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Z17Bm German WW2 mechanical bomb fuze


Well-Known Member
Premium Member
Cutaway model of a German WW2 Z17 Bm mechanical clockwork fuze as used in German aircraft bombs. In contrast to the normal German bomb fuzes, this fuze has no electrical parts and is fully mechanical. It is used in the following bombs : Hs 293 flying bomb, SC1000, PC1000, SC500, BSB1000, etc
Time setting of the fuze: Before the gaine (25 ) is screwed into the clockwork housing (2 ), time is set by rotating the time setting disc (15 ) anti clockwise by means of a special tool that hooks in the upstanding ridge (15A ). Time can be set between 5 minutes minimum and 135 minutes maximum, with an average deviation of plusminus 10%.
Functioning of the fuze : When the bomb is placed in the bomb bay of the aircraft , the ring on top of the fuze is connected to the plane by means of a steel cable with a hook. On release, the ring with the needle (4 ) is pulled out of the of the fuze cover (3 ), thereby releasing the Y formed slider plate (8 ) ?wich is locked up in the slider housing (7 ) and under the slider lock up plate (6 )- ,normally held in place by the needle (4 ). Both release pins (10 &12) are normally blocked in their upward movement by the outstanding legs of the Y formed slider plate.The slider plate spring (9 ) pushes the Y formed slider plate to the left, thereby releasing the safety release pin (10 ) and the geartrain release pin (12 ). Both move upward , forced by their spring. As a result of the risen safety release pin (10), the firing pin safety hook (11 ) can move to the right under influence of a spring (13); the safety mechanism is now removed.
The clockwork geartrain now starts running , powered by the clockwork spring in the main gearwheel (21 ); the unbalance on the end of the reduction geartrain (Where the geartrain release pin is normally blocking when safe) will enshure an even functioning of the clockwork geartrain. The clockwork will rotate the time setting dics (15 ) clockwise , until the lever of the cam shaft (16 ) will fall into the recess in the time setting disc (15), enabeling the cam shaft (16 ) to rotate. This cam shaft has a recess machined in the top of the shaft, which blocks the release lever (17 ) from mowing outward and releasing the firing pin (18 ). If the shaft (17 ) is rotated , the lever (17 ) can pass the recess and is pushed outward by the firing pin (18 ) under influence of the firing pin spring (19 ).
The firing pin ignites the firing cap (20 ); the flame of the firing cap is led into the detonator (23 ) of the Np 10 booster (24 ) through a small longitudal channel, machined into the clockwork housing (2 ) The gaine will now explode, igniting the main charge of the bomb.
As this fuze can Easilly be removed when the clockwork geartrain is still running ,I suppose it will probably be used in conjunction with a ZUS 40, especially when used with a long time delay. The setting of the timing disc (15 ) in the picture is short delay, the time setting disc only has to rotate a few degrees before the cam will fall into the recess in the time setting disc (15 ), releasing the firing pin (18 ).
A rubber O-ring (22) between the fuze body (1 ) and the clockwork housing (2 ), as well as a rubber clad steel disc (5 ) below the cover (3 )of the fuze enshure the inner parts of the fuze remain protected against moisture when stored for longer periods. The colour of the body of the fuze is red, the top of the fuze is aluminium coloured
With regards , Pzgr40

A very interresting post and a nice fuze !
I add pictures of mine (inert, of course).