Cello strings breaking after 5-string conversion

[Eric Maxey]

I (an amateur) just converted a 4-string cello to a 5-string. When tuning the strings, the E string and C strings both broke. They both broke at the peg, and there was significant tension right before they broke. The strings were Larsen Aurora C, and Larsen Original E, both medium tension.

Two breaking can't be coincidence, so something's wrong.

After the conversion, the string length is slightly longer, because their notches on the bridge are very near the sides, and also the bridge is unfinished (about 2 mm too high). Is that enough to cause this? Longer strings mean more tension, right?

Here are some solutions I thought of:

- Finish the bridge, of course

- Move the bridge towards the fingerboard.

- Tune the strings in a warm room, and two semitones below their note, for a day, to let them stretch.

- Buy low tension strings

What do you guys think?

[baroquecello]

What is the length of the vibrating string (mensur)? If it is full scale, 69,5 CM, then I think that is the first problem. I don't know what is recommmended by Larsen for the e string, but baroque 5 string cellos are usually shorter, more like 3/4 size or smaller. I think that is where you e string breakage comes from: too high tension.

Now in converting the the cello, you likely made a new peg setup, and I'm betting the c string moved closer to the chin. The angle the c string makes is now more acute. Even if that is all well-executed, the string goes over the nut, and the nut groove for the c string is now curved with a smaller diametre/higher angle than it was before. I've had Larsen Aurora c strings break twice, because the string was too long for the cello, and I had started winding the metal wound part onto the peg. Apparently, that part of the string is not flexible enough to withstand being bent. My bet is that either you also ended up winding the metal wound part onto the peg, and it broke there, or that the string was weakened because of it being pulled over a nut with a curve with a small diametre. Solution: a different string brand.

[Eric Maxey]

It is a full size cello. I'll measure it tomorrow. I didn't realize 5 string cellos are usually smaller. I'll try to find specs for e strings of various brands.

As for the C string peg, it didn't move. Neither did the G string peg. The E string is now wound on the former A peg. The A string is now wound on the former D peg. And the D string is on a new peg, added in the middle, in a fashion I'm sure no one on this forum would approve of.

I did make a new nut, but I made it very rounded. More so than the old nut.

I'll try a different brand. Thanks.

 

[Davide Sora]

One cause could be an excessive build-up of tension in the string section between the peg and the nut, due to too much friction on the nut. If the notches are too tight, not lubricated, or the string rides on the nut at an angle, when you tighten a string the tension will build up in the first trait before spreading over the entire string (this also applies to the bridge notches and the afterlength area). Solutions: make sure the strings ride on the nut with a smooth curve without any angles, that the notches are slightly wider than the strings and that there are no sharp edges to avoid pinching them, lubricate the notches with graphite, tighten the strings slowly and in stages, occasionally lifting the string with your fingers to help it slide on the nut.

[Eric Maxey]

My notches are sort of V shaped, because I don't have the right file. And zero lubrication. I forgot about that. I'll fix those.

[Mark Norfleet]

1 hour ago, Eric Maxey said:

My notches are sort of V shaped, because I don't have the right file. And zero lubrication. I forgot about that. I'll fix those.

As Davide suggests, that’s almost certainly the cause and the first likely source of the problem that came to mind when I read your post.  The right file and some attention to detail will cost you a lot less than more strings.

[Dwight Brown]

Make sure all the notches are smooth. Bridge and Nut.  Check that the holes in the pegs are smooth and have no jagged spots.  Check the tuners or other attachments at the tailpiece for any roughness. Use a very soft pencil to lubricate the notches. You should very carefully de-burr the holes in the pegs.  Give them a slight bevel to ease the sharp edge.  Hope you have better luck. Cello strings get pretty expensive.

 

DLB

[Eric Maxey]

Thanks for all the suggestions. They seem to have worked.

Here. I felt like assaulting your eyes with my pegbox.