In case its not immediately obvious, the small bevels are dimensionally precise replicas* of the first 1927 pattern 30a, which were cut with a 45 degree cone angle. Its one of the most under-rated gears in the Meccano system - probably because so few people have any originals. There are quite a few replicas out there, however most are not an exact copy of the original and so the arrangement shown below may not fit together in precisely the same way. This differential has also been built with original gears to prove that it is 'within the system' and not relying on a quirk of the dimensions of the replicas.

* All original early 30a are single tapped (and stamped MFEA). These replicas are double tapped, though in no way rely on that 'change' for this build.