Michael Sullivan's router gear cuttingMichael Sullivan writes:
When I rebuilt my table saw cabinet I decreased the space under my router lift making it too small for the handle on the bottom of the lift screw. I decided that a set of co-planar gears would allow me to raise and lower the lift the easiest.
While looking at your on-line gear generator, I realized that the concept of unwinding a "string" from the base radius to show the point of contact was exactly the same as "rolling" the base circle along a straight edge. Both were tangents. It occurred to me that if I rolled a base circle along the router fence, a half exposed straight cutter would be like the "point of contact" unwound from the base circle. Further if sized right I could cut both sides of the "notch" by just continuing to roll past the cutter. I used your template generator to get the base radius and gear tip radius. Initially I used an angle of 23°, a pitch of 12.7mm and 20 teeth.
I quickly realized three things;
Having set up a band saw circle cutting jig on my sander making pretty round disks was fast and easy so I just made two re-scaled pieces.
The starting point is really arbitrary but the index dividing lines need to be placed consistently at the same spot along the fence. I found numbering the dividing lines helped me keep track of where I had already been. The third gear turned out pretty good.
I then made a 10, another 20 and a 40 tooth sized disks and cut them. At left, base circles with index marks around the circumference. The 40 tooth seems to provide me with the right physical size to allow cranking and the right "force" level to easily raise and lower the lift. I did not have to sand, file, or fine tune any of the disks. I simply removed the whiskers and started using them.
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