Posts tagged friction
So… it was a graph that was bothering me… i couldn’t let it go. I was looking at data from a recent piano where the hammer weight was sloped (as it should be – there are larger hammer in the lower notes of a piano and small ones in the top) and what i found to be interesting was that the frictional component was also sloped. Why would that be? But there was no more time for today…I locked the door, closed the shop for the weekend. But it was on my mind. According to the stats, i needed to reduce about 3-5 grams of friction in the lower hammers. Then i got to thinkin’… what would happen if you had a wagon that was empty versus one that was full. The coefficient of friction would remain the same – meaning that the percent or ratio of friction would be the same – but the load would actually change the ‘weight’ of friction. Thinking again about the wagon… if it was empty it would be quite easy to move right? Load it full of bricks and all of a sudden, the force required to move the wagon increased proportional to the load. So in essence, the ratio doesn’t change but the weight of friction will change with the load. Back to the piano – the hammers i measured were slightly heavy… too heavy in fact for this piano. I referenced my graph again… i was examining the weight of friction and not the coefficient of friction. After i did many checks and balances again on certain joints, i finally did the reduction of weight which you can see the article on entitled Hammer Shaping. What gave me a tickle though was the fact that with the load reduced, so also the friction reduced by the exact amount i needed – a few grams.
PS… don’t know whether the coefficient of friction changes when the friction becomes the kids fighting… <sigh> i remember those days all too well
When you ask a child to draw a picture of a car, invariably it looks like this – wheels (with spokes hahaa), windows (again with panes lol) and exhaust. Much is the same when we think of pianos – black and white keys as well as strings and hammers. Everything in between magically gets glossed over. But it’s in the attention to such details that make a piano go from just ho-hum to exceptional. There are times that you sit at a piano and it REALLY responds. That piano makes you not only sound good but it also makes you want to play MORE! That’s because someone somewhere in the world has connected the dots from keyboard to string. More accurately, that’s the evolution of many hands spanning 200 years or more with the inception of keyboard instruments. It’s naive to say that one person designed the car as we know it today… so too many people have been involved over the years with the development of the piano.
But there are four basic elements from which we derive “good” touch at the piano. They all must be in check for a piano to function. And they are:
The down weight refers to the pressure required to press down a key on a piano. The up weight is the weight needed to bring the piano key back to resting position. Friction is the perceived weight on all the joint and moving parts while the action ratio is the lever system (called whippen assembly) that multiplies the speed, weight and force of the hammer from the key.
So… in my curious nature, i start asking questions. Why do we need friction? It’s not that we NEED friction but too little of it, and parts are usually too loose and will start producing noise. Too much of it (as on the Chickering grand i just worked on) and the touch feels too heavy. Concert instruments should range between 50 and 55 grams of touch with friction representing 10-15 grams of that touch weight. With too much friction, the piano i just worked on clocked in at just over 80 grams of touch – completely unreasonable for normal playing. Question 2 – well… why not just counterbalance the touch using weights in the keys? If you’ll notice on the sides of your piano keys there are small circular weights made out of lead. Well the lead weights will have some effect for the initial movement of the hammer but in dynamic playing those lead weights will not compensate for rotational inertia at all. Nor will they do any good for either friction or up weight. So why not then just have really light parts and light friction? Good idea but… the speed of the key is also determined by the return… the return requires weight.
The balance then is this – 2 elements of the four are relatively easy to control while 2 are not. The action ratio – the intrinsic design of the piano – not so easy. That’s like saying “Can we just change the pistons on this engine?” Not easily. The second part is the up weight. The up weight carries direct correlation to the hammer weight alone. The other two factors – friction and down weight can be readily altered. Friction is by far the biggest culprit that i’ve seen. And down weight can be counterbalanced with the aforementioned weights. Once the balance is achieved however, the piano becomes a wonderful and inspiring instrument. Below are two pics of lead weighting this last week – some tools of the trade and different lead weights across the keyboard ready to be installed.
This post speaks to the problem of sticking piano keys. There are usually about 6 spots to check on any piano if a note is not returning to normal playing position. But before we get into the mechanical, think of the obvious… is it getting blocked? I mean… believe me when i say i’ve seen LOTS of things inside pianos. Here’s my list thus far: pencils & pens, toys, hair pins and bands, sheet music, tools, rubber bands, paper clips, coins of various sizes, ladies press on nails (ewww… that kinda creeped me out finding that one… especially since i got the piano from a home where she had died), believe it or not metronomes and decorative piano blankets. Hmmm have i missed anything? So make sure it’s not getting blocked.
Once you’ve determined that it’s not blocked or broken, however, there’s a REAAAALLY good chance friction is to blame. Usually the hammer FLANGE is the culprit – it’s the joint connected to the hammer. About 80% of the time there’s wayyy too much friction on that joint and the centre pins need replacing. Two other joints – the action flange (flange is just another word for joint BTW) and the whippen (repetition lever) also have jointed parts. Any time you introduce a joint, you also have potential for problems. So that makes up 3 of the problem areas. Then the key stick has two bushings – each of which could also have too much friction. And finally, the key slip – the rail in front of the key sometimes catches on the front of the key. Invariably it’s one of the 6 parts. How do you go about fixing it? Hahaaaa… i didn’t mention i would give the solution… only the cause of the problem. MOST problems can’t be fixed without a technician. Sure you can look down inside and see if there’s something obvious but if it’s not… you need to get an expert in to address the problem.
Every piano has one… a black hole. It’s the place where all the pencils disappear to. Paperclips magically are sucked into it… Heaven forbid anyone should be doing their theory homework at the piano and an eraser falls inside. And once inside the abyss… gone forever! HAhaa… at least that’s what i used to think when articles would fall inside the piano when i was a kid. And on pain of death we were threatened to never go tinkering around the inside of the piano (which is still probably good advice for kids and pianos…lol). So when the piano tuner would come, he would unravel the mysteries of the universe… “Well… looks like that click sound is actually coming from a pen that fell inside. Oh and here’s another pencil.” I remember seeing the inside mechanism of a piano for the first time in my early teens. (Formally called the “action”). When i witnessed the hammers and levers i remember having this brainwave. “Sir? Can you make the keyboard on my piano heavier?” We had an old upright piano and with 4 kids – 3 of which ended up with diplomas in piano, you can imagine the beating it endured. But when i went to my teacher’s place where there was this beautiful modern 7′ Yamaha grand piano, i noticed how vastly different the touch was. And so the answer from the tuner? Simply “No”. No explanation. End of Story. I thought to myself, in all this gobbledeegook of levers maybe there was some adjustment that could be made to give me a grand touch. I was young and naive and this technician had no time to explain and so i was left with no alternative than to think that it’s impossible.
For the most part, however….unfortunately he was right. I’ve had MANY people ask me to transform their piano into a firmer touch but to understand piano touch more, i’d like you to think of your piano like a scale. On one side is the key of the piano – the black and white notes. On the other side remain the hammers and the action. So most pianos have about 55-60 grams of touch on each key. What that means is:
Finger Pressure (55grams) = Hammers + Friction
Most of the weight of a piano is in the physical motion of the hammer itself. Now if you know anything about hammers, put one on a scale and you’ll find out that it weighs about 8 grams. Attach it to a piano action and all of a sudden, there is a 5:1 ratio of hammer weight. What that means is that the lever system in the piano multiplies the hammer weight by 5. An 8 gram hammer then will feel like 40 grams at the keyboard. Add 15ish grams of friction and VOILA! Piano touch. A 9 gram hammer (times 5=45) plus 15 grams of friction forms a touch of 60 grams at the keyboard. ONE gram on the hammer makes a 5 gram difference at the keyboard. When you think that a nickel weighs 5 grams, adding one-fifth of that is not a whole lot of weight and yet you’ll EASILY feel the difference installed into a piano due to the ratio. Make sense? Is it not possible then to simply add friction to the piano? Adding friction is not the answer. Friction is a careful balance. Too little and the piano feels too ‘loose’ and results in noise. Too much friction and the piano has sticking parts and feels sluggish. If your piano is old however, you may have worn out “joints” or pivot points. There are 2 areas which can be monitored which make any piano feel more “positive”. One is key bushings (see the article entitled “Aye There’s the Rub) and the other is called the hammer flange. (A flange is just a fancy word for hinged part on a piano). The hammer flange… if you follow your eye down the stick (called the shank), you will see that it is jointed at the base. New flanges (albeit costly) and key bushings are the biggest culprits for too much/too little friction. And so without opening pandora’s box more… my original question to the tuner: Can’t you change simply change the touch on the piano? Operative word in that sentence is “simply”. It can be done. It’s just not simple.
Indeed, friction is one of the piano technician’s worst nightmares. At best, the piano is a simple machine – you depress a key, it lifts a hammer to strike a string. At worst, it’s a complex mechanism where levers and joints are in contact all the time and each surface area is potential for friction to either be too loose or too great: too loose and the piano feels ‘warbly’ and too tight and it either doesn’t function properly or feels like you have to work too hard to compensate for the touch.
I learned this only a few years back but the formula for touch on a piano is relatively simple (operative word being ‘relatively’). There is a 5:1 ratio of hammer weight to key. What that means is, for every gram of weight at the hammer there is 5 grams at the keyboard. An average hammer weighs in at about 8 grams (multiply by 5 = 40 grams). So if average touch on a piano is 55 grams per key, where are the other 15 grams of resistance coming from?? Answer: friction.
Today i had the opportunity to redo key bushings on a fabulous grand piano owned by one of the best jazz musicians in the area. With a lot of playing (both from his own practice and from his students), the bushings around the contact points on the keys were completely worn making almost a ‘knocking’ feel from side to side. A bushing is nothing more than a substance used to reduce friction between two contact points. In pianos, bushings are almost exclusively made out of cloth (some people mistakenly call it felt but truly it is cloth – woven together). The cloth then allows the interaction of joints. Centre pins are made out of steel and they need to interact with wood. Without bushings these two hard substances would click and knock together. As well, friction can be taken up by cloth in varying degrees of thickness. So the cloth is the perfect substance for acting as the ‘spacer’ inbetween.
Next time you’re at a piano, test the bushings. Take one key and swivel it from side to side and see if you sense a knock or a thunk. This will tell you they need replacement. Simply steam out the old ones (see pictures) and glue in new ones and you’re good for years to come.
I have this motto when i buy foods “if i can’t pronounce the ingredients on the label, i don’t eat it”. Sometimes i see chemical products on cans and boxes that leave me scratching my head (like propylene glycol alginate that thickens foods like icecream). Changing gears for a moment… the other day i’m talking with a friend of mine. He’s a printer and copier specialist. We’re talking about dry lubricants. Dry lubricants are powders that are used to reduce friction of parts but don’t have any liquids or solutions attached to them. In pianos, there are parts all over the place that have friction, especially the contact of what is called the knuckle. It interacts with a rotating reset lever called the whippen or jack. (For those of you who have never heard of that part before… then apparently you don’t know jack! lol). ANYWAY… i digress. So the most common substance for this lubrication has been teflon (or as i commonly like to call it… polytetrafluoroethylene). Only problem is… and i’ve discussed this with other techs… it appears that the no-stick doesn’t stick to the intended part it was stuck on. Enter printer repair friend. “Well why not use methuselah padding powder” to which my response was… “say wha?” He shuffled around in his kit and gave me a sample. Unbelievable! What is this? So i looked at the specs sheet. It’s mere mica powder ground REAAAALLY fine. The lubricity however is excellent! So… next time you’re thinking about whippen assemblies… or for that matter reading labels on soup cans and you remember polytetraflouroethylene… remember – it may be good for no stick pans and possibly pianos, but maybe i’m just an old fashioned guy. Maybe i like my glue – the same kind they used 200 years ago… and leather… and steel… and cast iron… and wood… maybe friction reduction should be just as simple – ground up mica powder.