 is moving along its surface line from right to left. This is retro motion.
Finally, the stiction is broken, the contact point moves back to its normal vertical position and the contact point moves away from you as it is supposed to do when the ramp is moved to the right.
Thus, the retro motion is due to the flexing of the Dec gear. This does not happen with the RA gear because of the way it is mounted so it cannot flex. All of the above takes place even if the rest of the mechanical system is perfect. Note that this flexing of the gear cannot take place with a hobbed gear because the hobbed gear is locked into the circumferential surface of the worm.
I hope this works for you while I try to get some diagrams to you in some way. I may have to write a document in word and convert it to html and then transfer it to my web site. That will take me a while.
> situation. Would a brass or a steel gear be better? Could a "stiff"
> plate be attached to the outside of the existing gear to reduce flexing.
> is a true worm wheel?
I am afraid my wording gave a wrong impression. It is not the actual gear that is flexing or distorting. It is the gear moving laterally at its edge because it is "rocking" on the end of the declination shaft. The way the gear is mounted on the 1" declination shaft is a very weak point of the design. The gear is simply placed on the end of the shaft and bolted in place with two small screws. These are the famous screws which have to be heated with a torch to remove them. The gear actually rocks on the end of the shaft because it is impossible to make this joint tight enough with two small screws no matter how tight you make them. The mounting of the gear could be improved by machining it to fit the shaft, adding strength at this point, splining or something like that. This joint is also, by the way, a source of looseness in the coupling between the rotary motion of the gear and the OTA which occurs when the screws work loose or are strained a bit. Many have experienced this problem.
> be a single point, but the angle of the contact would reduced.
Now this is getting into "deep thought." I have not tried the techniques mentioned here. I have my doubts that it would help much. Remember that the worm surface is already, supposedly, at the correct angle to engage the teeth on the gear which are also at an angle. While you do not get the intimate meshing here that you do with a hobbed gear, the two surfaces are at least osculating. I was a bit extreme to call it a point contact. I think an osculating contact would be a better description. So there is a small contact surface and as intimate contact as one can expect in this case. As a consequence changing this angle may do little good. Still this retro-motion effect is so small and depends on details of the contact that you might luck out trying this.
Momentary motion of a star in the opposite direction to the direction that is intended was discussed on MAPUG a number of months ago. Someone coined the term "retrograde backlash" to distinguish the phenomenon from ordinary backlash. As I recall, the exact cause of the problem was never pinned down. I was thinking about the puzzle again while trying to help someone solve a problem with ordinary backlash. I think I know the main culprit and one possible fix.
DEC motion can arise from two different worm motions. The first motion is the one that the LX200 designers would like to be the only motion: rotation of the worm causes the worm's teeth to advance the wormwheel (in that case, the axis of worm rotation and the axis of wormwheel rotation, or the DEC axis, are absolutely rigidly fixed relative to one another EXCEPT for the slight up-and-down motion allowed by the spring-loaded worm carriage). The second motion is the one that causes problems: several different mechanical failures can make it possible for the worm to slide in and out along a line parallel to the DEC axis, so that the angled worm teeth can move the wormwheel without any rotation of the worm (this defective motion follows from the fact that the worm teeth necessarily have a pitch angle).
The main culprits (I suspect) are the bearings in the hinge of the DEC motor assembly. This is the hinge that allows the (normal) slight up-and-down motion of the worm against the wormwheel, loaded by that little coil spring. I have taken the hinge apart, and I found that there are two bearings in it, one at each end of the hinge. Each bearing consists of a steel ball that is gripped by two hardened steel Allen-head set-screws. In the situation I mentioned above, the hinge bearing that is closer to the front of the OTA (the corrector plate end) had become damaged by excessive force on the OTA during transportation of the scope with the DEC axis locked. The person reported that the hinge had noticeable "wobble" in it, and the scope had developed a DEC backlash that made CCD work impossible. After I explained the construction of the hinge, he tightened the one bearing and the scope was as good as new. I think the original bearing set-screws probably had a high spot that had been functioning OK as a bearing surface, but the high spot had been flattened by the unusual force on the OTA, allowing slop in the hinge.
It can be calculated that a tenth of a millimeter slop in the hinge will translate into 180 arc seconds of DEC slop in the sky (backlash or GOTO slop or whatever). People with DEC backlash or slop (retrograde or standard) might check that hinge for tightness: it should have absolutely no slop (but still be freely movable by the slight pressure of the coil spring). If it needs to be tightened, be sure to use an exact-fit Allen wrench in good shape, because the set screw is locktited tightly and a bad-fit wrench would strip the head and then you'd need a machinist or, cheaper, a new DEC assembly. The hinge bearing that is on the end of the hinge that is closer to the eyepiece can be accessed (I think), by removing the two set-screws and the ball from the other bearing first and then inserting the Allen wrench into the resulting hole to get to the head of the hidden Allen screw (the alternative is to gain access to the other side by taking the gear-box apart and removing it, but that can be a scary task, although it is do-able). In the situation above, it was lucky that only the bearing at the more easily accessible end needed to be tightened.
This message is already long, so I won't go into the analysis that says that retrograde DEC backlash (as well as the typical backlash) would also be caused by a loose hinge (or by any other non-rigidity between the axes of the worm and wormwheel apart from that permitted by a well-adjusted hinge).
Both Howard Anderson and I have studied this problem intensively (independently) using laser-pointer reflections from the motor assembly. Some of Howard's comments are posted on his web page. The bottom line for me was that I eliminated retrograde backlash completely simply by unscrewing the motor assembly slightly (two allen-head screws) and then tightening it down again, in almost the very same position it had before I loosened it. It seems that the allowable slop in the mounting holes of the motor assembly had allowed my motor assembly to be located in a position that caused retrograde.
Ric solved this (or a regular backlash, perhaps he will comment further since I can't remember) by removing one of the two springs (on his scope) that push the motor assembly and worm against the wormwheel. It appears that some scopes have two springs there, some (mine being one) have only one spring. So your comment below is right on the mark.
The precise angle and position of the worm relative to the wormwheel, as affected by the slop in the motor-assembly-mount, needed to be optimized in my case. The laser was not really necessary, trial and error in loosening and tightening the two screws would have been sufficient.
Piper is being pessimistic about retrograde being inherent in the design. My scope now has no detectable retrograde, under a variety of loading conditions. I suppose Piper might have meant that, with the design used, it is not possible under production conditions to get the retrograde in all scopes small enough to be unnoticable. I could easily believe that, since it is a very touchy system. But I have the evidence of my own eyes to prove that retrograde can be eliminated, at least on some scopes.
Recently, I describe a more recent finding in a scope that had excessive ordinary DEC backlash. Slop in the motor-assembly forward hinge (induced by banging the locked OTA during transportation) had caused that problem. The owner and I worked by e-mail to diagnose and solve the problem by tightening the hinge allen screw a pinch. I suspect this same hinge may be part of the retrograde problem in some scopes, but I don't have any good evidence yet (no one to my knowledge has tried to fix retrograde by tightening a loose hinge bearing - and, knowing the touchiness of the system, I'm certainly not going to try to prove the point by loosening my scope's hinge). If anyone wants to look into this, the details of the hinge bearing construction are posted in my note a month ago (see preceeding note).
 Its inner face is a cylindrical face that bears down on what looks sort of like the roller-cage of a roller-bearing. Rather than wear (or