1. Balance point to bottom of tube.  The first thing to determine in making your telescope mount is the point where the optical tube balances with all hardware installed, including the mirror and mirror cell, secondary mirror and spider, focuser, finder scope or Telrad, and even your favorite eyepiece.  The tube must balance as perfectly as possible to give the best movement and to avoid the use of counterweights.  All measurements start here.
   

2. Balance point to base of rockerbox.  To find this distance you take the squareroot of the distance of the balance point to the bottom of the tube (A) squared, added to 1/2 the diameter of the tube (B) squared; squareroot of (A squared + B squared).  Add this figure to the height of the shortest rockerbox side wall and add a half inch for clearance to allow the scope to swing freely in the mount.
   

3. Diameter of tube.
   

4. Distance between sides of rockerbox.  The diameter of the optical tube plus a half inch for clearance.
   

5. Height of rockerbox sides.  Take the distance of the balance point to the base of the rockerbox found in paragraph 2 and subtract one half the diameter of the altitude wheels plus one quarter inch to allow for the Teflon bearings.  This will give you the distance between the base of the rockerbox and the bottom of the arc that forms the cradle for the altitude wheels.  The arc should cover at least ninety degrees to allow the Teflon to be mounted at forty-five degrees left and right of center.   This cradles the wheels well and provides the easiest movement.
   

6. Diameter of rockerbox base.  This measurement is somewhat arbitrary but I find that if the diameter of the base equals the distance between the balance point and the base of the rockerbox the mount will be very stable.
   

7. Height of short rockerbox sides.  This measurement is also somewhat flexible but I find that if you are using good quality materials two to three inches will suffice or one quarter of the optical tube diameter.  Many scopes are built with a high back wall but with high quality plywood or hardwood this is unneccesary and does not allow the scope the freedom to swing over center when finding or following a target.
   

8. Distance center to corner of equilateral triangle.  Measure radius of rockerbox base and add 1.5" to allow for rounding of the corner.  Make center point and draw three lines of this length 120 degrees apart, then connect the outer points.  To round corners, use the bottom of a soup can or something similar as a pattern to draw around. The feet of the groundboard mount directly under the Teflon bearings and can be simple blocks or some kind of adjustable unit for leveling your scope.
   

9. Diameter of altitude wheels.  Another arbitrary design element.  For this design I usually make the wheels 6" in diameter and 1.25" thick.  I cut the wheels out with a hole saw on my drill press and turn them on a lathe.  I recess the surface that rides on the Teflon to make the wheels self centering.  I find that varnished wood makes a good bearing surface for the Teflon.  There are many ways to make the wheels.  you can make a simple plywood disk that fits flush with the sides of the rockerbox and cover the bearing surface with Formica, then mount a Teflon guide on the side of the rockerbox that overlaps the side of the wheel to keep things centered.  I have shown a simple wheel installation method using two pieces of half round molding to align the wheels to the side of the optical tube and a central bolt for attachment.
   

10. .1/2" bronze bushing.  You will find these available at most hardware stores.  Sand the outside surface then use epoxy to bond it to the rockerbox.
    

11. .1/2" bolt.  You can use a stainless bolt and cut the head off if you want the rockerbox easily seperable from the groundboard or for a more accurate fit you can use a shoulder bolt usually used for an axle bolt on a push power mower.  In either case it must be tightly mounted to the groundboard and loosely fit to the rockerbox to allow freedom of movement.
    

12. .Teflon and formica bearings.  The bottom of the rockerbox is covered with a pebble grain Formica that rides on the Teflon bearings on the groundboard.  Formica is a brand name that has come to mean any plastic counter top laminate.  You see telescope makers refer to using Ebony Star Formica.  Ebony Star is a style of Wilson Art laminate (not Formica), and while it has a great sounding name, it is simply a glossy pebble grain laminate that allows smooth movement on the Teflon.  Any similarly textured laminate would do just fine.  Ebony Star is available from your local Wilson Art dealer, probably your local lumber or hardware stores.

A word about construction materials

To match my oak tubes you can use either red oak hardwood or plywood.  If you dont like the looks of the plywood edge, iron on veneer trim can be found at your local lumber store that can be attached and sanded flush so that only a very close inspection can tell it's plywood.  Plywood is often easier to use, provides a truer surface, and is less expensive.  A sheet of cabinet grade 3/4" oak plywood can be usually found for 50 to 60 dollars and will probably leave you with enough material for a matching chart table.  The small increase in cost from buying quality materials will seem very small indeed when looking at and through you beautiful scope ten years from now.  I include a Teflon set with my oak veneer tubes.  Mirror cells and spiders can be obtained from University Optics (800 521 2828) or Astrosystems (there is a link to thier site on my links page), There are too many mirror suppliers to list here including both of these companies.                    

            

For What It's Worth

This plan is here to give you some basic information on dobsonion telescope construction to show you how easy it is to build your own scope. No magic involved at all. For more detailed info there are many good books on the market and many other ways to build one. Join a local club and go to some star parties to learn what you might want before you buy. My favorite customer is one who knows why he wants one of my scopes.

For a handy newtonian telescope design program check out Newt25 for windows by Dale Keller. It's a fully functional $10 shareware application that will crunch all the numbers for you and show you how the different componets effect each other.  It can also be found at shareware.com, search for newt.  An older dos version, Newt20 is available from the SEDS ftp site at; ftp://seds.lpl.arizona.edu/pub/software/pc/optic/   . Both versions seem to work equally well.

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If you have any questions I might answer feel free to email me at;

info@skyvalleyscopes.com

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