Geared pegs for bowed stringed instruments are not a new invention. The first geared peg was the Casperi, the patent for which was approved in 1922, although widespread use wasn't seen until around the 1960's. If you have these old pegs, and have taken care of them and they work fine, there is no real reason to change them.
But new technologies, including high tech materials such as composites and light-weight alloys, have allowed for some major improvements in components used in the violin family of instruments. In addition to light-weight composite tailpieces and fine tuners, and carbon fiber or titanium endpins, geared pegs are one of the most useful and valuable upgrades that can be done on a cello's setup.
On a traditional instrument, the tuning pegs are simply tapered wood dowels fitted into a pair of matching, tapered holes on either side of your pegbox. Pressure and friction are what hold them in place, and as any player soon discovers, pressure and friction don't always work perfectly to keep our instruments in tune.
The biggest barrier to friction pegs continuing to work is wood movement due to weather changes. Your instrument, including the pegs, is very susceptible to humidity changes. The wood will swell up on humid days, and dry out on dry days. In areas with cold winters you may really struggle as your cello (or violin, viola, etc) dries out when the heat is turned on for the winter months.
Additionally, proper pegs are made of ebony, but ebony is now a protected wood and cannot be exported from its native countries unless first fashioned into a product. So many of the cellos purchased these days (especially from China) come with freshly made ebony pegs out of maybe-not-so-properly-dried ebony. As these ebony pegs dry, they frequently dry with a flat spot on either side, which keeps them from staying in tune. Pegs with this issue can be refitted by a luthier using a special tool that's like a giant pencil sharpener. This usually only needs to be done once.
A better option, though, is to just replace your friction pegs with geared pegs. These days, there are several options, including pegs with fancy wood heads that look just like traditional pegs, and pegs with composite heads (which also look amazingly like ebony) We have even installed geared pegs on an antique Grancino worth close to a million dollars. I say this so that you understand the value of being able to tune your instrument easily and have it STAY in tune is priceless. Below is an image of a Knilling Geared Peg with a Rosewood, Swiss-style head.
How do these things work, anyway? Well, while the head and the shaft that the string goes through turn, the part of the peg that goes through the head side of the pegbox is stationary (the bronze colored portion in the image above). Inside of that shaft are a set of gears that provide at least a 4 to 1 reduction (Wittner pegs are 8 to 1); which means one whole turn of the head will turn the shaft only a quarter turn. Your geared pegs, therefore, are also fine tuners.
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