Per a recent discussion, I was encouraged to offer some tear-downs of some of the high grade watches in my collection. I have several Walthams at the bank which I would like to present here, but haven't had a chance to go and get them. In the mean time, I thought I would offer something which I have on-hand, an Illinois Sangamo Special.
The Sangamo Special was positioned, at the time, as Illinois's best quality railroad watch. The Sangamo Special was offered in three jewel counts, 19, 21, and 23, with the three versions priced respectively. Visually the quality of finishing of all three is identical, although the 23j would presumably have been adjusted to the tightest standards. In later years, only the 23 jewel was offered.
My own personal example of this grade is a relatively early 21j example. These went through a number of variations, and mine is what is know as a "true bridge" model(meaning that the center bridge is a true separate piece rather than being attached to the barrel bridge by a "web" of metal). Mine also has the earlier feature of a diamond endstone on the balance. The 23j versions from this same general range were fitted with a standard jeweled going barrel, and the additional barrel jewels were not visible without disassembling the watch.
Here is the movement
Flipping it over reveals a high grade double sunk(constructed from three separate pieces) glass enamel dials. These high grade Illinois dials(along with the high grade dials from other makers) have a perfectly smooth and almost translucent appearance to the top layer of the enamel.
The hands are also polished and heat treated to a plum color rather than the standard blue. This is typical for many high grade American watches, particularly from Illinois
Removing the dial shows a good level of finish on the top plate. This also shows the corresponding diamond endstone on the pillar plate side of the movement. All American watches I've examined with diamond endstones have them present in pairs.
Note that one wire spring is used-the return spring for the set lever. It would no doubt be difficult to fit anything but a wire spring for this particular application.
And, here is the break-down of the individual components
Although the fork lacks the level of finishing expected of a truly high grade watch, it does have a number of nice treatments. Note that the all of the edges are nicely chamfered and polished. While this is likely purely cosmetic, the safety dart is gold.
Also please note that the balance arms and inner rim of the balance wheel are highly polished(black polished). The top edge of the balance wheel and the balance arms are also chamfered.
Although this is far from a top grade movement, it certainly is quite nicely finished especially for a railroad watch.