Let's get rid of the BL on the HEQ5 mount! A very simple way to do it.

[cuivenion]

Hi, yes I meant the main gear that meshes with the worm. vlaiv gave a good explanation in an earlier post.

[teoria_del_big_bang]

6 minutes ago, cuivenion said:

Hi, yes I meant the main gear that meshes with the worm. vlaiv gave a good explanation in an earlier post.

Thought so, then this is the error the modification should address, all being well.

Steve

[benzomobile]

2 hours ago, SpookyKatt said:

Many thanks for this thread, its interesting and the video is useful in explaining the final proposed operation.
I'd have thought the first step in removing the backlash would still have been to do a belt mod, are you going
to do one as well to the mount as there is still a source for backlash between the gears between the motor
and worm ?

Kathleen  

Hi Kathleen.

In reality the backlash due to the small gears  before the worm gear coupling is not so significant.

On the other hand, the complicated combination of eccentricity and irregularity of those gears tends to produce  a PE that is not easily correctable as it is almost unpredictable, so we cannot  counterbalance it by an easy PEC algorithm.

The most important backlash is that produced by the worm gear. My modification is effective in eliminating it, no matter if the large worm gear has eccentricity.

This mod - as Vlaiv correctly wrote - is based on a worm gear floating contact produced by the spring. 

Spring pressure force does not change at all, because  the eccentricity-related gear deviations remain within very small phisical limits (a tenth of a millimetre range). 

It is  absolutely irrelevant  in the sense of a pressure change  between the W/G  coupling.   This problem unfortunately occurs with tuning screws.

 

Edited April 8, 2021 by benzomobile

[SpookyKatt]

Hi Benzomobile,

Ah ok, thanks for that, I get the benefit of the floating worm and how that resolves eccentricity, but had just wondered
about the effect of the rest of the gearing.  A nice solution though I have to say.

Kathleen

[benzomobile]

22 minutes ago, SpookyKatt said:

Hi Benzomobile,

Ah ok, thanks for that, I get the benefit of the floating worm and how that resolves eccentricity, but had just wondered
about the effect of the rest of the gearing.  A nice solution though I have to say.

Kathleen

For both BL and PE,  belts & gears transmission  is  a pretty good  solution, but  'no gear/no belt'  one, i.e. the direct friction, or harmonic design (this one is very expensive!) are absolutely the best ones 🙂

Beppe

[benzomobile]

Hello to all, girls and boys  🙂

Now it's time to deal with:

Tuning  and everything else ...

You need:
- some wooden toothpicks (yes, you read that right!)                                                                                                                                                                                                                                                                                               

- always the same Uhu Plus resin (heaven bless it)                                                                                                                                                                                                                                                                                                           

- 6 hex M5 x 30mm stainless bolts shorter than the current ones
- 6 M5 x 5mm stainless grubs  (see pics below - note that I have removed the worm assy so that everything is clearer) 

                               

 

As I said before, the worm holder bolts should not be tightened. Why?  The worm assy does not need to be tightened on its bearing surface, BUT it does need to be able to slide smoothly on it, permitting only a little gap beetwin each other.
As you will see, the places where the bolts are inserted are wider than the bolts themselves. This is why the bolts - when not tightened,  allow the worm assy to move (it traslate) about one millimetre in each direction.           

It is of interest to us that this translation  occurs in one direction only, and this direction is exactly perpendicular to the worm mechanical axis. 
Now let's see how to force the worm to move in that direction ONLY  to mesh gear  in FLOATING mode and  in the best possible way.
We need to adjust the bolts in a stable manner, build the pivots and adjust these as well.

 

1) adjusting the bolts

You need to insert the three short  M5 grub in the bolt screws. 

After epoxy resin  melting,   place a small amount of it  on the tip of a toothpick, taking care not to touch the walls of the three threads on the base of the RA axis block.                                                                                        

You must deposit the resin on the deepest part of the threads (5-6 mm from the bottom). It is necessary to repeat this operation several times so that the resin is evenly spread where I have told you. 
Having done this, first screw the grubs into their seats until they get smeared with resin too, then unscrew them by 4-5mm.                                                                                                                                                               

Don't worry about the grubs sticking straight away as it takes at least three hours for the resin to cure a little. The grubs serve as a stop for the bolts so that they can be fully screwed in, while still allowing the worm assy to slide over the underlying bearing surface without excessive gap (half a mm is ok).  When you screw the bolts over the grubs and all is ok, please, do not tight these, for now. 

After epoxy get cured, only then you can do tight the bolts to complete the final assembly. 

I understand well this operation is the most tedious, but it is also the most delicate to reach a  successful mod.

You will have to do a few attempts to get each grub placed at the correct depth.                                                                                                                                                                                                                                     

If the  worm assy gets stuck or slides unevenly, you will have to pull up the grubs (always one at a time). Otherwise you will need to push them deeper. This is fine tuning, so try screwing (or unscrewing) in the grubs just half a turn at a time.

Have fun ... like I did 🙂

The story will continue soon.

Beppe                   

Edited April 9, 2021 by benzomobile

[benzomobile]

Penultimate episode

2) placing and adjusting the pivot.

The below clip illustrate how pivot work 

        

 

Edited April 10, 2021 by benzomobile

[benzomobile]

The hole on the holder is of necessity larger as the rod, why?   

That's because the rod must be inclined in the best direction before it can be fixed in place.  This 'trick' is essential so that the worm holder's play can be minimised. 

Let's see how to proceed  (pics below refer to Dec axis)

             

Degrease (alcohol or acetone are ok) both the stainless steel bushing and the bare metal area around the hole.

Apply a thin layer of mixed epoxy resin  all around the hole up to about one millimetre from its edges (no resin should get inside).  
Apply a very thin film of lubricant along the rod. Insert the rod into the bushing to make the pin and leave the grub loose.
Once this is done, insert the pin into the hole as far as it will go and then retract it about one millimetre. Now tighten the bushing grub.
Place the second bushing on top of the rod anf tighten its grub.
Levering your thumb over  the outer bushing, while keeping your index and middle finger on the worm holder (do not apply any force on another part of the mount body!), try to tilt the pin sideways in every direction while simultaneously rotating the worm  between the thumb and index of your other hand. 
You will find that in a particular position, the worm will spin smoothly and without backlash.

Well, now you're where you need to be! Use a rubber band to hold the plug in that position until the resin get hard enough (see pics above middle and right).
When the time comes, remove the rubber band and add every two to three hours just a little bit of resin (if it's too much, it drips!) all around the inner bushing base and border (but stay away from the grub!),  until it forms a small block like in the photo below left.  When epoxy cured, you can remove the grub.  The pin can then be pulled out to check that it is not stuck and then repositioned (see pics below, middle and right)

                                              

 

After you've correctly insert RA axle bar/gear smooth part inside the RA block (please do lubricate well these parts and don't forget the washer), 
do set the lower conical bearing and screw the large lock nut, the RA graticule ring and the polar scope carrier ring. Mod on RA axle is done. Don't forget to tight all grubs.

Do the all above operations on both axes.

When eventually Dec axis adjusting task is completed too, you can slip its bar/gear smooth parts (do lubricate!) inside their seat (don't forget the washer). 
Do set conical bearing and screw the counterweight collar. Do insert the counterweight shaft before the dovetail carrier.  Do tight all grubs.

Finally, I must tell you about the modification of the socket panel.
See you soon

 

 

 

 

 

 

Edited April 10, 2021 by benzomobile