Osco 70
Description
The Osco 70 is the massive version of the pillar caliber Osco 53. It is a 5 1/4 ligne windup movement for ladies’ watches.
version with 17 jewels
The standard execution used 15 jewels, but there also existed version, on which the minute wheel was ruby-beared on the movement side, and where the upper escape wheel bearing had a cap jewel to reach the “magical” number of 17 jewels.
base plate
There’s nothing to criticize in terms of quality, all important bearings contain rubies, so or sl.
There’s an odditity to be seen on the base plate near the balance wheel, the spring of the rocking bar winding system, which is located on the dial side.
The ratchet of this form movement is because of the rocking bar winding system also located on the dial side.
gear train
The gear train is both classically designed and unusual: The mainspring barrel drives the central minute wheel as usual, followed by the significantly smaller third and fourth wheels, and the normal-sized escape wheel. As is often the case with small form movements, the dial-side bearing of the seconds wheel is located halfway up, i.e., above the escape wheel.
What’s very unusual is that the positions of the balance wheel and mainspring barrel are reversed. Unlike usual, the mainspring barrel is at the top, at 12 o’clock, and the balance wheel is at the bottom, at 6 o’clock. Why Osco chose this positioning is anyone’s guess.
side view of the gear train
The Osco 70 uses a two-leg screw balance, which is beared in a pair of Rufarex
shock protections.
Its 18.000 A/h can be regulated at the hairspring key only.
Osco 70: Dial side
On the dial side, you can see the rocking bar winding system and the shock protection for the balance wheel.
dial side, 17 jewels version
The purpose of the numbers “44” and “45” on the dial side is, unfortunately, unknown.
In the lab
Timegrapher result
What is somewhat surprising is the very unsteady and therefore often difficult to measure rate; this may be due to a defect in the balance staff.| horizontal positions | |||
|---|---|---|---|
| dial up | +13 s/d | 320° | 0.9ms |
| dial down | +10 s/d | 305° | 0.6ms |
| vertical positions | |||
| crown right (12 up) | ~ +50 s/d | 268° | 1.4ms |
| crown up (3 up) | ~ +10 s/d | 246° | 0.8ms |
| crown left (6 up) | ~ -50 s/d | 260° | 0.6ms |
| crown down (9 up) | ~ -5 s/d | 256° | 1.2ms |
Technical data
| Manufacturer: | Osco |
| Caliber: | 70 |
| Size: | 5 1/4''' (measured: 13,0 x 19,3mm) |
| A/h: | 18000 |
| Number of jewels: | 15/17 |
| Escapement: | Pallet lever |
| Balance types: |
monometallic screw balance (two legs) |
| Shock protection(s): |
Rufarex |
| Balance bearing / direction hairspring: | Clockwise |
| Moveable stud: | no |
| Adjust mechanism: | Hairspring key |
| Construction: |
|
| Construction type: | solid construction |
| Winding mechanism: | rocking bar winding system |
| Setting lever spring: | 5 hole(s) |
| Attachment of setting lever: | screwed |
| References: |
Feilner: Bl. 41 3700 Flume: 1957 48 |
| Inventory number: | 24008 |
Usage gallery
Para Parat ladies' watch (dial only)
Berg Parat ladies' watch