Step 1: Telescopic Legs
Step 2: Tools and Materials - Part 1
While bamboo is hollow, each section is separated by a thin diaphragm. You'll need a long 3/4" bit to drill these out. Also, I wrapped some 60 grit paper around a bit of scrap dowel to sand the inside of the bamboo after I drilled it out. You just chuck the dowel in your drill. I cut the bamboo to about 16", so your drill only needs to be slightly longer than half that length, since you can drill from both ends.
I applied fiberglass to the ends of the bamboo to provide some additional strength. This step is optional, but recommended. You'll need resin and a couple feet of fiberglass tape, plus some other supplies. I'll give more details in a later section.
Step 3: Tools and Materials - Part 2
I've tried a couple techniques for the legs. In the first version, the three legs are composed of 3/4" wooden dowels, EMT compression connectors, and bamboo, plus some other bits. You'll need a 48" dowel that you can cut into three 16" pieces. The EMT (Electrical Metallic Tubing) connectors are 3/4" steel, thinwall conduit compression connectors, "rain and concrete tight". The compression connectors are available in the electrical section of your hardware store. Unfortunately, I found that these joints tend to loosen up too easily. So I came up with a much simpler approach: just cut four slots in the ends of the bamboo and use a stainless steel hose clamp to compress it.
The bamboo might be a bit tricky. I found 1" diameter, 5 foot bamboo stakes in the garden section at OSH. The bamboo canes, or culms, have a slight taper, so I looked for pieces where the larger opening was slightly bigger than the threaded end of the compression connector, and the smaller opening was just slightly smaller. How did I do that? I just picked up a compression connector from the bin in the electrical section at OSH, then walked over to the garden section and tried to insert it into various bits of bamboo. Try to be inconspicuous. Look for a culm that is fairly straight and free of cracks. And if you're using hose clamps the sizing is a bit easier, since you have more freedom in cutting the slots and/or building up the interior of the bamboo.
Step 4: Tools and Materials - Part 3
The final bits:
round wooden toothpicks (pointed on both ends) -- not the flat ones.
3/4" electrical tape
small brads or finish nails
3/4" cane tips
rubber gloves - get a big box, you'll need it.
plastic cutlery or popsicle sticks for working with epoxy.
epoxies - I used a 2 part 5 minute epoxy, and a large stick of Oatey Putty. The Oatey Putty is a system where the resin and hardener are combined in a tube, and you cut off a piece and knead it together to activate it. I got the Oatey Putty at Lowe's, and I've used similar products like the Devcon Epoxy Stick, or Hercules propoxy 20.
Step 5: Tools and Materials - Part 4
saw for cutting curves (optional)
long 3/4" drill bit (at least 10")
improvised sanding drum
3 foot piece of 1"x12" poplar S4S
1 48" piece of 3/4" diameter hardwood dowel, which will be cut into three 16" pieces.
1 piece of bamboo, approximately 1" diameter, at least 4' long, which will be cut into three 16" pieces
3 3/4" EMT compression connectors or 3 stainless steel hose clamps (1 3/4" diameter)
3 5/16" hanger bolts, about 2.5" long
3 mounting plates
additional washers, screws (maybe)
1 box round wooden toothpicks
3/4" electrical tape
about 1 dozen small brads or finish nails
3 3/4" cane tips
disposable rubber gloves (lots)
plastic cutlery or popsicle sticks suitable for working with epoxy
5 minute epoxy
Oatey putty or similar epoxy stick
Step 6: Bamboo
First, I cut the bamboo into three pieces about 18" long (I trimmed them down to 16" later). As I said, use a sharp saw and cut around the circumference to avoid tearout. If you use a miter box to make straight cuts, note that the bamboo is tapered, so you have to elevate the smaller end slightly -- about one-half the difference in diameters. That is, if the large end is 1" in diameter, and the small end is 3/4", 1/2*(1-3/4) = 1/8". Next, clamp each piece securely, and use the long 3/4" drill to clean out the interior. Don't try to hold the bamboo in your hand when you do this -- the drill can bind unexpectedly. Use the improvised sanding drum to clean up any rough spots at the segment junctions.
Step 7: How to Build a Gasket (but Don't Do This...)
The compression connector has a split ring underneath the big hex nut. Screwing down the nut causes the ring to, well, compress. When I first tried this experiment, I was disappointed to discover that a 3/4" compression connector refers to the inside diameter of the conduit, so it won't work with a piece of 3/4" dowel. And you can't substitute larger dowels, because the throat of the connector is only 3/4". So I came up with this "gasket" and surprise - it worked!
Lay out 2 parallel strips of electrical tape about 4 inches long. The spacing is determined by the length of a toothpick, minus the pointed ends, which you will trim off later. Lay about 15 or 16 toothpicks across the tape, tightly packed, with no empty space. Fold the remaining tape over so the toothpicks are sealed between 2 strips. Use a sharp knife or saw to trim off the exposed pointed ends, then carefully saw the toothpicks down the middle to obtain the two halves of your gasket. Trim off excess tape from the ends. Loosen the nut on the connector, then slide the gasket about halfway into the connector. Carefully work in a 3/4" dowel, twisting and pushing until the gasket is seated in the connector (see second photo). You should be able to tighten the nut, and the dowel will be held firmly in place. If the gaskets are too loose, you can add additional toothpicks. If the gaskets are too large, then use fewer toothpicks. Don't try to build up the gaskets with additional tape -- it just compresses.
The connectors are just epoxied in the ends of the bamboo. Always mount them in the narrow end -- the large end of the bamboo is for the hanger bolt (this will make sense later). If the small end is undersized, you can widen it a bit with some sanding with your dremel. If it is too large, you can use oatey putty instead of 5 minute epoxy. I found that one was too large, one was too small, and one was just right. In order to mount the EMT connectors in the end of the bamboo, first strip them down: remove the large compression nut and the narrow hex nut. Wrap the bamboo with saran wrap and mask off the end with masking tape to avoid getting epoxy on it. Tape over the threads for the large compression nut for the same reason. Put on your rubber gloves and mix up some epoxy. I used 5 minute epoxy for two of the legs, and since the third one was slightly oversize, I used oatey putty instead.
Step 8: The Hose Clamp Technique (very Easy)
Take your bamboo pieces, and on each one, find the small end where the opening is closest to the size of the 3/4" dowel. If the smallest opening is too small, you may need to trim a bit off the end until the diameter is large enough. In my case, I started with 18" pieces, and ended up trimming about 2" off the smallest piece, and then trimmed the others to match. We are using the hose clamp to compress the end, but if the opening is too large, you may need to build it up a bit later with some epoxy or wood wedges. But before you do that, you need to cut 4 slots, each about 2 inches long. My slots are about 3/16" inch wide. I tried cutting a narrow slot and then widened it with a dremel tool, but it was a pain. It was much easier to cut 2 parallel slots, and then use a 3/16" drill bit to drill out the very bottom.
Step 9: Cutting the Dowel
Stick a cane tip on the end of the dowel.
Step 10: Mounting the Hanger Bolts in the End of the Bamboo
First, screw one of the mounting plates to a flat piece of scrap wood, and place it on a level surface. Secure it if possible using tape, clamp, weights -- whatever works. Take a hanger bolt, and screw it firmly into the plate.
Next, cut a 1" piece of 3/4" dowel, drill a hole in the center, and mount it on the tip of the wood screw portion of the hanger bolt. Hey, since we used all the dowel for the legs already, where did this piece come from? Um, from your scrap dowel? So you can just cut a 1" piece off each leg if necessary. As a test, slide the bamboo down (use the larger opening) on top of the dowel so it is centered on the hanger bolt and mounting plate. It might be useful to position the plate next to something sturdy like a table or chair leg -- you can tape the bamboo to the leg when the epoxy is hardening. Use a square or some other reference to see if the leg is perpendicular to the floor. This is tricky because the leg tapers. Practice this a bit because you have to be able to set this up rather quickly once the epoxy is mixed.
Once you have figured out how to measure and mount the bamboo centered on the plate, perpendicular to the floor, set up for the epoxy steps. Wrap the bamboo in saran wrap and mask the end with masking tape. Neatly tape over your mounting plate with masking tape as well. You can trace a circle on the masking tape to help with centering the leg.
Get out your rubber gloves and get ready to mix some epoxy putty.
We are going to build up the sides of the little dowel stub on the end of the hanger bolt with a little bit of epoxy putty, just enough to center it in the bamboo and stick it in place. So use a disposable plastic knife to cut off a piece of oatey putty, and knead it until you achieve a uniform color. I use the "green onion pancake" method: roll the putty into a skinny snake, roll the snake into a snail, roll the snail into a ball, repeat.
If you just build up the dowel with putty a little bit, you should be able to slide the bamboo down and center it. Tape the bamboo to something sturdy (like a chair leg) and let the epoxy harden.
After the epoxy has hardened, carefully unscrew the bamboo from the mounting plate. It should rotate smoothly, without a large wobble (which would indicate that it isn't perpendicular). If you mess it up, don't fret. Only two of the legs need to look good -- no one can see the back leg of the table. But if you need to fix the leg, and you only used a little bit of epoxy, you might be able to pop the bolt out and try mounting it again.
If you look into the end of the bamboo, there should still be at least an inch or so of exposed thread above the dowel plug. We are going to fill this space in with epoxy in two steps.
First, tape over the end of the hanger bolt that sticks out beyond the bamboo. We don't want to get any epoxy in these threads. Next, mix up some more oatey putty and carefully pack it into the bottom half inch of the cavity with the wooden plug. Use toothpicks, popsicle sticks, whatever works to smooth the putty in place. But don't push too hard, since the plug might not be mounted too firmly, and you don't want to pop it out. Let the epoxy harden.
For the final epoxy step, we need to pack in the rest of the cavity up to just below the rim of the bamboo. The bamboo should be tapered from the large end, so the epoxy plug will stay wedged in place. I was worried that it might be able to rotate, though, so I drilled a couple tiny holes near the end of the bamboo and stuck in some brads -- once the epoxy hardened around them it wouldn't be able to move. So mix up the final batch of epoxy and firmly work it into the cavity. Don't make it too high -- you will be very unhappy if you can't unwrap the tape protecting the threads on the hanger bolt.
Step 11: Basic Sanding, Attaching Mounting Plates
The bamboo is naturally smooth, so I only used 80 grit sandpaper to start, and hand sanded each leg. You might want to tape over the exposed hanger bolt threads again just to keep them clean. I used 80, 180, then 320 grit for the final sanding. Note that if you plan to reinforce the ends of the bamboo with fiberglass tape, this is the place to fill in any little grooves with wood filler and sand them smooth. Don't sand the wooden dowels.
Before you screw on the mounting plates, you need to finish the table top. I added a slight arc on the end because I thought it looked nicer, and I used a router with a 3/4" roundover bit to put a bullnose on the edge. If you want to trim the ends like this you should use a circle cutter with a router or bandsaw -- it won't work well freehand. The radius of the curve that I used is
(w/2)2 + (r-1)2 = r2, where w is the width of board (solve for radius r in inches). If you don't have a router you should use a power sander to round over the edges a bit.
Note that the table top may look smooth already. This is an illusion. The factory planer has left ridges in the top that will only show up when you apply a finish. So use a power sander with 60 grit paper to really smooth down the top, then follow up with 80 grit, 180, and finally 320. If you are lazy, you only need to sand the top of the table, not the bottom.
Once the table top is complete you can attach the three mounting plate -- one in the center of the rear, and one in each front corner. I ended up buying straight mounting plates, and then I used stacks of washers to angle them out at 15 degrees from the surface of the top. This angle is not particularly critical. Note that back leg is angled to point straight back (ie perpendicular to the axis of the table), but the front legs point out on about a 30 degree angle from the long axis. Very important: make sure that you use screws which are long enough that they still go at least halfway thru the top, but don't use screws that are too long.
Step 12: Wooden Donuts (optional)
Step 13: Staining and Finishing
So prior to finishing, use masking tape to shield any hardware like screw threads or mounting plates, and then use a tack cloth to clean off any sawdust. Apply the shellac is several thin coats. You might want to sand in between using 400 grit paper, and tack each time. Don't shellac the wooden dowels.
So, now you are done! Unless...you want to try some fiberglass reinforcement.
Step 14: Fiberglass and Bamboo, an Unnatural Combination (optional)
Note that if you just use stainless steel hose clamps on both ends of the legs, you don't have to worry about cracks or checks -- the clamps will hold the bamboo together.
In my original design, I used EMT connectors, so I reinforced both ends of the bamboo. If you use hose clamps you only need to worry about end with the hanger bolt.
Also, I used polyester resin, which is described as smelling "pungent". I did get good results with this material, but the stench is so hellish that you must use a respirator to work with it. It is unbelievably bad. The epoxy resin is more expensive, but it is stronger and stinks less. So you could use that, but I am not sure if it works with the techniques which I describe. In particular, the polyester resin is compatibly with the shellac finish, but I don't know if the same is true for the epoxy.
Here are the tools and materials:
1" wide fiberglass tape (you only need 3 inches per end, so 9 inches will cover 3 ends)
TAP laminating resin - bond coat B (less than 1 oz per end)
mylar sheet (a couple feet)
a handmade "fork"
various measuring cups, mixing sticks, spatulas
I took a scrap piece of wood and taped three brads on the end to make a fork. The fork is for maneuvering the wet fiberglass.
First, prepare an area far from civilization where you can mix the polyester resin. Protect your work surface with cardboard. Wear clothing you are not fond of. Wrap up the bamboo with saran wrap and mask off any screw threads. Cut a small sheet of mylar (maybe 6" x 6") and tape it down. Cut three 3" pieces of fiberglass tape and lay them on the mylar. Cut 3 mylar strips that are slightly larger than the tape (about 1.5"x4") and set aside. Precut half a dozen pieces of masking tape.
Fiberglass fact: fiberglass wants to lay flat. It does not want to fill in little holes or gaps or wrap around small bamboo cylinders. So we have to cheat.
Get suited up, and mix up an ounce of resin with catalyst. Dribble some resin on a piece of tape lying on the mylar, and work it in with the spatula. Don't use too much. When the tape fully absorbs the resin it turns transparent (much like frying onions). When this happens, take the spatula and work a little resin around the base of the bamboo that you wish to reinforce. The tape isn't doing much good lying on the mylar sheet, so poke into it with your "fork" and peel it off.
The tricky bit: using your fork, neatly flop the tape onto the end of the bamboo, and twist the bamboo to roll it on neatly. You might have to use a gloved hand to help here. Slather a bit of extra resin on the outside and work it in neatly with the spatula.
If you just leave the fiberglass on the bamboo like this, it tends to slump off, and the resin drips down into a puddle.
When professionals work with fiberglass, they use a vacuum bag to hold the resin into the mold. Our cheap approximation is to wrap the end of the bamboo with a strip of mylar and tape it in place. And if you do it correctly, it works quite well -- you get a beautiful, glass-smooth finish without any bubbles or visible fabric weave. And while the polyester bond coat B normally stays tacky if exposed to air, it cures to a hard finish if wrapped in mylar. And the mylar peels off quite easily.
But is it worth the pain and suffering? Perhaps. Perhaps not.