You have 600mAh Nicads. The recommended charge rate is the 0.1C rate, 0.1*600mA, or 60mA. To fully charge these, you put in 40% more than the capacity, or 0.84mAh, which means 60mA for 14h. You need a constant-current charger for this. The circuit you have posted is not a constant-current charger suitable for Nicads; it is a current-limited constant-voltage charger which is better suited for charging lead-acid batteries, either flooded or SLAs.
For Nicads, you use constant-current charging that is time limited (use a programmable timer to terminate the charging). Faster charging above a 0.3C rate requires monitoring the temperature of the Nicads, and terminating the charging when the temperature of the batteries rises above a limit specified by the maker.
Here is a schematic of an LM317 used as a constant current source suitable for charging Nicads. **broken link removed** (taken right off the spec sheet). To get 60mA, R1 should be 1.25/0.06=20Ω. Since at full charge, your Nicad pack will be approximately 1.4v/cell*7 cells ≈ 10v, and the dropout voltage of the 317 is ≈ 2V, you need to start with a 12Vmin d.c. supply.