Brad Dorsey

Need help with mechanical pegs

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I took in a cello for repairs today that has a type of mechanical peg that I've never seen before:

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The pegs are made of plastic.  They have no screws to regulate the torque required to turn them.  They have no maker's name or logo visible.  Each has a joint immediately outside the peg box at the point indicated by the arrow in the bottom picture.  From this joint outward the peg is all one piece.  I see no indication that the pegs are glued or threaded into the peg box walls.  They are installed in a 1983 Roderich Paesold cello, and I think there's a good chance that they were installed when the cello was new.

The problem is that I cannot turn these pegs in either direction as hard as I try with my hands.  Unless I can come up with a better idea, my next step will be to try turning them with a wrench, which may break them.  If I can't figure out how they're supposed to work and get them working properly, my only recourse will be drill or hammer them out and replace them with regular ebony pegs.  This will require bushings because the holes on the sides away from the heads are quite large.

I would much prefer to get these pegs working rather than replacing them.  Does anyone here know how they are supposed to work?

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Maybe tapping them with a wooden dowel from the small shaft end while supporting the opposing side with some form of mass, might show some movement of some kind..

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Maybe they're not mechanical, but simply have a reduced diameter for the string wrap, allowing a more sensitive tuning. (?) Try holding a magnet near to them to see if there's any ferrous metal present. If they're nothing but plastic you might be able to drill through them with a small diameter drill bit first, then slowly increase the drill size looking for a release.

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11 hours ago, Evan Smith said:

Maybe tapping them with a wooden dowel from the small shaft end while supporting the opposing side with some form of mass, might show some movement of some kind..

I did this and got a peg out:

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These work by friction the same as regular wooden pegs.  The bosses that contact the peg box walls are tapered, but the tapers are much less than regular pegs, by which I  mean they are closer to cylindrical.  The smaller tapers means that have much less tendency to move axially as the peg box responds to humidity changes.  But it also means that the peg hole diameters only have to change a tiny bit to either loosen the pegs so they don't hold or lock them solidly the way they were when I received the cello.

Now that I know how they work, I have to figure out what will make a good peg dope for plastic pegs with small tapers.

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2 minutes ago, Brad Dorsey said:

Now that I know how they work, I have to figure out what will make a good peg dope for plastic pegs with small tapers.

Perhaps graphite. It's a common filler for plastics that need to slide. 

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Are you certain they're plastic? The part that fits into the pegbox kind of looks like machined and anodized aluminum. Either way, I don't see why regular peg dope wouldn't be perfectly suited to the task.

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The Music school I work at has a Cello with such pegs. They make for terrible Tuning, just impossible to turn. On the other Hand, as you say, they don't loosen, and for Kids, that is good. If you figure out a way to make the turn smoothly, please let us know!

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18 hours ago, Brad Dorsey said:

I took in a cello for repairs today that has a type of mechanical peg that I've never seen before:

P1060609.thumb.JPG.084512a8c25126995ef261a927bd6b95.JPG

I would much prefer to get these pegs working rather than replacing them.  Does anyone here know how they are supposed to work?

The way they work is...Wait, is that the Bat insignia?  Quick, Robin, to the Batmobile!  Our crime fighting mission compels us to spring into action at once!

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20 hours ago, MarkBouquet clearsky said:

...The part that fits into the pegbox kind of looks like machined and anodized aluminum...

You're right.  The two bosses that contact the peg box walls and the shaft between them are aluminum.  The peg head and the shaft running up to the peg box is plastic.

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On ‎2‎/‎11‎/‎2018 at 2:03 PM, baroquecello said:

The Music school I work at has a Cello with such pegs. They make for terrible Tuning, just impossible to turn. On the other Hand, as you say, they don't loosen, and for Kids, that is good. If you figure out a way to make the turn smoothly, please let us know!

I seem to have them working well now, but that could change when the humidity changes.  Because the tapers are so small, these pegs will respond markedly to any slight swelling or shrinking of the peg box wood, either becoming too loose to hold the strings in tune or too tight to turn.

After I got the pegs out and I re-inserted them, it seemed that when they were loose enough in the tapers for me to turn them they were too slippery to hold the strings in tune.  So I dusted the friction surfaces of the pegs with a bit of powdered rosin to make them a bit stickier and they are working nicely now.

I carved the wooden piece pictured below for the customer so that she could get a better grip on the pegs and possibly be able to turn them when they lock up tight again.

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