Using wedges

To attach a larger Schmidt-Cassegrain telescope to a wedge, you must bolt it to three holes. The manufacturers expect you to insert three screws and tighten

Figure 4.9. Author's method for attaching a Schmidt-Cassegrain telescope to a wedge. Long bolt (at top) is put in place in advance, wing nut is tightened with one hand while wedge supports weight of telescope. Then thumbscrews are placed in the two remaining holes.

them with hex wrenches every time you do this. Finding this procedure tedious and clumsy, I've simplified it in two ways (Figure 4.9).

First, one long bolt, with a wing nut and washer on it, is put in place before I pick up the telescope. Then I place the telescope onto the wedge, sliding this bolt into the slot, and tighten the wing nut with one hand while holding the telescope with the other.

The telescope is then secure, and, without tools, I can install thumbscrews (Figure 4.10) in the two remaining holes. These thumbscrews are homemade, built by joining wing nuts to bolts or pieces of threaded rod with high-strength epoxy. For strength, the wing nut is tightened against the bolt head or another nut, so that it would be moderately strong even without the epoxy.

Be sure not to insert screws too deeply into the telescope base, as they can bump into the internal mechanism and damage it (see p. 171). The manufacturer's original screws are a good indication of how deep you can safely go. Little or no strength is gained by threading a screw farther into a hole than a distance equal to its own diameter, and nothing at all is gained by going past the threaded portion of the hole.

Also, do not overtighten screws. A 9-mm screw can easily support a ton - but much or all of this ton may consist of the tension with which the screw is tightened! Screws that carry heavy weight should be tight enough to be snug, but no more. Excessively vigorous use of a wrench can break screws and strip threads.

Beware of cross-threading. Telescope mount castings, tripod heads, and wedges are generally aluminum; screws are steel. If the two come into conflict,

Figure 4.10. Homemade thumbscrews. Left: wing nut, ordinary nut, and threaded rod. Right: wing nut and bolt. High-strength epoxy holds the wing nuts in place.

steel will win. You can easily ruin the threads in a hole by putting a steel screw into it at an angle.

Use a sturdy wedge. The Meade Superwedge, designed for the 12-inch LX200, is usable with the 7-inch, 8-inch, and 10-inch. It is very steady but somewhat hard to adjust in altitude and azimuth. Alternatives to the Superwedge are marketed by Ken Milburn (Bonney Lake Astro Works, 20508 125th Street Court East, Sumner, WA 98390, U.S.A.) and by Jim Mettler (3200 West 450 North, West Lafayette, IN 47906, U.S.A.). Both are elegantly machined, shiny, smooth-operating, and not a great deal more expensive than the Superwedge.

If you are content to make adjustments by moving the tripod legs, or if the wedge is to be installed on a permanent pier, it is easy to make your own wedge, cut for a fixed angle matching your latitude. Wood is a good material since it absorbs vibration. Figure 4.11 shows the wooden wedge on my permanent pier.

Adjustable wedges are harder to make, at least for heavy telescopes; one design that works well with lighter telescopes uses a hinged panel and a turnbuckle, relying on the telescope's off-center weight to keep the turnbuckle tight.

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