Why don’t I polish or buff your valves?
This question has come up quite often over the years. I tell my customers that I never polish or buff the valves of an instrument. Why? Very simply, it is perhaps the worst things that can be done to a brass instrument. To understand why this is the case you need to understand a few terms:
- Polishing: Polishing is simply the act of making something smooth and shiny by the act of rubbing it. When polishing something you are replacing a rougher surface with a less rough surface by removing material. Polishing does not remove scratches but replaces scratches with ever smaller ones until we perceive the surface as smooth.
- Buffing: is just a synonym of polishing. In the musical instrument world, buffing is generally considered as a mechanical means of polishing. We use big, heavy machines to make quick work of making brass or other soft metal shiny. We use a fast spinning cloth wheel coated in various compounds that have a different “cut” depending on the need, like using different sandpaper.
- Compression: in this case, compression refers to the air tightness of a musical instrument. An instrument that loses minimal amounts of air is said to have good compression while one that has air escaping, say through an open water key, would have poor compression. Good compression makes an instrument play better by being more efficient and easier to play. Compression affects an instrument’s response, dynamics and intonation as well as a players endurance.
- Tolerance: is the amount of variation in a machined part. Tolerance is what allows a valve to work. For example, like a brass instrument valve, a cylinder that is exactly 3cm in diameter will not fit in a tube sith an opening that is exactly 3cm in diameter, it needs to be ever so slightly smaller. That difference is the tolerance.
Short of a bugle with no moving parts, a brass instrument is never going to be completely airtight or have perfect compression. A trumpet has valves that need to move. Those valves have a tolerance that allow them to move. That tolerance will, no matter what, allow some air to escape. What is critical is the amount of air that is allowed to escape. A new brass instrument piston will have a tolerance of 0.0005” or 0.0127mm between the wall of the piston and the casing. That tolerance means a piston (a cylinder) that measures 0.663” (16.840mm) fits into a casing (a tube) with an internal opening of 0.664” (16.866mm). The average human hair is 0.002” (0.051mm) in diameter - twice the width of the tolerance of a brass valve. We are talking some pretty small distances.
We use valve oil to fill this gap. Valve oil not only reduces friction but also fills the gap made by the tolerance, helping our valve to be more airtight. Water, like the moisture from our breath, add to this but evaporates quickly and deposits impurities, hence why we wipe down our valves and oil them regularly.
Looking at a piston valve, we can see a silver cylinder, the piston, which goes into a brass tube, the valve casing. Why is it silver? The piston is typically made of a nickel alloy called Monel, stainless steel or is nickel plated brass. The casing is almost always brass. These two metals are well known to work smoothly against one another so has become the industry standard. Regardless of the construction of the piston, it was manufactured to fit precisely, with minimal tolerances to allow for a smooth stroke and as close to airtight operation as possible.
Taking this information we can now see the problem with buffing or polishing a valve: a precision fit that is being destroyed by the removal of metal. Let’s assume that the buffing process removes 0.0005” (0.0127mm) evenly across the surface (it doesn’t do this evenly - see more about this in the rotor valve section below). Bear in mind this is a cylinder so removing material from the surface reduces the diameter of the cylinder by twice that amount - in this case by 0.001” (0.0254mm). You now have a valve with 0.001” (0.0254mm) tolerance, double that of the manufactured specification. Now bring that instrument in for a second service and buff the valves again. Within a few years, two services, the original 0.663” valves now have a diameter of 0.661”. Is it going to leak more air? Yes. Is it going to be less efficient? Yes. Will it be harder to make a sound, more difficult to play in tune, have a reduced dynamic range? Sadly, yes to all. You are likely to find your valves work worse as they “chatter” (rise unevenly) from the looseness in the casings. If you want to make the valves seal better and work smoothly you will need to use a heavier oil. That heavier, thicker oil will make your valves work more slowly. Does it seem like this is a bad idea?
Piston valve comparison:
Here’s a comparison of four trumpets. these instruments are either new or have been recently serviced. They are all clean and freshly lubricated. We have:
- A Bach TR600 student trumpet: brand new, taken right off the shelf.
- Two Yamaha T100S trumpets. I can’t tell you when these trumpets were made but Yamaha ceased production of this model in 1994. T100 #1 has had a harder life than #2 which itself is a retired school instrument.
- A Yamaha YTR2330 student trumpet. I don’t know the exact age of this trumpet either but I know Yamaha began production of this model in 2012. The owner of this trumpet is quite young so I’d reckon this trumpet is no more than five years old. This trumpet has had all the pistons buffed at least once by a repair technician.
This is a Magnehelic Machine or MAG Machine:
This MAG Machine has been specifically designed to test brass and woodwind instruments for leaks. It measures compression by use of applying air pressure in units called “inches of water”. Inches of water is simply a unit of measurement of pressure, similar to PSI or Bars but much smaller units with one inch of water the equivalent of .0025 bars or .036 psi. When the hose is unrestricted it is calibrated to 8 inches of water, as per the manufacture’s recommendation. The machine pumps air through the blue hose and can accurately read how much air is being lost. If the hose is completely shut off it will read 0 on the dial and anywhere in between 0 and 8 if the airstream is partially restricted. The manufacturer notes that a brass instrument with a reading of 2 inches of water or higher has compromised compression and recommends either valve replacement or re-plating and refitting of the piston.
Here’s a look at the first valves of the four instruments:
The new Bach valve (left) is constructed of Monel, a nickel alloy, the two T100S trumpets (centre) have nickel plated valves and the YTR2330 (right) has Monel valves that have been made shiny by buffing. Note the rounded edges of the ports (the tubes through the valve) caused by the buffing as opposed to the sharper edge of all the others.
Now let’s test these instruments. For this test I inserted the hose of the MAG Machine into the lower end of the main tuning slide for each instrument, bypassing the leadpipe and main tuning slide which could skew the results if any leaks were present. I then plugged the upper tube of the first slide. By depressing all the valves during the test we have air pressure passing through two ports of the 2nd and 3rd as well as the tubing of those valves and one port and tube of the first valve. It is the most complete test that can be done easily since plugging the bell is difficult and potentially less accurate. All individual slides and tubes including water keys were tested as airtight prior to this test.
The TR600 tests as I would expect for any new name brand instrument with a result around 0.10 inches of water. I would expect similar results from a new Yamaha, Jupiter, Eastman, or other decent quality instrument.
Yamaha T100S #1:
This trumpet is roughly 30 years old and has not seen the greatest treatment over the years. The valves, however, have never been buffed. The reading for this trumpet reads approximately 1.1 inches of water.
Yamaha T100S #2:
Also around 30 years of age, this trumpet received better care throughout its life. The valves of this instrument have not been buffed and I suspect this trumpet received regular servicing. The compression reading for this trumpet is .4 inches of water.
I would expect a YTR2330 with only a few years of use to have excellent compression with a reading close to a new trumpet. This trumpet, however, with the buffed pistons has a much poorer result of just above 2 inches of water.
Comparing the readings, we can see:
- a new instrument has, as expected, excellent compression
- an instrument will lose compression over time and use but the wear is actually relatively slow
- maintaining an instrument over the long run can positively impact its compression
- the instrument with the buffed valves had the worst results
We can see that buffing the valves has unnecessarily compromised the compression of an otherwise perfectly good instrument. The process of buffing the valves has done the equivalent of 50 or more years of use. Remember that the MAG Machine manufacturer recommends valve replacement or refinishing when a reading of 2 inches of water is reached. This trumpet is there now. This was done as part of a nearby shop's standard maintenance, not to "fix" something that was problematic*. Consider that new pistons can cost more than $120AU per valve and still need to be fitted. Re-plating and fitting pistons starts at $350AU per valve. This is expensive damage that often exceeds the value of the instrument.
*Recently, a trumpet arrived at my shop with the dent in the valve casing. The customer took it tho the same shop that serviced the above YTR2330. This technician left the dent untouched (a dent in a valve casing is easily removed with the proper tool) instead choosing to attack the undamaged piston with heavy buffing, reducing the diameter by several thousandths of an inch. The valve did clear the remaining bump on the inside of the valve casing caused by the dent but the dent is still felt as the piston passes the damage with each and every pressing of the valve. This expensive "repair" left the owner with a poorly playing, leaky instrument that has a valve with an uneven stroke that still intermittently sticks.
Rotor valves are even more susceptible to damage by buffing than a piston valve. Rotor valves are made of raw brass. Raw brass is a much softer metal than the Monel of the piston in the above example. Irreversible damage takes mere seconds at the buffing wheel as seen in the examples below.
There's more then just rotation of a rotor valve that differentiates it to the up and down motion of a piston valve. The rotor itself, the central core of the valve, is most often made of raw brass though occasionally you might see rotors made of nickel silver, plastic or even titanium. Most rotors are formed from one solid piece of metal with the ports cut out of the material. The rotor casings are often made of brass but nickel silver is not uncommon. A rotor valve is designed to not touch the outer wall of the casing. It comes extremely close but it should not touch. The rotor is suspended in the casing by a top and bottom bearing. At least one, sometimes both, of these bearings are removable. On a horn, that removable bearing is called the top bearing. The two bearings provide the stability the rotor requires, allowing it to rotate with ease whilst suspending it firmly in place in the casing, not allowing it to wobble side to side or move up and down.
Here we go again with the tolerances... like the piston, the rotor needs close tolerances to operate well. For a rotor valve to work well the tolerance must be maintained. Variations cause unwanted motion, sticky valve, noise and leaks. Lets look at what some of the damage buffing your rotors and top bearing can do:
Here are some Yamaha horn rotors that has been buffed so heavily that the horn had to be written off:
An experienced player found this instrument difficult to centre pitches, hopeless for the poor child trying to learn. The exterior of the rotor a pointless and unnecessary bright, shiny brass but the ports and the casings covered with a thick, green layer of yuck because the valves haven't actually been cleaned properly.
Here's one these valves on a leveling stone. Note the uneven rounding and gaps around the port cut-outs caused by the buffing:
Contrast that to this undamaged rotor - In this case a tuba valve but the principal is the same - note how it lays perfectly flat against the level stone:
If the above is not proof that buffing aggressively removes metal from a surface, check out this top bearing plate form a horn used in the compression tests farther down the page:
For absolutely no discernible purpose whatsoever, the top bearing plate of this horn was buffed on the outside surface. I cannot fathom for what purpose this was done, there is no problem to fix by doing it - the effort literally does nothing but damage. The red arrows point out the damage caused by the buffing. Each one of these spots took mere seconds to make. In three quick passes this butcher clumsily made three deep digs into the raised bearing at the centre. This now uneven surface renders this bearing impossible to tighten, a procedure that a competent repair person will use to make a valve operate better. The pointless deep cut at the alignment notch on the outer edge (top left in the image) highlight how quickly and uncontrollably metal can be removed by this process.
Of course if the outside surface of the top bearing is buffed then surely the flip side was buffed, too:
Here we see the undersides of two Yamaha YHR567 top rotor bearings. Yamaha is a very reliable producer, the valves on their horns typically work well from day one and hold up very well over time. The top example is untouched, the bottom one has been buffed. A top bearing when installed will not only hold the spindles of the rotor in place but keep that rotor locked in place between itself and the opposing side with a tolerance of 0.0005" to 0.001". This tolerance, called end play, will increase with wear over time and cause a rotor to become clattery and noisy. Had the surface of the lower bearing in the picture not been made uneven by buffing, this bearing could be easily refitted to remove the end play. The only reason the end play is now problematic is because the valve was buffed in the first place. Had the tolerance not been destroyed by the buffing it would not even be an issue! In the current condition, the surface would need to be re-milled to level and then, only if there is enough material left, could that bearing be refitted. The first video below demonstrates the valve noise of the horn with the bearings in original condition, the second video shows the horn with the buffed bearings. In neither case did the customer want the bearings refitted so nothing besides reseating the valve and lubrication has been done.
Let's now compare the compression of three Yamaha YHR567 horns. This test is through the F side of the horns. Unlike the trumpets above, I performed this test through just one port of each rotor. Like I did with the trumpets, the leadpipe, tuning slide and water key have been bypassed.
- Horn 1 is three month old
- Horn 2 has seen many years of heavy use
- Horn 3 has rotor valves that have been buffed to oblivion
This new horn, as expected, reveals it has excellent compression with a reading around 0.2 inches of water.
With many years of use, this horn shows evidence of wear with a compression reading around 1.4 inches of water. It's not a great reading but is below the threshold of 2 inches of water. This damage would not be perceptible to a student player so this horn will have many more years of use.
Wow - I'm speechless... With a compression reading of 7 this horn is essentially unplayable.
I see this damage far too often and it is completely unnecessary. In these modern times, with all the knowledge resources and tools at a technician’s disposal, the fact that this is a consistently recurrent problem is incomprehensible. That the very basic principal of precision can be so foreign to a person representing themselves as an expert is astounding.
We can’t halt entropy but we can all do our best to slow it. You, the owner and player, can do more than anyone. Keeping your instrument clean and well lubricated is the absolute best way to ensure that you will enjoy it for years to come. Wash it out regularly with warm, soapy water and soft brushes. Move all your slides daily and keep those slides moving smoothly with a regular application of grease. Keep your valves working lightning fast by wiping them down and oiling often. And finally, get it regularly serviced by a reliable technician. Ask that technician if they buff valves. Most don’t. If they do, DO NOT LET THEM NEAR YOUR INSTRUMENT!