WS 19: Servicing a SEIKO Chronograph 6138

The other term often heard with chronograph movements is the "Column Wheel". The column wheel is like the name says, a plate with columns on it. It serves as a switch between start, stop and reset functions. The SEIKO 6138 is featuring and nice and big column wheel. And in addition the column wheel teeth are nicely beveled to reduce the forces of the levers entering and exiting.
The SEIKO 6138 column wheel has been placed onto a Valjoux 72 movement just to show those differences.

The Valjoux column wheel with smaller diameter and higher teeth (not visible in this picture taken perpendicularly) is more prone to breaking. I made this experience when disassembling a Valjoux 72 movement. The picture of the broken column of a Valjoux 72 chronograph is shown below.

And since I had the picture below prepared already (I had used this in a PMWF contest a while back) explaining the functioning of a column wheel, it is a good change to include it at this point.
Please note, the picture below explains the functions of the column wheel of so called sliding chronograph wheel as opposed to the VERTICAL CLUTCH chronograph wheel on the 6138 that we discussed in detail before. The sliding chronograph wheel is definitely a less elegant solution. Because the chronograph wheel with 300 teeth randomly "crashes" on wheel b. The result, more wear and less accurate measuring of the fractions on the seconds. A vertical clutch represents a mechanically ideal solution to engaging a chronograph wheel and is today only found in expensive high-grade movements

Please click on the picture to read on >>>