Grasshopper escapement

All escapements are intriguing to watch, but the all-time Oscar winner must be a grasshopper.

 

The grasshopper escapement is arguably the most outstanding device created by John Harrison, being friction free and requiring no lubrication in operation.

 

In the original clock, the escapement is mounted on a bronze arbor and supported on knife edges running in glass bearing blocks. However, in my clock, instead of glass, I have made the bearing blocks from hardened steel.

 

Making the escapement has been fascinating, not least because of the snake wood employed for making the pallet legs. Snake wood was one of many exotic woods available in Harrison’s day and used in bow making for musical instruments.

It is a hard, close-grained wood and machinable to a fine finish. The pallet arms pivot on 9 carat hardened gold wire which helps ensures the essential free movement of the legs.

 

Within the escapement assembly, the two pallet legs and their composer arms are counterbalanced to ensure crisp engagement and release in use. Once this balance is established, the complete pallet assembly is balanced with a lead weight mounted within the pallet frame.

 

Rather than make any adjustments within an assembled clock, which would be difficult, I made a test rig to ascertain precise balance.

 

Alternative escapement pallet

I made the first grasshopper to Harrison’s pattern. For comparison, I made a second grasshopper to a different design. The escapements are interchangeable and work on the same escapement wheel.

In Harrison’s design, the escapement operates with one leg pulling and the other pushing, which results in asymmetric torque.

The second grasshopper has been made to a design by Peter Hastings. This twin pivot design providing equal torque through identical legs. It is not possible to balance the complete assembly as in the Harrison pattern, therefore a separate counterbalance will be used on the mounting arbor. For this version I made the pallet legs from lignum vitae.

 

I will be posting information on the setting up and testing in a future post.

I have not discussed the working of the mechanism as this has been covered comprehensively in various publications.

Harrison pattern grasshopper components
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Assembled Harrison pattern grasshopper
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Peter Hastings design grasshopper components
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Peter Hastings pattern grasshopper assembled
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Alternative grasshopper escapements
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