Pneumatic Adjustable Piano Bench

Piano Benches are expensive!! And quality or specialty ones even more so. And Kathleen's Piano Studio (That's my wife's piano studio, Please click the link and help raise her Google profile, Thank You very much!) needed a new one.

Everyone knows that quality tools help you do quality work. And teaching piano is no different. Since my wife teaches classical piano, we bought a nice piano, a Yamaha grand piano, for her to play and compose on, and for students to learn on. But since the students are all of such varying sizes, the bench needs to be able to adjust to get them to the proper height against the piano so their finger and arm position are correct.

The options for an adjustable piano bench are relatively few.

• Place blocks or books under the students or bench (Time consuming, kind of unprofessional, and was the current system in use)
• Buy a scissor jack sort of adjustable bench (Expensive, creaky, Slow to adjust, lots of pinch points, tend to have mechanical issues from the unbalance if being used for duets with an adult teacher on one end of the bench and a small child on the other)
• Buy a pneumatically adjustable piano bench (Simple fast operation, but very expensive. Thousands of dollars for a classy looking quality one in Duet length)

The more I looked at the Pneumatic ones, the more I thought I could build one. Eventually I convinced myself I could. Here I must warn you that I have no carpentry, joinery, finishing, or upholstery training, so if you follow along and question what I did and why, it's because I am bumbling around a bit here....

Once I decided on a Pneumatic bench, I wanted to start the design. But I couldn't start the design until I had acquired my cylinders. So I found a cheap pair of identical used office chairs. Once I bought them, I stripped them down to the cylinders and seat bases.

I had already decided to make this out of laminated MDF layers so I could hopefully smooth and finish it well. With that in mind, I started my design thought process. Here are the considerations I had in mind as I made my design:

• What is the maximum height the bench will be used at?
• What is the minimum height the bench will be used at?
• How much height adjustment can I get out of my cylinders?
• How thick am I planning on padding the top?
• How wide must my base material be in order to support the cylinders?
• How deep must the base be to prevent tipping?
• How wide must the bench be in order to be used as a duet bench?
• How do I make this exceedingly sturdy yet not too heavy?
• Aesthetically, what must I do in order to match the bench to the finish and curves of the Piano?
• How can I fit all my pieces onto one cut of material?

Once I had all of that figured, I drew them all up with curves and angles to match the existing Piano. Since the cylinders worked out to be 2" diameter on the section I would embed, I decided to make the legs out of laminated 1" MDF and just leave a giant cutout for them. That would keep them square and vertical, so they hon't bind when going up or down. I also decided on a base connector to go in between the legs to lock them straight and keep everything sturdy.

Everything was drawn on Microsoft Visio, just due to my familiarity on it since I use it all the time at my work. I created the legs, then sliced it into 1" pieces and created a plate with all my cuts. I also positioned them all to maximize the materials yet still allow for the 1/4" bit allowance on the CNC. I exported that as a .DXF file for the CNC machine to cut...

(I've attached the Visio files as .vsdx, and the .dxf file as well. If you can find 2" cylinders, you're in luck!)

So before you start drooling over the tools I get to use in there, just know that I don't own them. I teach (Electronics, PLC's, Electrical, Automation) at the Trades and Technology centre for our local university, The University of the Fraser Valley. They have a beautiful shop and tool room, and after getting safety-orientation and training by the joinery instructor and my unofficial mentor, Mark, I was allowed to use them. You can use all these tools too, if you take the UFV Joinery course!

Although I will be using some pretty sweet equipment, you could accomplish the same thing at home with a much smaller tool list (and a lot more effort)

• Tracing paper for the Drawings
• Jigsaw
• Belt sander
• Sanding block
• Random orbital sander
• Clamps (or a bunch of bicycle inner-tubes)
• Dust masks

However, I was lucky enough to be able to use full joinery shop afterhours. So I had access to and used:

• SCM CNC machine
• Stationary 4' belt sander
• Pneumatic orbital sanders with dust extraction
• Bar clamps with 3D printed foot protectors
• Full ventilated paint booth
• Router with 1/4" round bit
• Trotec Laser cutter/engraver
• Paint Booth

Here is what I used for this project.

• 1" MDF
• cylinders from 2 old office chairs
• Green Epoxy
• Black Epoxy
• Lacquer
• Titebond glue
• sandpaper (320, 600)
• Chrome plumbing trim rings
• Automotive grade Vinyl
• 1.25" plywood
• Leather coated buttons
• 3" firm open-cell upholstery foam
• 1/4" plywood
• 1" steel tubing
• Assorted nuts, bolts, washers, and screws
• Coffee

Being an electronics and electrical guy, I did a spindle upgrade on Mark's Shopbot last month, and so now it was my turn to call in a favour. (Although he would have helped out just for fun as well. Because he likes fun projects. And I know he is watching to see how mine turns out so he can then make the improved version 2.0) Anyways, I asked for some time and cuts on the precious SCM CNC machine. We loaded on the extremely heavy sheet of 1" MDF, he loaded my .DXF file and adjusted the feedrate, and the machine did the rest.

The cut came out perfectly, and I pulled them out of the machine and did a quick cleanup. All the edges were perfectly cut, and there were no tears. A few small burns on some tight corners, but nothing that wouldn't sand out.

Before I glued anything, I test fit both cylinders in place. They fit like a glove. I then dry clamped the assembly and tested again. Still fit. Ok, so time to get glueing.

I used Titebond original. There were some issue with the pieces skating around a bit when I applied the clamps. In hindsight I should have created some blind dowel pockets in the pieces to align them as well as provide lateral strength. Mark now says that his version 2.0 will have those and therefor be more awesome. Fair enough.

After glueing up, I left them alone to dry for 48 hours. Although I desperately wanted to unclamp them just to see how they looked.

After 48 hours of drying, I took the clamps off. More or less, the legs looked pretty good. But there were some small alignment issues that had happened during gluing.

I did all the rough work on the 4' stationary belt sander, running a 100 grit belt. It fairly quickly took everything down to a level surface. Once I had them all roughed down and made sure the bases were still level, I then took the edges off with a 1/4" radius router bit.

Finally, I did test fit with the spine to see how it looks. I felt that it looked pretty good and went home a very happy and dusty man.

Since I wanted a glossy Black finish to match the Piano, I knew I had to get the underlying surface smooth and true first or I would never accomplish that. So I used a pneumatic sander with 220 grit and and then a second run with 320 grit. You can see the difference between the 100 grit smoothed surfaces, and the 320 grit finish sanded parts in the pictures. It took a while, and the inner curves were a bit tricky to get into, but I had purposely made sure they were wide enough I would be able to get into them easily.

I did not bother going smoother than 320 grit, as once I apply finish, I know the wood grain will swell up a bit and lift. Any further reductions in grit for sandings would be completely useless and a waste of my time.

Once both the legs and spine were smooth, I glued them all together as well with some more Titebond.

Since MDF is thirsty and can wick up obscene amounts of finish, I needed a filler coat that would be thick, as well as dry relatively quickly. Enter the "Rebar Epoxy" coating.

From a previous hobby of building surfboards in my youth, I had learned the ways of epoxy, and quite like working with the substance. And Rebar epoxy is cheap ($8 per rattle can), bonds well, and hardens up tough. And who cares about the colour if it's just getting painted over.

I sprayed on a thin, even coat over the entire surface, and by the time I had finished the back, the front was tacked-up and ready for it's second coat. Despite how thick it is, the MDF still vacuumed it into the pores at the core of the each lamination. I used the entire $8 can on the first coat (Big Spender!) , and it was thick enough that I had good coverage and no runs. It left it to dry and cure overnight in the 25 degree paintbooth. (Celcuis, obviously.)

When I took the legs out the next day, the epoxy had hardened up quite well, but you could see 5 parallel "rough" looking lines along the laminations where the epoxy had wicked into the lower density core of the MDF and raised the grain. This was why I hadn't wanted to sand down past 320 grit on my initial pass.

Well, I got out the 320 grit and sanded the assembly again. I went right down to the wood in a lot of places, but that didn't bother me as I knew that the epoxy was soaked in and the grain was now stabilized. Now I did want a smooth base as I knew it wouldn't wick up anymore.

Once it was sanded down, I took it back into the booth and shot a second $8 can of epoxy onto it. You could really see it evened out now. This one I had to be more careful with though, as the epoxy now wasn't pulling in as fast and had a tendency to run.

Once the second coat had dried and cure overnight, I sanded once more with 320 grit. This time I was careful not to go down to the wood, as I wanted the to just smooth the epoxy surface.

With that done, I then shot the first coat of Black epoxy over. (This was another epoxy, an appliance one this time, and I had done a test panel to ensure that it was compatible to bond with the first green one.) I did seal the bottom of the legs again as well, as this will sit on a carpeted slab-on-grade in the studio and could otherwise absorb moisture and swell and crack.

At this point the base was looking very smooth and black, but not glossy enough yet. Still, it was enough to start getting excited over...

Have I mentioned that I have sanded this thing yet? I feel like I'm stuck on a loop here. But you can see that the epoxy did not fully lay flat, and so I once again sanded it down(400 grit now) and then shot another coat of black epoxy. This would be my final epoxy coat.

Although most of the other coating were a day apart, once this one was on, I left it to cure for a minimum of 2 days before I would start the Lacquer and polishing process....

Time to lay on the Lacquer! Which is really kinda neat, as true shellac is an extract made from harvesting and cooking the Lac beetle of central Asia. Lacquer dries fast, and each successive layer melts into the previous ones. Once again, I did multiple coats, but with way finer sanding between, down to 600-800 grit now.

Now that the base was finished, I needed to dress up the tops where the cylinders were inserted into the wooden base.

Most piano hardware is brass. But because the cylinders are stainless, I wanted to match that as otherwise the brass would look dumb against the stainless. I measured the cylinders, and then went back to the Home Depot. There I found chrome trim rings in the plumbing department. I then cut two rings out of black acrylic, and glued them together. The bottom ring was sized to generously cover the square recesses in the wooden legs. The upper one was glued to that to center the chrome ring around the cylinder, as the inner hole of the trim ring was about 5mm larger than the cylinder rod.

I took the cylinder out of it's base, then slipped the rings on in order and inserted the cylinders back into the base.

Since each gas cylinder has it's own release, I needed to tie them together. I thought this could be best accomplished through the use of a common piece fo 1" steel tubing tieing them together.

So I cut off the existing paddle shaped grips. I then threaded the rod so I could use nuts to hold the new handle in place. (I started with a 3/8" tap, which lightly scored the rob, and then went over it again with a 5/16" tap to get to final depth.) Once that was done, I measured, drilled, and cut a piece of 1" steel tube. After test fitting it, I gave it (as well as the piece of 1/2" plywood that would tie the seat bases together) a coat of black appliance epoxy.

Once that was done, I mounted it onto the threaded bars. Now pulling up anywhere along that bar will activate the release on both cylinder simultaneously.

Because the seat bases and activating bar are not the most pleasing aesthetic, I decided to build a 4" skirt to hide them all. I cut and beveled 4 pieces of 1/4" plywood to fit the seat base. I then used spray adhesive to attache them to a piece of black automotive vinyl. Each of the edges was trimmed and folded over and stapled down.

Once the skirt pieces were all clad, I then assembled them with glue and screwed on corner clamps.

What is not shown here, is the evening I spent watching YouTube videos on creating diamond tufted upholstery. I've never upholstered before, so this was going to be an adventure.

I started by cutting apiece of 1.25" plywood for the seat base. I made all dimensions divisible by 7, as I wanted an mathematically even pattern. So the finished dimensions were 14" x 42". A bit OCD, but I like it. I then laid out all 17 of my button positions, each arranged around a 3.5" grid

I drilled a 3/16 hole with the drill press at each location. Once that was done, I set the wood base aside.

I then trimmed the 3" foam for a 1/2" overlap all the way around. Then I transferred the same hole pattern onto the foam. Since I wanted to control the fold better, I also traced lines between the button positions so I could slit the foam along those lines. These would hold the excess vinyl fabric straight between the button dimples. I cut along those lines with a razor blade.

At each of the button positions, I then took a 1" holesaw and cut out the foam all the way through. I should have done this before I made my control slits though, as I did get a bit of tear out that could have been avoided. but it was fixable, I just glued the chunks back in as needed. Then the whole foam slab was aligned with and glued to the wooden seat base via spray adhesive.

Last of all, I took waxed upholstery thread and tied a length to each of my buttons. I folded it over and through the button eyelet, so that both ends of the tread would come through the bench. Last of all I marked each of the threads at 2" so I could make sure each dimple would be uniform.

At this point I took the base with the prepared foam, and flipped it over the vinyl and centered my piece. I tacked the cover roughly in place with a few staples, but left them proud so I would be able to remove them easily later.

I started the tufting the the very centre of the bench, and then uniformly worked outward from there. I don't have a reason for that, it just seemed to make sense so I wouldn't end up with any weird bunching later. Each button was done in 4 steps.

First, I pushed a 10" upholstery needle through from the back of the bench. The 3/16 hole in the woode was sized to be just bigger than the eye of the needle. So the 1.25" wood aligned the needle well, and the needle came out dead centre of the desired button position.

Second, I pulled the entire needle through, reversed it through the hole it had just made, and probed until I found the hole through the back again.

Third, I threaded the waxed upholstery thread through the eye of the needle and pulled it through the back.

Fourth, I tensioned the thread until the mark on the thread was right at the edge of the hole. Once it was there, I shot a staple, folded the thread back over that staple and drove another one. I tapped those flush with a hammer, then tied a knot in the tails. Then I folded that thread back the opposite way one more time and drove a final staple to hold that, then trimmed the free ends.

Once the top was tufted, I removed the temporary staples that had been holding the edges down. I then used a knife to bevel the edges.

Once that was done, I tensioned the vinyl and stapled it down around the perimeter. The corners were tricky, but I folded them neatly and stapled them underneath. (I wish I had a sewing machine to have done them. They're my biggest regret on this project)

Last of all, I screwed the skirt brackets onto the underside of the benchtop to fasten those pieces together.

Last step was to center the benchtop onto the base and cylinders, and fasten with screws. That was easy.

The bench works well, and smoothly goes up and down, but it is a bit stiff for Kat's weight. At 220 lb (100kg), I can compress both cylinders with my weight. But she is lighter and has a bit of trouble getting it all the way down by herself. Good thing it is a full duet length at 42", as the extra weight of a student on the other end of the bench is usually enough to bring it down. I'm still trying to figure out how to bleed a bit of nitrogen from the cylinders.

The base is 1/4" rounded all the way around, and even though the bench is heavy and sturdy, it slides really easily on the studio carpet. So positioning is not a problem. Since that is so easy, I anm contemplating taking the benchtop off, flipping it over, routing some slots, and pouring some lead to into the benchtop to add the requisite weight for her to adjust it.