120T Escapement wheel
This large 120 tooth escapement is made from sheet material and mounted on a collet and secured with 10BA countersunk brass screws. I have covered the building process from start to finish as this process is common to other large wheels to be made for this clock.
The sheet material 16g brass is screwed to a wood-faced mounting arbor which can be fitted to both lathe mandrel and indexing head.
On the lathe the outside diameter is brought to size. To ensure concentricity the central bore for mounting is cut at the same setting.
The mounting arbor is removed from the lathe and mounted on a stub mandrel for fixing to a dividing head set up for 120 divisions. I made the dividing head to the excellent design by the late Geo. Thomas.
I cut the tooth form with a specially ground high speed steel cutter. The grinding was done on my Quorn tool and cutter grinder. I made the grinder to the design of the late Professor Dennis Chaddock.
The cutter is held in a stub mandrel which is securely held by an R8 collet in the vertical milling machine.
The teeth were cut in a single pass.
The wheel was then removed from the mandrel and marked out for quartering with lightly tapered spokes.
The spokes were formed on the fretsaw and then filed to shape with needle files 0, 2, and 4 cut. The side profiles were then polished.
The mounting collet was then turned from brass, with final profile cut with hand graver.
Indexing for lifting pins and mounting screws was undertaken with a headstock indexing attachment before removal from the lathe. Tapping was done with the aid of the tapping attachment.
Mounting screws were cut to length using a simple depthing block, to ensure correct length and finish of each screw.