Since it looks like there's little or no progress on an update to the STL format, there is work going on for 3D printer G-code post processing to refine and smooth curves or even convert curves defined by a series of straights to real arcs for printers that have hardware and firmware capable of doing real arcs. Supposedly units are arbitrary in STL. There's nothing in the file format (unless with a proprietary command that only specific printers understand) for indicating what unit or scale to use. Assume 1 unit = 1mm and design accordingly. In the 3D software I use, for STL export it makes a meter, centimeter, or millimeter all equal 1mm. I use the different model and world unit settings to best fit whatever I'm doing on the screen. Design tiny stuff in Meters in a Centimeter world and big stuff in Centimeters in a Meter world. Working in US units produces STLs that aren't the expected size. It's all the fault of 3D Systems. When they created STL they were only thinking of millimeters because their early stereo lithography printers that scanned a LASER across the top of a tank of resin only made rather small parts. One of the first products prototyped with those was the roller clamp used on IV fluid lines and that was a pretty large 3D print in its day. A little bit of foresight and they would have made STL able to support many types of units. Just a simple UNITS= line at the start and have the printer software able to read that and adapt the movements. On Wednesday, November 11, 2020, 09:47:14 AM MST, Chris Albertson <[email protected]> wrote: Remember the workflow. You start with a 3D model where the resolution is literally "perfect" as the curves are defined by mathematical functions. Then you convert the 3D model to an STL and an STL can contain only straight lines. No circles, no curves. When you make the STL you get to specify a maximum error but small errors mean big files.
So when you look for a gear or sprocket ALWAYS look to see if you can get the 3D CAD file and not just the STL. The best places are the big resellers like Boston Gear, McMaster Carr, SPD,.. they all have "perfect" 3D CAD models, usually.STEP file type. If you do download an STL then you are accepting some other random person's idea of what is a good error tolerance without even knowing what he specified. *So make the STL file yourself. * I usually go overboard with resolution in the STL and specify something like 0.001 mm or less allowed error. The next step is manufacturing where you get to specify how it is sliced and printed or how the file is cut on a mill. _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
