6 inch dob telescope
6
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The Builder
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Building a
Telescope:
Intro
Tube
Rocker Box
Base
Mirror Cell
Secondary Holder
Focuser
Finishing

Other projects:
Folding Table
Denver
Observing Chair

Aluminum
Observing Chair

Bino Chair
Portable
Observatory

Adirondack Chair
Josh's Stool

Resources:
My Buddy Shane
Chuck Fellows
Newt Software
Siebert Optics
Orion Telescopes

Building the Coopered Tube

Why build a coopered tube for the scope? I looks cool and blew me away when I saw Shane's. To see some really outstanding scopes built this way by a real craftsman check out Chuck Fellows' website. Follow the custom telescope link and check out his work. He has complete instructions on his site for calculating the tube. NOTE: you must have already calculated what you need your tube diameter and length to be before beginning this step. I used Newt Software and a lot of help from Shane to figure this out.

You will quickly discover when playing with the math to figure the angles to cut on your slats that it is difficult to come up with a slat width that give exact angles to equal 360 degrees. I did not get perfect but the glue filled the gaps and the tube is very strong. HOWEVER, I could not sand the tube completely round because if the wood does not fit tight you will expose glue at your seams and glue does not accept stain. Turns out I really like the tube with its' slightly ribbed feel, adds character.

I used oak and poplar from Lowe's for the wood slats. Purchased in 1/4" x 6" x 48" stock, I divided the width of the stock by the number of pieces I could get out of it and then cut it into seperate strips with the first angle cut. Be sure and leave enough waste width on your cut strips to make your second pass putting the final angle on with enough drop to be able to control your piece while cutting.

Be sure and cut all of your base stock very carefully to the same length before you start ripping them. They vary in length from the lumber yard and as you can see in a later picture it will give you differing lenght ends on your tube. i sanded them down with a drum sander using a combination square for refference and then my rings covered them up.

Coopered Tube Telescope
The basic wood material used for this telescope. Two 18" laminated ponderosa pine table tops, 1/4" x 6" x 48" poplar and oak, 3/4" x 12" x 24" oak plank all purchased at Lowe's. The table tops make the base and azimuth joint. The 1/4" poplar and oak are used for the tube slats. The oak plank is for the various parts of the base. Not shown is one 3/4" x 12" x 6' laminated knotty pine was used for the rocker box.
Coopered Tube Telescope
This picture documents my very basic tablesaw. One thing to plan for here; notice the red plate that mounts between the blade and the fence. This plate did not fill the full depth of the table and it flexed when any pressure was placed on it. This caused some error while cutting the angle on the slats for the tube. If your saw is like this I suggest cutting a piece of 1/4" plywood or masonite, cutting a slot for the blade with a skill saw or jig saw, (do not use the table saw for this, injury to your body will result), and then clamping it to the table to ensure a solid, even surface for cutting your slats.
Coopered Tube Telescope
Here you can see what I did to keep my slats from riding up while being cut on the table saw. My daughter also held down on the slat with another hold down tool after it came off the blade, this helped quite a bit. I found it very difficult to repeat my cuts from piece to piece, a more experienced wood meister probably knows a trick or two for this.
Coopered Tube Telescope
This trusty dusty adjustable protractor purchased from Lowe's for $12.96 was used over and over on this project and something comparable is needed to measure the angle for your slats and many other layout portions of the project. If you don't have a push tool for your table saw make one! My slats were 7/8" wide and not having one would have resulted in lost digits for sure.
Coopered Tube Telescope
Here is the tube after it has been taped, glued and clamped. See Chuck Fellows' website for complete instructions on doing this. Be absolutely certain the clamp screws are over tape as they do leave small marks that must be sanded out. I found it necessary to re-orient the clamp screws around the tube to get it round instead of oval. The more care you spend here getting the best circle you can will pay dividends during assembly later.
Coopered Tube Telescope
Here is the tube after sitting 24 hours and with the tape removed. I used a plastic 3" putty knife to spread the glue that presses out of the slats which turned out to be a VERY good idea during mounting of the spider and the mirror cell. If I had gone ahead and gotten messy smoothing it all the way through it would have made the baffles go in easier as well.
Coopered Tube Telescope
Shot of the tube after finishing with the focuser hole cut. Notice the small crome screw head beside the focuser hole. That is the adjustment nut for the bicycle spokes I used to make the spider. More on that in another section, but suffice it to say Shane had a great idea on this. Spikes on the stars are very small and very sharp. The light spots on the tube are glue that I did not get sanded off completely that did not take stain. More on how I stained and finished the wood and the questions, problems, success and frustrations I had in the finished section. Shane is right; "Ya gotta love the wood".
Coopered Tube Telescope
Arrggghh.... the finish rings for the tube! Made the first one 4 times before getting one without breaking it. I was intent on using the laminated pine used for the rocker box but it kept breaking at the glue joints during the routing of it. Finally switched to 3/4" oak plywood and it held up well. I don't see how this could be done without a router table. I have a cheap plastic one from Black and Decker, it worked for this and other things just fine.
Coopered Tube Telescope
Here are a couple of shots of the baffles going in. I used the split, foam insulation you can buy at Lowe's for pipe. They have two styles, one a very closed cell that is pretty black but is soft and I didn't think it would hold its' shape. The other, more open cell, was much stiffer but was reflective. I used it and painted it and it got really dark. Used Krylon flat black antique crynkle finish spray paint.

To make your baffles, take the inside diameter given by the Newt program, subtract that from the inside diameter of your tube, divide by two and use the table saw to rip the foam to that dimension. Cut the length longer than the actual circumference, place the flat edge against the sides of your tube and it will hold itself in without adhesive.

Coopered Tube Telescope