Bowed Keyboard #3: More on the wheelharp

This is amazing stuff. Thanks for sharing!

-- Tom, Surfside Beach, SC - Romans 8:28

I have absolutely no idea what this is, but it looks interesting, and the workmanship is great.
Looking forward to more updates.

-- Still learning everything

Wow, I am new here and had not seen your previous post. As a mechanical engineer I can say that the design is pretty neat and as a woodworker I can say the execution is that of a true master. So I have a bunch of questions:

1. How do you deal with the speed/drag variations as you apply or remove strings? I would expect that these variations would change the pitch or volume.

2. Is the mass of the rotating drum (and corresponding lower wheel) enough to act like a flywheel?

3. Are the pins the second point of the string defining the length of the string or is it the “hammer”?

4. What material do you use for the hammer to keep it from muffling the sound?

5. Why do you use nylon coated strings? I would expect although the nylon would reduce the friction between the drum and the wire it would also absorb some of the energy of the sound

6. How do you keep the hundreds of pounds worth of combined compressive force on the drum from distorting the shape?

7. Do you have an opening in the resonance drum to let the sound out?

8. How do you tune it? (pegs under the keyboard?)

9. Do you have a method for applying the rosin?

10. When are you going to make the equivalent thing for the glass harmonica? :)

Great job!!!!

Tim

I’m listening. Keep ‘em coming.

-- Thos. Angle

Ok so I found your photo bucket page and that answered the stress question. How well does the steel ring, force transfer system work? I assume the “hooks” on the bottom of the system are to counteract the compression on the upper side of the drum.

How much do the flywheel and rosin disk weigh?

What CAD software package do you use?

Lastly, the final detail I could see would be an interesting way to hold the music over the keyboard.

I love this type of stuff – engineering and woodworking together.

Tim

Thanks for all the compliments!
Very insightful questions, I’ll try to answer them , but I have no training in this field…except for tearing stuff apart to see how it works and observing things since I was a kid.

1. How do you deal with the speed/drag variations as you apply or remove strings? I would expect that these variations would change the pitch or volume.

see below

2. Is the mass of the rotating drum (and corresponding lower wheel) enough to act like a flywheel?

Yes, the flywheel attached to the treadle is quite heavy, as well as the friction wheel that contacts the strings. I never weighed them, but even when keying 10 notes at once (which I never do) there is very little drop in RPM. Part of this is also attributed to the belt reduction. I guessed that drag from the strings and RPM consistancy would be a problem, so I figured the reduction in from the beginning. I just guessed at it, but it worked out to about a 3:1, which worked out very well. Moving the treadle at a comfortable rythm moves the friction wheel at I believe around 30 rpm, with lots of torque (been so long since I’ve thought about it, that may be off a bit)

3. Are the pins the second point of the string defining the length of the string or is it the “hammer”?

defining legth…they just allow the string to move down without changing legth or pitch (much)

4. What material do you use for the hammer to keep it from muffling the sound?

There are no hammers…just fingers located on the back side of the vibrating length where they have no effect. They only push the string into the wheel, which can be done by hand, it’s just confusing without a keyboard with all the sharps mixed in.

5. Why do you use nylon coated strings? I would expect although the nylon would reduce the friction between the drum and the wire it would also absorb some of the energy of the sound

these are all nylon, some are harp strings, and some weed eater line. Steel is somewhat harsher sounding, although louder. I also figured it would exert more stress. I experimented with different wraps at the point of friction. If you are familiar with hurdy gurdies, they use cotton. After trying cotton, silk, felt, spider web, and parchment, I found felt worked best for some reason

6. How do you keep the hundreds of pounds worth of combined compressive force on the drum from distorting the shape?

I see you peeked ahead, so I’ll leave this one alone :)

7. Do you have an opening in the resonance drum to let the sound out?

Yes, about a 4” hole in each cylinder-towards the wheel

8. How do you tune it? (pegs under the keyboard?)

yes

9. Do you have a method for applying the rosin?

I just hold it to it- a little will last for days or weeks

10. When are you going to make the equivalent thing for the glass harmonica? :)

Funny you mentioned that…that was my dream of mine when I realized you can bow about anything. I have a room full of glass that I experiment with, trying both wet and dry bows. I have several sketches I’ve come up with for glass instruments…just not enough time to do everything I want to :) I LOVE armonicas-

Great job!!!!

thanks!

-- Jon

:)

-- Bob Vila would be so proud of you!

Ok so I found your photo bucket page and that answered the stress question. How well does the steel ring, force transfer system work? I assume the “hooks” on the bottom of the system are to counteract the compression on the upper side of the drum.

Aww man I wasn’t expecting company, the photobucket page is a mess! The rings work well- no movement since installed. and yes, there are counter tension rods underneath that you tighten as you tune the upper half.

How much do the flywheel and rosin disk weigh?

not sure, but they are solid oak and heavy!

What CAD software package do you use?

Most parts I sketch and make up as I go using paper, cardbard or whatever for templates. If I do make something on PC, I just use photoshop. I have been using it at work for 11 years to do technical drawings. Kinda like driving a nail with your crescent wrench, but it works.

Lastly, the final detail I could see would be an interesting way to hold the music over the keyboard.

I can’t read music, but I may work on it for other folks!

I love this type of stuff – engineering and woodworking together.

Tim

-- Jon

Well Tim and Jon, your conversations are above my pay grade – but the workmanship I do understand and appreciate. Nice work.

-- Bill - "Suit yourself and let the rest be pleased." http://www.cajunpen.com/

So the fingers are behind the pins and the pins are the back point defining the length?

So to determine the string length for each string did you use the formula using string mass/tension/length to find the resonant frequency and convert to a note or did you simply do tests? (Or measure them on a piano)

How long to the strings resonate after you let off the keys? I am thinking of the pedals of a piano and how the vary the “loudness” of the instrument.

Tim

This is really a fascinating project to watch.

Tim.. calm down hehehehe you sound like a kid in a candy store… !!! :)
quite the compliment to Jon :)

this is truly amazing, Jon.. truly amazing

-- ~ Debbie, Canada (http://www.execulink.com/~yohan)

So the fingers are behind the pins and the pins are the back point defining the length?

correct, pins define length. I’ll post a cross section of the whole thing soon.

So to determine the string length for each string did you use the formula using string mass/tension/length to find the resonant frequency and convert to a note or did you simply do tests? (Or measure them on a piano)

I guessed, and adjusted bridges on random strings every octave or so till I found what seemed to be a “sweet spot” – Then I created a harmonic curve using these reference points.
I have since bought a book with a chart that shows a window of acceptable string lengths. Most of my strings were in the window, and the ones that aren’t work pretty well, so I’m not going to mess with them.
My book however, does not cover calculating string mass…can you do this? I am planning another instrument that uses a harpsichord body, and I am trying to figure out a stringing chart. At first, I planned on stringing it like a aharpsichord, but I rigged some prototype monofilament strings according to my optimum length chart and didn’t much care for the sound. I want to simulate bowed viol strings, not a bowed harpsichord. Although harpsichord strings make the correct note, it is thin, and of a different timbre. My plan (unless a person schooled in this comes to my rescue, wink, wink) is to work out a stringing chart using string sizing and lengths taken from actual bowed instruments. I will have to make a string winder and make my own wound strings, as I can barely afford 4 store bought strings for my double bass- can’t imagine buying lots of ‘em!

How long to the strings resonate after you let off the keys? I am thinking of the pedals of a piano and how the vary the “loudness” of the instrument.

They don’t resonate long. What sustain there is, I like, so I don’t incorporate dampners. I control volume by treadle speed, or key pressure.

-- Jon

I am not sure I understand the difference in the strings. What does the string winder buy you? What material are the harpsichord strings and how do they compare to the violin? Can you go to McMaster and get bulk monofilament at different diameters or piano wire?

I can help with the formulas but I can gaurantee that there will be a margin of error based on the reality of science :)

I think harpsichord strings are usually brass or iron , and they follow the monofilament stringing chart, which means your bass notes are fairly long. With wound strings, the same note can be made with a much shorter speaking length, and also is a little bit richer sounding, with more bass. This is how the low E string on a guitar can be the exact same length as the high E, and still have very close to the same tension. If I understand it right, a solid string is more rigid than a wound one. A heavy solid string just produces a dull thud that quickly decays, whereas a wound string is more free to vibrate back and forth, and produces a warmer tone.

The treble notes shouldn’t be much of a problem- I allready have quite a bit of that string bought in bulk. It’s just the wound stuff that creates a problem, as I don’t think you can buy it prewound in bulk- they are wound one at a time, hence the higher cost.

I will check McMaster Carr for the monofilament wire, that would make good cores I bet. Thanks for the tip!

I also use mig wire of different diameters for strings…works pretty good, for as cheap as it is.

-- Jon

Great discussion. But I’m crawling around on the floor on this. You guys are way over my head.

-- What happens in the workshop stays in the workshop. No wait that doesn't sound right. Karson Southern Delaware karson_morrison@bigfoot.com †

But I’m crawling around on the floor on this.

Sorry Karson,
Is that a nice way of saying your bored to tears?
I’ll try to wrap this one up soon, and get started on woodworking again with my new instrument :)

-- Jon

No not at all. It’s interesting reading but I don’t have a full grasp of the intricacies of the differences in string length and size and materials. I would almost call it an overwhelming problem to try to bring it under control.

I mean from Mig wire to Weed Whacker string. there seems to be a lot of differences.

I’m guessing that the wheel that is spinning has rosen on it and the string is pressed into it and that starts the vibrations which provides the sounds.

-- What happens in the workshop stays in the workshop. No wait that doesn't sound right. Karson Southern Delaware karson_morrison@bigfoot.com †

”With wound strings, the same note can be made with a much shorter speaking length, and also is a little bit richer sounding, with more bass. This is how the low E string on a guitar can be the exact same length as the high E, and still have very close to the same tension”

Ok forgot about one of the variables – mass. Thanks for reminding me.

Karson the general concept of what we are talking about is this: Think of a pendulum (the swinging thing on an old clock)

If you add weight to the end it swings slower, if you remove weight it swings faster, make it longer and it is slower, make it shorter and it is faster.

Same general concept with strings. Make the string longer and it vibrates slower. Make the string shorter and it vibrates faster. The old ruler on the edge of a table trick is the same here. When you have 2/3 of the ruler off the table it will vibrate slowly (slow equals lower tone) when you move more of the ruler on the table (shortening the vibrating part) it vibrates faster (we hear a higher tone)

If you have two strings the same length but different masses (weights) they will be different tones. The heavier string is a lower tone.

The last factor in the equation is tension (How tight is the string) Perfect example here is to take a rubber band, pull it tight and pluck it. Then pull it tighter and pluck it again. Tighter = higher tone.

Once you have the tone you need to know what it = as a musical note. So is 137 Hz a D-flat or an A-sharp?

There are lookup tables and tuning devices for that.

Never understood why they wound the heavier cables instead of just using a heavier gauge. Thanks for the explanation Jon.

This site seems to be pretty good at determing the mass of the string and the lookup of the note:

String Calculations

Jon, Speaking of gauges, have you tried stranded electrical wire? That has a wide variety of gauges and has the flexibility of a wound string. You could even use solder to stiffen the wire at the ends (for attachement) and the region where the wheel would hit it. For that matter you could feed it through a 1” long brass tube that has an ID just larger than the OD of the wire and solder the tube in place over the region that hits the wheel so it does not fray. I suppose you could experiment with just stripping the wire in regions.

Tim

Tim, thanks for the link to the string calculations page. I looked at it, but that will be one of those things I’ll have to look at a LONG time with total quite to ever have soak in. (if it ever does)

I have been looking at electrical wire for a source of winding wire to go around a steel core- looks to be a good source of fairly cheap and readily available wire.

-- Jon

Thanks for the explanation.

-- What happens in the workshop stays in the workshop. No wait that doesn't sound right. Karson Southern Delaware karson_morrison@bigfoot.com †