Funny, I came across that very diagram while googling how to do that conversion. Which makes sense, once you understand the basics of how each file is created.I understand your frustration but like everything there is a learning curve, that why there are whole industries dedicated to these programs. Typically the more powerful the program the more difficult it is to learn. think MS paint vs Photoshop. If you want a very simple CAD program that is really easy yo use check out Sketchup. I dont think its free anymore but its cheap. However its not parametric, and not precise, but you will be able to generate simple drawings with it.
STL files are lossy. I would not use that file type AT ALL except exporting final output for 3d printing or machining a very complex curvature. You can cheat it by increasing the triangle count but its still not great.
I know its not what you want to hear but this is why you draw it yourself correctly the first time. Lol. Take the time to learn a one of the CAD programs and learning others will be easy. I started with Alibre about 10 years ago and now I am well versed in Rhino, Solidworks, Fusion, Alias, AutoCAD and Sketchup. I use sketchup everyday for work becuase its incredibly fast for ideation. Once the design intent is solidified I will move to Solidworks or ACAD.
If you don't want to take the time to learn a CAD program just draft this part by hand. Its really not that complex.
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I would have had that diagram drawn by hand a long time ago, if the machinist would take it. Lol. I agree, it's not complex.
I talked to a different machinist and he told me that the setup time for CNC would take longer than it would take him to do this on a manual lathe.
Does any CNC aficionado here know what he means? It was my understanding that you set a price in the machine, load up the tools needed in the tool head and press start *shrug*
I watched some YouTube videos but they all skip over the setup process. Is it as complex as the other machinist made it seem?
(I'd really like to invest in a small hobby lathe. I think one of those 7"x14" units would be awesome to have in the garage. I cant justify the cost and shipping right now, but hoping one pops up for sale used locally. I'd really like that)