Hi all,
Nothing that we do will have a greater effect on the tone of the harpsichord than what we do to the soundboard. In this part, we’ll make a rose, cut a hole for it in the soundboard, locate the bridges on the soundboard and mark the 8’ bridge for bridge pins, and make the 4’ hitchpin rail. If you remember, we built the soundboard in Part 14. Let’s get started.
A couple of weeks ago, we put the two bridges into the soaking tank for a two day swim. Then we traced the curve of the bridges onto some tracing paper and nailed the bridges, through the tracing paper, onto a workbench. The bridges are left to dry for a week or so.
After the bridges were fully dried, we removed the nails and placed the bridges on the blueprint to see how well the curve of the bridges match the plan. As you can see in the next photo, they’re very close indeed.
The rear end of the 8' bridge has to take a short, but rather severe, left turn. Since it isn’t possible to bend the end of the bridge this severely, we left the bridge too short and we’ll epoxy a piece, sawn to the proper curve, to it. Here’s the bridge and the short piece, called a hook.
And here’s the finished bridge after the hook has been glued on.
In a harpsichord, the end of the string closest to the player terminates at the tuning pin, which is turned clockwise to increase the string’s tension, or counter-clockwise to decrease it. The other end of the string is the fixed end. This end of the string is twisted into a loop and placed on a small steel pin called a hitchpin. This pin must be embedded into a solid piece of wood which will hold the pin tightly enough to resist the tension of the string. The strings on the large bridge (called 8’ strings) loop around hitchpins that are embedded into the soundboard liners which surround the perimeter of the case (see Part 7). The strings on the small bridge (called the 4’ strings) have no rail to embed their hitchpins into – the soundboard behind the 4’ bridge is too weak and thin to hold them tightly. So, we’ll make a 4’ hitchpin rail out of ¾” poplar and glue it to the underside of the soundboard. The 4’ hitchpins will be driven through the soundboard and into this rail.
While we could cut this rail out of a single, wide piece of poplar, we’ll make it out of two pieces of stock edge glued together. This will allow us to keep the grain running in the general direction of the rail.
The two pieces are glued together the same way we glued the hook to the 8’ bridge. Then, some carbon paper is taped onto the hitchpin rail blank and it’s placed in rough position under the blueprint. The outline of the 4’ hitchpin rail is traced onto the poplar.
The carbon paper is removed and the rail is cut out on the bandsaw. Here’s the finished rail.
Now we’ll nail the two bridges and the 4' hitchpin rail in place with padded nails that go through the soundboard and into the workbench. These holes in the soundboard will act as locater holes when the time comes to glue these assemblies down. The 4’ hitchpin rail will, of course, be glued to the underside of the soundboard – but the process is the same. Padded nails will be pushed through the locater holes on top of the soundboard and slip into the holes in the 4’ hitchpin rail to properly locate that rail. Here’s what it looks like now.
Nothing else need be done to the 4’ hitchpin rail now, so we’ll mark the two ends for length and remove it from the blueprint. While we’re thinking about the 4’ hitchpin rail, this is a good time to mark the holes for these hitchpins onto the soundboard. The position of these holes are clearly shown on the blueprint so all we have to do is make dimple marks with an awl.
Now we'll mark the 8’ bridge to show where the 8’ strings will cross it. This will tell us where to place the bridge pins. At the front end, where I can look directly down onto the bridges, it’s easy enough to see where the string will cross the bridge, so these marks are eye-balled and a pencil dot is placed on the bridge at each crossing point. As we move further toward the back, I can no longer look directly down onto the bridge (remember, the bridge and soundboard are now nailed to the workbench so I can’t move them into a better viewing position). So I made a little marking jig which is little more than two parallel arms. The edge of the bottom arm is placed right on the string. The upper arm is spring loaded and can move up or down to accommodate the height of the bridge which is tapered in height as well as width. As long as the lower arm is exactly on the string line on the blueprint, the upper arm will cross the bridge exactly where the string will cross it. Here’s a photo of the jig in use.
Here’s part of the bridge with the pencil dots clearly visible. Sometimes, you get lucky – this is one of those times. None of the nails were exactly where a bridge pin dot needed to be. Before we leave this bridge, we’ll use an awl to place a dimple at every dot mark – pencil dots can be erased or smudged, dimples can’t (at least not easily).
Next, we’ll drive a brad into the center of the rose hole to let me know where on the soundboard to drill the 2 ½” hole for the rose.
Next, we’ll drill the hole for the rose with a 2 ½” diameter hole saw. The next photo shows this hole with an old rose placed underneath it. You can see that this casting was not good – part of the “E” is missing and there are a couple of cracks in the plastic resin.
A little detective work showed that the problem was with the mold – not the casting. I’ve been using this same mold for over 15 years so I guess it’s time to make a new one. We’ll do that now. To make the mold, we need an original to copy. In the 1980’s I bought a metal rose which shows an angel playing a harp. To this metal rose, I added my initials with letters I cut out on a scroll-saw.
Making the mold is quite easy. First, using some scrap MDF, we build a small form slightly larger than the rose. The form and the metal rose are sprayed with a Mold Release agent which will help us demold the rose after the rubber has set.
Next, we mix Part A and Part B of the rubber compound (ReoFlex 30 made by Smooth-on) in a 1:1 ratio, and pour it over the metal rose, filling up the form almost to the top.
It takes 16 hours for the rubber compound to cure. After curing, the form is knocked apart and the rubber mold removed from the metal rose. The rubber mold is an exact negative of the metal rose. Here’s what it looks like.
Now we can make as many duplicates of the metal rose as we want. The plastic resin we use is Smooth-Cast 300, also made by Smooth-On. It comes in two bottles (Part A and Part B). The two parts are mixed in a 1:1 ratio and poured into the rubber mold after spraying the rubber with Mold Release agent. Here’s what it looks like after two minutes – you can see parts of the liquid turning white. When it’s all white and no longer feels warm to the touch (about 10 to 15 minutes), the plastic has cured and is ready to de-mold.
After removing the plastic rose from the mold it looks like this.
Finally, here’s the new rose in position under the rose hole of the soundboard. The rose will be gold-leafed before it’s installed permanently.
That’s all we can do for now. Next time we’ll make the cut-off bar and ribs that will be glued to the under side of the soundboard, glue everything on both sides of the soundboard, and install (with glue) the soundboard into the case. This will have to wait until this cold weather has left us because the humidity in my shop is down to 20%. If I knew for sure that this harpsichord would end up living its life in Arizona, I would go ahead and install the soundboard. Unfortunately, I don’t know where the instrument will end up so I’ll wait until the humidity levels reach 40% for a few days. This will give the instrument a better chance at a good life regardless of where it ends up.
Thanks for following along. Till next time,
Ernie
Nothing that we do will have a greater effect on the tone of the harpsichord than what we do to the soundboard. In this part, we’ll make a rose, cut a hole for it in the soundboard, locate the bridges on the soundboard and mark the 8’ bridge for bridge pins, and make the 4’ hitchpin rail. If you remember, we built the soundboard in Part 14. Let’s get started.
A couple of weeks ago, we put the two bridges into the soaking tank for a two day swim. Then we traced the curve of the bridges onto some tracing paper and nailed the bridges, through the tracing paper, onto a workbench. The bridges are left to dry for a week or so.
After the bridges were fully dried, we removed the nails and placed the bridges on the blueprint to see how well the curve of the bridges match the plan. As you can see in the next photo, they’re very close indeed.
The rear end of the 8' bridge has to take a short, but rather severe, left turn. Since it isn’t possible to bend the end of the bridge this severely, we left the bridge too short and we’ll epoxy a piece, sawn to the proper curve, to it. Here’s the bridge and the short piece, called a hook.
And here’s the finished bridge after the hook has been glued on.
In a harpsichord, the end of the string closest to the player terminates at the tuning pin, which is turned clockwise to increase the string’s tension, or counter-clockwise to decrease it. The other end of the string is the fixed end. This end of the string is twisted into a loop and placed on a small steel pin called a hitchpin. This pin must be embedded into a solid piece of wood which will hold the pin tightly enough to resist the tension of the string. The strings on the large bridge (called 8’ strings) loop around hitchpins that are embedded into the soundboard liners which surround the perimeter of the case (see Part 7). The strings on the small bridge (called the 4’ strings) have no rail to embed their hitchpins into – the soundboard behind the 4’ bridge is too weak and thin to hold them tightly. So, we’ll make a 4’ hitchpin rail out of ¾” poplar and glue it to the underside of the soundboard. The 4’ hitchpins will be driven through the soundboard and into this rail.
While we could cut this rail out of a single, wide piece of poplar, we’ll make it out of two pieces of stock edge glued together. This will allow us to keep the grain running in the general direction of the rail.
The two pieces are glued together the same way we glued the hook to the 8’ bridge. Then, some carbon paper is taped onto the hitchpin rail blank and it’s placed in rough position under the blueprint. The outline of the 4’ hitchpin rail is traced onto the poplar.
The carbon paper is removed and the rail is cut out on the bandsaw. Here’s the finished rail.
Now we’ll nail the two bridges and the 4' hitchpin rail in place with padded nails that go through the soundboard and into the workbench. These holes in the soundboard will act as locater holes when the time comes to glue these assemblies down. The 4’ hitchpin rail will, of course, be glued to the underside of the soundboard – but the process is the same. Padded nails will be pushed through the locater holes on top of the soundboard and slip into the holes in the 4’ hitchpin rail to properly locate that rail. Here’s what it looks like now.
Nothing else need be done to the 4’ hitchpin rail now, so we’ll mark the two ends for length and remove it from the blueprint. While we’re thinking about the 4’ hitchpin rail, this is a good time to mark the holes for these hitchpins onto the soundboard. The position of these holes are clearly shown on the blueprint so all we have to do is make dimple marks with an awl.
Now we'll mark the 8’ bridge to show where the 8’ strings will cross it. This will tell us where to place the bridge pins. At the front end, where I can look directly down onto the bridges, it’s easy enough to see where the string will cross the bridge, so these marks are eye-balled and a pencil dot is placed on the bridge at each crossing point. As we move further toward the back, I can no longer look directly down onto the bridge (remember, the bridge and soundboard are now nailed to the workbench so I can’t move them into a better viewing position). So I made a little marking jig which is little more than two parallel arms. The edge of the bottom arm is placed right on the string. The upper arm is spring loaded and can move up or down to accommodate the height of the bridge which is tapered in height as well as width. As long as the lower arm is exactly on the string line on the blueprint, the upper arm will cross the bridge exactly where the string will cross it. Here’s a photo of the jig in use.
Here’s part of the bridge with the pencil dots clearly visible. Sometimes, you get lucky – this is one of those times. None of the nails were exactly where a bridge pin dot needed to be. Before we leave this bridge, we’ll use an awl to place a dimple at every dot mark – pencil dots can be erased or smudged, dimples can’t (at least not easily).
Next, we’ll drive a brad into the center of the rose hole to let me know where on the soundboard to drill the 2 ½” hole for the rose.
Next, we’ll drill the hole for the rose with a 2 ½” diameter hole saw. The next photo shows this hole with an old rose placed underneath it. You can see that this casting was not good – part of the “E” is missing and there are a couple of cracks in the plastic resin.
A little detective work showed that the problem was with the mold – not the casting. I’ve been using this same mold for over 15 years so I guess it’s time to make a new one. We’ll do that now. To make the mold, we need an original to copy. In the 1980’s I bought a metal rose which shows an angel playing a harp. To this metal rose, I added my initials with letters I cut out on a scroll-saw.
Making the mold is quite easy. First, using some scrap MDF, we build a small form slightly larger than the rose. The form and the metal rose are sprayed with a Mold Release agent which will help us demold the rose after the rubber has set.
Next, we mix Part A and Part B of the rubber compound (ReoFlex 30 made by Smooth-on) in a 1:1 ratio, and pour it over the metal rose, filling up the form almost to the top.
It takes 16 hours for the rubber compound to cure. After curing, the form is knocked apart and the rubber mold removed from the metal rose. The rubber mold is an exact negative of the metal rose. Here’s what it looks like.
Now we can make as many duplicates of the metal rose as we want. The plastic resin we use is Smooth-Cast 300, also made by Smooth-On. It comes in two bottles (Part A and Part B). The two parts are mixed in a 1:1 ratio and poured into the rubber mold after spraying the rubber with Mold Release agent. Here’s what it looks like after two minutes – you can see parts of the liquid turning white. When it’s all white and no longer feels warm to the touch (about 10 to 15 minutes), the plastic has cured and is ready to de-mold.
After removing the plastic rose from the mold it looks like this.
Finally, here’s the new rose in position under the rose hole of the soundboard. The rose will be gold-leafed before it’s installed permanently.
That’s all we can do for now. Next time we’ll make the cut-off bar and ribs that will be glued to the under side of the soundboard, glue everything on both sides of the soundboard, and install (with glue) the soundboard into the case. This will have to wait until this cold weather has left us because the humidity in my shop is down to 20%. If I knew for sure that this harpsichord would end up living its life in Arizona, I would go ahead and install the soundboard. Unfortunately, I don’t know where the instrument will end up so I’ll wait until the humidity levels reach 40% for a few days. This will give the instrument a better chance at a good life regardless of where it ends up.
Thanks for following along. Till next time,
Ernie
