Working up the Design ...

... Crunching the Numbers.

A Newtonian telescope is a simple design consisting of:
1) a paraboloidal primary mirror, which focuses the incoming light to form an image;
2) a flat secondary mirror, which reflects the converging light beam to the side, where it can be observed without the observer's head blocking the incoming light; and
3) an eyepiece used to examine the image formed by the primary mirror.
The eyepiece is normally placed in a focuser, which allows small changes in the separation between the primary mirror and the eyepiece, to properly align the eyepiece with the image formed by the primary mirror.

The mirror Kevin F. sent me is a 6" f/10.6.  This simply means that the mirror is 6 inches in diameter (which for a Newtonian design will also be the aperture) and that the focus is 10.6 diameters away from the mirror, or 63.6 inches.

The secondary 'flat' mirror is an elliptical shape and 1" wide along its smallest dimension (minor axis).  Since it will be tilted at 45 degrees to reflect the light cone outside the tube, the elliptical shape will present a circular shape to both the incoming light beam and the eyepiece (held in the focuser) ... this minimizes the amount of light blocked by the secondary mirror.

We now have enough information to properly design the Optical Tube Assembly (OTA) and be confident that it will work after construction.  There is a very nice web-based program that will help us design our Newtonian telescope called 'Newt for the Web' and you can find it here:
http://stellafane.org/tm/newt-web/newt-web.html

Under the Specifications tab I entered the following data:

The information for the "Optics" section comes from my mirrors.  The information for the "Tube" section is based on my 'ideal' tube; it may be adjusted later if necessary to account for small changes in diameter or thickness.  The information for the "Focuser" section is based upon the data given for the Moonlight focuser from the company web site.

Moving to the "Ray Trace" tab, we can see what our design will look like:

I turned the 'baffles' option off, as there is no real advantage to baffling the tube of a Newtonian (unlike a refractor); and honestly, including tube baffles in a Newtonian may prove detrimental to the performance as the baffles will force the warm air rising from the mirror as the night time temperatures drop into the incoming light path ... remember those 'thermals' we are trying to avoid?

The "Performance" tab has some interesting information:

The main things here are that the 1" secondary mirror will produce a 17% central obstruction to the incoming light path.  We desire this to be small, the goal being <20%; so we are good here.  Also note that the fully illuminated field (100%) is 0.467"; close enough to the 0.5" that is often referenced as adequate for visual use.

And finally, the Dimensions" tab:

This tab is where we find the critical measurements for construction of the OTA.  I've already determined the diameter of the tube (which was input in the "Specifications" page); and now I can see that I'll need a tube at least 67" long.  Again, we will ignore the baffles data as tube baffles will not be used.  :)