Hi, nice job. Half the battle with 3D printing is working out the best way to break down a model so that it prints well.
Vertical walls and tubes print best with smooth sides, flat pieces a pretty good, angled parts tend to be ridged as they show the layers more clearly.
If you have a vertical surface that splits along the layers then it normally implies uneven cooling. It's the reason a lot of new printers are enclosing the printing bed to keep the temperature steady. This helps when the most recent layers are much hotter than the older lower layers.
Without my Brother getting a Makerbot printer some years back I would never have been able to build my MK1 Tank model. Not had access to a printer for a couple of years now... miss it sooo much!
You may already know all this but just wanted to encourage you to keep at it and get designing.
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