About: A retired electronics engineer -motorola. delveing into new craft ideas and contest entries.


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Step 1: INTRODUCTION to a Novel String Instrument

The device outlined in this Instructable is similar to  an Instructable published 'Vari-pitch string music player' by Mistic on July 7,2011.
Refer to that publication for all important details pertaining to  construction, string tuning, and  tools.
Also , information on stretchable strings as used for a Ukulele can be found in Mistic's Instructable 'How to make a miniuke' dated Jan.14,2010.
      The difference  here is the tuning and playing method improvement. A wheel or pulley stretches the  3 strings of plastic in a rotating fashion and the variation in tension  changes the pitch  of each string in a controlled fashion.
Refer to the figure for the Vari-Pitch instructable. It is played by pulling  on the strings in a linear  direction. The new variation changes the tensioning method by rotating the string around a pulley.

Step 2: TOOLS

Refer  to the figure for tools used here.

Not shown is a vise. used for cutting  tubing ,etc.
Item 2 and 3  a  hand drill is used to cut slots and  sound holes in the top of the resonator box.
Wood finishing sand paper  and lacquer are used as needed.

If  you are  good at wood working you can make a wood resonator  out of pine . Be sure the top of the resonator is a thin  [.1/8 in.] wood sheet.. The size of box  here is from a craft store  and is octagonal but can be rectangular.or anysided but must be at least 12 in. long.


Material of Construction--
Refer to the Mechanical figure--
Almost every thing here is from our junk pile and garbage  pile.
Fig 1- Over-all  view: The string , box and tuning screws are purchased.  Cost  total  $10.00 .
Stretch string is 1mm.dia and can be purchased in 15 ft. lengths on a spool from Micheals craft store.
The crimping eyelets also can be found at Micheals or Jo-An's.  in a package of 25 for a dollar. The eyelets can be used for anchoring the strings to the pulley and the tuning screws. Tuner screws of 5/8 size Hook and Eye  steel type can be found at any hardware store.
     Most dimensions  shown are not critical.
 Item 4- Rotator drum--An actual pulley  of plastic could not be found of the size  shown [approx. 4.0 in. dia.]We had some coffee cans  that  were used for the top and bottom of the pulley. The middle  or center cover from a powder can was the right size [3.75 in. dia x .50 in thick.  We do not have a band saw or we could have made the pulley of wood. The center  would be a ring and top and bottom would be two thin discs with the top disc center cut out .Over-all thickness not to exceed 1 shown in item 6.
Long tuning rod-or Play lever-- lg. can be a 1/8 dia needle for knitting.
Bridge Item 5--tubing can be any hard plastic  or a rod of plastic but  must be about 1/4 in. for the bottom bridge and .35 to .50 in. for the center bridge.
Spacer tube Item 6. can be brass or steel or plastic  approc 1/2 in dia and a hole for  a6-32 screw to pass thru easily.
String spacers- Item5-any smooth plastic  credit or gift card materials.Cut slits with scissors.
Notes Locator-Item3-Any stiff plastic.
Machine  screws and nuts and washers
. 6-32.x 1.5 and . Item 2. 2 nuts are used to lock together on the 1.5 in. axle item 2 and 6.
Tuning screws-Item 5---.5/8 brass plated  steel hook-eye type .squeezed closed eyelet with pliers.Must have a collar .


1-Resonator  box-- sand and finish. Cut  top sound holes in it.. drill two holes . One for the axle and other for the stop screw.Item2.

axle hole isone inch out from the top left edge of the box.not critical. The stop  hole for the 6-32 screw is 2.5 in. out from the axle hole.
Drill 3 holes with a .093 drill  at one end of the box  Item 5. spaced .70 in apart.  insert 3 hook-eye screws all way in and then 2 more turns in to decrease the torque.
2-Bridges-  No 1 bottom-
glue goop- on under side and position at edge of box. No 2 center  glue a .5 in high wood base. Then position a tube of about .4in. dia. on this base. Position a plastic  slot cut out and glue in place.
3-Rotator or pulley if available.. See assembly Item 4 Rotator drum. The drum  is prepared as follows: drill .15 dia bit thru center for easy fit of 6-32 screw axle. Drill hole for rotate stop screw and assemble a 6-32 screw  here with a 6-32 nut.
Drill or punch 3 holes .075 dia. at right of this stop. Space the holes 1.8 in. apart for the string holes.See Item 2.
Assemble the pulley to the box with a bottom tube Item6. and axle. Use 2 6-32 nuts on the axle and tighten them against each other.
4-Play lever- Item3.Drill two holes in the pulley .top hole to be to left of stop screw.Other hole directly across from it.
5 Rotator stop on box.
Use a 1 in 6-32 screw and a nut.
6- Sheet note locator. Cut  a circle out of plastic. drill a center hole .15 dia.  and place on axle. Cap nut on top or a 6-32 nut  which is screwed down slightly and adhered with RTV- silicone glue on top OF NUT only..
7-String assembly-cut 3 lengths of string about 14 in. long each.Attach string no.1 at right. Use a eyelet and anchor  it to the closed loop 5/8 tuner. Wrap ccw  around screw 2 turns and run to the first hole in the drum. Pull through hole  with forceps and strum while pulling till you get the note B under Cm of piano.Lock  with an crimp eyelet and pliers.Cut off excess. Do same for the other  two strings. but tune them as follows -string 2  G note  String 3  E note under Cm.  {E G B}   Mark note locator sheet at T-pin with a Sharppie pen. with B note.  Rotate drum slow and hold at Cm on string no 1. Mark Cm. Continue for rest of notes  up to F note in second octave.
8.Box bottom  Use .200 plywood and cut out a base and glue to the bottom of the box.    END.

Step 5: PLAYING -

PLAY IT-  See last step on tuning the instrument when rotator is at minimum rotation.This should be a triplet of   EGB. When struck all at one time this is similar to a chord.  String 1 and 2 can be played as a couplet.
    If you can hum a tune you can play this RVP-Uk the first time  believe it or not.  You will be hooked on it - I am no Uk player but was this easy to play...

Note- As in any stringed instrument the notes will drift down ward over time and stabilize. If they drift then the tuner is used to re-tune them.

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    4 Discussions


    Reply 8 years ago on Introduction

    Thanks R. I'm becoming somewhat of an expert on stretch-string music instruments. I definitely should video my new orchestra when they are ready...


    8 years ago on Introduction

    This is an awesome musical project! If I may make a suggestion though- Videos are a great way to demonstrate your work, but an embedded video is much easier for Instructabrarians to play. Upload some of your vids on Youtube and copy the "Embed URL" into your 'ible.

    Other than that great job!


    Reply 8 years ago on Introduction

    thanks for the suggestion. I have never published a vid on Youtube but why not. I will attempt to do so this week. wish me luck.