Bushing Keys

Bushing Keys

Removing old Bushings

For years I have used a method I discovered while visiting a shop that does hundreds of keyboards per year for the trade.

Most original key bushings are put in with hide glue (hot animal glue). You must first make a set of felt wedges. I took a stack of spare new bass hammers and cut 88 or more wedges out of them. You can make 5 or 6 wedges from a large bass hammer. Do not use the center colored felt as it bleeds color onto the wood. If you have hammer trimmings from Ronsen, they are already the correct wedge shape to slice into the correct widths.

The wedges should be about 3/4" to 1" long and pointy enough to go 1/4" or more into the bushed hole. Soak your wedges in hot water until they seem to have taken up all the water they can. This takes 15 minutes or so the first time. Thereafter they take up water as soon as you submerge them.

I clamp all the keys together in 2 or 3 groups just like they sit in the piano -- usually clamped together by section, so I can move them all at once. You can also just lay them out on a table and do one rail at a time. In the piano supply places, they make long clamps that hold half the keyboard at once. These work well.

When the wedges are wet put one into each hole and let them soak for 15 to 20 minutes. Sometimes if they did not get wet enough I take a hypodermic or squeeze bottle of water and drip a few drops of hot water on each one. When they have soaked enough pull each wedge, use a sharp pair of tweezers to reach in and remove the felt that just lifts out. If it takes more than 2 seconds to remove one bushing then they are not wet enough. The whole process can take as much as an hour per keyboard until you get used to it.

Make sure you put the new bushings in with hot glue so the next guy can get them out easily, too. Dry out your wedges so they don't sour and use them on the next piano. The only possible problem is if someone used Elmer's glue [casein glue] or if the factory used the white ivory keytop glue. Wet wedges won't work as easily on Elmer's glue, but the ivory glue will come out eventually; it just takes more wet time and sometimes you still have to slice some of them out. The ivory keytop glue is just hot glue and whiting, but it makes it more tenacious.

Before I learned this trick, I spent hours and hours scraping out bushings. The electric bushing removers never worked very well and burn the wood half the time unless they are used with a rheostat.


When I'm Caulling you oo-oo-oo

Caul refers to the aluminum or brass forms that piano suppliers sell for us to bush keys with. I have several sets for use with different thicknesses of center or front rail pins. The most commonly used is .147" (147 thousandths) I also had one special size made for use with reed organs and another for Chickering oval top center rail pins. (088")

When you screw in a screw with your screwdriver and the blade comes out of the slot it is said, in the trade, to "caul out" When you have this problem over and over with one of those trashy new Asian wood screws, you tear up the head of the screw so badly that when you get the screw screwed in the first time, you then have to remove it, throw it away and put an another new one. This is caused by poor quality Asian metal and manufacturers but that is another subject for later.

After removal of old bushings.

You must use woven key bushing felt. Unwoven nameboard or dress makers felt WILL NOT WORK. (At least not for more than a month or two) I keep at least four thicknesses of key bushing felt at all times in the shop. I use them all when it comes to bushing keys of pianos, pipe organs, reed organs and harpsichords. Sometimes I have to cut my own strips from appropriate thicknesses of felt when the felt needed does not come in strips. Use a straightedge and a rotary cutter as found at the cloth store. Early pianos will use leather for bushing.

To determine which felt to use, you must first measure the thickness of the center and front rail pins. Use a micrometer to find out their thicknesses. They may not both be the same. Remember the front rail pins are oval shaped and you measure the thinnest point because before you return the newly bushed keys to the key frame you will turn all front rail pins so that the points of the ovals point perfectly to the front and back. Previous technicians may have turned those pins to tighten up the wobble of the keys in years past and you are bushing them like they were when new. Do not use pliers with grooves or teeth in the jaws. Use a tool made for this purpose. In a pinch you may use smooth jawed duckbilled pliers.

You will find that most modern piano keys use a pin that is .145" (145 thousandths of an inch) thick. This means you will use the standard cauls of .147". Chickering, Fischer and some others use tiny cauls because the center pins are only .088" thick. Those center rail pins are also oval at the top so they must also be turned to point front to back as well. On rare occasions, I have to make new cauls to fit odd sizes. If I think I will have enough reason to use that odd size I will have a new brass set made. They are reasonably priced but they are not cheap.

Take a strip of felt, put it across the hole and push in a caul of the correct size. You are pushing in the felt and caul as if it were being bushed. Turn over the key. If the caul falls out, it is too loose and you need thicker felt. If it must be pushed in and pulled out with great strength, it is too tight and you need thinner felt. The correct thickness felt will hold the caul moderately tightly so that you can firmly pull it out. It should not be close to falling out but should take some pull to get out.

To begin bushing, cut two strips of felt 15-20 inches or so long. Use hot hide glue to install bushings. I use the glue in plastic bottles in the hot glue pot. (See technical articles on Hot Glue.) Squeeze a drop of glue onto the end of one strip of felt. Use the end of the other strip to spread the glue on both strips. Place the glued ends into the hole. (Glue toward the wood sides, of course.)

You should have glue covering 1/4" of felt on both strips--a little more for front rail holes. You do not want too much glue nor do you want it too thin since it will soak all the way through the felt and make the felt as hard as the wood that you are trying to cover with soft felt. Also with too much glue there can be a blob of glue that oozes below the felt and will partially close the hole. If you do not use enough glue, the bushings will fall out.

Make sure you get just over 1/8" of felt inside the hole. You are trying not to get felt past the glue joint for the key button in the center of the key. If you get too much past that joint you may have to go in later and slice the felt about there and remove excess felt as it can cause sticking keys. While holding the loose felt coming out of the hole, insert the caul. You do not want the caul to push in more felt. The technique is to hold the felt firmly enough and with no loose felt between your finger and the hole so that the caul must go in without dragging in more felt. The first few you may want to pull out the caul to see how much felt is in the hole. When you put it back in be sure you hold the felt again firmly. If you judged correctly on the thickness of your bushing felt, it will resist your pulling out the caul but not be extremely tight. If the caul will fall out or slip out easily, your felt is too thin.

You saw how much felt came out of the hole when you removed the old bushings. If they were factory bushings, they indicate how much felt to go in this time.

Once the caul is in place, use single sided razor blade, chisel point exacto blade, or other very sharp pointed blade to remove excess. For the center rail bushings run the single sided razor blade in between the wood and the felt perpendicular to the caul to just press the blade up against the metal caul and cut the felt even with the top of the key button. Once dry you can sand the button tops to make them neat and remove any excess glue that dried on the wood.

For the front rail bushings, you may cut down next to the side of the caul with the razor blade parallel to the caul and cut into the wood. You will notice that originally the hole was cut out for the shape of the wide part of the caul and the felt was cut just like you are now doing. It is desirable for the bushing to make a 90 degree turn and be glued down to both surfaces. It is also desirable for the whole felt bushing to be recessed into the key. This will assist with key dip so that the key goes down and is pressed with wood flat against the front rail punchings and not with edges of glued felt pressing into the front rail punchings.

The cauls should stay in 6 hours or overnight if at all possible. The shape of the caul will hold the felt where it is until glue dries completely. This will mean less use of the key easing pliers when you install the keys back onto the pins in the keyframe.

When installing the keys back into the piano or keyframe, there should be no more than 5 or 6 keys sticking. Find out why the keys stick by looking into the holes for felt that went in too far. The keys should simply fall all the way down. whichever end goes down, push the other end down. The key should fall immediately back to the rest position. If not then use the key easing pliers. Without those you could use duckbilled pliers but those don't work as well. They will help break loose blobs of glue in the hole. Dump out the loose glue or pull it out with tweezers. If the felt goes in too far you will need to slice off the excess and pull it out with tweezers.

Using the spring type wood or metal clamps or wedges for bushing as was done in the past gives an unpredictable amount of key easing. Using these newer brass or aluminum cauls with the correct thickness of felt will give only a small number of keys to ease.

The finished keys should be very easily moved without hard spots. You may test with key leveling weights, since you will need them for leveling the keyboard. But that is another page.

I will try to get some photos of this process to help your understanding to be added soon.

Doug L. Bullock, June 18, 2009

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