Type 4 Two-arm Tangent Drive
Here's a rear view of the upgraded Type 4 two-arm tangent drive. The newly installed finder is shown, held in place by a Losmandy 60mm finder bracket. This bracket has a dovetail base plate, so the finder can be removed for transport and still hold its alignment with the primary hinge pretty close. A watch has been installed on top of the threaded rod, to allow continuous operation of the drive. The trick is to keep the second hand stationary relative to the mount while the knob underneath is turned. It's actually easier than it sounds.