Checking a Bassoon for Air-tightness

For a bassoon to work properly, especially to control quiet, low notes, the instrument must be as air-tight (hermetically sealed) as possible. It should be tested joint by joint every month or so or if things don't feel 'quite right'. Players often spend ages struggling to get a reed to work when the problem is actually a leaky instrument.

 

1) The crook (bocal): test this by putting a finger or thumb over the wide end and also (with a clean finger) closing the 'pin hole'. Then suck out some air and close it off with your tongue. This vacuum should hold for several minutes. There's not usually a problem, but occasionally, a crook can develop a split along the seam that is made in the construction process. If this happens, seal it up with some sellotape until you can get it to a good repairman (this is not a job for a cowboy).

 

2) The tenor joint: put a finger over the narrow end of the tenor joint, close the finger holes and suck air out from the wider end. If you can hold a vacuum for 90 seconds, that is extremely good and we should be aiming for this (you might even need to wet your fingers to hold the vacuum this long). 20 - 30 seconds is still good while most instruments only manage about 10 seconds. If it is much less than 10 seconds it must be improved.


3) The butt joint: close all the holes by fingering a low E and seal up the wide end with your cheek and suck air out from the narrow end. If you have a beard, you'll have to remove the U-bend and test each half separately (or shave your beard off!). A 30 second vacuum is excellent and anything less than 10 seconds should be sorted out.

 

4) The long joint: roll up your trouser leg press the low B key down and close the wide end with your calf and suck through the narrow end. 15 seconds is fine and anything less than 10 seconds, again, should be sorted out.

 

5) The bell joint: as above or use the palm of your hand to close the end.

With all except the tenor joint, the length of time for holding a vacuum is measured by taking off the fingers that hold down keys that are normally open and waiting for them to pop open.

 

6) The cork connections between the joints and the linkages between the joints: to test these put the whole instrument together and get a friend to cover the end of the bell joint with the palm of his or her hand .


Locating a leak

Having tested your bassoon for air-tightness, now let's find out how to find where the  leak you probably found is coming from.

Most major leaks are caused by pads that have become hard, damaged or unseated (perhaps by the keywork being knocked out of alignment) or not being pressed down far enough (perhaps an adjusting cork needs replacing) or a spring has come adrift.

 

To work out where a leak is, you can:

 

1) Instead of sucking when doing a vacuum test, inhale some cigarette smoke and then blow and see where the smoke comes out. Disgusting really!

 

2) Or you can get a friend to try to  feel for any escaping air as you blow or to try pushing down on each pad as you suck.

 

3)Make a thin strip of cigarette paper and use this as a 'feeler' round the edge of each pad. It should have equal resistance all round the pad when you pull it out.

 

4)This next method is rather time consuming, but is quite foolproof. Get hold of a roll of a type of Sellotape called 'Magic Tape' or 'Pressure Sensitive Tape' http://www.ryman.co.uk/3M-Magic-Tape-19mm-x-25m-Single-0605023390.asp made by Scotch (3M) and stick it over each tone hole on the joint where the leak is and then press it down firmly with the pad. If you use ordinary Sellotape, you will find that, when you remove it, it might bring some varnish from around the hole with it. If you use Magic Tape and this still happens, the varnish was loose before you started and would have been a source of a leak in any case. Tape called 'Removable Tape' tends to leave behind a sticky mess and should not be used. Next perform the vacuum test and if it improves it, you'll know that at least one pad will need to be replaced or reseated. Then it's just a matter of removing each bit of Magic Tape in turn to find where the problem lies. Then replace pads as necessary. Pads will last a long time if properly looked after. Most importantly, they should never get wet. But in the real world, pads do get hard or deteriorate.

 

 

Improving the air-tightness of a bassoon

 

If all the pads on your instrument are OK, we must look elsewhere for a leak. Check that there no cracks in the instrument. These really only occur in brand new or very old, neglected, instruments. We have at this stage to confront the uncomfortable fact that maple wood (which all German system bassoons are made of (French ones use rosewood)) is porous. This porosity is greatly reduced by oiling the bore (see above) but still we need to close things up as much as we can.

 

First, if there are any chips in the varnish, repair them. Clear nail varnish is fine. To apply tiny amounts, use a toothpick. Next, seal up (again with nail varnish) all the bits of exposed end grain at the ends of each joint. For example, round where the crook fits in.

 

Then tackle the base of the butt joint. Unless this has already had some leak-proofing treatment or it is a new and well made bassoon, it will leak. To demonstrate this, get a bowl of water a couple of inches deep, take off the metal cap and carefully submerge the u-bend until the water reaches the varnish (don't get the A flat or G holes wet) then close up the joint as you do in the vacuum test and blow. Bubbles will come out. They may come from the cork gasket to the u-bend in which case first check the screws are tight enough (finger tight plus another eighth of a turn with pliers is about right) and then check that there is a tiny smear of Vaseline petroleum jelly (grease) on the cork and, if necessary, replace the cork. This is a straightforward process but take care to get cork thick enough to be just the right thickness after it's been compressed for a long time. There will probably be a leak from under the metal collar thing through the wood. If the collar thing is actually loose, you'll need to take it to a good repairman but you'll probably be able to stop the leak by melting candle wax (Americans call this paraffin wax, I think) into the join between metal and wood or sealing it with nail varnish (first put some masking tape over the varnish on the surface of the instrument to keep it looking neat) or doing both.

 

If your bassoon's air-tightness needs further improvement, you might need to dub microscopic amounts if nail varnish round each pillar that supports the keywork. Finally, rub some beeswax all over the outside of the instrument (but not on the pad seats) with a soft cloth and then polish off. You'll probably need to remove keywork to do this, so do a bit at a time. Don't lose any screws, make sure that each screw goes back where it came from and don't stab yourself with a spring! Can anyone tell me why the springs on a bassoon have such a sharp point on them?

All this is very time consuming, but not highly skilled so, if you're reasonably good at working with your hands, you can save yourself a bill from a repairman and, by spending longer doing it, get a better job done.

 

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