Most visitors online was 1990 , on 7 Feb 2022
Thank you so much Graham! now I can understand.Hi Miguel,
The drops in any escapement are the period or distance between one tooth being released by one pallet and another tooth being stopped by the other pallet. There has to be some drop on each pallet, usually measured as a degree of rotation, but it should be minimal and both drops should be the same. In a verge, the drops are adjusted by moving the escape wheel inner pivot, (closest to the verge staff), laterally, since the verge flags are acting on diametrically opposite escape teeth. This is done in English watches by a simple dovetail slide on the potence, but on French watches mostly by a more complex arrangement of slides with screw adjusters.
If the pallets are jewelled in the modern way, ie, visibly, the stones may be moved relative to the pallet frame, but that isn't something to be fiddled with without knowing exactly what one is doing, because moving one affects the other. In English levers with hidden jewels, they can't easily be moved.How are drops adjusted in levers?
No, and I don't think it's ever completely instantaneous. Since the escapement is continously starting and stopping the whole train, there's an inertia factor.Does unlock and impulse occur at the same instance in all escapements?
My point was that there is rotation of the escape as soon as it becomes unlocked, and therefore there is rotation of the escape after unlocking and before impulse.
For cylinders, my feeling is that the delay would be shorter, since the escape wheel is engaging directly with the balance and not via an intermediary, although I have no way of proving this.Am I correct in assuming that the delay is greater with duplex & detent escapements?
I think it's a design issue here; if the angle of separation between the two rollers isn't precisely matched to the escape wheel dimensions, it could result in a longer delay.Lastly, in a duplex, in which the balance is directly impulsed by a pallet on the roller, (as in a detent), there must be some clearance to allow the reverse swing, so the unlocking action of the long escape teeth with the small slotted roller on the staff has to be very slightly ahead of the short escape teeth which hit the impulse pallet. Being only impulsed in one direction, (again like a detent), it's almost detached on the reverse swing, except for the unlocking teeth on the tiny slotted roller
I think much of this discussion revolves around exactly when the 'impulse' happens, because this has a finite duration, and the size of the drop depends on which point it's measured from;All I am trying to establish is the correct definition - whether the difference is small or not.
Graham surely if the definition is in terms of rotation of the escape, the key events are the release of the escape so that it can rotate and the point when the rotation ceases. The impulse will occur at some point after the escape is released - it cannot happen while the escape is locked.revolves around exactly when the 'impulse' happens
He's saying that its free travel can only occur when there's no contact with the pallets.By introducing the term 'free travel' is Britten restricting the rotation of the escape when there is no contact with the pallets?
Yes, it is for the detached lever. I think you're right about the duplex and detent escapements, but although they must have drops, I'm not sure that it's possible to arrive at a generic definition. The duplex has a very tiny amount of free travel between unlocking and impulse, but after impulse the next locking tooth is moving until it's stopped by the ruby cylinder, which is also free movement.This is for the lever, is it not? I think the definition should be applicable to all escapements and I do not believe this sequence can be applied to duplex or detent.
I thought free travel begins before the impulse in these two escapements.