I have described that FDM type 3D printers can not draw layers when there is no lower surface to support. In fact, that is not a true. In some cases, drawing lines across the air is possible. If there are more than two places that can be connect with straight lines, 3D printers can draw lines by sweeping those two points.
There is no lower layers below the line that is being drawn. The printer head will extrude plastic, and at same time, drag the extruded plastic to opposite side. By repeating this action, 3D printers are able to draw layer across the air. It sounds nice, but is it really possible?
I have tried actual print. This is the preview of G-code of test model. You can see there are not supports or lower layers below two faces. It may look impossible to print.
But, if it is not too long, it can be printed. Actually, my printer setting was not perfect. The centers of faces that were printed by bridges droop little a bit.
In addition, when we look it closer, we will find that the surface that was built by bridges have bad quality. Anyway, bridges are still very useful when we can not create supports.
Well, in many cases, we can not use supports that are generated automatically. For example, when we try to print full assembled models, automatically generated supports may fill the gap between joint. It will be impossible to remove and will ruin whole print by interrupting movements. In this case, by designing the model using bridges instead of supports, we can avoid the problem.
For generating bridges, we don’t have to do any additional job. Slicer software generates bridges automatically at where they needed, and we can adjust parameters of bridges like move speed. The qualities of bridges are affected by sweeping speed. I can’t mention about the optimised values, because it varies by materials and even manufacturers.
