I too have the construction book, it’s a fascinating design, and looks fantastic.   I’d like to have a go at one, but have resisted the urge so far, as I’ve too many things on the go, I’m good at starting projects, but not so good at finishing them.

I wish you well with it,

Colin Drakes.

It does, however, remain an “inspired” design.

https://www.christies.com/en/lot/lot-4642730

MichaelG.

Mike C cited the NAWCC thread above which refers to the possibility of using a helical gear.  It mentions that Merlin’s design predated the McDowalls who pioneered the use of such gearing in clocks.  Kenneth Cobb investigated the manufacture of helical gears of this type and published an article in Antiquarian Horology March 2021.  This includes a photo of a helical wheel driving a worm ddirectly on the ‘scape arbor.  Macdowall’s teeth had square driving faces and seemed to have been successful. I was intrigued by the article and had a go at making wheels and pinions by CNC milling using my rotary axis.  It seemed to work.  Though it might be ideal to faithfully follow the MB design perhaps using a helical form for the wheel and the worm it drives might be a good approach?

There is a good photo of a Macdowall clock at Greenwich which shows the escape arbor drive well if you zoom in:

https://www.rmg.co.uk/collections/objects/rmgc-object-79628

Edit: actually looking more closely there are 3 cascaded helical stages.  These all have parallel axes but somewhere there is a photo of one with the scape axis perpendicular. Whilst I was looking at making these I came across a website for a Swiss company making some very specialised helical low-friction step-up gearboxes but didn’t note the URL!