Posts tagged sanding
Have you ever heard someone describe an object as being “jet black”? Jet is derived from the French word “jaiet”, a process that dates back to the 1300’s where lignite (a type of coal) was polished to a deep sheen. It was referenced as the benchmark for black as early as the 1700’s. But jet black has been overtaken by “piano black” as the example for the deepest, darkest, smoothest finish of comparison. In recent decades, with the advancement of technology and engineering, piano finishes have been perfected and there is now an association with “modern piano” as being black. This is evidenced by the fact that the majority of piano sales today are finished in high polish black.
But how do they achieve this mirror finish? Piano parts are not dipped in some magically smooth plastic coating and come out looking this way. Achieving the perfect piano black is an exacting process. Just like a mirror, the piano reveals any and all slight imperfections. The reflective qualities are a testimony to not only innovation but manufacturing prowess.
As I’ve had opportunity to visit some piano factories, I’ve learned that piano finishes are not as much about applying the perfect finish in a dust free environment but more about levelling and polishing the black polyurethane finish to perfection. If you’re interested in how they do that, here are the basic steps in making perfect piano black:
1. Smooth substrate construction
“Substrate” refers to what’s underneath the finish. The first step in achieving a perfectly smooth finish is to have perfectly smooth wooden parts. All pianos must have some sort of wood substrate construction that is perfectly smooth (either medium density fiberboard or laminated layers of wood for
strength but also to prevent warping). Planing and sanding is done with precision. After all, the black finish is merely a coating over top of raw wood. If there are grooves, gouges, scratches or scrapes, they will be easily seen by the mirror finish when completed.
2. Sprayed layers of polyurethane:
Using a spray gun, primer coats (preparation layers for top coat layers) and polyurethane (black shiny coating) are sprayed. Multiple layers are sprayed in succession and with each layer, the finish gets thicker and thicker. One would think that if you’re spraying a shiny finish that the process would be done but at this stage, it’s hardly considered anywhere close to completed. These sprayed layers accomplish merely the build up of material which will have most it sanded off.
3. Levelling the layers
There is a big difference between shiny sprayed finish and a levelled finish that has been polished. Shiny simply means that there is reflective sheen in the finish. When a piano has been sprayed, it is definitely shiny but it is also textured. Spraying a finish in a dust free, properly ventilated room still does not make a perfect finish. You can get decent finishes but not perfect finishes “straight out of the gun” meaning that it’s left as-is when the spraying is completed. The automotive industry robotically sprays car finishes that are so good “out of the gun” that most are left that way. It’s pragmatic when millions of cars are being manufactured annually. The piano industry however is held to a much higher standard. When you look up close to a surface that has been sprayed, there are anomalies from the spraying application and drying process known as orange peel (which looks rippled like an orange). Against the light, this ripple effect blurs the mirror quality. The process for pianos has only begun. It now must be made level.
What’s the difference between shiny and level? A sprayed “out of the gun” finish will be shiny but not smooth like a mirror. The only way to reflect light perfectly is to level or sand the finish until all of the layers are smooth. Ironically, this means sanding the polyurethane to a dull gray. The reason? It all has to do with light reflection. If the finish is smooth and flat, the subsequent finish will reflect perfectly. But the sheen must be taken down first and be made level before polishing can begin.
Sanding is the removal of material until the surface has become a dull gray. To be able to cut the finish to level, several grades of paper are used. While we think of sandpaper as rough grit, finish sanding uses really soft papers.
The diagrams above show both side and top profiles of finishes. Successively the finish is removed until the surface is smooth.
If sanding is the removal of finish, polishing then is the removal of scratches. This process has become streamlined due to advancements both in tools and the science of finishes. Giant polishing machinery has been utilised to create consistent results in many of the piano factories that produce thousands of pianos annually, but hand finishing by boutique makers still creates the same end result. The advent of orbital polishers (machinery that spins many times faster than by hand) make finishes consistent and perfect. As seen in the short videos, these processes are now done on industrial level to exacting precision. But hand sanding and polishing are still involved in corners and hard to reach places. Compounds containing slight grit are used to take the dull sheen back to shine. The combination of friction from the wheels as well as the compounds rubbing on the piano parts create the desired results. Buffing wheels are used in final stages for developing sheen.
The end result? A piano with beautiful reflective qualities. The finishes of today are both beautiful and durable making the piano an instrument of admiration and wonder. A special thanks to Sauter, Petrof and Hailun piano factories for video footage helping to describe piano finishing.
Every piano has one. It is the backbone to structural integrity. It’s also what gives a piano most of its weight. What is it? Commonly called the frame, harp or plate, this iron mass in the piano withstands the 19+ tons of string tension.
While iron reinforcement pieces were introduced into the piano by the year 1799, it wasn’t until 1825 that a full cast iron frame was patented by a man named Alpheus Babcock (The Piano: An Encyclopedia. Palmieri). All of the piano manufacturing world then saw the great advantage of the implementation of iron, and have incorporated iron frames into their instruments ever since. The addition of metal to the piano all of a sudden meant that the string design could have greater tension, making the resonance, far greater and the power, magnified. It is this frame that turned the page away from predeccesors of harpsichords and clavichords and established the piano more akin to the instrument we know today. It also meant that tuning stability was finally possible.
I’ve been wanting to feature cast iron making in the piano for some time and found that Doug Atkins (Registered Piano Technician from Dayton, Ohio) had visited the OS Kelly Foundry in Springfield, Ohio where they cast Steinway, Grotrian and Charles Walter piano plates. His photo tour was perfect and he has graciously allowed us to use these pictures. Shown above is exciting process of pouring molten iron to form a piano frame. But before we get to that, let’s step back and take a look at how this method of sand casting works.
To begin with, it is helpful to understand the basics process of casting. In its simplest form, casting starts with a pattern, a master template to be reproduced in metal. The pattern can be made from anything ~ wood, styrofoam, plaster ~ anything that can be carved to make the shape that is desired. While there are 2 major types of casting processes for pianos (sand cast and vacuum processed), we are going to examine green sand casting (also known as wet sand casting). After the desired shape has been made, it is then pressed into the sand to make a mold. Once the pattern has been removed from the sand, the negative imprint remains. The compressed sand form impression is filled with molten iron and within seconds, the mold cavity is filled. The iron cools, the sand is broken away and reclaimed, leaving behind the iron shape, the exact representation in metal.
If you’re interested in casting on a small scale, here are 2 excellent explanatory videos seeing this process in action (Sand Casting Tutorial & Aluminum Sign Casting). They walk through everything from filling forms to pressing sand and show the iron being poured into the forms. They are an excellent resource in understanding the finer details of casting.
At the OS Kelly Foundry (now owned by Steinway), casting piano frames happens on a much larger production scale. They’re not casting small pieces but frames that weigh hundreds of pounds.
Like books on a shelf, the cast iron molds stand vertically in a row; each one, a pattern to become the next iron frame of a piano. Notice both the brand and model for each model are written on the side of the template. These are life size patterns that stand sometimes greater than 6 feet tall.
The Model: Echoing the aforementioned process, all casting starts with a master model. Shown (right) is a model of a grand piano ready to be pressed into the sand.
The Impression: Pressing the cast into the sand. Pictured are the detailed lines left in the sand of an upright piano after removing the model. Each of those lines will become a supportive bar in the frame of the piano. Details such as lettering and decorative elements will also transfer effectively from the master model to the sand. Pictured below is the a 30 second clip of the moment when they pour the molten iron into the mold.
Casting: Pouring the molten iron into the mold, the frames quickly fill the cavity and harden. After cooling, the sand is then removed from the form.
Finishing: Cooled and cleaned, the frames are ready for sanding, finishing and spraying. Extensive time must be taken to process each frame, making it ready for the piano. CNC (Computer controlled lathes) are often used by larger companies after casting to more accurately smooth out the details of the plate and with precision, accurately process each frame to be uniform. Once the grinding and sanding have been completed, the piano plate is then painted with primer. Traditionally, the frames are sprayed in bronze powder mixed with lacquer, gold metallic paint or occasionally silver and then clear coated to appear smooth as glass. Pictured is a cast iron frame installed inside the rim of the grand piano.
Thanks again to Doug Atkins for supplying pictures from his tour. If you want to see the entire tour, click HERE. There are over 100 photos and videos to look at more closely. Enjoy.
The soundboard of a piano ~ to the naked eye, it looks like a giant sheet of wood located under the strings. To piano makers, this is one of the most critical elements of science in the instrument. Why? The job of the soundboard is to transform tone of the vibrating piano strings into audible waves which also color the tone. Truly, it is inseparable from the voice of the piano.
Doing some light reading 😀 (Wood for Sound by Wegst, 2006, American Journal of Botany) it becomes apparent that soundboards are this careful balance of elasticity and stiffness or rigidity. In the diagram, it reveals that there is a correlation between density of wood and elasticity (Young’s Modulus). Generally the lower the density, the greater the vibrational properties. Balancing this concept is stiffness required to resist what is called the down bearing of the strings – the pressure of piano strings pressing down on the soundboard. So the soundboard makeup is this marriage between rigidity (resistance) to pressure while maintaining elasticity for vibration allowing optimal dynamic range and sound radiation.
What then makes for a good soundboard? We thought it would be appropriate to go to the source. Bolduc, one of the few independent piano soundboard makers in the world allowed us a glimpse at what is involved in the making of a soundboard. Situated in bucolic Quebec, Canada, they supply both to piano makers as well as independent piano rebuilders. So without further, adieu, let’s talk to Christian Bolduc, factory superintendent.
Glen Barkman: Tone wood – why white spruce? Is it structural, is it the density or mass? What makes it ideal for piano soundboards?
Christian Bolduc: The North American White spruce has been used for over a century for the making of piano soundboards, as well as violins and other stringed instruments. It has proven its outstanding tonal properties with the most prestigious North-American piano manufacturers. The cold and vigorous North American climate contributes to the strength of the spruce which offers appropriate structure and elasticity required for making a good and resistant soundboard.
GB: When choosing a great log for tonal purposes, what characteristics are you looking for when you view a log in its natural state? Ie. What diameter, length, areas without branches, bark etc.
CB: We need the nicest spruce logs available for making piano soundboards. Most of the time, we use only the base of the tree and cut just under the first branches. The length of the logs we use can vary from 2.5 meters long up to 5 meters (8-16 ft). The tree needs to have grown slowly, gradually, without any twisting, blue marks or other impurities. After having selected the best logs, only 20 to 25% of the tree will be selected for making a 1st grade grand piano soundboard. The rest of the wood will be used for making upright soundboards because the colour is less important because they face the wall. The remaining wood can also be used for other products such as house mouldings and lumber.
GB:Do you happen to know usually how old the trees are when they are logged and when it is the best time to harvest these trees and why?
CB:The tree needs to be cut in the winter time to prevent any sap that would affect the stability of the wood. We need at least 15” diameter at the small end of the log in order to be able to make the quarter-sawn cut. Most of the time, the trees are at least 100 years old.
GB:Do different types of spruce or other woods exhibit different fundamentals in the piano as well as overtones?
CB:There have been many experiments made by piano manufacturers in the last century using different species of woods for soundboards. The spruce tree is definitely the best material as far as tone is concerned.
GB: What is the rough timeline from logging to soundboard? Logging, drying, cutting, curing, shaping, sanding…
CB: The spruce needs to be cured slowly before moving into production. The most important criteria is that the tree needs to be cut during the winter time when moisture is at its lowest. The logs will first be cut into lumber at our saw-mill and stacked outside for months for a slow drying process. The wood will then be kiln dried a few weeks and stacked again for many additional months. The spruce is at least a year old when we start making the soundboard panels.
GB: What is the ideal “curing” humidity or moisture content in the wood?
CB: The soundboard will need different drying periods during the process of production. In the final step, while gluing it into the piano, the soundboard can reach as low as 4-5% humidity content.
GB: Are soundboards planed and then sanded or rough cut and then thickness sanded?
CB: The spruce lumber is cut into oversized planks. The pieces are color and grain matched and then glued together. The soundboards are sanded to their final thickness in a 74″ wide abrasive wood planer.
GB: Do you customize pianos for specific companies and how do you go about doing that?
CB: We manufacture all types of soundboards based on the piano manufacturers’ specifications. Thickness, shape and grain alignment vary from one piano to the other.
GB: How thick on average is a piano soundboard?
CB: A regular piano soundboard can vary from ¼”(6.5mm) for a small model up to 3/8”(9.5mm) for a concert grand piano.
GB: Why quarter sawn? Why vertical grain?
CB: The main reasons are for stability, strength and sound transmission. The soundboard is firmly glued into the piano but still needs to expand and retract without splitting, depending on the ambient conditions and humidity variations. Maintaining the annual rings in a vertical position guarantees that the wood will change dimensions without cracking. The quarter sawn cut makes it also stronger to support the downward force applied to the soundboard by the strings which can reach over 600lbs.
GB: What is the purpose of ribs to a soundboard? How do you incorporate crown (slight arc) into your soundboards?
CB: The ribs help maintain the crown of the soundboard and also counterbalance for the down force exercised by the strings. The ribs can be pre-shaped to match the crown or glued under tension in a press.
GB: What types of glues hold the planks together?
CB: Most manufacturers from the 19th and 20th centuries have been using the hot-hide glue for gluing soundboard panels, pinblocks, veneers, etc. The hot-hide glue was not only good to fix the parts together but also a very good sound transmitter. Today, we use a glue which was developed with the same philosophy of “sound transmission” as it becomes as hard as glass but with a superior resistance to any type of environment.
GB: Obviously with 19 tons of string tension on a piano bearing down onto a soundboard, the soundboard needs to be stable enough to withstand that pressure. Do you measure clamping pressure when joining planks or have other measurements to determine adhesion and subsequent rigidity and stiffness?
CB: The glue used for laminating the soundboard panels is actually stronger than the wood itself. We may think having maximum force is better, but too much pressure with the clamps is not good. There must still be room left for the glue itself.
GB: Are soundboards finished with resins or lacquers or left in their natural state? Or are they finished by the piano manufacturers who purchase them?
CB: The finishing of the soundboard is done by the manufacturer after its installation into the piano. The soundboard needs to be lacquered in order to seal and protect the wood.’’
GB:How is the soundboard adhered to the inner rim of the piano?
The soundboard is glued to the inner rim as a flat glue joint. There are notches in the inner rim to allow room for the ends of the ribs to fit within.’’
I just want to express my thanks to everyone at Pianos Bolduc for answering questions and also supplying most of the images. Due to the wasteful nature of quarter sawn lumber, it makes me happy to see that Bolduc is also concerned with the environment and not letting any scraps go to waste. They only work with suppliers involved in reforestation. The shorter pieces unusable for pianos are sold to guitar luthiers and the sawdust is used by local farmers for litter while the bark for heating sugar shacks and cottages. Excellent!
For more information about Bolduc, visit their beautifully designed website. There’s lots more information on their company, soundboards and pinblocks as well as an array of tools that they also sell.
One final note ~ if you’re anything like me, you’re curious as to their inscription on their logo “Je veux, Je peux”. Translated from French it literally reads “I want, I can” and the insinuation is that we can really make things happen if the desire is strong enough to succeed. Congrats to Bolduc for nearly 40 years of this pursuit!
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