can warp thin parts. Playing with the exposure times might help.

[Jsk]

Thanks. Yeah, they're small. The small guns are suppose to be 3 and 4 pounder Hotchkiss (I think). They're no more than 0.5 inch from muzzle to butt. I've tweaked the model with beefier barrels and shoulder stocks and will try again.

[thibaultron]

As the parts are so small. you might want to have a solid base with the parts then supported by sacrificial standoffs. This makes it easier to remove them without risking separating them from a larger support. I did this for two small step plates for a HO scale tender bunker I designed.

 

The graphic below shows this with thin walls going from the base to the curved base (horizontal in this view) that the step is mounted to. One of the support walls is circled in red.