dobsonian telescope

Hello gang,Im trying to finish my new dob and all I lack is the focuser and spider w/diagonal.I'm building a 6" dob with an 8" tube 48" long.My primary is f/8.Having never done anything like this and a real amerature to astronomy I'm starting to get a little nervous about these last few steps.My primary w/cell is 2" from bottom of tube,focal length is 48".First of all do I install the focuser first then line up the diagonal from there? It would seem to be easier for me that way.Does it go a little below the focuser or directly out from it? How far down from the end of the tube do I need to drill my focuser hole?My focuser fully racked in is 4".It is a Meade rack and pinion focuser for a newtonian dobsonian project.It was origanally for .965 eyepieces but I installed an adapter for 1.25.The diamater of the hole will be 1.5".So back to my question,can someone help me out and tell me where to drill my hole and please show me the math you use so that when I build my next dob(which hopefully will be at least 10"If I can get a good deal on a mirror-I'm just a postal worker.)Any assistance would be so greatly appreciated as I am so anxious to try out my new telescope thatI built.I must say it really looks good,good enough that my wife said I could bring it in the house.Well----Maybe.Thanx so much Darrell Hensley

I second the Newt as the starting point. It will give you an idea of where you are at and what you need to do.
The focuser needs to me mounted in the rights spot. It is not a guessing game and once the hole is cut, you are committed. You can move the primary up and down to get the small error taken care of as long as you do not permanently mount it by drilling the holes for the cell bolts. You can slide the mirror up or down until you get the position correct. But you can not mount the focuser until you get the measurements figured out.