1/8 " LX80 Play in AZ axis acceptable?
Posted 10 December 2012 - 05:52 PM
Posted 10 December 2012 - 06:00 PM
I believe Meade spring-loads many of their systems, so play may simply be forceful compressing of the spring/worm. My LX90 will give if you push it in one direction, but it comes back. It has no discernible effect during tracking.
You really need to have followed all of the trials and tribulations of the LX80 to understand the problem with this mount and how it is different from normal spring mounted worms. The LX90 works, the LX80 does not work with the rated loads.
Posted 10 December 2012 - 11:22 PM
Posted 10 December 2012 - 11:41 PM
Without seeing it, everyone is just guessing.
Pretty much everyone who has loaded up an LX80 has seen it (consistently) .
The earlier threads posted pictures of the worm itself and the carrier.
These photos clearly show the mechanism, and where the errors can come from.
The worm itself is closer to a 60deg thread profile than a true worm.
As such it can spring out of mesh much more easily when under load,
and it also has a lot less play before it disengages.
To counter this, Meades worm carrier uses a much stronger spring than in any of its other scopes to push the worm in, but it also uses a backing screw to stop the worm from being pushed "into" the wormwheel too hard. I personally have not seen any other worm carriers with this secondary backing screw.
Soo, there are two immediate sources of slop.
If the secondary screw is set too tight, it will prevent the worm and wormwheel from fully engaging, hence you will see slop under no load at all.
If that screw is adjusted correctly, such that the worm and wormwheel are always in contact, then the play seen can still occur "under load", as the worm springs out.
It also is dependent on how concentric the wormwheel is when the clutches are tightened, as if there is any eccentricity there, the meshing loads will change as the axis rotates.
It doesnt look like a very easy system to set up correctly.
Posted 11 December 2012 - 12:00 AM
Posted 11 December 2012 - 12:55 AM
How did you measure the gear face of the worm? I've always found that difficult.
Macro photography and a good guess in paintshop .
I took piccies of the worms from an LX200GPS, and LX90, an LS and an ETX-125, and compared them to pictures of the worm profiles provided by several members here who took their mounts apart trying to fix the slop.
Have reposted it here as i cant find the old posts.
The piccy with the thread gauge gives a very good idea of the LX80 profile.
Posted 11 December 2012 - 01:23 AM
Looking at the piccy,
to properly adjust the mechanism, you need to
a) Back out the backstop screw
Adjust the Spring tensioner screw till you get approx the correct preload ( you have to guess )
c) Adjust the new "Frontstop screw such that the worm doesnt get "jammed" into the wormwheel under the high preload, but is close
d) Readjust then c) iteratively if reqd.
e) Once happy, screw in the backstop so that the worm cant disengage under load.
Now, unlike the other springloaded Meade worms, the new frontstop screw comes into play here.
Too tight and the worm wont engage, hence you get slop under no load. Too loose and the worm grinds into the wormwheel and judders etc.
Not a simple adjustment to do, and have it maintain its setting, esp as the wormwheel readjusts itself as the clutch is released.
Adjusted properly, it will work well for light loads, but experience to date appears to show that under load, the spring isnt strong enough to keep the new worm profile engaged.
Posted 11 December 2012 - 01:33 AM
After all this time I had been thinking. There might be a way to fix this problem but it would require some modification.
The small arm that the spring pushes against has a screw going through the middle of the spring. when you tighten the screw it limits the amount the worm can disengage. This works good with a small light ota but if you use something like my 9.25 weighing 20lbs it doesn't work. The arm the spring pushes against is thin and long enough that it can bend like a spring. When I tightened the screw going all the way through the spring to limit the worm from disengaging the arm flexed and the worm disengaged anyways. And very easily because the leverage from the worms angle was too great.
If you were able to make a stronger, thicker arm that wouldn't flex like a spring at all. Then you might be able to adjust the screw to not allow the worm to disengage at all, or very little. And the spring would keep pressure on the worm. You would have to adjust that screw just right.
This is only a theory and I have not thought this out or tested it in any way. I remember tightening that screw all the way and watching that little arm moving. On the first mount the arm actually bent when I tried it.
I remember thinking that wouldn't work because I thought the worm disengaged to protect the plastic gears during starts and stops. I think you proved me wrong on that theory, but I never thought to go back and make a solid arm and try it out. Too bad I don't have that mount anymore or I would try it. That arm was only held on by 2 very small screws.
I was writing this before your picture above but now you can see what I am talking about. Another note is if you adjust any of those screws you should apply some loctite on the adjustment screws or they will unscrew, especially the new front stop screw. If you don't have any than clean the screw with alcohol and put a drop of super glue works as a last resort.
Posted 11 December 2012 - 02:29 AM
After all this time I had been thinking.
Did it hurt??
My personal opinion is that a stronger arm as you note wont help,
as you shouldnt need the sort of preloads required to stop the
worm springing out in the first place.
All the other springloaded Meade drives use tiny springs relative to the LX80.
What is required is a drive that can apply ( or resist ) a high tangential load to/from the wormwheel for a minimal radial load pushing the worm outwards.
To do that requires a worm with a low pressure angle.
Its just a basic mechanical equation of balancing forces.
Posted 12 December 2012 - 12:31 AM
Posted 12 December 2012 - 01:17 AM
Whilst i agree that changing the worm is required to give
a more rigid system re RA slop, i still cant help wondering
how much flexure ( and hence springiness ) there will be in the base
when polar, due to the way the RA axle is mounted.
It is effectively a cantilevered beam bolted to a flat plate.
I really think this whole mount design is limited to low payloads
when polar, no matter what worm design is in it.
Posted 12 December 2012 - 11:58 AM
Posted 17 January 2013 - 10:11 PM