fancy gears
Posted: Sat Jun 22, 2019 3:28 pm
Gary's Wooden Clocks has a web site at http://garysclocks.sawdustcorner.com/fancy-gears.html with a description of what he calls fancy gears for clocks. The concept is that clocks only rotate in one direction, so the back side flank of each gear tooth can be cut away to provide additional clearance.
This is good for a wooden gear clock, but the teeth might become weak. I applied the concept to a 3D printed clock with amazing results. The biggest benefit was made by optimizing each gear by observing the slicer output. I started with 20DP gears at 14.5 degree PA. The active tooth surface was drawn and the tooth was made 0.060" wide. This prints with 2 inner and 3 outer passes. The rim and spokes were made 0.090" thick to print with 6 passes.
The pictures below show the sliced output of fancy gears and normal gears. Notice all the tiny infill segments on the normal gears (marked in green). Each one has a retraction and the possibility of creating a string or a small blob. These small imperfections add slightly to the surface roughness. The fancy gears print about 25% faster and are amazingly smooth.
It looks like involute gears could be made with as few as 8 teeth or possibly even 6 teeth using this method. One downside is that the gears become directional so you have to be careful to always use the active side of each tooth.
I changed out the gear train in my clock (https://www.thingiverse.com/thing:3524448) and it works great. The gear train without the escapement starts moving with 7 ounces of weight compared to 8.5 ounces for the normal gears. This design uses 12 tooth pinions, but I may try a smaller design with 6 or 8 tooth pinions.
Steve
This is good for a wooden gear clock, but the teeth might become weak. I applied the concept to a 3D printed clock with amazing results. The biggest benefit was made by optimizing each gear by observing the slicer output. I started with 20DP gears at 14.5 degree PA. The active tooth surface was drawn and the tooth was made 0.060" wide. This prints with 2 inner and 3 outer passes. The rim and spokes were made 0.090" thick to print with 6 passes.
The pictures below show the sliced output of fancy gears and normal gears. Notice all the tiny infill segments on the normal gears (marked in green). Each one has a retraction and the possibility of creating a string or a small blob. These small imperfections add slightly to the surface roughness. The fancy gears print about 25% faster and are amazingly smooth.
It looks like involute gears could be made with as few as 8 teeth or possibly even 6 teeth using this method. One downside is that the gears become directional so you have to be careful to always use the active side of each tooth.
I changed out the gear train in my clock (https://www.thingiverse.com/thing:3524448) and it works great. The gear train without the escapement starts moving with 7 ounces of weight compared to 8.5 ounces for the normal gears. This design uses 12 tooth pinions, but I may try a smaller design with 6 or 8 tooth pinions.
Steve