This is a decent student cello that had two major problems.
- A very large bass bar crack
- A bad sound post crack
Because of these two cracks, the bass bar was caved in by about 1/2 of an inch, and the sound post side was bulging out about a 1/4 of an inch. I believe these two cracks had ben glued before but didn't hold. I'm not really sure why the bass bar side was sunk in so much, perhaps there is another problem with the bass bar that's not apparent without taking the top off.
Anyway, the customer does not want to remove the top and fix the bass bar and the sound post crack with a patch. Eventually she want's to do that but for now she wants to fix it from the outside.
Ugh, so that's a challenge, but an interesting one. First thing I did was estimate how much the bass bar needs to come up to create the correct top arch. Here are the basic steps.
- Estimate the length of the post that's needed
- Make a "V" grove in one end of the post and create an angle that matches the arch of the back.
- Remove the end pin so it's easier to check the angles.
- Using a sound post setter stick the V grove aghenst the bass bar and move the other end of the post until the top rises to the correct arch.
- Then glue the crack with hide glue
This somewhat stabalized the top arch and the soundpost crack was now lining up better. Here are the steps from the sound post side.
- Remove the sound post
- Glue the sound post crack from the outside.
- Form a mold that fits the shape of the top
- Create a oval fiber piece
- Have another temporary plastic oval that slightly smaller than the final fiber oval
- At first I tried to fish this in through the ff hole but although it was very close, I couldn't get it in.
- Switched tactics and used some string to suppend the patch in the correct spot and then clamp it in place
- Remove the temporary white clamping piece
- Refit the sound post a little and put it in.
- Tune it up and it's done.
Since this was the first time I attempted this, the patch shifted to the center of the cello more than I wanted and I wasn't able to pull it closer to the ff hole. I didn''t take into account hos the bass bar's height would pull the string to the center as the clamps were tightened. The post still is on the patch and the patch supports the crack, but it's not centered like I wanted.
Next time I will have two little holes drilled at the ends of each oval with strings that go to each side of the ff holes. Then when I clamp one side of the oval, I can pull the other end of the oval to either side because it will pivot on the clamp, then clamp that side and adjust the other side of the oval using the same method.
Oops, as usual I don't have a before picture, but here is the shot of gluing and clamping the bass bar carack.
IMG 20220518 175335 982 IMG 20220521 124726 484 IMG 20220521 125109 407
IMG 20220521 175835 505 IMG 20220521 180738 524 IMG 20220523 095244 214
IMG 20220523 095723 710 IMG 20220523 095857 793 | |
Because the top was so caved in and there is some unknown problem with the bass bar, I left the bass bar post in there and strung it up. It actually sounded pretty good. I'll have her try it and see how it sounds since she knows the before sound. Perhaps if it sounds good or better than before, just for fun, I'll leave it in. ;-)