3D printed bell / buzzer demonstration

bell 1

Summary of how it works
To help understand how the bell or buzzer works please see the diagram and photos. Initially (on power on) the bolt (or screw) makes contact with the hack saw blade, the wiring (see diagram) completes the circuit and a current flows in the electromagnet. This will attract the hack saw blade bending it toward the magnet making the end of the blade hit the bell - we get a single 'ring'.

bell circuit

As it bends, the hack saw disconnects from the bolt, interrupting the electrical current. The electromagnet now no longer has current passing though it so it turns off. The hack saw blade is now no longer being attracted, so it springs back. Returning to its original position it then reconnects once more with the bolt to start the whole cycle again. The result is that the hack saw blade oscillates / buzzs to and fro - continiously ringing the bell.

Getting it to work
All the parts are assembled and fitted into place (see pictures) on a wooden base and then wired up. If you wire up the 6V battery directly to the two wires of the electromagnet the current that flows will create a magnetic field that will attract the iron hack saw blade. The blade will be attracted to the magnet (the head of the nail) and it will bend towards it. The end of the blade will hit the bell creating a single 'ring' or 'ding'. This will just create a single noise, not a repeating ringing. So we need to use the various metal parts on the demo to create a moving switch that will alternately make-and-break a connection so that the magnet current will oscillate ON and OFF, making the bell striker constantly move back and forth to constantly ring the bell. We make a moving switch using the bolt and hack saw blade. One wire of the battery goes to the bolt using a croc-clip lead. Screw the bolt into the plastic holder just far enough so it touches the hack saw blade and makes electrical connection with it. Connect another croc-clip lead to the far end of the blade (the fixed end) and wire it to one of the electromagnet connections (either one). Finally wire the other electromagnet wire back to the battery to complete the circuit.

bell 1

When you apply power the blade should rapidly move (buzz) back and forth, and if the bell has been positioned properly it should be being hit by the end of the blade and so will constantly ring. If nothing happens then you need to carefully adjust the bolt position by screwing it in (or out) to vary the connection onto the moving blade.

3D printed parts
There are three parts that are 3D printed: i) the bell support, ii) electromagnet support and iii) the flexible iron hack saw blade support. Each of the 3D printed parts has bolt holes printed in them. The blade and electromagnet holder parts can be fixed using the four long self tap screws with the screws going in from behind the wooden base. The bell support is secured using self tap screws from above.

bell 1

Other parts
The non 3D printed parts include:
1 x long iron nail (ca 6 mm diameter ca. 10 cm long)
1 x hack saw blade (from junior hack saw)
long bolt (3M cam 3cm long)
Enough copper enamelled wire for 100 turns on the last 2.5cm of the head end of the bolt (18 SWG wire ca. 5m),
6 x self tap screws (4 long ca. 1.5 cm, 2 short ca. 1cm).
4 x ca. 30cm long crocodile clip leads to enable wiring up the bell parts and to connect to the battery.
2 x 1.5V batteries or a 6 V lantern battery (spring connection type)

saw blade and
electro mag holder:

".stl" file
".scad" file
".g" file
bell support:
".stl" file
".scad" file
".g" file
electro mag support:
".stl" file
".scad" file
".g" file
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3D page


Dr Jonathan Hare University of Sussex, Brighton.
e-mail: j.p.hare@sussex.ac.uk

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