Improved Music Spool Holder

by Melvyn Wright

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Improved Music Spool Holder
When I made my first Busker Organ I had a major problem with the music spool holders.  When the roll got near to the end, the spool tended to ride up out of the slot and then the bias spring clicked in underneath it and prevented it from falling back into position again. This only happened at the end with the spring, so the spool ended up being totally misaligned, but amazingly the tracking was not affected and it still played perfectly!

At the beginning of the music, the weight of the paper keeps the spool in place, but as the spool gets lighter and turns faster  the weight of the paper is no longer sufficient to prevent it from riding up the slot in the spool holder. The bias spring is the root cause of the problem because it increases the friction to a point where the spool would rather ride up the slot than rotate, then it clicks in underneath the spool to prevent it from correcting itself.  Not surprisingly, commercial organs do not have a bias spring, so the problem doesn't occur.

Unfortunately, because of the difficulty of access with a screwdriver, I had glued the spool holders to the sides of the pressure box, so I couldn't remove the bias spring!  I also found that the spool holders were very fiddly to place in the correct position and adjust to get the spool to run squarely and in the correct alignment.  I found it completely impossible to hold the spool and both holders in position, check the alignment of the music, take measurements, and check for squareness all at the same time, without the whole thing collapsing!  This wasn't helped by the fact that all my rulers and squares were too big to fit into the roll compartment anyway!

I solved all these problems by making up a one-piece spool holder that can be made up separately, and simply drops into the pressure box.  The two spool holder side pieces are made up exactly as shown in the plans, but are not fixed to the side of the pressure box (not yet anyway).  Instead, they are connected together at the bottom by a piece of 1/8" plywood or MDF.  This is 148mm long and sets the approximate distance between the two spool holders.  This measurement does not have to be exact because the distance between the top of the spool holders is adjustable.  The piece of plywood or MDF should be cut reasonably square as this ensures that the spool holders are maintained parallel and aligned with each other.  Short battens are glued on at the corners to strengthen the joints.  You may need to drill a hole in the base to prevent it from covering the air tube, if you have taken the air tube from the bottom of the pressure box.

One-piece spool holder assembly.  Note the angled slot and horizontal section to stop the spool from rising up.
Probably not strictly necessary but I wasn't going to be caught out again!

 

When this assembly is finished, you will have a stand-alone spool holder that can be easily tested with a spool of music for accuracy and squareness outside the organ.  Do not fit the bias spring. It is not necessary, and only causes problems.  The music spool should be free to float sideways by a small amount.  Instead of the bias spring, the spool holders are mounted so that there is just enough clearance between them for the spool to drop in, plus about 1mm of end float.  The exact clearance is adjusted after the whole assembly is mounted inside the pressure box.

The spool assembly dropped into the pressure box, but not yet adjusted or fixed in position. The simple idea of fixing the spool holders together rather than fixing each one separately to the side of the box makes a tremendous difference to the ease of setting-up.  A music roll can be mounted and the tracking checked before final fixing takes place.
 

Drop the assembly into the pressure box, put a music spool in, and move the whole assembly about until you are satisfied that it is in the correct position and alignment.  (You will need to make a cutout in the side of the pressure box to allow the rewind boss to pass through - as shown in these photos and in the plans.)  The music spool should be about central, but it doesn't have to be.  It all depends on the position of your take-up roller and the tracker bar.  When you are satisfied of the position, the tops of the spool holders are fixed to the side of the pressure box with strips of wood to act as spacers.  These spacing strips can be glued or screwed into position.  The thickness of these strips of wood determines the exact clearance between the spool holders, so you must cut or plane these spacing strips to the exact thickness required to hold the music spool with just a small amount of end float.  Bear in mind that the plastic spools are not high-precision components, and the length may vary very slightly, so do allow about 1mm clearance.  If possible, check the clearance with a few spools before finally glueing the strips into position.  You may wish to glue or screw the bottom of the spool holder assembly onto the bottom of the pressure box, but it's not essential.

In my case, I mounted the take-up roller into position first, then I fitted the music spool holder and adjusted it to line up with the take-up roller.  After checking that the paper ran accurately and squarely through the roll box, I then glued the tracker bar into position so that the holes lined up with the holes in the music. There is no real need to make the tracker bar adjustable.  Align it carefully with a commercial roll of music, and glue it into place.

Even though there is no bias spring fitted, you will probably find that the music spool will usually float to the same end all the time.  So the 1mm end float does not usually have any effect at all on the alignment of the paper.

Wooden spacing strips now fixed in position.  In my case, these were each about 4mm thick.
Note the cut-out in the pressure box to allow the rewind boss to pass through.

 

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