Why 2 c/weights rather than 1?

[Rusted]

The mounting must be balanced in all planes. Not only from side to side but vertically and nose to tail.
The simplest balance arrangement is for a single telescope with the finder outboard and in line with the declination axis.

I have three different telescopes mounted at once. 180, 150 & 90 mm refractors.
Despite my best efforts these require extended sub-counterweights, on threaded stalks, below the lightest telescope of the three.
These balance the vertical imbalance of the three telescopes combination.
I was careful to bring all three instruments as close to the polar axis as possible to reduce the necessary Declination counterweighting.

You must release the clutches or shaft locks and move the telescopes to all possible sky positions.
They must not move when released at any sky pointing position.
It is often easier to give the telescopes a gentle push to ensure any static friction [in the clutches] is overcome.
This gives a much better idea of any slight imbalance.
Any imbalance will cause the telescopes to continue to move more easily in one direction rather than the opposite way.
Balancing should always take place with the heaviest accessories fitted. Large solar prisms, filter wheels and cameras, etc.

To add to the confusion it is considered wise in imaging circles to have a slight imbalance which ensures the telescope must be constantly lifted "uphill."
This ensures that only one side of the teeth of the drive wormwheel remain in constant contact with the worm.
Were the telescopes perfectly balanced the wormwheel could rock between teeth where it meets the worm due to wind gusts.

[Rainer]

1 hour ago, Rusted said:

To add to the confusion it is considered wise in imaging circles to have a slight imbalance which ensures the telescope must be constantly lifted "uphill."
This ensures that only one side of the teeth of the drive wormwheel remain in constant contact with the worm.
Were the telescopes perfectly balanced the wormwheel could rock between teeth where it meets the worm due to wind gusts.

Great explanation except the famous slight imbalance is only necessary for mounts with backlash. When you have a mount with no backlash then slight imbalance can even develop to be a problem.

[Rusted]

10 hours ago, Rainer said:

Great explanation except the famous slight imbalance is only necessary for mounts with backlash.

When you have a mount with no backlash then slight imbalance can even develop to be a problem.

Many mounts have undersized wormwheels to avoid spoiling the styling or reducing the profit margin.
Lower tooth counts have larger gaps between the wormwheel "teeth" to provide increased backlash.

In mechanical theory, worms should never be jammed into the wormwheel to kill backlash.
There should always be some clearance to avoid high friction and wear.
It also assumes that perfection exists in wormwheel concentricity with the shafts and bearings.
Otherwise there will [inevitably] be loose arcs of rotation and tight arcs.
Under these circumstances an "uphill" drive bias may be all one can possibly hope for.

[kirkster501]

It is easier to move a heavier object closer to you than a smaller object further away, all other things being equal and in proportion.  This can matter with PHD guiding changing the mount directions minutely.

So mount two weights closer to the mount rather than one at the end of the spindly extension bar.  Also less in the way to accidentally bang into in the dark.

[Rainer]

On 25/10/2019 at 01:28, Rusted said:

Many mounts have undersized wormwheels to avoid spoiling the styling or reducing the profit margin.
Lower tooth counts have larger gaps between the wormwheel "teeth" to provide increased backlash.

In mechanical theory, worms should never be jammed into the wormwheel to kill backlash.
There should always be some clearance to avoid high friction and wear.
It also assumes that perfection exists in wormwheel concentricity with the shafts and bearings.
Otherwise there will [inevitably] be loose arcs of rotation and tight arcs.
Under these circumstances an "uphill" drive bias may be all one can possibly hope for.

Interesting and OK I accept your point of view. We are talking heere of worm and worm wheel gears which most of the time have a speed of 1 revolution in 24 hours.

Backlash in our case is more annoying then any friction and wear we will have all over the time we use our mounts.

So as far as I know there are some " Premium " mount producers which do lap the worm against the worm wheel. They do not adjust the gear for having backlash. 🤔

I used to have two Losmandy G11 and had too adjust the worm gear at night after having adjusted it for Sun imaging and that is a total NO NO. So I made a custom floating worm with springs and since then I did not have to adjust them anymore. I also lapped my worm and worm wheel.

The newest mounts from any brand are now using spring loaded worm assemblies pushing against the worm wheel ¿ why ?

But OK, we can adjust our mounts as we think we need them, but my problem is now that I can not adjust my mount to have backlash 

Have a nice week 👍

[Rusted]

Sorry, I missed your interesting post.

Large, professional telescopes of the past had their worms burnished against their wormwheels.

I have tried tension spring loading the worm housing on my 11" [280mm] RA wormwheel.
Sadly, it almost always ends with the stepper motor stalling loudly and unexpectedly.
Perhaps the springs I used were simply too strong! I chose the suspension springs from a scrap washing machine.
Tension was applied via a long screw to allow fine adjustment.

There are serious, potential, mechanical problems to spring loading. No free play of the worm housing in any direction is permissible.
A really solid pivot at one end of the worm housing is probably ideal. Then the worm is pressed into the wheel in an arc.
Which it probably doesn't care about given the very small degree of movement.

Springs do have the advantage of removing errors of concentricity in the wormwheel.
I must try much harder on this problem and find some lighter tension springs.
My 7' long refractor will always find the slightest backlash due to the enormous leverage.

We have now completely left the path of the original thread.