Article by Bob Caletti Photos by Bob Caletti and Jonathan Hoyt
My first impression of a rare Jean Billon-Haller music box, upon receiving it from its owner, was that the box was in pretty bad condition. Gears were worn or broken and the comb was missing teeth. The governor was missing a fan blade and there were other missing parts as well. The first order of business was to document what we had so we could start to make a list of what we would need and what we would need to do to bring this box back to life. The fact that this music box is rare meant there wasn’t much information about it from easily-accessible sources like the internet. Deeper digging would be needed.
We started a thorough examination by removing the mechanism from the case and examining it carefully for any broken or missing parts.
The first, and most obvious, things noted were the broken worm gear and spur gear teeth. As it turned out, these parts would become the biggest chal- lenge to remake. The spur gear was an unusual pitch and tooth profile and the worm gear was also very special.
I contacted a number of people I had worked with before to see if any of them could remake the special worm gear. Nobody I contacted or anybody they contacted could do it.
I turned to a local clock guy that I know and he suggested I talk with MBSI member Roger Slocum, who is an expert machinist. Roger makes a lot of custom tooling to do special jobs and he lives near me in the San Francisco Bay area in California, which was a bonus. Roger said he could make both the spur gear and the worm gear to match.
The music box as it was received. It is a Jean Billon-Haller music box with six interchangeable cylinders. The cylinder is removed in this image.
View showing how cylinders were identified with a paper strip showing the tune title, cylinder number, and composer.
The comb had several broken teeth and the bedplate plus associated parts were grimy with age.
A close up of the broken gear teeth and damaged worm gear that would both need to be replaced.
The logo of the music box maker and place of manufacture shown on top of governor.
Using an optical comparator, Roger determined the critical dimensions of both the worm gear (endless screw) and the spur gear profile. He then made CAD drawings for the gears and any other parts he would need to make. Next he made a special cutter to produce the specific profile needed for the spur gear. The spur gear is cut in the conventional manner, but the worm gear is quite another thing. For this he made another special cutter to match the worm gear profile. Then using a special variable ratio mechanism he made himself, Roger cuts the correct pitch worm gear. This involves selecting the correct set of gears to drive the helical gear cutting tooling that will produce the desired worm gear pitch. Setup screws are cut and tested to make sure everything is correct and then the final screw is cut, polished, and hardened. Roger has built many custom fixtures to make very specialized parts so this job was right up his alley.
Worm gear machining set up.
Worm gear index head with spiral cut set up
Worm gear machining set up showing gear changes.
View of trial worm gears made to check set up accuracy
Close up of new worm gear and mating spur gear installed.
Wider view of the replacement worm gear and mating spur gear.
View of the restored start/stop knob, cylinder and comb all polished to a high shine.
While the work to reproduce the gears was going on, the other tasks required to restore this music box to its former glory were started. This box has an unusual start/stop mechanism that requires you to turn the knob counter-clockwise to play and clockwise to stop the mechanism. There is a small spring inside the lower bearing cup for the worm gear that raises the worm gear up during play. During play the worm and knob turn freely against the spring barrel gear. The mechanism is stopped by a jamming action (nondestructive) of the worm gear against another gear which is forced downward against its lower collar when the knob is turned clockwise. The worm and gears should not be lubricated so that there will be adequate friction between the two gears to facilitate the lock up.
Looking at the mechanism you can trace the power flow through the mechanism. The power comes from the spring barrel on the left, through the start stop gears to the cylinder which is in turn coupled to the governor on the right. The governor is what controls the speed of the cylinder rotation and determines the tempo of the music.
If the cylinder is not present, and the start/stop knob is turned to thestart position, the spring barrel would unwind violently. I have a feeling that a violent unwinding is probably what did the damage to this music box gear train in the first place.
There may have been additional parts missing from this mechanism that might have facilitated stopping the governor as well as adding an additional level of safety to the stopping function, but no information could be found about them. Since the control knob started and stopped the mechanism as intended, we restored it the way it was.
View of the restored governor and gears on the right side of the cylinder.
Overall view of Finished Music Box. The six interchangeable cylinders are stored in the drawer in the bottom of the case.