What sets the balance wheel into motion

[Carramrod]

I'm relatively new to mechanical watches and have quickly become fascinated but have an elementary level question that hopefully someone can answer.

If the hairspring and balance wheel come to a complete stop due to the main spring running out of power, what is it about winding that sets the balance wheel back into motion?  I understand the way the escapement works once it is in motion to input a small amount of energy into the balance wheel, but don't understand how winding alone sets it back into motion.  I know with grandfather clocks you have to restart the pendulum manually and I'm wondering why this isn't the case for watches also. TIA.

[clockboy]

The power from the mainspring is transferred through the train wheels but this energy is released under the control of the escape pallets. This an old vid but explains it better than I can.

 

 

[vinn3]

you may have noticed,  when the main spring is totaly  wound down,  3  or 4  turns of the crown will start it running. .with out shaking !  if it dosent you need to go to work on it or perhaps it a cheep watch     welcome to the forum,  vinn

[Carramrod]

Thanks for the responses.  So it seems that when the hairspring and balance wheel stop, the chamfer of one of the pallets is able to be engaged by a tooth on the escape wheel, and once the main spring has been wound a few turns it has enough energy to allow the escape wheel to set the balance wheel and hair spring back into motion.

[oldhippy]

27 minutes ago, Carramrod said:

Thanks for the responses.  So it seems that when the hairspring and balance wheel stop, the chamfer of one of the pallets is able to be engaged by a tooth on the escape wheel, and once the main spring has been wound a few turns it has enough energy to allow the escape wheel to set the balance wheel and hair spring back into motion.

Don't forget there could be many reasons why this might not happen. You should expect this in a well serviced watch, even with a new mechanical watch, dirt is the main reason why a watch stops, gummed up oil is another and wear so unless the movement is squeaky clean don't expect it with every mechanical watch.

[vinn3]

these are the kind of symptoms that  require " open and inspect"  or  send it out for service.    vinn

[StuartBaker104]

On 12/07/2016 at 7:16 PM, Carramrod said:

Thanks for the responses.  So it seems that when the hairspring and balance wheel stop, the chamfer of one of the pallets is able to be engaged by a tooth on the escape wheel, and once the main spring has been wound a few turns it has enough energy to allow the escape wheel to set the balance wheel and hair spring back into motion.

Yes. As the power runs down, eventually the balance amplitude reduces to almost nothing, but its neutral position with no power is with the roller jewel in the middle of the pallet fork horns, with the pallet fork centred. In this position, the pallet jewel angled face rests against the face of a tooth on the escape wheel, and a little torque on the escape wheel will push the pallet fork away setting the watch in motion.

When the roller jewel is disengaged from the pallet horns, the pallet lever mechanism is essentially bistable and should flick to one side or the other where the pallet jewels just lock the lever in place. For this reason, it is important to set the hairsping on the balance wheel so that in its neutral position it would hold the roller jewel in the centre of the horns as described above, otherwise (amongst other problems), it will be necessary to shake the watch to move the balance and set it in motion.

in practice the neutral position is best tested with the watch in motion. A timing machine can listen to the noises the escapement makes and reports any misalignment as a "beat" error. This is resolved by rotating the hairsping attachment (collet) to the balance or to the balance cock, depending on the watch.