Making a heavy dob base more manageable: divide and conquer!

The problem

I’ve had my 10-inch solid tube Dobsonian telescope, a Hardin "Deep Space Hunter" made by Guan Sheng Optical (GSO), for 20 years now and it has served me well. In fact, it’s doing better than my own body at this point. I’ve found it harder to load it in and out of the car to get to my darker sky sites. I needed to make it easier.

The solution

I can’t do much about the tube, which weighs about 32 lbs., but a post on Cloudy Nights got the neurons firing in my brain. It showed what one amateur astronomer did with the base of his 12-inch, and I decided to try it on my 10-inch.

The base is made of particle board and weighs about 38 lbs. It's heavy and awkward to get into the car. What if I could split it into two pieces that could be easily reassembled? That’s the idea, and it works! I separated the two round ground boards as one section, actually the round bottom of the rocker box and the ground board, from the rocker box as the other section. These are shown in the pink boxes below. These two sections were originally put together with six long wood screws coming up from underneath the rocker box bottom and into the bottom edges of the rocker box (indicated by the blue arrow below). The pink boxes denote the sections that would be separated:

 

To reassemble the two sections, I bolted two aluminum angles to the inside of each side of the rocker box and fastened them to the round rocker box bottom with four knobs inserted into holes drilled in the horizontal leg of each angle and screwed into t-nuts inserted in the underside of the rocker box bottom.

Inside the rocker box, showing the first angle
fully assembled. The knobs will be used to disassemble
 and reassemble the base.

The outside of the rocker box, showing the
bolts holding the angle. These will stay put.

The whole project took one afternoon, and was only complicated by the fact that I had replaced the original “lazy Susan” azimuth bearing (as shown in the diagram above) with Teflon pads riding on Ebony Star Formica (alas, no longer available). The pads would be in the way of the holes for the knobs, so I had to relocate them closer to the center. Telescope makers will tell you the pads should be located directly over the feet, but I found that in this scope it caused too much friction, so I had located the pads about a third of the way in from the edges, and the azimuth bearing was a lot smoother. Moving them further in would be pushing it, but it actually moves even more smoothly now.

The base is now easy to disassemble and reassemble.

Fully assembled. (The scope sits on a plywood
 dolly I made to make it easy to roll out on the
 driveway when I set up my Redneck Observatory.)

The rocker box now fits around
the tube in the car, saving much-
needed space.

How to do it

If you try this at home, think carefully about where you will put all the holes and measure everything precisely. I had to dodge the holes in the rocker sides from the original wood screws, make sure the knobs didn’t intersect with the circular path of the Teflon pads, avoid a pipe that I installed that holds a swivel table, and leave room to turn the knobs. It was a tight fit, but it works.

The tools and materials I used:

Materials (links to the ones I used):

Two aluminum angles, 1/4” thick, 2” legs (that turned out to be 1-3/4” in reality), and 12” lengths (that were actually 11-5/8”, although they were 1/4" thick, as advertised).

Four male knobs with 1” 1/4-20 threads. (3/4” might have been better- fewer turns needed as long as they reached the threads of the t-nuts.)

Four t-nuts (1/4-20 x 7/16 length); epoxy 

Eight 1-1/2" 1/4-20 bolts, eight 1/4-20 nylon lock nuts, 24 1/4” ID - 3/4” OD flat washers

Tools:

Cordless drill with 1/16”, 1/4”, and 5/16” drill bits, and one 3/4” Forstner bit

Hammer and short thick rusty bolt for hammering in the t-nuts below flush

Two 6” quick-release clamps

Metal file and sandpaper to round the sharp edges of the aluminum angles.

Hand vacuum to keep the aluminum shavings from getting everywhere

Process (for my particular dob, but most should be similar):

Caution! Aluminum angle edges may be extremely sharp. File and sand them before working with them.

Measure and plan where you are going to position the angles and drill all the holes. Do it a few times and set the angles, bolts, and nuts in position to see if there will be any issues before you start drilling. Mark the drill points clearly in pencil on the angles.

Disassemble and then reassemble the rocker box and round rocker box bottom, leaving the round ground board off. You will need to drill in the botton of the round rocker box bottom piece.

Cut the angles if needed (with a metal hacksaw), file any sharp edges that will be exposed, and clamp to the rocker box sides. In my case, there is a front stiffener board that precluded clamping on that end, so I found a piece of wood that fit tightly inside between the two angles that kept the front ends pressed against the sides. Improvise as needed.

I found it easier to do one side first, then the other.

Using a small drill bit, 1/16” or so, drill pilot holes for the two knobs from above, through the angle and the round rocker box bottom. (I did each hole one at a time.) You need to keep these holes small because the Forstner bit you will use to inset the t-nuts on the underside of the rocker box bottom needs to be able to center and it can’t do so with a larger hole drilled through.

Turn the assembly on its side and use the 3/4” Forstner bit to inset the two holes about 1/8”. This ensures that the t-nuts won’t stick out and scrape the ground board surface. I found later that the t-nuts don't hold well in the particle board, only an issue when the base is disassembled, so I epoxied them in.

T-nut epoxied and hammered into place on the
underside of the rocker box bottom. Note the
1/8" recess cut using a 3/4" Forstner bit.

Turn the assembly upright again and drill out the two holes with a 1/4” bit, all the way through.

Turn the assembly on its side again and widen the centers of the t-nut insets with a 5/16” bit.

Hammer a t-nut partially in, then fit the knob from the other side and make sure they meet up properly and there is no binding. I had to use the Forstner bit to widen the sides for several of the holes due to, ahem, user error, but got them all working. Once they line up, coat them with epoxy, being careful not to get any into the threaded tube, and hammer the t-nuts all the way in so they are below the level of the bearing surface.

Turn the assembly upright again and once both knob holes are drilled, screw in the knobs tightly.

With the sides still clamped/braced to the angles, drill small (1/6”) pilot holes horizontally through the angles and the sides from inside (aluminum first) to outside. Widen the holes with a 1/4” bit and insert the bolts from the outside with flat washers and put the nylon lock nuts with flat washers on the inside (aluminum surface).

Before assembling the base to the ground board, a little trick for Teflon bearings is to rub a bar of soap on the bearing surface that contacts the Teflon to give it a little more smoothness.

Once you are done, remove the original wood screws holding the rocker box to the ground boards, assemble the base with the knobs, and test the fully assembled telescope for function.

Now when you have to transport the telescope, you only have four knobs to separate and reassemble the two parts of the base, which is no longer a heavy, ungainly bulk. In fact, you should be able to cradle the rocker box around the bottom of the tube to save space in your vehicle, as in the image above.

What if you want a 10-inch solid tube dob, but don't want to mess with this mod?

All dobs are not created equal. If you are in the market for a lighter weight basic Dobsonian, consider the Orion Sky Quest series. Now that they are apparently made by Jinghua Optical Corporation (JOC), they are even lighter than the Synta-made scopes, and are the lightest mass-produced solid tube basic dobs I have come across. For example, the XT 10 has a 24.2 lb. tube, a 21.5 lb base, for a total of 46 lbs. In contrast, an Apertura AD10, made by Guan Sheng Optical (GSO), has a 34.8 lb. tube, a 31.4 lb. base, for a total of 66.2 lbs., a difference of 20.2 lbs. for the same size aperture! [7-12-24 update: Orion's parent company has closed up, so Orion may not be around much longer. If you're interested, make your decision quickly. 7-19-24 update: Looks like Orion is belly up. Maybe another company will supply the XT10s under a different name??]