Here is a coaxial, push-pull collimator that Don Clement designed. It was intended for a C-14, and uses no springs (which is typical for a push-pull arrangement). Collimation controls are accessible from the rear of the telescope.

Figure 1

Figure 2

Figure 3

Comments from Don:

The coax collimator was a design for collimating a moving mirror focuser that I built for a C14. The collimator allowed the entire focuser with 14" mirror to be tilted and collimated from the outside rear of the telescope. The coax collimator design may be useful for mounting the secondary or the main mirror for a Newtonian. The collimator uses no springs.

In the illustrations the triangular plate is the base of my compliant focuser, which replaced the original C14 sliding tube focuser. My 1" thick focuser fit inside the telescope tube between the 14" mirror and rear casting.

Shown in figure 1 is the triangular base that three ¼" SS allthread rods (shown in green) are threaded into. Each threaded rod fits into a countersunk hole. (Or alternately a spherical hole made with a ball end mill.)

Figure 2 shows the same triangular plate with two additional components, the 3/8 rod (shown in gray) and the ¼"acorn nut (shown in red). The 3/8 rod is made from 3/8-24 SS allthread. A 5/16 hole is drilled axially through. The end of the 3/8 rod that fits into the triangular base is machined spherical. The opposite end has a countersink hole drilled. (Or alternately a spherical hole made with a ball end mill.) Also hexagonal flats were machined on this end. The ¼" acorn nut is made from a SS ¼" acorn nut, drilled and tapped through.

Figure 3 shows a backplate added to the assembly. In the backplate are three 3/8-24 through-tapped holes that the 3/8 rods thread into. On the C14 these holes happen to coincide with the lock down stud holes for the original focuser.

To make adjustments, adjust the 3/8 rod using the hex flats while simultaneously adjusting the acorn nut. This is the coax push pull arrangement.

I have since replaced the acorn nut and spherical rod end with a monolithic compliant joint.

Also, Don recommends that you refer to the following books:

- "Precision Machine Design" by Alexander Slocum

- "Engineering Metrology" by K.J. Hume.

All feedback is encouraged!

email: t-k-r-a-j-c-i-@-s-a-n-.-o-s-d-.-m-i-l (remove the dashes)

Last update: 21 Dec 2002