Just an observation from my latest tweaking of my 10" dob, which may be of benefit to others.
When re-assembling my secondary, I realised there is a simple way of setting up a good basis for later collimation.
The centre hole of the secondary holder aligned with the centre spot of the mirror, and the reflection of the secondary holder.
Probably a basic step that I have missed before, but others may have too.
Cheers
Chris