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Haynes woodwind maintenance manuals
Notes from a small workshop - anecdotes & musings from the workbench
Haynes woodwind maintenance manuals

The vent event

I had a bit of quandary deciding precisely where to document what follows in this article. It refers to a fault I found on a new Chinese bass clarinet, and as such it seemed logical to pop it into the corresponding review of that instrument. Then again it was critical fault that turned out to be confoundedly difficult to pin down, and one that required both the tester at the factory and the same at the retailer to fail spotting it - and thus richly deserved a place in my Black Museum.
Finally though I decided on a Notes article, for two reasons. One, it would perhaps convey some of the frustration associated with locating and fixing unusual problems, and two - it might afford some readers a touch of schadenfreude given that, on the whole, I'm quite positive about the influx of cheap but usable instruments from the East.

In some ways I suppose I could say that what these cheap instruments have brought to my profession is a touch of excitement (or maybe I need to get out more). The thing is, when you're faced with the prospect of examining an item for, shall we say, functionality, you tend to start off with a preconceived set of standards - even if you're not an expert. Let's say you just bought a new DVD player and you're checking it over prior to installing it. What would you look for?
I guess you'd check that it looked physically OK, that there weren't any obvious bits missing or hanging off and that it had all the parts you'd expect - such as an on/off button, somewhere for the disc to go and a plug for the power. You wouldn't really expect to have to check that it actually had any electronics inside of it or that the manufacturers hadn't forgotten something fundamental like a set of output sockets.

That's more or less the sort of pattern I follow when I'm checking over a new instrument from one of the established manufacturers - I start off with the assumption that all the bits that are necessary to make it work are there, and in the right places - and by and large that seems to be the case.
When it comes to cheap Chinese instruments though I have to be rather more on the ball, and although it's rare to find an instrument that has bits missing it's far more common to find some of the bits aren't as well-made and fitted as they ought to be. Thus I've seen flutes where the foot joint doesn't stand even half a chance of fitting onto the tenon joint, plastic piccolos where the entire action (which is held onto the body with screws) moves when the keys are pressed and resin-bodied clarinets that have air bubble holes in the body that have encroached into tone holes. In other words if you consider your inspection of that DVD player to warrant a level of, say, 3 on a scale of 1 to 10, I'd be running at a level of 20...out of ten. It's about as near to 'seat of your pants' excitement as it gets in the repair business.
To be fair things aren't that bad these days, the overall quality has improved immensely in the last couple of years, but it's still not quite at the point where you can take such things for granted.
This is why it's still important to buy from a retailer who makes an effort to at least casually inspect the goods that go out, and who hopefully impresses upon the manufacturer the importance of some quality control at the point of origin.

Every now and again though there's bound to be the odd rogue that escapes the net - and one of these landed on my bench in the shape of this bass clarinet. I'll admit I was partially fooled - the instrument was made by Conn Selmer, so although still very much a cheap one it should at least have had the benefit of a factory inspection. I was also fooled by the retailer's tag hanging from the case handle that assured me they check each and every instrument out before it leaves the warehouse.
Someone was lying.

As it happens I wasn't all that impressed by the instrument anyway, it felt like too many economic corners had been cut and the setup was, frankly, appalling. So I set to making things right in the hope that the instrument would redeem itself in the blowing, as many a cheap and cheerful instrument often does.
Having sorted out the badly seated pads, the heavy springing and the arbitrary regulation of the action I set to testing each joint in turn for air-tightness. This is a standard test that shows whether or not the pads are leaking and in this case it was done by popping a bung in the bottom end of each joint, closing all the keys and blowing into the other end of the joint using my lips to seal the tube. It's a bit tricky with bass clarinet upper joints as you have to get all of the crook socket in your gob, and that's not nice if the instrument's seen a few years of use. In some respects it's an academic test (or at least it ought to be). If you've set every pad right and adjusted every key properly you'll know it's going to work - but then it never hurts to be a tad obsessive as a repairer.
So there I was, merrily testing the joints for air-tightness when I found a leak in the top joint. Well, I say I 'found' a leak - because although I could hear and feel air escaping I couldn't quite pin down where it was coming from. With a bit of prodding and poking, squeezing and puffing I managed to narrow the field down to somewhere around the forefinger/thumb area, but what with the size of the joint it was difficult to accurately home in on the leak. So, back to the cigarette papers and testing each pad in turn. No faults showed up though, and at this point in time I began to consider the other possibilities that might cause a leak on a cheap resin-bodied clarinet.

Perhaps the most annoying symptom was that no matter how hard I pressed the keys down, the leak remained constant.
Pressing keys down hard usually has one of two effects; it either stops the leak dead by virtue of a poorly seated pad being squashed down onto the tonehole, or it increases the leak as the key arms flex under the pressure and cause the cups to distort...though this tends to happen more on saxes where the keys are that much larger (which is why ramming your little fingers hard down on the low C and B/Bb keys doesn't always help an iffy low note). What this told me was that the leak was a constant, which generally means a hole in the body somewhere.
By far the most common cause of these is pillar sockets that have been drilled right through the body into the bore. Naturally this is 'not a good thing', but it's usually easy enough to spot simply by peering down the bore. Nearly as common would be leaks around the thumbhole chimney, but the bass clarinet doesn't have one - but it does have two speaker key chimneys...neither of which were leaking around the edges, and were out of range of the fault anyway.
There were no burrs or chips to the tone holes, no splits or cracks in the body and as far as I could see no splits or holes in any of the pads.

It was time for the smoke test.
Smoke testing is very much a last resort. Yes, it's effective and fast, but it has several drawbacks in that it requires you to clean out the bore of the instrument afterwards ('cos it makes it smell) and clean the pads. It also requires you to smoke - which is not such a good idea anyway. The trick is to be quick - and perform the test in front of a mirror so as to afford you the best possible view of where the smoke escapes from. As soon as the leak is located you need to get the smoke out of the bore.
So the test was made and smoke poured out of the forefinger pad cup. This came as a bit of a surprise because the cigarette paper test showed a perfect pad seal.

The pad in question is slightly unusual because the cup is vented. That's to say that it's an ordinary pad cup, about 15mm in diameter, but it has a small hole drilled in its centre, of 3 or 4mm or so. This is to allow the key to be vented when playing in the upper registers - a small disc attached to the pad cup allows you to close the pad whilst the hole in the cup lets out a small amount of air, which helps to stabilise the notes. It's a little like the octave key holes on a sax inasmuch as in the lower octave their opening would constitute a leak and yet in the upper octave they're vital to the note quality.
The pad that sits in this cup is equally special and constitutes a solid ring with a small hole punched in the middle.
Typically these vented pads were made of cork, but these days they're just as likely to be made of synthetic material - and in this case it was a ring of dense white foam rubber.
There's a maxim attributed to the renowned fictional detective Sherlock Holmes that states "When you rule out the impossible, that which remains however improbable is likely the truth" - and the truth that I was considering was that the foam ring was porous.
If so this would explain the leak and the difficulty in placing it, and be something of a manufacturing faux pas - so the next step was to whip the key off and have a closer look at the pad.
One of the slight benefits of the smoke test is that it leaves a little brown stain at the point where the smoke escapes (assuming it comes out via a pad), but I could see no such staining on the foam. I decided to take the pad out to further examine it...and that's when the culprit was discovered.

The pads on this instrument had been fixed in with plastic glue. This is quite common these days and a lot of manufacturers use it in place of the more traditional (and far superior in my opinion) shellac. In order to speed up production the manufacturer was using small chips of this glue, and the pad was held in place by three or four such chips - but they hadn't fully melted when the pad was set, probably because the heat required to do so would be close to that which would melt the foam there were these blocks which had melted enough to hold the pad in the cup but not sufficiently to merge together to form a seal. The pad was being held off the base of the cup and air was able to come up the small central hole, find its way through the gaps between the blocks of glue and then leak out of the side of the key cup.

I started off this article by saying how frustrating it can be at times to track down unusual faults like this, but in some ways it's also quite satisfying to be rewarded with a spectacle so bizarre that it makes you think "Well I'll be...". It's the difference between sitting in a traffic jam for two hours and finding no apparent reason when you finally get under way again, or getting to the end of it and finding a sedated hippopotamus in a tutu lying on the verge.

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