Equipment

The EQ6 has standard brass gears on the stepper motor and worm gear, with a ‘transfer’ gear to translate the stepper motion to the worm gear.

These gears introduce errors and backlash, the belt drive mod is designed to replace these gears with a timing belt

Replacement of the gears for a belt drive is straightforward but will take a day to do properly. Instructions are provided with the kit from Rowan Astronomy and another useful resource is the hyper-tune instructions from astro-baby.com

There are a couple of tricky steps

1. Removing the adapter at the bottom of the polar scope shaft – you will need a steal belt, oil filter wrench (from Halfords)
2. Removing the worm gear caps and the worm gear retaining ring, these can be removed using pointed pose plyers, but you risk damaging the caps if you slip, a better approach is to use the specially designed tool (available from Rowan Astronomy)
3. The bolts holding the mount together are steel bolts with M6 threads tapped into the aluminium body – it is very easy to strip the threads be vary careful – if you do strip them you can repair them easily with a Helicoil thread repair kit.

Fitting the belts is easier if you have locking tweezers, but it can be done with your fingers – if you are nimble – there is not much room to manoeuvre inside the mount.

The EQ6 hyper tune is a procedure to strip down and rebuild your mount to improve performance, the exact details are best followed from astro-baby.com so I won’t copy them here. The tune-up includes replacing the plastic shims and replacing them with PTFE ones and replacing the bearings, I replaced the small worm gear bearings and cleaned and re-greased the large bearings.

The best attitude to take when doing this modification is slow and deliberate, if something is not going well or as described in the instructions the best course of action is to stop, have a cup of tea, re-read the instructions and try again.

I took the time to make-up an EQ6 tool set, this includes all the tools needed for the hyper tume, most are common tools you are likely to have available such as screwdrivers and allen keys, the two less common tools are the metal band oil filter wrench (available from Halfords) and the worm bearing cap and retainer removal tool (available from Rowan Astronomy – makers of the EQ6 belt drive mod) the latter you can get away with pointy nosed plyers but you are more likely to scratch the caps without the tool.

The strip-down and rebuild took a total of 20 hours, requires a lot of space and somewhere reasonably clean to lay everything out. It is straightforward if you are mechanically minded, but is a large commitment of time. 

To complete the hyper tune required the following parts and consumables.

• 2 rolls of paper towels
• 2L of white spirit
• old tooth brush – for cleaning parts
• clean containers – e.g. ice cream tubs for cleaning parts
• lithium grease for re-greasing bearings and all parts
• PTFE shims of various thicknesses to replace the plastic shims 
• New bearings (I just changed the small worm gear bearings)

Expect to spend about £60 on these parts

There was a lot of dirt and grit in the main bearings, quite how this gets in, given they have never been taken apart, is beyond me. To re-grease them requires removing the bearing caps that seal the bearings in, this was done using a modified modelling knife. The bearings were then de-greased using white spirit, the process of removing all the dirt from the bearings took a long time, we kept spinning the bearings in the white spirit to dislodge the dirt until no bits were visible in the pot, regularly changing the white spirit. They were then left to dry naturally on paper towel and before re-greasing were warmed with a hot air gun to ensure all the white spirit had evaporated.

Any parts that required cosmetic repairs were repainted and I also replaced all the rusty screws with new ones.

When we reassembled the EQ6 the Declination worm felt ‘notchy’, so we took the EQ6 apart again and inspected the worm gear, it had a small surface scratch, almost too small to see, but this scratch was getting amplified in the mount, so we polished it out using 2000 grip emery paper on a lathe (you could probably do this in a drill if you don’t have a lathe), this cured the problem.

A massive thank you to Julian Tworek for offering to help complete the hyper-tune, Julian’s patience, experience and perfectionism is exactly what is required to complete this project successfully.

The Eq6 is fixed to the pier/tripod using a central bolt, but this generates significant friction between the tripod/pier and EQ6 which can make polar alignment along the azimuth axis difficult, you need the central bolt to be tight to ensure no movement but loose to adjust the azimuth for polar alignment, but it can’t be both, fortunately this can be easily fixed.

If you haven’t done it already complete the knobs mod.

Parts:

• 200mm x 200mm 1mm thick PTFE sheet

Instructions:

I used 1mm thick PTFE sheet, but I know others who have had success with thinner PTFE sheet, you can cut this using sturdy scissors, but I opted to scribe the PTFE using a pair of engineering dividers. Simply place the sheet between the mount and the pier adapter/tripod.

Note image below doesn’t show the hole you have to cut for the lug that protrudes from the pier/tripod which the  azimuth adjustment bolts push against.