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Building an 8" Closed Tube Reflector

Construction Pictures
Finishing the Tube

After all the parts have been made and the spider and focuser fitted you can begin the process of turning this ugly tube into a thing of beauty you'll be proud to show your friends. I hate sanding, and filling, and sanding but it does wonders.

The first step is just to sand the tube as smooth as you can with 220 grit paper. As voids appear fill in with more auto body putty and sand again. Stuffing a plastic bag(s) into the tube will keep out a lot of dust.

After the tube is smooth and all of the major voids have been filled buy a couple of cans of auto body paint filler. Protostar has a whole section you can download (scroll down to bottom of their page) on finishing these tubes and they recommend a couple of brands of surface filler. Advance Auto has Dupli-Color sandable primer. This comes in two types, thick (high-build) and not so thick. I used both. After the surface has been sealed and sanded with 400 paper you can apply the exterior paint. I used Rustoleum Hammered finish, which looks good, is tough and further hides defects. Practice your spray painting technique with the sealer/filler. It won't matter here but it will when you put on the finish coat. Some will try and make a super-shiny, super-smooth exterior finish, but this takes a huge amount of work. The Hammered finish works for me.

As a jig to hold the tube I put a 2 x 4 on my table saw and held one end down with weights and slipped the tube over the other end - works great for painting and sanding. You can easily rotate the tube as you work.

Those damn spirals will never go away entirely but do the best you can. After you're done vacuum out the tube.

Putting 2" wide masking tape inside the ends lets you paint without getting exterior into the interior. When you apply the exterior coat use long sweeping strokes holding the can about a foot from the tube. Never stop moving your arm. Always start a paint stroke pointing the nozzle away from the surface and sweep in and across the tube. Never start a stroke pointing the nozzle at the tube - they spit globs of paint. You will use about two or three cans of paint for the tube. Buy the cans together for color match. Plan on finishing the tube in one shot, which is why I use the 2 x 4 jig.

Lastly, dust in some flat black to clean up and deaden the interior. Not too much here, a little will really improve the appearance and clean up drill hole tears and dings. After you tear off the tape you can paint the inside of the ring with a small hobby brush and Floquil Engine Black.

The end cap and fan plate can be painted a slightly different shade of color. I used a gray for the tube and  black for the end cap. If you take a little time it looks like a million bucks.