My recollection, Leigh, is that when I took the spider out and replaced it, the collimation was hardly affected. Make sure your three secondary adjustment screws are in firm against the holder - that should keep it well in place. I cannot remember how I got it out. Of course, the ends of the screws are wider than the OTA. Must have undone them all then was able to push the spider further through two holes to release the other two ends so it could be lifted out.
ps. here is where I make brief mention of removing and re-installing the spider in my 8".
http://www.iceinspace.com.au/forum/s...ad.php?t=20612