Crack Repair

Details

Published on Monday, 11 October 2004 17:00

Written by Simon Cole

On one occasion I actually heard the clarinet crack, not a sound I ever want to hear again. Many clarinets and oboes come to us each year for crack repair. Pins almost always work but in some cases I think they further stress the wood. Gluing is an option for cracks that are very small or will not be under much stress. .

We use all these methods. Overall the carbon fiber band seems to work the best, we also use it for rings on our custom clarinet barrels.

It can be heart breaking to have one's beloved instrument crack but it does not mean that the instrument will play less well once it has been repaired

A crack is not the end of the world. The instrument will play just as well, perhaps even better once it has been fixed. Unless the crack is huge and gone right through changing the bore . Crack's through tone holes need special care but again are fixable

Why cracks happen

Without going into a long dissertation there are a few things that cause wood to split.

1. Inside wet and outside dry

 Especially for new instruments the bore inside absorbs water and expands. New Instruments should be played for only a few minutes at a time, swabbing out frequently. If it's very dry where you live I vote for oiling at regular intervals. Do not however oil a dry clarinet. Oil the ends of the tenons. Dry the instrument very well after playing. Blot water out of the top tone holes.

2. Temperature.

If it is too cold you will blowing warm moist air down the inside while the outside stays cold. The inside of your instrument expands and the outside does not, the result  a crack, sudden temperature changes or cold drafts can make it crack also. Don't play if it is less than 20c, the dryer the air in your locality the more important this is, conversely if it is very humid where you live you might be ok playing when it is not  20c.

3. Physical trauma

Dropping it and other physical trauma can also cause a crack or break. I have had to replace broken raised tone holes for instance. (If you ever get your swab stuck in the clarinet never try and lever it out by putting something like a pencil in the tone hole as it make a perfect lever to break the top of the hole.)
Just treat the horn with care.

What to do when you first see a crack

If you can, stop playing. It might be an old stable crack or it may be a new one. If you are playing under conditions like I described above it's most likely a new one. Over the years I have gone through some changes of heart on what to do next. Some say seal it off with crazy glue. This I would not advise, mostly because I have had to repair the effects of this gone horribly wrong. If it is a tiny hairline crack this may be ok.

There are many types of these glues, some are thin and will penetrate farther into the crack some are filler type glues. There are solvents that can remove them but both tend to dry the wood. Filling it with whatever, wax for instance is also debatable, as it tends to make subsequent repairs harder. The safest thing to do is cover the crack with tape.

 I have seen hairline cracks that were repaired just by gluing that lasted forever but they are the exception. It's partly up to the experience and instincts of the repairman as to what is appropriate for each particular crack. The size and location of the crack and the general state of the wood are important considerations.

I plot the location of the bands

Then I cut the groove it is .030 deep and .072 wide.

The sides of the groove are smoothed and the surrounding area is waxed to protect it from the epoxy.

Carbon fiber is selected and cut to correct length it will be soaked in epoxy

I wear gloves to stop the fine fibers from getting in my skin.

The fiber is wrapped tightly around but not so tightly that it squeezes out the glue.

It then dries for 3 days to achieve maximum strength.

The final product, after machining on the metal lathe and then finishing by hand, (finishing must be by hand as few wood instruments are truly round). We also pin cracks and glue them as is appropriate.    

                                                        Note: this is not a how to do it manual, details have been left out or over simplified . This is just so you understand the basic process. Making a mistake during any part of these procedures or using the wrong tools will most likely destroy the instrument