I will make a habit of paying more attention when viewing the build process in print preview mode.
Yes…always spend some time looking at the layer preview mode and slicing through all the layers. A few minutes there can save you hours of having to reprint a part for an error you didn’t catch!
You say when you use multiple process and have configured a non-standard first layer height that you don’t change the the first layer height in subsequent processes. Would doing this not result in a noticeable layer size inconsistency in the first layer of each process as compared to adjacent printed layers on your part?
Theoretically yes, but we’re talking about 1 layer that is maybe .3mm thick vs all the other layers that are 0.2mm thick. One layer that is 0.1mm thicker at the start of a process I couldn’t even notice. After all, a lot of what processes are used for is to speed up your print. we print very thin layers in areas with lots of curves or that needs lots of detail. We print thicker layers on vertical walls where details aren’t important. Basically, you are correct, but in actual application when you’re looking at a part from half an arms length away, do you really notice a 0.1mm different for one layer? Hardly…unless you’re reeeeeeeally trying. If it does bother you, I explained above how to mathematically take care of it so subsequent processes don’t have a thicker initial layer 
**Regarding the other items you pointed out:
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- While I did not create these processes, I can shed some light on why some settings were chosen. The part we are printing is a connector that requires a high degree of strength and structural integrity. We install these connectors with blunt force using a heavy hammer. The shape is unique in that, for us being fairly new to 3D printing, it isn’t readily apparent how to achieve the required level of strength without going overboard on layers and infill.**
While infill does add some strength to a degree, what really adds your strength is the number of outside VERTICAL walls or “perimeter shells” as simplify3D calls them. Cura calls them “shell thickness”. Let’s stick with S3D for now since that seems to be what you’re using.
We want to increase the overall wall thickness. Assuming you’re using a standard Taz 5 or 6, your nozzle diameter is probably 0.5mm. This is important to know when dealing with shells. Each “shell” is one pass with the nozzle on the print. Example: If you set the shells as “2” you’ll have a 1mm vertical wall thickness. If you have 4 shells your vertical wall thickness will be 2mm = 0.5 * 4. Adding more shells will thicken your vertical walls and add strength.
I’ve attached a couple of images of the model here. There are some challenging angles that require strong walls. Would you have any advice as to how to how to achieve our strength goal with regard to applying uniform walls across angles like those in the model? When we specify the number of perimeters are they applied uniformly to exterior angles of the elbow arms?
What you’re missing here is the definition of “top solid layers” and “bottom solid layers”. Bottom solid layers are any horizontal or near horizontal layers on the bottom of the part NOT NECESSARILY touching the build plate.
Top solid layers are the opposite. Layers that are horizontal or nearly horizontal on top of the part NOT NECESSARILY the upper most layer and the subsequent layers before that. It’s easier if I use some pictures:
If I tell S3D I want 10 solid bottom layers and 2 solid top layers, look at what I get in the print preview:
Note that your ramped areas also have 10 solid bottom layers. (Ignoring your initial layer thickness increase for simplicity of math) , I set my layer thickness to 0.2mm, there are 10 layers, 0.2mm *10 = 2mm, my bottom walls are 2mm thick uniformly.
Now let’s change my top layers from 2 layers as in the last picture and change them to 10 layers:
Note that now all my top layers, even the angled ones, are 10 layers thick, or 2mm total wall thickness. Great! However, notice my left and right vertical walls are still 2 shells thick. Since our nozzle is 0.5mm wide, our vertical walls are only 0.5*2 = 1mm thick. Boo! I want uniform thickness. Since we agree that the top and bottom walls are 2mm thick each, we want the vertical walls the same thickness. The nozzle is 0.5mm wide so if we have 4 shells, 0.5mm x 4 = 2mm. What does that look like in S3d?
Ah ha! Now notice all outside walls are of uniform thickness. You should repeat these steps for 3mm wall thickness etc. This was all done in 1 process and does not require multiple processes.
Angus over at Maker’s Muse has a nice Youtube video giving some part strength 101 on how to build tougher parts here: https://www.youtube.com/watch?v=1NzDr1YAb8Q
And, since there is a portion of the center cube that prints (~2.2mm) before the elbow arms begin to print, and say for example we specify 11 bottom layers and print with a 100% first layer height, am I correct to assume that there will only be one bottom layer applied to the elbow arms if we are using only one process?
Hopefully my explanation above answers this question
As you can surmise I am having difficulty grasping how to print a uniform shell across all angles of the model.
Taking the above into account, what would your final advice be regarding our chosen infill percentage?
Since this seems to be a small part, you could print this part with a uniform outer shell thickness and the standard 20% infill and print it again at 50% infill and try it out. Most strength comes from the outer shell thickness. Of course you said you’re hammering these blocks. Impact resistance is a function of the material too.
Here is a chart that helps choose that material to use. Note there is a line there for impact resistance:
TPU has the best impact resistance, but these are rubberized materials and not probably useful for your application. Nylon is an extremely tough material, but it can be a little more challenging to print with and is hygroscopic so you have to keep it very dry or you’ll need to put it in an oven to dry it out to be able to print with it. ABS or PET are your best bets for these parts. Polycarbonate is tough, but you have to print it at a very high temperature which can lead to other problems if you switch materials and you’re not careful. PLA is TERRIBLE for impacts, don’t use it in this application.
I hope this helps! If you have any other questions, please don’t hesitate you ask. I’m happy to help!
Jim
