Declination Backlash

Hi Rob,

Reducing the backlash is definitely recommended if you can . A mount such as the EQ6-R should not need to be limited to unidirectional guiding and you will be able to get much better out of your mount with some tweaking. The process is not too difficult but it can take a few iterations especially if it's your first time - but the good news is these mounts are very difficult to actually 'break' or do irreversible damage when you pull them apart.

There are two adjustments you can make that affect the backlash - timing belt adjustment and worm gear mesh adjustment. 

The timing belt adjustment is less involved so the first thing to do would be to unscrew the dec belt cover on the side of the mount and see what state the belt is in. Set the mount to a slew speed of maybe 3 or 4 and run the axis back a forward a few times (you might need a slower or faster speed but the aim is to be able to see how the belt engages the pullies). Watch what the belt does as it goes through a reversal of direction. Does the belt look loose or take a while to truly start engaging the mount in the opposite direction. Or does it inflect more than a few mm with moderate finger tip pressure applied?  If either of these look to be true then it could be manifesting as backlash from a loose belt engagement. You can tighten the belt mesh engagement by slightly loosening the motor mounting screws enough to allow tightening of set screw that 'pushes' the motor further away from the mount housing in effect stretching the belt. Just be careful not to go too tight. You should be able to induce a few mm of inflection with moderate finger pressure or else you risk shortening the life of the belt. It doesn't need to be guitar string tight. 

The next thing to try would be rocking the saddle back and forward and seeing if you can hear or feel a telltale 'tick tick tick' of loose gear teeth engaging in each direction. If your mount ticks that box then you likely need to adjust the worm gear mesh which is much better explained in this excellent video by Glen aka Astrobloke https://www.youtube.com/watch?v=qujs7Kt_6_c&t=2656s&ab_channel=Astrobloke  than I could in a forum post. The ending 6-7 minutes covers what you'd want to know but the whole video is a great watch if you want to learn how your mount works. This adjustment can be a bit tricky and time consuming first time around so if you go for it, I'd try and set aside a good few hours of time and wait for a period of cloudy skies so you can take your time if needed. 

Best of luck, 
Matt

Matthew Sole:
Hi Rob,

Reducing the backlash is definitely recommended if you can . A mount such as the EQ6-R should not need to be limited to unidirectional guiding and you will be able to get much better out of your mount with some tweaking. The process is not too difficult but it can take a few iterations especially if it's your first time - but the good news is these mounts are very difficult to actually 'break' or do irreversible damage when you pull them apart.

There are two adjustments you can make that affect the backlash - timing belt adjustment and worm gear mesh adjustment. 

The timing belt adjustment is less involved so the first thing to do would be to unscrew the dec belt cover on the side of the mount and see what state the belt is in. Set the mount to a slew speed of maybe 3 or 4 and run the axis back a forward a few times (you might need a slower or faster speed but the aim is to be able to see how the belt engages the pullies). Watch what the belt does as it goes through a reversal of direction. Does the belt look loose or take a while to truly start engaging the mount in the opposite direction. Or does it inflect more than a few mm with moderate finger tip pressure applied?  If either of these look to be true then it could be manifesting as backlash from a loose belt engagement. You can tighten the belt mesh engagement by slightly loosening the motor mounting screws enough to allow tightening of set screw that 'pushes' the motor further away from the mount housing in effect stretching the belt. Just be careful not to go too tight. You should be able to induce a few mm of inflection with moderate finger pressure or else you risk shortening the life of the belt. It doesn't need to be guitar string tight. 

The next thing to try would be rocking the saddle back and forward and seeing if you can hear or feel a telltale 'tick tick tick' of loose gear teeth engaging in each direction. If your mount ticks that box then you likely need to adjust the worm gear mesh which is much better explained in this excellent video by Glen aka Astrobloke https://www.youtube.com/watch?v=qujs7Kt_6_c&t=2656s&ab_channel=Astrobloke  than I could in a forum post. The ending 6-7 minutes covers what you'd want to know but the whole video is a great watch if you want to learn how your mount works. This adjustment can be a bit tricky and time consuming first time around so if you go for it, I'd try and set aside a good few hours of time and wait for a period of cloudy skies so you can take your time if needed. 

Best of luck, 
Matt

Yes this is how I've tweaked the RA/DEC belts and worm mesh. Funny enough I recently did a complete, strip/clean/tune of my belt modded NEQ6 because of a sticky, high-backlash DEC and a slightly "jumpy" RA (been almost two years of heavy use since it was last serviced). After optimizing the belt tension and worm mesh I practically have a new mount as the DEC backlash is ~15% what is was prior and the RA is smoother.

Pete Bouras:
Hi Ben,

Yes I also did the worm adjustment procedure, there is a tutorial here
www.astro-baby.com/EQ6 rebuild guide/EQ6 worm alignment.htm

This made a big difference.

CS
Pete

Second that! Eliminated my backlash , even with a big load to about 200ms which PHD2 can compensate easily for.

Also for a more simplified version of the above, check the Cuiv's video:
https://www.youtube.com/watch?v=1hzAh6ro8YU

The process is very easy, even I was able to do it, but it needs patience an trial an error a lot before you nail it. Also, I recommend loosening the Dec axis of the EQ6R to have the best possilbe balance ,like that below:
https://www.youtube.com/watch?v=0yzFTjlpZaI

Tha RA Axis is very tight from the factory and I did not manage to loosen it, but it has no impact in my guiding thankfully

Good luck!

Matthew Sole:
Hi Rob,

Reducing the backlash is definitely recommended if you can . A mount such as the EQ6-R should not need to be limited to unidirectional guiding and you will be able to get much better out of your mount with some tweaking. The process is not too difficult but it can take a few iterations especially if it's your first time - but the good news is these mounts are very difficult to actually 'break' or do irreversible damage when you pull them apart.

There are two adjustments you can make that affect the backlash - timing belt adjustment and worm gear mesh adjustment. 

The timing belt adjustment is less involved so the first thing to do would be to unscrew the dec belt cover on the side of the mount and see what state the belt is in. Set the mount to a slew speed of maybe 3 or 4 and run the axis back a forward a few times (you might need a slower or faster speed but the aim is to be able to see how the belt engages the pullies). Watch what the belt does as it goes through a reversal of direction. Does the belt look loose or take a while to truly start engaging the mount in the opposite direction. Or does it inflect more than a few mm with moderate finger tip pressure applied?  If either of these look to be true then it could be manifesting as backlash from a loose belt engagement. You can tighten the belt mesh engagement by slightly loosening the motor mounting screws enough to allow tightening of set screw that 'pushes' the motor further away from the mount housing in effect stretching the belt. Just be careful not to go too tight. You should be able to induce a few mm of inflection with moderate finger pressure or else you risk shortening the life of the belt. It doesn't need to be guitar string tight. 

The next thing to try would be rocking the saddle back and forward and seeing if you can hear or feel a telltale 'tick tick tick' of loose gear teeth engaging in each direction. If your mount ticks that box then you likely need to adjust the worm gear mesh which is much better explained in this excellent video by Glen aka Astrobloke https://www.youtube.com/watch?v=qujs7Kt_6_c&t=2656s&ab_channel=Astrobloke  than I could in a forum post. The ending 6-7 minutes covers what you'd want to know but the whole video is a great watch if you want to learn how your mount works. This adjustment can be a bit tricky and time consuming first time around so if you go for it, I'd try and set aside a good few hours of time and wait for a period of cloudy skies so you can take your time if needed. 

Best of luck, 
Matt

*** Thanks Matt. That's super helpful 😊***

I'll have the day off next Monday so I'll set aside the afternoon to properly look at it!

My story is a bit different because I have an HEQ5-Pro and not the EQR-Pro, but probably not too different.

When I first used the mount, PHD2 reported about 4000ms DEC backlash. 

Like mentioned here, I also adjusted the DEC (and RA) worms. Just before that though, I did the Rowan Belt modification, so the drive system is similar to the EQ6R-Pro. 

Definitely check for anything off in the belt assembly first as Mathieu suggested. Loose belt or grub screws can cause issues.

The worm adjustment is kind of finicky to find the sweet spot. Just make sure that after adjustment, run the DEC axis 360 degrees and listen for any gear binding. On mine, I removed the DEC drive belt and rotated the worm gear by hand (it was much easier to "feel" for binding in the worm). 
Even though, I had to back off of the worm "tightness" due to feeling some tight spots when manually rotating the axis (by turning the worm drive sprocket), the adjustment made a huge difference. PHD2 reports the DEC backlash under 200ms each time. I do use DEC backlash compensation in PHD2 and DEC dither recovery is almost instantaneous. 

Good luck and please report back on your findings!

Jim