OpenSCAD will not even open an STL. So it loses in this competition. However, a number of designers have created and made public their OpenSCAD design files for many different gear and hub configurations.
I appreciate your method for mounting a printed gear. It’s a good example of Integrating 3d printing fab process with machine-building; use it only for the highly complex, low stress parts. I also didn’t even think to download STL models from hardware suppliers. > On May 30, 2020, at 1:12 PM, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > [image: image.jpeg] > > On Sat, May 30, 2020 at 7:31 AM cogoman via Emc-users < > emc-users@lists.sourceforge.net <mailto:emc-users@lists.sourceforge.net>> > wrote: > >> >> On 5/29/20 8:44 PM, Gene Heskett wrote: >>> In this case, openscad gives me the tools I want right now, and I could >>> even do a set of gears for stage 2 of the reduction since that spacing >>> is almost too close for a belt coupling. So by using the correct tooth >>> profiles it could make a very usefull gearset, no belt at all, and a >>> higher reduction at the same time. But would those teeth be strong >>> enough. Worth a try IMO. And a swarf cover from the printer should be >>> doable. >> > > Two points: > > 1) can you (you, not someone else) actually modify a downloaded gear design > using openscad? Try it Go get any random gear from SPD/SI or Grainger and > change the hub and face width and save as STL. I bet this is not easy. > It is nearly trivial in Fusion or Onshape or any that work like them. > Seriously, go through the steps using each system. Downloading and > installing 3 or 4 CAD systems takes days but doing the same test project in > each is the only way to see what each can do. Downloading a gear and > making a trivial modification like (boring out the hub) then saving as STL > is a good test case. > > 2) Yes, the TEETH would be strong enough to carry the force from any > reasonable size motor. Remember that a 1NM motor can only generate 1NM of > torque. What is the radius of the gear? lets guess at 0.1 meter. If so > then the force n the tooth is 10 Newtons (or in barbarian units about 2.5 > pounds) and this is in the worst case where the motor is stalled at full > current against a hard stop. > > When you slice the gear you can specify the wall thickness and the infill > percent and style. For gears of this size in PLA I'd go with 1.6mm walls > and skin and 50% infill density. Cutting those numbers in half to 0.8 > and 25% would still make a serviceable gear for a small < 2NM motor. PLA > is the most rigid plastic. It is not the toughest against impacts but for > driving a CNC machine rigidity matters more than impact resistance > > I've been doing experiments with plastic gears. I can print small ones > down to module 0.5 but the percent error in tooth shape is very high for > small gears. For my self-drive car project I am using module 2.0 spur > gears with 24mm face width. These gears are huge but the front tire will > be hitting rocks and the computer will be making fast steering corrections. > These gears are very strong so that "something else" will break first. > > But notice I said the TEETH are very strong. In a gear the stres is > greatest near the hub and minimal on the teeth. Larger diameter gears have > less force on the teeth then do smaller diameter gears. So you always > want to use the largest gears possible. If the gear fails, it fails at > the hub. It slips on the shaft after the keywhy shears off of the threads > holding the setscrew strip out. With PLA gear slipping on the hub is a > "death spiral" because slipping make heat and heat softens the PLA and > makes it slip more. And the hub to shaft interfce is the highest stressed > place. It fails if not over-engineered. > > My solution is to make my plastic gears with a 24mm (or larger) diameter > borehole. Then turn a 24mm steel bushing that fits the shaft and has set > screws. he gear is press fit with epoxy to the bushing. This way the > hub is steel and will never fail and the teeth never do fail. (Later I > might try making hexagonal hub.) > > That said. When you design the gear, just figure that PLA s about 1/3rd > as strong as metal and give the plastic gear a wider face and try to use > module 1.0 size at least if you can. > > Finally one more thing: With plastic gears, you really can benefit from > using *helical* gears as more tooth area is in contact and they > slide better. It costs no more to print a helix than a spur gear. > Next, you think you don't want to deal with axial loads (side force) so you > use TWO helix gears to make herringbone gears. These have zero side force, > are self-aligning, and cost no more than spur gears. MANY people doing > gears with printers use this kind of gear. They are expensive to cut in > steel but cost no more in plastic. > > If you have a CAD system herringbone gears are easy. (1) find a helix gear > some place like Grainger or McMaster Carr, Download both the left and > right-hand versions. (2) in the CAD system stick them together, side by > side, (3) cut the face width as required, (3) bore the hub to 24mm, (4) > slice and print. Try doing the full exercise using OnShape then > Oopenscad then with fusion and see which works best for you. (If you are a > hard-core Linux user I bet onshape works best) > > As a further exercise try getting you CAD system to make g-code for a > 4-axis mill to make the same herringbone gears. Try using a tiny ball-end > cutter. > > Here is a photo. > > [image: images.jpeg] > > > > > >> >> >> Strength of 3d printed parts is a deep subject. PLA if done right can >> be pretty strong, but other filaments done right are stronger. >> >> I like this video showing how a veteran at 3d printing goes about >> refining his process for printing in nylon. >> >> https://www.youtube.com/watch?v=5MFX1whwjGg >> >> Here is a video where some guys test out different filaments on a 15 >> horsepower outboard motor. >> >> https://www.youtube.com/watch?v=scUEEQyC0GI >> >> >> Keep in mind, the odor will be much worse using any filament besides >> PLA, and most will need a hot end that can do the higher temperatures. >> >> Also with higher temperatures you might want to put a box around the >> printer to keep drafts from messing up a print. One guy uses grow tents >> around his printers. >> >> >> >> >> >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users >> > > > -- > > Chris Albertson > Redondo Beach, California > <images.jpeg><image.jpeg>_______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net <mailto:Emc-users@lists.sourceforge.net> > https://lists.sourceforge.net/lists/listinfo/emc-users > <https://lists.sourceforge.net/lists/listinfo/emc-users> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
