TheSkySearchers

I love my 12" Zhumell Dob, but I've noticed recently that whenever the tube is pointed relatively high in the sky, the azimuth motion has a tendency to stick a bit, and when it's pointed near the zenith, becomes almost unusable. As I usually do, I decided to head to Google and YouTube and see what others had come up with for solutions. There were the usual answers, of course: Ebony star rings (expensive and I'm not sure they're still available), a sheet of Teflon, waxing the rocker box base board, installing a lazy susan, and even cutting out washers made from milk jugs (empty, of course).

As is typical for me, I decided to go the cheapest route first. I happened to have a gallon of milk that I had finished earlier that morning, so quickly cut out a couple of donuts and installed them on top of my bearing ring. Little, if any, improvement. So I put them underneath the bearing ring instead... Still not much improvement.

I was intrigued by the idea of using a lazy susan bearing and had already put it on my shopping list as the next thing to try when I came across a video where a guy just installed some furniture sliders between the ground board and the rocker box baseboard. He had the exact same bearing mechanism as my dob, and the exact same problem and his solution looked to work pretty well, so I crossed the lazy susan off my list and added a few packages of furniture sliders.

I purchased 2 4-packs for $5 each and planned originally to just use 6 of them, but then had the brilliant idea that the 8 spokes on my bearing ring would be perfect for showing me exactly where to place the pads.
You can tell where the ground board has rubbed a bit with the rocker box baseboard. The furniture sliders came with about 1/4 inch of adhesive padding, so the rocker box sits slightly higher and doesn't touch the original bearing ring assembly at all. I just left it attached because I didn't know what else to do with it.

The thumbscrew holding the rocker box to the ground board had plenty of length, so I was able to reuse it.

So, how did it work out? Amazing! There's still some friction (the bottom of the rocker box baseboard is still the original paint/coating), but it's just the right amount. I ran the telescope through its paces last night and even set up in a sloped part of the driveway to see how well it could handle things when it wasn't quite level. The motion is very smooth. I won't say buttery-smooth, because you can't just give the base a spin and watch it go round and round ... as soon as you let go of it, motion stops, but will begin moving again with just a very small amount of force.

I decided to give it a bit more of a test. Dobson's Hole. M57 and M13 were both pretty close to Zenith, so I hunted them down. It was easy enough to get them to show up in the finder, but how easy would it be to get them centered on the target, where you have to move the telescope back and forth along both axes in order to get it to the sweet spot?

As it turned out, it was pretty easy. I let out an audible giggle as M13 slid right into the center of my crosshair and showed up in my eyepiece. As it slowly drifted out of view, I gave the scope a gentle nudge and it snapped right back into the center of the field again. Dobson's Hole was now just a minor inconvenience.

I can't say whether or not this will work for anyone else, but it gave new life to a Dob mount that has been used, abused, and carted all over town on hundreds of outreach events, and it made observing a lot more enjoyable again.

A dob needs to glide smoothly without sticking. It also has to have enough friction to stop where you push it. I’ve heard this balance referred to as “stiction”. Glad your solution works. I have doubts about using a lazy Susan, it might be too prone to rotate easily.

avid.astronomer wrote: ↑Mon Aug 01, 2022 11:33 pm I was intrigued by the idea of using a lazy susan bearing and had already put it on my shopping list as the next thing to try when I came across a video where a guy just installed some furniture sliders between the ground board and the rocker box baseboard. He had the exact same bearing mechanism as my dob, and the exact same problem and his solution looked to work pretty well, so I crossed the lazy susan off my list and added a few packages of furniture sliders.

I was a bit confused by that since your Z12 has a Lazy Susan in Az to begin with. But I see your damage, did the base plate bend as a result of moisture? Nice that you were able to use furniture movers to fix it. My own Z12 is still pristine (well except of course that I cut the tube in half to make it collapsible), and I hope to use it for a long time. It has been trouble-free so far. The bearings of the Z12 are the best around. Enjoy your fixed Z12.

SkyHiker wrote: ↑Tue Aug 02, 2022 1:22 pm

avid.astronomer wrote: ↑Mon Aug 01, 2022 11:33 pm I was intrigued by the idea of using a lazy susan bearing and had already put it on my shopping list as the next thing to try when I came across a video where a guy just installed some furniture sliders between the ground board and the rocker box baseboard. He had the exact same bearing mechanism as my dob, and the exact same problem and his solution looked to work pretty well, so I crossed the lazy susan off my list and added a few packages of furniture sliders.

I was a bit confused by that since your Z12 has a Lazy Susan in Az to begin with. But I see your damage, did the base plate bend as a result of moisture? Nice that you were able to use furniture movers to fix it. My own Z12 is still pristine (well except of course that I cut the tube in half to make it collapsible), and I hope to use it for a long time. It has been trouble-free so far. The bearings of the Z12 are the best around. Enjoy your fixed Z12.

Well, now that you mention it, I suppose it IS a lazy susan. But when I heard the term, I was thinking more along the lines of something like this:
The base plate doesn't appear to be warped, but when I pulled the base apart to look at what was going on, I noticed a couple of screws had worked their way loose on one of the side boards (that held one of the altitude bearings), and that slight imbalance may have been the culprit. I did tighten the screws to see if that would solve the problem on its own, and it didn't. I think there was too much wear in the bearings by this point.