The_bluester
07-01-2019, 11:29 AM
Just thought I would share this one. I decided to lash out after Christmas and buy a new cooled OSC camera, giving one last night with my old Canon 350D.
On that night and the first couple with the new camera I was running into tracking problems, the RA clutch would occasionally slip even when tightened down more than I was happy with mechanically.
Eventually I tracked it down to the design of the clutches in the AZEQ6 which are a completely different arrangement to the EQ6. In the EQ6 the axis are supported on tapered roller bearings like a car wheel bearing, with end play/float set by shimming the bearings for correct tension and spacing of the various parts when the retaining nut is tightened. The clutch appears to be a matter of the worm driving the ring gear which is a large drum, this turns freely inside the mount until you lock the clutch when the clutch drum is locked in place inside the fixed part of the axis so the worm then turns the axis around the now fixed ring gear.
In the AZEQ mount the axis is supported by two needle roller bearings instead of tapered bearings. The driven/ring gear is on a bearing of some description (I did not pull mine down far enough to see what it was, I just pulled the RA and Dec shafts from the housings)
The ring gear turns freely inside the mount and the clutch is now a felt disc between the ring gear and the fixed part of the relevant axis. The retaining nuts on both axis instead of setting up tension in the bearing, are more or less there to keep the shaft from falling out! With the clutches released each axis will have heaps of end play that you won't see on an EQ6. When you tighten the clutch, the end play is removed by pulling the shaft through the fixed housing and bearings, compressing the clutch disc between the fixed part of the housing body and the ring gear.
All good in theory and I can see some advantages, however what I identified as happening to my mount is that as the felt clutch discs have compressed over time, the moving part of each axis (RA most noticeably) has started to foul on fixed parts, making the clutch slip and encouraging you to tighten it further, which compresses the disc even more and increases the friction on the parts fouling, a viscous circle. In the end mine would sometimes just stop tracking but when I pulled the side cover off, the RA worm was still turning happily away.
I am now waiting on some spare parts to replace the clutch discs with new ones having tested the theory by adding heavy paper card shims to pack the thickness of the clutch out and found it to track nicely again. I am going to look at shimming it by adding the new discs when they arrive but leaving the old compressed ones in it, if the secondary encoders still work with the extra spacing, all good.
When I tear it down I might as well go the whole hog and strip it completely and clean the gears etc and set it up with some care/tune it properly. I will take pics as I go as there do not seem to be too many teardown guides for this mount.
If you think it might be happening there is a quick test. If with the locking screws loosened on the setting circles you can turn them freely with the axis clutch released but not with it tightened, welcome to my world! The only sort of teardown guide I have found on these mounts showed clear witness marks on the encoder cover that this was happening to that user too.
TL;DR version.
There is an inherent issue in the clutch design of the AZEQ6 type mount which many users will probably confront sooner or later with clutches slipping. Don't do the clutches up tighter than you need to for good drive and you will get longer before it happens. Your mileage may vary, I consider myself to have lots of mechanical sympathy and purposely avoided going to town on the clutches and it has happened to me after maybe two dozen observing sessions. I have heard of people breaking the RA clutch lever on these!
On that night and the first couple with the new camera I was running into tracking problems, the RA clutch would occasionally slip even when tightened down more than I was happy with mechanically.
Eventually I tracked it down to the design of the clutches in the AZEQ6 which are a completely different arrangement to the EQ6. In the EQ6 the axis are supported on tapered roller bearings like a car wheel bearing, with end play/float set by shimming the bearings for correct tension and spacing of the various parts when the retaining nut is tightened. The clutch appears to be a matter of the worm driving the ring gear which is a large drum, this turns freely inside the mount until you lock the clutch when the clutch drum is locked in place inside the fixed part of the axis so the worm then turns the axis around the now fixed ring gear.
In the AZEQ mount the axis is supported by two needle roller bearings instead of tapered bearings. The driven/ring gear is on a bearing of some description (I did not pull mine down far enough to see what it was, I just pulled the RA and Dec shafts from the housings)
The ring gear turns freely inside the mount and the clutch is now a felt disc between the ring gear and the fixed part of the relevant axis. The retaining nuts on both axis instead of setting up tension in the bearing, are more or less there to keep the shaft from falling out! With the clutches released each axis will have heaps of end play that you won't see on an EQ6. When you tighten the clutch, the end play is removed by pulling the shaft through the fixed housing and bearings, compressing the clutch disc between the fixed part of the housing body and the ring gear.
All good in theory and I can see some advantages, however what I identified as happening to my mount is that as the felt clutch discs have compressed over time, the moving part of each axis (RA most noticeably) has started to foul on fixed parts, making the clutch slip and encouraging you to tighten it further, which compresses the disc even more and increases the friction on the parts fouling, a viscous circle. In the end mine would sometimes just stop tracking but when I pulled the side cover off, the RA worm was still turning happily away.
I am now waiting on some spare parts to replace the clutch discs with new ones having tested the theory by adding heavy paper card shims to pack the thickness of the clutch out and found it to track nicely again. I am going to look at shimming it by adding the new discs when they arrive but leaving the old compressed ones in it, if the secondary encoders still work with the extra spacing, all good.
When I tear it down I might as well go the whole hog and strip it completely and clean the gears etc and set it up with some care/tune it properly. I will take pics as I go as there do not seem to be too many teardown guides for this mount.
If you think it might be happening there is a quick test. If with the locking screws loosened on the setting circles you can turn them freely with the axis clutch released but not with it tightened, welcome to my world! The only sort of teardown guide I have found on these mounts showed clear witness marks on the encoder cover that this was happening to that user too.
TL;DR version.
There is an inherent issue in the clutch design of the AZEQ6 type mount which many users will probably confront sooner or later with clutches slipping. Don't do the clutches up tighter than you need to for good drive and you will get longer before it happens. Your mileage may vary, I consider myself to have lots of mechanical sympathy and purposely avoided going to town on the clutches and it has happened to me after maybe two dozen observing sessions. I have heard of people breaking the RA clutch lever on these!