Building an equitorial mount (Some Math)

I want to build a simple equatorial mount, which is to say a mount that can be aimed at the North Celestial Pole, and then turn at the rate of 1 turn per sidereal day. Or 1 turn in 1436.06 minutes. This will match the rate at which the stars move across the sky.

To do this I will need a main gear which will be a wood disk cut on a router of radius R.
This will be driven by a threaded rod with 20 turns per inch turning at 1 rpm. This will move the disk at the rate of 1/2oth of an inch per minute. As such the circumference of the drive wheel must be (1436.06 minutes * 1/20 inches /minute) which is 71.8 inches.

Thus the radius (R) of the drive wheel should be 11.4278 Inches. I expect 11.45 or so will be about as close as I can machine the thing, this should be close enough for visual use and for astrophotoraphy as long as the exposures are short (say 10-15 minutes max).

Starting Small

So I think I am going to start by building a 4.5" F8 small dob. The primary & Secondary will cost me about $53 (USD) with shipping plus any customs. I sent an email to the customs service to see how much that will be.

The next thing to decide is do I want to make it a solid sonotube or some sort of truss travel scope. I am looking around talpiot for sonotube, and will try to see how much it goes for. From there I can decide if I want to lug the scope around in 1 piece or not. I'm thinking with this one a solid tube makes sense.