It’s common practice to have a fan on the ‘cold end’ of the print head to keep the heater and motor from prematurely softening the filament.
N. Christopher Perry > On May 31, 2020, at 1:29 PM, Chris Albertson <[email protected]> > wrote: > > 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 _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
