Harmonic Gear Drives??? 1

[cadfish]

I need to create a zero backlash roatary table for an NC milling machine and it needs to be accurate down to the tenths of a degree. Is a harmonic drive the only way to go, any other options are open.
Thank you for your time in advance.

 

[gearcutter]

Another option is a dual lead worm & gear. They are constructed with two leads. One flank of the thread and its mating sides of the wheel teeth are manufactured with one lead, and the other flank and its mating wheel teeth are manufactured to a slightly different lead. As far as the worm is concerned this has the effect of producing a worm thread which increases in thickness from one end of the worm to the other. If the worm is therefore moved in an axial direction when in mesh with the wormwheel, backlash between the pair can be adjusted to the required amount. In practice the gears are manufactured so that the initial backlash is achieved at a certain distance relative to a datum plane on the worm. The worm can then be adjusted from this point as and when necessary during the life of the gears.

http://www.renold.com/Products/Gears/LooseGears/Dual_Lead_Wormgears_.asp

 

[cadfish]

Thank you Gearcutter, I thought of a single lead at first but then realized that it would have untollarable backlash so I crossed wormgears off my list, but now that you said dual lead I will give it some more thought.

 

[jmaurel]

I think that a slightly tapered worm could lead to the same result. It's possible also to press radialy the worm onto the wheel as this is made on many rotary tables. An other solution is to use a wheel made with two parts joined on the throat plane.