Screw Me
 

Miss Dallas' cello has machine tuners at the top. (The kind normally found on string bases, as opposed to just plain pegs, which are more common on cellos.) One of the screws fell off, and we need a replacement. In my naievety, I thought I could take a sample down to the hardware store and get a replacement.

Since I'm posting this, I'm sure you can already guess that everything was either too small or too large. After consultation with a handful of string instrument repair experts (one of whom actually laughed at Mrs. Dallas on the phone--way to make friends and earn future business from a family with a violinist and a cellist), we've learned that such screws are actually custom made, and that we can get a replacement made for $100-$200.

Now, this screw is not structural or functional--I mean in the sense that it affects the tuning. There is a gear that adjusts the string tension, and these screws only serve to hold the gears onto the side of the pegbox.

So, thoughts? I figure surely somebody here knows where I can have a simple machine screw like this duplicated for less than $100.

(I forgot to include something for scale... the size is somewhere in between 10-24 and 1/4-20.)

What about the manufacturer/artist that made the cello? Is there any way to contact them and see if they have any spares?

Any chance its just the threads that are off & not the actual diameter of the screw? Perhaps a metric size might work. What type of material is it going into - brass, steel, wood...?
You may be able to tap out a slightly larger diameter and use a standard sized screw.

Oh and the Lowes near me has a pretty good assortment of furniture hardware that has some goofy sized screws that might fit.

Is the intent to preserve the instrument so as to maintain its worth, or is the intent to make it securely tunable and playable, no matter what has to be done? (i.e., would you accept puttying/gluing and re-threading the hole? that could be done on the cheap)

Why would somebody craft a screw that's more like a machine screw, than a wood screw, to securely hold something to wood? Seems like it's a design failure if it came out.

Was this an older instrument or was it bought new?

the assembly is surely brass. can you not simply replace the entire tuning mech section? they sell them for acoustic guitars....gear and all. oh. and my next door neighbor has a machine shop in paoili, but he's a nutter.

If it screws into metal get Loc-tite

A long time ago, in a Germany far far away . . . .
It's brass, and I believe it is indeed the threads. My experiments with metric screws were unsuccessful.
The intent is to get my daughter back to practicing again! :D The cello is on loan from her teacher, so we want to keep it close to the original. This screw screws into metal.. the metal plate assembly that it screws into is attached to the wood. In my non-professional opinion refitting it for pegs would probably cost as much as a good student instrument.
It's an interesting idea, but I'm not sure it could be done and still let the gears turn.

Here's what it looks like.

SD Maybe just use a drop on threads and be sure and keep off moving parts. They make a thread thing, e-zcoil, I think to replace things with. Someone else will have to comment on that.

Did you actually get a measurement of the diameter and threads?

Try McMaster Carr or Reid Tool and Supply. They have a large selection of fasteners.

This link has two sizes "somewhere in between 10-24 and 1/4-20."


One final idea, you work at a college, right? There must be a machine shop somewhere in that place that could help you. Many physics departments have machine shops.

Aisle 13, near the end on the right, sir.

Oh, what? Sorry...habit.

A 10 screw would be about 0.190 diameter.
A 12 screw would be about 0.215 diameter.
A 1/4 screw would be about 0.245 diameter.
What is the pitch? How many threads per inch? Just count the number of threads along a ruler. If it's not an inch long count the threads in a half inch and double it. Don't count the thread you start from.

But, being old and German, everything above is probably moot.

How does it work? Do you have to loosen the screw before adjusting the string tension?
If not, Green loc-tite will fill up to 0.015 gap and hold with a death grip.
Red loc-tite won't fill much gap, but will hold tight and be removable, if the threads are fairly close.
Blue loc-tite will keep fairly snug threads from moving.

What about trying to find an old cello of the same kind and taking the screw out of that? who knows, you might get lucky. Maybe try instrument refurbishers. I think that's your best bet.

What sort of cello is it?

Ya know.. what's the reason for the curly-Q at the end? Tradition? No modern instruments have that, the headstock is just a design to be trademarked and sued over.

You may be able to tap out a slightly larger diameter hole and use a standard sized screw.

This is still the only idea i can come up with - sorry.