Step 6

I need to get my head around the Verge and Foliot, which I have ignored up to now. The verge escapement consists of a wheel shaped like a crown, with sawtooth-shaped teeth protruding axially toward the front, and with its axis oriented horizontally. In front of it is a vertical rod, the verge, with two metal plates, the pallets, that engage the teeth at opposite sides of the crown wheel. The pallets are not parallel, but are oriented with an angle in between them so only one catches the teeth at a time. The balance wheel (or weights) is mounted at the end of the verge rod. As the clock’s gears turn the crown wheel, it pushes the first pallet, rotating the verge in one direction, and rotating the second pallet into the path of the teeth, until the tooth pushes past the first pallet. Then a tooth on the wheel's opposite side catches the second pallet, rotating the verge back the other direction, and the cycle repeats. The result is to change the rotary motion of the wheel to an oscillating motion of the verge. Each stroke of the foliot thus advances the wheel train of the clock, moving the hands forward at a constant rate. As might be expected from this early invention, the verge is the most inaccurate of the widely-used escapements. It suffers from these problems: - Verge clocks are sensitive to changes in the drive force. The crown wheel is always pushing on the pallets, driving the verge throughout its cycle; it is never allowed to swing freely, unlike a pendulum. - It is a recoil type escapement, meaning that the momentum of the foliot causes the wheel train to move slightly backward during part of its cycle - a bit of a stutter rather than a smooth action. This increases friction and wear, resulting in further inaccuracy. The invention of the pendulum around 1656 increased the accuracy of the verge clock from hours a day to minutes a day, even when continuing to use the crown wheel and pallets.   .The usual angle between the pallets was 90° to 105°, resulting in a foliot  swing of around 80° to 100°. The French used larger pallet angles, upwards of 115° in order to reduce the pendulum's swing (when replacing the verge) to make it more isochronous, . This reduced the pendulum swing to around 50° and reduced recoil, but required the verge to be located so near the crown wheel that the teeth fell on the pallets very near the axis, reducing initial leverage and increasing friction, thus requiring lighter pendulums.  But it might be an idea to reduce the swing if possible.   Here is a diagram of the mechanism using pins Enough of history and a general description! Clayton's design uses bent pallets, set at 100 degrees apart - thus -> I assume this bent end is an attempt to reduce the amount of wobble at the end of the freely handing verge as the pallet pushes against the pin on the rebound. I notice that some people have added weights at the bottom of the verge to reduce this wobble and one person has actually added bearings to keep it vertical. In all cases, inspecting the various images on the web, the pallets do not look as though they have been bent exactly the same. As you may have guessed, I'm trying to build a green clock, i.e. re-using bits and pieces I have knocking around the garage. I have a length of old brass stair carpet rod, so I'll use that for the verge as it is nice and heavy.  Also I want to be able to experiment with different ideas, so everything must be easily adjustable.  I will try using a bolt and nut through the verge at 90 degrees to the crown wheel, as shown opposite (not to scale!).  This will allow me to adjust them back and forth as well as in and out. I can therefore create different pallet angles and be accurate about it. Another problem that Clayton mentioned was the verge thread slipping forward on its support over time.  I shall use another thread bar, rebated into the support, to stop this.  It also has the advantage of allowing consistent and accurate placement of the support position. The other possibility is to place a J shaped wire from the stationary Crown arbor Cap to constrain the movement of the verge.  But this may add too much friction.  It must be J shaped or I would have to remove the Cap to disengage or remove the verge. Well those are my thoughts - but how about real life?

Before I construct this for real, I'll just bend some aluminium (easy to cut with scissors) as the pallets and make the foliot from some offcuts.

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