In message <_fmdnQmOQsudmevVnZ2dnUVZ8uOdnZ2d@posted.plusnet>, Mortimer 
 writes
>What is the profile of a dog clutch? Does it have rectangular castelations
>like two chess castles/rooks enmeshing top-to-top or does it have a sawtooth
>profile. I'd have thought that with a rectangular profile there was a 50:50
>chance of the clutches meeting peak-to-peak and trough-to-trough, whereas at
>least with a sawtooth the teeth will force each other to engage
>peak-to-trough except in the very unlikely event of the points of the teeth
>meeting absolutely level with each other.
Depends on the situation.   On Voith transmissions on the early diesel 
hydraulics the reverse was a uniform tessellation and the transmissions 
had a "tooth on tooth" button to increase pressure on the dogs to try to 
drive them home.   Nine times out of 10, it was easier just to let the 
locomotive roll a few inches to get into the correct direction gear.
On Mekydro transmission, the dogs had a higher leading edge with a 
falling trail that allowed the dogs to be forced together and engage 
once the speed difference had gone.   It was quite a frightening 
experience (the first time) to sit on a gearbox during the up change as 
the ratchet noise was quite loud and as the gears engaged there was a 
loud thump with a corresponding jump of the entire transmission casing.
-- 
Clive