Fron nop head: I don't consider individual dimensions. I just model with the actual dimensions I wan't and then scale the whole print up by 1.0059 in the slicer. That’s an interesting approach I hadn’t thought of. So you make all your measurements nominal? I (and I suspect almost all of us) add a tolerance to holes and subtract it from volumes when necessary. Does this scale work for everything? What are the exceptions? The case I would worry most about is a round hole printed horizontally when I need a round peg to rotate smoothly in it. Because it involves an overhang I used a vertical scaling on the hole to compensate. The scaling I found to work was larger than your 1.0059. -Bob Tucson AZ

I model everything including holes with real dimensions. For vertical holes I use polyholes() to get the size right and for horizontal holes I use teardrop_plus(). The 1.0059 scale factor came from measuring a large PLA print made on HydraRaptor, which had exact XY motion accurate to six microns but seems to work on all my machines with ABS and PLA. Not sure why, as I would have expected ABS to shrink more. With belt driven machines it is hard to separate the XY motion calibration from the plastic shrinkage. I recently had to change the steps per mm on X as it was about 2% wrong compared to Y on a machine I had fitted new belts to. Before that I always used 80 steps per mm on all my machines. Not sure where the GT2 belt came from, as I haven't bought any for about six years but maybe it was a free sample from somewhere and had slightly the wrong pitch. It must depend on tensions to some extent but I have never noticed it being out before. I only scale XY, I don't scale Z but to make a horizontal peg I use horicylinder() from NopSCADlib that makes sure each rounded filament edge just touches the specified circle. Here is a drag chain with horicylinder() pegs that fit into teadrop() holes [image: image.png] On Sun, 4 Dec 2022 at 17:31, Bob Carlson <bob@rjcarlson.com> wrote: > Fron nop head: I don't consider individual dimensions. I just model with > the actual dimensions I wan't and then scale the whole print up by 1.0059 > in the slicer. > > That’s an interesting approach I hadn’t thought of. So you make all your > measurements nominal? I (and I suspect almost all of us) add a tolerance to > holes and subtract it from volumes when necessary. Does this scale work for > everything? What are the exceptions? > > The case I would worry most about is a round hole printed horizontally > when I need a round peg to rotate smoothly in it. Because it involves an > overhang I used a vertical scaling on the hole to compensate. The scaling I > found to work was larger than your 1.0059. > > -Bob > Tucson AZ > > > > _______________________________________________ > OpenSCAD mailing list > To unsubscribe send an email to discuss-leave@lists.openscad.org >

On 12/4/22 12:31, Bob Carlson wrote: > Fron nop head: I don't consider individual dimensions. I just model with the actual dimensions I wan't and then scale the whole print up by 1.0059 in the slicer. > > That’s an interesting approach I hadn’t thought of. So you make all your measurements nominal? I (and I suspect almost all of us) add a tolerance to holes and subtract it from volumes when necessary. Does this scale work for everything? What are the exceptions? > > The case I would worry most about is a round hole printed horizontally when I need a round peg to rotate smoothly in it. Because it involves an overhang I used a vertical scaling on the hole to compensate. The scaling I found to work was larger than your 1.0059. > > -Bob > Tucson AZ The fact that its being printed horizontally is a whole different problem, not the xy shrinkage we were discussing as the part cools, and in my experience quite highly dependent on the printer and the plastic its being fed. Bigger holes might be supported, which for deep holes is a pita to remove. Generally I make such holes .5mm bigger, then clear them with a number drill of the wanted size. That has worked well for holes deep enough I have to clear them from both ends, these were 7mm holes 7" deep. Prints well in PETG or PETG+CF. 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, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/>