Build Your Own Plywood Tubes

Tubular plywood? Yes, you can build your own in four easy steps (form, glue, wrap, strap)! I was in need of 16 inch diameter plywood and this Instructable documents my process, with tips, techniques, and failures. You may be able to adjust this process down to about 12 inch diameter before requiring more advanced techniques. Larger diameters are easier. There are over FIFTY images here, so make sure to look through them all.

The reason for needing the tubular plywood is part of a larger project involving more than woodworking. The reason for the tubular plywood will be revealed after the final steps.

3/4 x 3/4 x 48 inch strips

scrap sheet lumber for framing

1/8 inch 2-ply veneer (I used 4 4x8' sheets)

Wood glue

Tools

Table saw

Power nailer

Long straightedge

Utility knife

Paint roller

Spray bottle

Cargo straps (about a dozen)

CNC router (or a jigsaw/scroll saw would work)

You can't build a tube without a form (frame or mold). Here is a great example of a drum manufacturer and their machine forming process (view at 3:20). That is an amazing machine! My process is the opposite approach, building a form to wrap the tube around, rather than being pressed inside one.

Video link to drum making https://www.youtube.com/watch?v=VerYJ-g7Bs4&t=49s

I created my ribs by ripping 3/4" strips from 1x8 pine boards. I did not have a table saw at the time, so I attached my circular saw to a piece of scrap and mounted it upside down next to my workbench (Danger, Will Robinson!!). I designed some planar supports to hold the ribs, just a basic circle with indents to attach the ribs. I used available scraps I had, and some had to be halved and joined based on available scraps. These supports were cut on a CNC machine, but a jigsaw or scroll saw could be used as well. Once the supports were created (I built six of them), I stapled the ribs on, one at a time. 30 ribs and six supports, 180 staples. The lobster cage is now ready to be wrapped.

It was difficult to locate some thin 2-ply veneer locally, but I found a location about an hour from my home. I purchased 4 sheets of 4x8' in White Birch. I actually rolled it up and put it in the back seat of my Honda Civic. The material I received had seen better days. Lots of corner damage and edge issues. There was even some delamination where the two plies were separating. Some of these defects could be trimmed off, some just had to be incorporated into the build.

1. Apply glue
2. Wrap it on, strap it on, and let it dry
3. Repeat until you have the desired thickness

A Few Learned Tips: 

• The grain on the outside of the bend should be in axial alignment, the cross grain should go with the tangent on the inside (did I word that correctly?).
• Warp the pieces before gluing, by wetting and bending, and then hold them in place (string, twine, extra cargo straps) until they dry overnight.
• When adding a layer, paint on the glue and keep it wet by spraying it evenly and lightly with water. This will increase your set time, as the wood is like a sponge and will suck up the glue.
• Mind the gaps. When you apply the cargo straps, they may not pull evenly and you can end up with some air pockets or edges that are not fully flat (or aligned to the curvature).

Minor failure: You cannot wrap multiple layers at once to hasten the process, unless you have some heavy duty equipment or about six extra limbs. Wrap them one layer at a time, letting them dry in between. That drum machine did three layers at once, and I learned that I am not a machine.

Major failure: The most important step forgotten? Releasing your final product from the form. Somehow I thought it would just slide off. Oh, I was so wrong. The process to free the product from the form was intense. I used a locking pliers (vice grip) to grab a rib, and pried it out lengthwise. After removing a few ribs, I could get the form to move a little. I ended up having to smash and cut the support panels get it all separated. The lobster cage was pretty mangled in the end.

The final product was three layers (3/8" thick), and I added a 4th layer ring on the inside ends to make it look like 1/2" plywood while keeping it the weight of 3 layers.

Oops, I realized I needed more tube than the single four foot piece. I could manage my project with another two feet and two feet of a slightly larger diameter so they will overlap. I had to rebuild the lobster cage, but with only three platters it was only about 26" long. That was enough to get what I needed. Start the steps all over again (form, glue, wrap, strap).

I wrapped 4 layers for a solid 1/2" tube. I used a piece of "engineered wood under mat" foam to separate my layers (another colossal failure on my part). And I proceeded to wrap 4 more layers of wood veneer. Getting those two half inch tubes apart was another nightmare. Using a flat steel ruler, I was able to eventually push enough of the foam out of the way to get the two layers separated. Then I smashed the inner form again to get rid of that. No more tube building with that form unless I build a complete new one from scratch.

Final pieces: 1/2" thick 16" diameter 48" long, 1/2" thick 16" diameter 24" long, 1/2" thick 16.5" diameter 24" long.

I am building a telescope with an unconventional mount (take a look at my CNC Semi-Nasmyth mount). It is a Newtonian reflector, but I want the tube to pivot near where the eyepiece is centered so that the user does not have to move so much. A traditional Dobsonian mount can have you up on a ladder or crouched over for long periods of time.

I have a 14" primary mirror that was in storage since 2008 when it was purchased. The tube was a major part of the telescope design. The focal length is over 56", so I needed a tube longer than 48". Hence the stacking sizes. I 3D printed thumb screws to go over 1/4-20 bolts. This makes it somewhat collapsible to fit into a vehicle for moving it. Final length of the assembled tube is over 75".

I installed an 18" Lazy Susan just below the eyepiece so that the eyepiece can be rotated about the tube axis when the viewing angle gets too far away from the user.

I built an 18 point floating mirror cell that goes in the base. I also built a makeshift stand to test it for first light, while the rest of the mount gets built. Another photo shows the laser collimation.

Summary Q&A

• Could I have built this out of aluminum? Likely, but it may have been more expensive and difficult to roll or form on my own.
• Why not use PVC pipe? Too heavy and expensive
• Why not SonoTube or concrete post carboard tubes? They are rather flimsy and would require significant interior supports. I could not find thicker walled tubes.
• Why not a box or square tube? I think it's much cooler making your own tubular plywood instead of a box.