Spindle clamping, dividing heads and CNC drive.

Hi all.
I've found that with my Cowells dividing head, I need to clamp the spindle every time I take a cut to get good results (I'm making clock wheels) - there's a nut provided for exactly that purpose. I guess this is normal (it's a feature I've seen on other dividing heads and tables) - but it's the only dividing head I've ever used, so bear with me if I'm totally off with this.
I'm toying with the idea of doing the rotary indexing CNC style (a la Division master, for example) but I've noticed that there is no mention of spindle clamping in the user instructions or anywhere else that I've read.
Is the assumption that spindle clamping should not be necessary, and that I'm doing something amiss to need it, or is it just that it's so obvious that no-one thinks of mentioning it... ?
Enlightenment received with thanks,
Youra.

  Quoted Text Here  
If the dividing head is properly adjusted to have minimal backlash between worm and wheel locking should not be needed for a "light" job like a clock wheel, but is beneficial for heavier tasks.
In the CNC variety usually you keep current flowing in the stepper motors to keep a decent holding torque. This means you need to remember to switch off when finished! The normal permanent magnet holding torque is insufficient. Again it assumes worm & wheel are well adjusted.
On the other hand I find with my home made head for an 8mm lathe clamping is necessary, but my workmanship was far from perfect in this head!
Alan