For a single helical gear the angle used is normally 6,8,10,12,15,20 degrees. Be aware that a greater angle will result in a greater axial load (see below). If you have an empty space for a shaft in the centre then just hold down shift while hovering the protractor over a horizontal area to lock it in that orientation. Then its just a matter of choosing your desired angle. With the top face still selected position the protractor over at the centre of the gear and right click. To create a helical gear simply follow the same process as for the involute gear but with one extra step.Īfter you have ‘pulled’ your gear surface up to make it 3d, select only the top face of the gear and choose the rotate tool (hot key ‘Q’). Make sure the centre of your gear is still positioned at the point 0.0. Add your centre shaft hole and then use the Push/Pull tool (hot key ‘P’) to make the object 3d. The gear outline will appear at the point 0,0 so its good idea to mark the centre position before moving it. To create an involute gear, use the plugin as described above to first create the gear outline. When you have finalised your gear design you can export the file as an STL. Once you are comfortable with these settings its quite simple to make a range of different gears. If you wanted a ratio of 1:3 then your large gear would need 30 teeth and pitch ratio of 30mm. For example, lets say you have a small gear with 10 teeth and a pitch radius of 10mm. The key point here is that if you want two gears to mesh well, then the pitch radius must be increase or decreased by the same ratio as your number of teeth. However, no matter the number of teeth, the ‘pitch point’ will remain constant for all gears. The pitch radius is the distance from the centre of the gear to the ‘ pitch point‘, the point of contact between the two gears.Īs such, the outermost radius of the gear for a fixed pitch radius will change for different numbers of teeth. This is not the outermost radius of the gear (the root circle). I would recomend sticking to a pressure angle of 20. What ever pressure angle you choose, make sure it is constant among all gears used together. A low pressure angle (14.5) is normally used with high number of teeth (40+) and will give a greater contact area but lead to increased noise and backlash.
The pressure angle effects the geometry of the gear teeth.
Have no less than 12 teeth and try to avoid a gear ratio any higher than 1:6. Try and select the highest number of teeth possible while still maintaining a printable resolution. For example, Wade’s geared extruder has 11 teeth on the pinion and 39 teeth on the gear wheel. This helps to distribute lubricant and reduce ware. By having an odd number of teeth each tooth will meet a different counterpart on every rotation. However, an even number of teeth will result in the same pair of teeth meeting over and over again. However, your gear with more teeth would need need to be twice the size in order to have the same sized teeth.īy choosing an even number of teeth you have a range of different exact gear ratios. If you desire a gear ratio of 2:1 then your gear wheel will have twice as many teeth as your pinion. The number of teeth on your small gear (pinion gear) relative to your large gear (gear wheel) will determine the gear ratio. From the dialogue box you are presented with three options. Then open sketchup and choose ‘Involute Gear’ from the draw menu. This plug-in was not produced by me and all credit goes to Cadalog Inc for writing this very useful tool.
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To begin with, download the involute gear plugin and copy it to your sketchup plugin directory. For an introduction to sketchup see the sketchup related links this page.Ī collection of the gears seen in this page can be downloaded from the 3d warehouse. For a good introduction in general gear design see here. The following is a guide for designing gears in sketchup for 3D printing, CNC milling or similar. Restart sketchup and then access it from the “Draw” menu. Just copy the plugin to your Sketchup plugins directory Eg: C:\Program Files (x86)\Google\Google SketchUp 8\Plugins or see here for newer sketchup versions).
If you have trouble with this copy on older sketchup versions then try the original file which can be found here. This version has been updated to work with the newer versions of sketchup. For a copy of the plugin please see this link (use download link in top right, please do not ask for edit access) as the original owner appears to have moved the site.