Easy-build Adjustable Equatorial Wedge for ETX
March 2009

In the hopes of doing some long exposure photography I wanted to get my ETX mounted on an equatorial mount. Mike Weasner's Mighty ETX Site Tech Tips page has many such wedges. I looked at a lot of them plus more on other sites and stole the ideas I liked best! (See the Mettler Wedge in particular.)

Like everyone else, I wanted to overcome certain deficiencies in the Meade #884 Deluxe Tripod:

In addition, the design needed to be pretty simple so that I could build it. What follows is the solution I came up with.

Base disc

The wedge is designed to mount on the cheaper Meade #882 Standard Tripod. This sturdy mount is topped by a cast steel top plate with two holes that match the ETX base, plus two extra long screws to attach it. For my design, I first made a 6" disc and drilled two holes to match those in the steel top. Two matching t-nuts from the hardware store are inserted so the disc can be attached with the existing long bolts. In the middle, I drilled another hole and inserted a 5/16" t-nut facing the opposite way. My plywood was too thin, you should use 3/4" material to avoid having the attachment screws poke up through the top. To provide a smooth surface for the wedge to rotate on I drilled holes for three plastic auto trim pieces. They look like slippery nylon. A good hardware store will carry these or something similar.

Wedge assembly

The wedge itself consists of two pieces: a horizontal piece and hinged piece. A section of continuous "piano hinge" attaches the two. Turnbuckles provide a sturdy yet adjustable mechanism for setting the angle. You'll need to adjust your design to accommodate the turnbuckles your hardware store carries and your site's latitude. I can't shorten my bottom piece any or my turnbuckles won't adjust short enough to attach.

The hinge should be as close to the center hole as possible without interfering with the base attachment knob (the 5/16" threaded knob). The ETX will be mounted on the hinged part. Place the ETX as low as possible on this piece, with sufficient clearance to reach in and insert two 1/4" attachment knobs. The completed wedge assembly is shown on the workbench, with the angle shown by my iPod Touch running an app called "Clinometer".

Usage

Here's the mounted scope. Looks there's room for an eyepiece holder or something near the handbox hanger, plus another nook under the wedge. The center of balance is not perfect, it's still about 1" from the center but I can't move the scope any lower on the hinged piece and still have room to put my hand underneath to attach mounting screws.

Parts list:

by Charles Hall