I have an antique Standard Rotary Sewing Machine in its original state (needs some work) which is both on the wood frame as well as the machine, with the serial number 448423. Punched into the plate by the needles it reads the following (which I do not know what it means). If someone could possible tell me the appx. Value of the machine and the year it was manufactured that would be helphful:
Standard Sewing Machine Co.
Cleveland, OHIO U.S.A.
pat. Jan 18'87 pat. Jun 11'89
pat. Feb 24'91 pat. Nov 7'93
pat. Dec 12'93 pat. May 8'94
pat. May 5'96 pat. May 26'96

Were you able to get the date of production on your Standard Machine? I have been looking at one and from the information I have been able to find Standard sold out to Osann so the production date would have been prior to 1931. Osann then sold out to Singer after that. I am just guessing that the different patent dates apply to different parts of the machine. In the one photo of the bobbin shuttle I have I can see where it is marked patent applied for.

The serial # on my Standard sewing machine is 700818. It has the same Pat. Dates as yours plus "DEC 28:97, AUG 24:98, OCT 17:99, OTHER PATENTS PENDING". I think that your machine was manufactured between May 26,1896 and Dec 28,1897.