I didn't have time to cut the pinions this afternoon but I figured out how to do it and started turning my arbors. The milling machine I intend to use has a dividing head with a collet chuck with collet sizes every millimetre starting with 2mm. This is on the right of the horizontal slide and there is a tailstock on the left for supporting the other end of the work (2nd and 3rd pictures). For the 3rd wheel arbor of the quarter repeat I turned some silver steel rod down to 4mm for most of its length, including where the pinion will be, and 2mm beyond the pinion. The 4mm section other than where the pinion is will need to be reduced later but keeping it thicker initially should provide more support (first pic). I intend to mount the arbor in a 4mm collet and support the 2mm end with a half centre, as shown. The nearest Thornton cutter available to cut the 6 leaf pinion is for an 8 leaf, 0.5 module (see first pic). The pinion will need modifying after cutting, which I intend to do by hand filing using the original work as a guide to the required shape and thickness. My tutor suggested it would be a good idea to cut a trial pinion first using a piece of brass rod turned first in the same way as the steel arbor.