Pictures of the 6" MakNewt I made

This is a picture of the strips being taped up. Note the end strip at the upper right corner of the picture. Each strip is butted up nst this strip to keep the ends even as I’m taping. Also, there is a raised strip running across the top left edge. It holds the assembly square to the end strip and provides a stop to push against when pulling the next strip in tight against the previous strip. Notice that I put down three or four strips at a time and hold them in place with three pieces of tape running across the joints. Then I go back and run a length of masking tape down the full length of each seam. This is important to hold everything in place, and to keep glue from seeping out between the joints when you’re rolling it into a tube. Makes things a whole lot neater.

	This is the completed assembly with all strips taped into a single sheet. The entire sheet is ready to be flipped over, tape side down, so the v grooves between the strips formed by the beveled edges can be filled with a bead of glue.
	This is the sheet flipped over, taped side on the bottom, ready to apply the glue. Although you can’t see it in this picture, there is a v-groove between each pair of strips formed by the beveled edges of the strips.
	Here you see the sheet has been rolled into a tube and the clamps have been applied. The tube is about 8.5” outside diameter and to make the clamps big enough, two of them had to be attached end to end. If the bevels are reasonably accurate and consistent (easy to do with a tablesaw), and the strips are fairly straight, the clamps will pull the tube into a nearly perfectl circular tube with no other forms or guides required.
	This is the tube with the clamps and tape removed. The joints between each of the strips have been planed with a hand plane to remove excess glue and the ridge where the two edges meet. This makes sanding into a finished tube go a lot faster.
	The mirror cell is made up of several components. The black ring is made from HDPE (High Density Polyethylene), also known as Seaboard and Starboard. It's is somewhat resilient and easily worked with a router or a lathe. The triangular aluminum plate is attached to the HDPE ring with 1/4" bolts and very stiff springs for collimation adjustments. The mirror itself is cored, lies flat on the aluminum plate and is held in place with a flanged plug, also made from HDPE, with a 1/4" bolt through the center and through the aluminum plate. Both components made from HDPE could as easily be made from a good plywood.
	The corrector cell is also made of HDPE. The corrector lens is held with screws and plastic washers in the back.
	The baffle structure is made of evenly spaced baffle rings made of Masonite or Hardboard. They are held together by three long hardwood strips which are notched to hold the rings. Generous amounts of white glue are used to secure the rings to the strips. After everything is dry, the baffle structure is painted entirely with flat black paint. The entire structure is a tight sliding fit in the Optical Tube and can be removed later if desired. The vertical strips hold the rings about 1/8" away from the inner tube wall so that any convection currents which do occur are next to the all and not around the inner diameter of the baffles.

Making a telescope tube out of coopered wood strips

1. Determine the number and size of strips required for the tube.

a. Assuming you know the approximate dimensions you want for the tube, take the outside diameter, OD, and multiply by PI (3.14159) to get the outer tube circumference.

Example: An outside tube diameter of 12 inches has a circumference of 12 x 3.14159 = 37.70 inches.

b. It’s best to figure on using wood strips ¾ (.75)” wide. This lets you rip the strips from stock dimensioned lumber. So the next step is to divide the circumference by .75 to get the number of strips required.

Example: The circumference listed above, 37.70 / .75 = 50.27 strips.

You can round this number up or down to suit your needs. Each full strip you add or subtract will add or subtract approximately .25 (¼)” to the tube diameter. I usually like to use a number of strips that are evenly divisible by 4, so I can incorporate a pattern of 3 strips one color and 1 strip a second color. So, in this case, I would round down to 48 strips or up to 52 strips. If you round down to 48 strips, the resulting tube OD will be 11.46 inches (48 * .75 / 3.14159). If you round up to 52 strips, the OD will be 12.41 inches. If you really want to keep the tube OD pretty close to 12”, but want to use more strips, say 52, then divide the circumference (37.7 inches) by 52 to get the width of strip needed to get a 12” diameter using 52 strips. In this example, the width of strip would be .725. My experience shows it’s usually better to start your calculations with a .75” width strip, then plan on winding up with more, thinner strips in the end. This gives a little more wiggle room on the width of the strips since the thickness of ¾” boards varies some.

c. Once you’ve determined the number of strips you need, divide 180 degrees by that number.

Example: In our example above, 180 / 52 (strips) = 3.46 degrees. This is the angle of the bevel on both sides of each strip.

In my experience, this angle setting on the table saw doesn’t need to be exact. It can be ¼ of a degree off either direction and everything will be OK. In this example, I would aim at getting the angle set to 3.5 degrees and that would be close enough.

d. The last calculation is the thickness of the strips. For tubes up to about 8” diameter, 3/16” thickness is adequate. For anything bigger, I’d use ¼” thickness. Remember that double this number subtracted from the OD is going to be your tube inside diameter.

Example: From the previous example, a 12” OD tube should use ¼” thick strips. This results in a tube wall thickness of ¼” so the ID of the tube will be 11.5”

2. Cutting the strips.

a. The strips are first ripped from boards at least as thick as the resulting strips need to be. I usually cut a couple of extra strips in case one gets damaged or beveled incorrectly.

b. For best result, the boards from which the strips are cut should be knot-free, straight grained, and not warped or cupped. The cut strips can be somewhat bent without ill effect, but they shouldn’t be twisted or warped too badly.

c. The strips need to be beveled on both sides. Obviously the fastest way is to bevel all the strips on one side with a single setting of the fence, then move the fence to the appropriate width and bevel the second side of all the strips.

3. Assembling

a. The easiest way to form a tube is to first create a flat sheet. This is done by taping the strips together, side by side, beveled side down. The tape used is ¾” wide masking tape. It’s cheap and sufficiently strong to hold things together during the assembly and gluing process.

b. An important element is to keep the ends of the strips even and to make sure the edge formed by the strip’s ends is perpendicular to the edge of the strip. I do this by nailing a straight strip of wood across the the bench and another along the front edge of the bench at 90 degrees to the first strip. This forms a large L.

c. The process involves laying a strip, BEVELED SIDE DOWN along the front leg of the “L”, pushed up against the perpendicular leg of the “L”. A second strip is placed beside the first, pulled tightly against it and taped the full length of the joint with the masking tape. Then a third strip is taped to the second, and so on, until all the strips are taped together. It’s important to get each strip tightly taped to the strip preceding it. It’s also important to make sure the end of each strip is pushed up against the perpendicular strip at the end.

d. After all the strips are taped together, the entire sheet is flipped over so the bevel sides are up. The two beveled sides of each strip form a v-way between the strips. A bead of glue is now run down the full length of every V way between the strips. This process takes a little while, so be sure to use a slow setting glue. I prefer polyurethane glue for this reason, and because it tends to fill any voids as it hardens. The setup time on polyurethane glue is 4 to 6 hours depending on heat and humidity.

e. When all the joints have been filled with glue, the entire assembly is rolled into a tube, with the glue filled beveled edges on the inside. It may take a little coaxing to get the tube closed since excess glue has to be forced out of the seams. Be sure to put glue on one of the outer edges before rolling to hold the tube together.

f. The clamps used for the tube are worm gear hose clamps. These can be purchased at Home Depot, Lowes, or hardware stores in diameters up to about 8”. Two more can be fastened end-to-end to accommodate tubes with an OD larger than 8”. I usually use a clamp for every 12” of tube length.

g. If the strips used are relatively straight and the bevels are cut accurately, the pressure of the clamps alone will form a nearly perfect circular tube with no other forms or jigs required.

h. If you want to clean off the excess glue, you should do it before the glue begins to set up. This is particularly true of polyurethane glue which dries to a tough, foam-like consistency which is nearly impossible to scrape off. And, you should wear rubber gloves. You will get this glue all over your hands, guaranteed, and the polyurethane glue is not removable by any solvent that I’ve found. You can remove it with paint thinner when it’s still wet, but once it dries, it has to wear off.