Use a metal hub on the gear, especially if it connects directly to a motor that gets hot. The other thing is to use ABS plastic or maybe PET plastic. PLA is easy to print but has the lowest melt temperature.
I had the idea the other day to make the metal gear hub extend well past the end of the motor shaft and then cut some groves so it might act as a heat sink. You really have to measure the shaft temperature after an hour of warm-up. "Can't touch it" covers a wide range of temperatures. it is had to keep your hand on an object that is just 60C but the PLA works well enough at 60C. But 120C is to warm for PLA. As I said earlier, with a gear r pulley, all the stress is on the hub, not the teeth so make the metal. Tell you cad system you want (1) a 24mm hole and (2) a hub width about 2X the gear's face width. This gives lots of plastic the metal surface area. PLA is about 1/3rd as strong as metal so so a large diameter and wide design is correct. As for dimensional accuracy. Print a hockey puck that is about the size of the parts you want to make and measure the puck. YOu only have to do this once for each plastic and print temperature. NOTE: Write which way is X and which is Y on the puck before you remove it from the printer. Measure both X and Y and Z with calipers. If the puck is monimally 100mm diameter when you drew it n the CAD system and prints are 99.5, you know then you have to make them 0.5% larger The percent will change with size. I assume no one prints solid plastic and we all use 15 to 50 percent infill. 3D printed parts are not uniform material but a shell and infill. All that said, just ignore all this untill you can make everything work Pulleys and gears have teeth ad keep their ratio even if printed 2% wrong size. On Sun, May 31, 2020 at 9:11 AM Martin Dobbins <[email protected]> wrote: > Caveats: > > 1:I'm not a 3d printer user, but I may become one after reading this > thread: Thanks (I think<grin>) > > 2:I have very little experience with Openscad. > > Serve the required grains of salt with the following as required > > Gene Heskett wrote: > > >1; Which is a measure of the OD of the rendered pulley, those areas of > >the preview gfx are blank, although the scale marks are there, they are > >drawn behind the sprocket image. so one could get a very rough idea of > >the total radius of the finished gear in mm. Am I missing a font, or is > >this a more serious concern that will need me to make the gear before I > >can determine how it fits? > > Melted plastic contracts as it cools, so getting something on size is an > iterative process > > Print, measure, calculate percentage shrinkage and reprint that percentage > oversize. I understand that most slicer > > software includes an easy way of doing this (at least I hope so). Rinse > and repeat to get something that meets > > tolerances. I don't know the answer to the openscad rendering question, > but don't you have the parameter values > > for everything drawn? > > > >2; This motor runs uncomfortably hot, and I've not found anything to > >indicate the controller goes into a low current mode at balance, I left > >it running at about 1500 revs for half an hour and cannot lay a hand on > >it to pick it up, and an extended stop didn't seem to cool it any, and > >since that heat will telegraph up the motors 8mm shaft to the PLA, is > >this going to be a life of the sprocket limiting factor because the PLA > >will soften and eventually cold flow to a loose and likely out of > >concentricity warpage? > > That's something that you can figure out now, melt temperature and (I just > found out from the link below) > > glass transition temperature 111 to 145F. Can you squeeze a metallic hub > in? Or maybe an aluminum heat sink > > on the shaft between the motor and where the gear will sit? > > > https://www.creativemechanisms.com/blog/learn-about-polylactic-acid-pla-prototypes > > > >3; I have the pi3b I took off the Sheldon, and another of those 5v5a > >supplies, and I've downloaded the octo-pi image that includes that > >slicer. So that I think solves the slic3r problem of having to compose > >a working multi-variable config for slic3r. Unless someone has a slic3r > >config to drive an Ender that they can share. > > Nope, but a google search found this-any good? > > https://www.youtube.com/watch?v=3yIebnVjADM > > > > I hope some of that helps? > > Martin > > > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
