This is a model from the 1961 set 7–8 manual, model 7.21. It is a deceptively simple model with hand-operated luffing, slew and hoisting motions.
The model has a number of constructional issues, particularly with the tower and hoisting brakes.
The tower, as described, was found to be lacking in strength and distorted due to lack of suitable parts in set 7 at the time. The tower has been extensively rebuilt in this version.
The superstructure has been mounted on a 4” ball race, instead of 3” pulleys, giving a 360° slewing.
The hand slew drive is a blue Metallus hand wheel with a worm and 57-toothed gear fixed to the vertical composite shaft. A bush wheel secures the rod at the superstructure end.
The cabin is built largely as per the manual, with two handles for jib luff and hoisting. The brake on the luff motion consists of a bolt engaging a further bolt, and by moving the handle outwards can be disengaged. The hoist relies on friction as a brake, and is not entirely satisfactory, this being due to the parts in set 7. A better brake could have been arranged for the hoist, but may have been outside the set contents at the time.
Some modifications have been made (see photo), in that the tower has been improved, the travelling wheels have been changed to bogies, and various small issues have been corrected to make it travel without damage.