On Wednesday 11 November 2020 21:20:48 Chris Albertson wrote: > The information is gone. There is no way to automatically reconstruct > a curve from a sequence of straight lines. A human can do this > because he can see what was intended. > > A better approach is to create a slicer that can work with .STEP files > directly. The trouble with that is the mathematics gets hard. If > you remember basic algebra, it is easy to find where two lines > intersect if you have the equations for each of them. There is no > need to guess, you get an exact solution in one shot. It is easy > enough that they can even teach this to 13-year-old kids. But just > try and find the intersection of a line and a curve. Except for > special cases, you are forced to solve it numerically which is very > slow and a slicer needs to do this many millions of times. Slow, > but in theory, it could be done. > > So the practical solution, what we all use is to create STL files that > have a specified maximum deviation from the ideal surface. You can > set this to 1/10,000 inch if you like and then any error is > undetectable. Slicing a file like that would be slow but slicing a > STEP file would be way-slower. > > The OTHER thing we can do to make better 3D prints and I suspect if > you found a good design, this was done, is to design around the > capabilities of the printer. Use simple ideas like filets and wall > thicknesses that are multiples of the nozzle diameter. It is not hard > and if you are designing from scratch you can make a wall 1.60 mm > thick rather than 1.5 mm and it will come out better if using a 0.4 mm > nozzle. There are probably a dozen more tricks like that. > > On Wed, Nov 11, 2020 at 5:41 PM Gregg Eshelman via Emc-users < > > [email protected]> wrote: > > 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.
And freecad-19 can load that. But can it export the .stl's? > > 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. And this obviously is a major PITA for someone like me, looking for a usable bit of code. > > *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. Which will result in huge .stl and .gcode files. And therein lies another problem. Re-slicing after changing filaments, like from PLA to PETG, which changes all the temps, and using a root copy of mc to overwrite the files that are changed by this on the sd card, I find the file on the sd card is NOT changed by the overwrite, so I have to yet again change the TF card, take it back to this machine, mount the sob as /media/sdf1 and hand edit the file with a root copy of geany to apply the temp updates. We need a file system that actually can be called a file system, and for sd cards, vfat from my experience with it, isn't it, not by a hell of a long row of apple trees. Somebody mentioned exfat the other day, but whats the difference? There should be man pages for this stuff so we can deal with these modern sd cards that are way bigger than vfats limits w/o taking Bills word for it. But the smallest card I can buy at wallies was 16Gigs. And exfat wasn't found on the card when I tried it. vfat works but only just barely. And the card I got turned out to be full sized when I extracted from the blister pack just now, not a micro, so its worthless for this printer. I may be able to use it in one of my cameras. Also, in marlin, the lack of the ability to pause the print, raise Z high enough to clean the trash off the nozzle with a damp paper towel, give it time to reheat the nozzle and then resume the print. But you can't raise the Z to do that. That is more of the same stuff. Difficult just for the sake of being difficult. I'm going back to bed, maybe that will improve my attitude. Stay safe and well everybody. > > 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. And never shall they meet at what is supposed to be a common language. Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
