Making a geared head for a photo tripod

Background: The raison d'être for this project is simple. I wanted a useful, ambitious and interesting metalwork project - suitable for a senior secondary student. Brass cannons and steam engines are fun, but one has limits... I have long been annoyed at the inadequacy of standard photo tripods when using long telephoto lenses or small telescopes (or binoculars). In a nutshell: It is practically impossible to accurately aim a high magnification device using a standard pan-and-tilt tripod head. What's needed is something akin to a telescope mount with a geared drive, to allow fine and precise control of movement. Tripod manufacturer Manfrotto makes a series of very nice geared heads, but I could give you thou$and$ of reasons why I'm not getting one of them. German Equatorial Mounts (GEMs) for telescopes are common and cheap - but its more fun to make one... What follows on these pages is a visual chronicle of the construction of just such a device.

I make no claim that the techniques and practices shown here are either state-of-the-art or best practice. They are, however, practical, safe, effective and economical. All machining work was undertaken in the practical rooms at Parramatta High School.

The Worm Wheel I toyed with the idea of using a tangent-arm assembly to drive the two axes, but worm-and-worm-wheel won out for reasons of aesthetics and plain fun. Here is the process for turning and hobbing the smaller of the two worm wheels...

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	Plan with a micrometer, mark out with a rule, cut with an axe (joke). The wheels are marked out on 3/8" (~9.5mm) brass plate.
	The blanks are cut out on the bandsaw.
	Not too neat, but well within tolerance.
	The central hole is drilled on the pedestal drill press. The blank fits very neatly under the machine vice jaws, providing a very substantial grip.
	Yes, it is a school machine vice. Why do you ask? (sigghhhh...)
	Parallel turning the blank to the desired diameter. I just love turning brass.
	Top view shows the form tool used to turn the gear profile.
	The thread to be used for the hobbing is M10. The minor diameter is close enough to 8.5mm, so this sized drill is used as a gauge to check the blank.
	Not bad. Certainly close enough for government work.
	The blank is mounted horizontally on the carriage - carefully shimmed to centre height. Here the first cut is about 2/3 complete.
	The blank is free to rotate as the tap bears upon it. It "auto-rotates" as the tap bites in and cuts the grooves.
	The tap is mounted in the chuck, and is run at low speed. I used the lowest back-gears speed, even though this was a little conservative.
	A spiral-fluted tap is used so that the teeth are engaged with the blank at all times.
	Sadly, the spiral-fluted tap is not centre-drilled, so can only be supported at the headstock. You can see evidence of my attempt (feeble) to grind a centre depression. Only succeeded in flattening the grinding burr. :-(
	Top view, nearing completion. Watch them chips fly!
	The cut has reached the bottom of the minor diameter groove, but is still a few revolutions from full depth.
	After a few light chamfering cuts on the edge, the gear is complete. The asymmetrical profile is due to excessive clearance on the shaft which supported the blank during the hobbing. This allowed the blank to tilt down during the cutting process. Next time...

Click the "NEXT" button to see the construction of the first axis barrel

Break out of this frame.