| Upon a visit at the Chemnitz Industrial Museum, I saw a nice infinity machine, i.e. a multistage gear train where the rotation of the third stage is already imperceptible. The last gear wheel embedded in concreate... what is all that about? | |
After twelve worm gears, each with a transmission ratio of 1:50, the motor rpm of 200 is "slowed to nearly nothing". One full rotation of the third gear wheel takes an entire 10.4 hours. You will only be able to witness the 6th gear wheel making one complete turn if you live to an age of 148.6 years.
I had always wanted to build a model of this machine, but shied away because of the high price of the required worm gears. Then I bought worms at a model engineering show, assuming that I would be able to acquire matching worm wheels -- an assumption that turned out to be a real big fallacy.
In the German CNC forum ("CNC Ecke"), Achim Steinke described a gear hobbing technique suitable for homebuilding gear wheels: http://www.metallmodellbau.de/GEAR-CUTTING.php
With that infomation, I was able to start the project eventually.
These are the finished aluminum gears, shown here together with the respective gear hob and the brass worms. The other photo depicts several bearing blocks and shafts ready for assembly.
Instead of using a granite block, I bolted the last gear wheel to a steel block. The motor turns the input shaft at a rate of 60 min-1, each transmission stage has a 1:40 ratio. To prevent this transmission from getting covered in dust while it is taking its sweet time, I am protecting it with a glass cover which was very accurately built by Rainer Isbitzki.