On Sun, Aug 1, 2021 at 03:45 AM, Michael Ben-Yehuda wrote:
Under normal operation if the clutch is never released and the relationship between the worm gear and CWD is maintained all the wear on the worm gear occurs on only one side over some portion less than 180 degrees. Over time the condition you report of a 'tight worm' at 180 degrees from CWD? is expected. Normally I would expect no wear on the ring gear anywhere around 180 degrees from what is normally your CWD position. Long period PE and PEC is impacted by absolute ring gear position because of the impact on worm mesh. This is somewhat mitigated by spring loading the worm so it can float in and out to maintain mesh and consistent worm/worm gear pressure.? ?Any shift in the DEC axis relationship to the worm gear by relaxation of the RA clutch will throw off your PEC because the absolute position of the worm gear has changed. Even with spring loading, there will be slight differences.
The problem with the clutched design is that there is no index of the DEC axis (CWD) to the RA ring gear absolute position. .? This destroys the 'sync' for guiding, PEC and backlash along with your worm mesh adjustment.
So, how can we set a consistent 'start position' for the mount that maintains the relationship???
I suggest the following:
Scribe the worm gear along it's top surface where it can be seen with the worm cover off. For some worm gear types where the cover cannot be removed a notched window may need to created to see this mark. The mark needs to be able to be matched to a specific mark on the mount housing at perhaps an existing landmark on he housing (window edge?) .?
Creae an index mark to match the DEC axis position to a known orientation to the mount RA housing. You might need to attach and extend a pointer.??
Although less critical for DEC, a similar situation exists because of the relationship between worm mesh and backlash.?
A similar solution can be applied.
Michael,
Thanks for your comments. Let me comment of a few of the points you raise.
"Under normal operation if the clutch is never released and the relationship between the worm gear and CWD is maintained all the wear on the worm gear occurs on only one side over some portion less than 180 degrees."
If you use SharpCap to polar align your scope you will be loosening off the Ra clutch. I've never seen wear on the ring gear. The G11 ring gear if steel. The worm is brass and this is where the wear will occur. The Dec and Ra axes are different animals. To image objects in the Milkyway like the Lagoon Nebula you will need to rotate the Dec a full 180 degrees in both directions, so it's not like you can used just a portion of the Dec ring gear unless during Galaxy season perhaps.?
"Over time the condition you report of a 'tight worm' at 180 degrees from CWD is expected "
I assume you are making this statement because you expect wear to occur.? Lets assume wear is negligible for a moment. The fact that the Dec shaft can not sit perfectly centered on it's axis because of the needle bearing slop due exacerbated by the weight of the scope. When the clutch is tightened and you rotate the full 180 degrees it is unable to adjust it's position, hence pressure is placed on the ring gear that forces it into the worm at the 180 degree position. Of coarse as one rotates from CDW position this force steadily increases with the degree of rotation. If there was no movement between the shaft and the needle bearings then this problem would not exist.?
"Long period PE and PEC is impacted by absolute ring gear position because of the impact on worm mesh."
Agree.
"This is somewhat mitigated by spring loading the worm so it can float in and out to maintain mesh and consistent worm/worm gear pressure. "
My Ra is spring loaded and I hope that this is the case. Dec is a different animal because backlash impacts guiding. I recommended not spring loading.?
"Any shift in the DEC axis relationship to the worm gear by relaxation of the RA clutch will throw off your PEC because the absolute position of the worm gear has changed. Even with spring loading, there will be slight differences."
True.
As for your idea of indexing the worm position, I feel this might be quite difficult to implement, however I'm fortunate in that my Dec worm is fully visible based on the mods I've made.? Really the right fix is to sort out the needle bearing ID shaft fit problem. I have some ideas on how this might be done and will if successful post a video. It hinges on getting the correct press fit which these bearings do not currently have.
Best,
Peter
