Here is my latest completed project: American Watch Company Grade 20 Size Keywind movement SN 50,042, with Nashua Watch Company assembly number 163, in an eagle-marked Charles E. Hale & Co. gold engine turned KW20 case.
The movement was purchased in an incorrect silver case last November, and it needed a lot of TLC. Aside from the expertly done cosmetic restoration, the replacement balance staff that came in the movement had been poorly made, with nonconcentric pivots. My superlative watchmaker, John Wilson, made me a new staff and finished it to AWCo grade standards. When fully wound the watch now keeps time to within less than 5 seconds a day in all six positions.
An AT&Co Grade KW20 movement in the 80,000 SN range gave up its case for the cause. The net gold weight in the case is 46 DWT. The gold purity is not marked on this case, which is not uncommon on very early American gold cases. Acid tests on a streak indicate that it is at least 14K pure, and my watchmaker is convinced it is a strong 16K, if not even 17K.
I learned that there are numerous construction differences, several more than I had realized, between the First Run of Nashua numbered KW20s and the later AWCo Grade KW20s:
- Three out of the four First Run 19 jewel KW20 movements on which I have data, including SN 50,042, have flat hairsprings. Later AWCo Grade KW20s nearly all have Breguet overcoils.
- The jeweling configuration on First Run movements is different from that on the later 19 jewel runs, with no hole jewels on the center wheel, but endstones on the top side of the pallet bridge and escape wheel.
- First Run movements feature an unique winged escutcheon around the center pinion hole.
- The balance staff is rivetted to the balance wheel on First Run KW20 movements, and only on the First Run movements. In all the later runs, the staff is friction fit.
- First Run movements have a subsidiary plate (a.k.a., a "false plate") on the dial side, visible here in the last picture. These are not present on the later movements.
- The pillar screws, which were clearly made at Nashua, are unique to Nashua. They have hemispherical heads, thicker shanks, and a different thread pitch than later Waltham screws.
It has been fascinating to follow the evolution of this watch model from the First Run through to the final run, such as the example I showed in post #698 on this thread. The watches of the final run of KW20's have Breguet hairsprings, Fogg's cam regulator and safety pinion, gold train wheels, center hole jewels one of which is in a gold top plate setting, and curb pin adjusting screws. Some, like the example I show, also have glass enamel dials, large diameter balance wheels, and superfine pitched hairsprings.
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