HEQ5 Backlash Adjustment
If you’ve ever stripped down an HEQ5 mount (either the standard or Pro versions) you’ll know that you need to carefully adjust the backlash in the gear trains. This includes both the motor to worm drive trio of gears and the worm drive to ‘giant brass cylinder’ gear.
It’s a fiddly job and requires a delicate hand to find that perfect balance point between too loose and having backlash, and too tight and finding the gears are binding.
I fitted the Rowan belt-mod kit to mine, which replaces the motor drive trio of gears with pulleys and a belt. This removes any backlash before the worm drive. It dropped my guiding from about 1.5 - 2 arc-seconds of error to about 1 arc-second or less with good guiding. It also made the mount a lot quieter when it’s slewing at maximum speed.
Recently, I noticed that a substantial amount of backlash had crept into my DEC axis. So I did the usual trick of removing it, only to find that the backlash was still present.
I eventually worked out that the lock nut holding the worm drive in place had loosened by about 1/4 of a turn. Not a lot, but enough to cause about 5 degrees of slop.
To check these lock nuts, remove the round rubber plugs from the side of the mount and use a thin-bladed screwdriver to tighten them up again.
Simple but effective, and not the first thing you’d think of when trying to tune your mount.