Zhumell Azimuth Axis Improvements

The newer Zhumell Dobsonian models come with a roller bearing setup for the azimuth axis. This roller bearing setup is comprised of the top and bottom sections of a lazy susan, with two bearing plates and the bearing retainer between them. Although this gives an incredibly smooth azimuth motion, some people, including myself, find this too smooth. Sometimes just a slight breeze can blow the telescope off target; a real pain at high magnification. This mod is a two-fold mod, however. While I had the base apart, I also replaced the problematic center bolt. The center bolt is held on by a nylon lock-nut, but it doesn't seem to lock very well. This is how I fixed both.


This picture shows the disassembled turntable base. To add a little friction, and stiffen up the azimuth axis, I added four 2" long pieces of Velcro to the bottom half of the turntable. The Velcro was not tall enough to touch the top half of the turntable when assembled, so I simply stuck two pieces on top of each other, a sort of Velcro sandwich.


This picture shows both the old center pin setup and the new parts, which I bought at Lowe's. The bolt in the old setup would frequently come loose after a night of observing, and when I went to pick up the base, the two halves would come apart, sending the bearing plates flying. Make sure to take the old setup with you so you can get the right size pins!


Insert the new pin just like the old bolt, with the stock washers installed in the same manner. Then simply put the retainer pin through and you're done! No more loose nuts!


Here you can see, from the bottom, the new retaining pin. Putting the pin on the bottom is nice, because from the top, all you can see is a round silver button where the bolt used to be.

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A Map Pocket For Your Telescope

Have you ever wanted a nice way to hold your various star maps and astronomical books at the telescope? I thought of getting a little table for this, but the problem there is that as you slew your telescope around on its base, you might hit this table, or the table will become out of reach. I have a large table near where I observe, but sometimes its a pain to need to go over to the table to get a map, especially if you're using high magnification. After going over to the table, you'll need to find your target again. My solution was to make a map pocket for my telescope.


I made this map pocket using a "wall pocket" from Office Max. I got the metal mesh type so that it would be a little more durable than plastic. I figured the mesh would be better to keep dew off of my maps than smooth plastic. Here you can see a copy of Turn Left at Orion, a logbook, and a folder full of Telrad maps. I had to use shorter self-tapping screws than the ones the pocket came with, because the provided screws were longer than the base's wood is wide. So I just got some self-tapping screws of the same size, but shorter. I then drilled a small pilot hole and screwed it all together. Notice that on the Zhumell 10" Dob, the map pocket fits nicely under the eyepieces. On smaller models, it may be necessary to relocate the eyepiece rack. Should be pretty handy when using the scope!

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Zhumell Mod: Balance your OTA

Now that you've got that big aperture Dobsonian and all the accessories to go with it, does it still balance in its base? This was the problem I encountered once I attached my Telrad to the OTA. I realized that with the extra weight of the Telrad and my biggest eyepiece, the OTA wouldn't stay still if I put the telescope under 45 degrees altitude. This is a problem, but fortunately, one easily dealt with. Of course, one could just get stiffer altitude springs, or use Scope-Gripps, but that just works around the problem. I decided to actually fix it by adding a counterweight to the rear of the OTA. This is how I made my counterweight:

1. Remove everything from the scope that did not come preinstalled. This included removing the Telrad from its base and no eyepiece in the focuser for me. Take these items (use your heaviest eyepiece for this) and weigh them. I used a kitchen scale. If you can't use a scale, my Telrad and 32mm wide-field eyepiece were approximately 1.25 pounds. Your mileage may vary.
   
   
2. Okay, now we know that we need to balance out 1.25 pounds. Problem is, the business end of the OTA is longer than the mirror cell end, so it won't simply be 1.25 pounds of counterweight. To figure out how much weight you need, use this formula: Multiply the weight of these accessories by the length from the altitude bearing center to the tip of the OTA. This is the amount of torque that these accessories exert, and we need to counter this. Divide this torque number by the length from the center of the altitude bearing to the mirror cell. This will give you the weight you need to counterbalance your telescope. Mine came out to 2.34 pounds with a Telrad and big eyepiece on a 10" Zhumell.
   
   
3. I went to Wal-Mart and got this running pack and a 2 pound dumbbell. I figured that was close enough to the 2.34 pounds I needed. The nice thing about this pack is that it has a hole for iPod headphones. This works great, because it lets you put the battery pack for your cooling fan in there, too. Just feed the wire out the hole, and plug it in to the port on the mirror cell.
   
   
   
4. Then just strap the pack around the end of the OTA, making sure it is good and snug, and you're ready to observe without the OTA sagging near horizon!
   
   

Disclaimer: I cannot take any responsibility for any damages, to you or to your property, occuring before, during, or after performing this telescope mod or resulting from any advice taken from this website. Do so at your own risk.

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Zhumell Mod: OTA Knob

When I first got my Zhumell 10" Dobsonian, I pointed and moved it by grabbing the end of the optical tube assembly. While this works, it can sometimes be hard to operate the scope like this. So I decided to add a knob onto the end of the OTA. This is a pretty common mod, actually. The advantage of having an OTA knob is that it is a consistent place to control the scope from. It will help you learn to operate your Dobsonian more consistenly, by placing your hand always in the same spot.

First, unscrew one of the screws at the end of the OTA. Then, go to the hardware store and buy a cabinet knob. Any knob will do, but I bought a black porcelain one to match the telescope. Check to make sure the screw it comes with is the same size and thread pitch as the ones from the end of the OTA (The screw is reportedly a metric M4/0.7). Taking the small OTA screw to the hardware store will help you determine this fit.

Cut the head off of the screw that came with the knob, and use a small nut to secure this newly made stud into the end of the OTA, where you removed the screw earlier. The nut could be purchased at the hardware store, I just had some laying around the garage.


Now simply screw the knob onto the stud and you've got an OTA knob!

Disclaimer: I cannot take any responsibility for any damages, to you or to your property, occuring before, during, or after performing this telescope mod or resulting from any advice taken from this website. Do so at your own risk.


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Zhumell Mod: Telrad Finder

The Telrad finder is what's known as a "reflex" finder. This means that when you look through the finder, the sky is not magnified. It works much like a red dot scope for a rifle or a jet fighter's heads-up display, and projects three concentric rings on the sky. The rings are 0.5, 2, and 4 degrees wide, respectively. This can be useful as a star-hopping tool, when using the Telrad maps. Every telescope, big or small, should be equipped with a Telrad in addition to a good finderscope. The Telrad gets you "in the ballpark" with a correct image (i.e. up is up, down is down) and no magnification. As many experienced astronomers know, the Telrad is more of a necessity than an accessory.


The Telrad mounts to the telescope using a supplied base. It is then mounted to the OTA (Optical Tube Assembly) using supplied double-sided sticky tape. This stuff is permanent once installed, so choose a good location. Extra bases are available, so sharing a Telrad between two scopes is possible. The best spot I could find on the Zhumell is shown above. Some people notch the base and put the Telrad between the finderscope and the focuser, but I believe that breath from your nose could fog the Telrad while using the finderscope.


Note the three concentric circles. The three knobs on the Telrad, visible here, are for aiming the Telrad, just like you would for your finderscope. If you sight your Telrad in well enough, when you put an object in the center of the Telrad sight, it should be mostly centered in your eyepiece.

The Telrad is one of the best finder solutions on the market currently. It is simple, relatively cheap, and makes locating objects via starhopping much, much easier. Try one and you'll be hooked!

Disclaimer: I cannot take any responsibility for any damages, to you or to your property, occuring before, during, or after performing this telescope mod or resulting from any advice taken from this website. Do so at your own risk.

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Zhumell Mod: Tension Springs

The Zhumell Dobsonian line of telescopes uses a spring system to add tension to the altitude bearings. The springs pull down on a bolt that holds the telescope firmly in its cradle. The more tension on these springs, the more "stiction" the altitude movement has. This can help if you have a heavy eyepiece or Barlow. Heavy springs, however, can be difficult to attach in the field. One could use lighter springs, but then you would lose tension.

A good compromise is to use a short spring that is just as stiff as the stock springs, and use a clip to attach the springs. This mod can be done using parts from your local hardware store and the setup I came up with for my 10" Zhumell cost me less than $10 at Lowe's. Lemme tell you, it makes a world of a difference when assembling the telescope!

This is what you'll need:

• 1" welded ring (Quantity: 2) -- $0.47 each at Lowe's
  
• 3-13/32" brass double-ended bolt snap (Quantity: 2) -- $1.67 each at Lowe's
  
• 5/8" x 2-1/2" x 0.072" extension spring (Quantity: 1 bag) -- $3.47 at Lowe's
  

Once you have the pieces, this is how to put it together:

1. First, remove the stock springs and the posts which they attach to.
   
   
2. Put the welded ring on the top post. Put the ring on, then the spacer. It will not fit over the knob. This is an intentional safety feature, so your springs cannot fly off and whack your expensive 2" eyepiece in the eyepiece rack.
   
   
3. Next, put the spring onto the bottom post. The spring will not fit over the washer, you'll have to put the washer on, then the spring, then the spacer. Again, just a safety feature. You shouldn't need to remove the spring or the welded ring ever again. Then clip the double-ended bolt snap to the spring.
   
   
4. Reinstall the posts onto the telescope. Once the posts are back on the telescope, simply grab the double-ended snap, and hook it onto the welded ring like this:
   
   

Now you can easily hook up your tension springs, while only sacrificing a tiny amount of tension. I find that with my 32mm "hand grenade" eyepiece, I still have no problems needing more tension. It seems to be just like stock for me. But now you won't have to worry about flying springs and pinched palms!

This should also work on any telescope that uses a spring based tension system. I believe Orion uses a similar system. If the telescope is any other than a Zhumell 10" Dobsonian, you may need to experiment with different spring sizes.

Disclaimer: I cannot take any responsibility for any damages, to you or to your property, occuring before, during, or after performing this telescope mod or resulting from any advice taken from this website. Do so at your own risk.

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Zhumell Mod: Fix Altitude Bearing Nuts

Zhumell Dobsonian telescopes' altitude bearings are attached to the OTA (Optical Tube Assembly) by two bolts on each bearing. These bolts, however, do not have lock washers on them, and they frequently come loose, sometimes after only a night of observing. This can be frustrating and even dangerous if one of these nuts were to fall onto your primary mirror.

The solution to this of course is to add lock washers or Loc-Tite, whichever you prefer. I preferred both, so I used both. I don't plan on ever needing to remove these bolts. This is a really simple mod, and can be accomplished in less than an hour and costs nearly nothing.

1. Start by marking the tube and mirror cell with a Sharpie pen. This will ensure that when you reassemble the OTA, you will get the mirror cell back in exactly the way it came out.
   
   
2. Next, unscrew the screws at the bottom of the OTA. These hold in the mirror cell, so be careful. Once you unscrew them all, VERY carefully lift the OTA away from the mirror cell. You don't want to nick your primary mirror with the OTA.
   
   
3. This is the altitude bearing. Note the bolt I left sitting out a little bit. These are the bolts you need to remove. Once you've removed these, the altitude bearing will come off. Note on the inside of the tube, the lack of lock washers.
   
   
4. Okay, now that you've got the bolts out, simply add a lock washer in place of the stock washers. These lock washer can be found at any hardware store, such as Lowe's or Home Depot. Bring the bolt with you so you can properly size the lock washer. I had these laying around in the garage, so I didn't need to buy them. Don't put the stock washers in there with the lock washers, as that would defeat the purpose of the lock washer. You may also add some Loc-Tite to the nut if you'd like, but you'll have to wait for the Loc-Tite to dry before reinstalling the primary mirror cell. You don't want Loc-Tite to drip onto your mirror, and Loc-Tite can take a while to dry.
   
   
5. Now, reinstall the altitude bearings in the reverse order you removed them. Tighten the bolts, but don't overtighten them. This could distort your OTA. "Snug" is good enough here.
   
   
6. Reinstall the OTA onto the mirror cell, noting the marks you made in step 1 (you did do step 1, right?) Take the utmost of care not to bump your mirror with the OTA. This would be catastrophic at best. Then reinstall the mirror cell screws, and you're good to go!

This should take care of your wobbly altitude bearing problems on any Zhumell Dobsonian. The telescope shown here is a Zhumell 10" Dobsonian.

Disclaimer: I cannot take any responsibility for any damages, to you or to your property, occuring before, during, or after performing this telescope mod or resulting from any advice taken from this website. Do so at your own risk.

Clear skies!

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