Joinery Experiment

I just tried both the methods listed below (Joinery 2 & 3). For the hanger-bolt joint (joinery 2), I omitted the epoxy, since I hoped to reuse the materials. For the mortise-and-tenon joint (joinery 3) I used a piece of 1/8" ply cut in a modified rectangle for the tenon and bamboo skewers for pins. The modification was essentially a tail, an extention of the rectangle at a width slightly less, so that it could slide inside the cavity of the crosspole, giving more pinning length while requiring the bamboo to be cut less.

Hanger-Bolt Joint
Joining caused splitting of the hardwood dowel, and subsequent stress and splitting of the crosspole. Joint was not square. No problems with compression of the bamboo from the bolt. There was minimal wiggling in the joint, but when I applied pressure the screw of the hanger-bolt pulled out of the dowel, due to its split.

The non-squareness of the joint was likely due to the difficulty I had centering the hole for the screw-side of the hanger-bolt, and making the hole perpendicular. Also, I did not perfect the curvature of the crosspole cut to fit the main pole. The splitting dowel was encouraged because of the difficulty getting a snug fit between the dowel and the bamboo cavity.

Also, screwing in the hanger-bolt is challenging.

Mortise and Tenon Joint
Fitting the mortise-and-tenon to each other was easily done with a dremel. Getting a tight fit was not difficult (the hanger bolt pulls the parts together in the other joint, in this joint this must be done manually). Pins held without glue. The resulting joint was square with minimal wiggling. However, when force was applied, the wiggling gradually increased. Eventually, pins cracked, one failed entirely, and the tenon tail split off.

Conclusions
I like the mortise-and-tenon joint, despite its failures. 1/4" ply and larger diameter pins (bamboo chopsticks? wood dowels?) will improve strength. Epoxy in the joint will not only give adhesion, put will also fill gaps and minimize the wiggling. Triangulating joints will also minimize wiggling. If wiggling can be eliminated, the progressive growth in wiggling should also disappear.

Most important, of course, was the ease with which I was able to get a good-looking joint. Precision is not a strength of mine, so any method that doesn't require me to hold my drill perfectly vertical is a better method.

Bamboo Joinery 3

Here is an alternative joinery technique I just found on the web. It has a number of advantages over the technique I planned in the previous post:

• It doesn't rely on glue anywhere
• It doesn't use expensive hardware (hanger bolts, at 50¢ each, add quickly)
• It doesn't compress the bamboo as a bolt does, something the literature says is not good for bamboo.
• It doesn't require one to make a precise fit between a dowel and the bamboo interior.

On the other hand, it does require one to make a careful joining tenon, to drill the bamboo four times rather than one (which has proven tricky for me), and to fit pins precisely. Here it is:

1. Use a dremel cutting wheel or similar tool to cut a slot in the main pole, the dimensions of the tenon you will make. Make another cut in the end of the cross-pole the length of the tenon.
2. Make a tenon out of plywood the thickness of the slots (mortises) you have just cut. I show above a triangular tenon, which would give more support for bending of the cross-pole, but requires the slot on the main pole to be slightly longer than the joint, leaving it visible. A rectangular tenon, the width of cross-pole, would not have this defect. Insert this tenon into the two mortises and close the joint.
3. Drill four holes through the bamboo and the tenon, making sure that the joint is very tightly closed as you do so. Two holes lengthwise on the crosspole, and two lengthwise on the main pole.
4. Cut four pins and insert into the holes. You may use a weatherproof glue to hold the pins in place. This glue does not hold the joint: no force applied to the joint is resisted by the glue, but it does prevent the pins, that hold the joint, from working loose. What to use for the pins? Smaller-diameter bamboo is recommended. In some applications, bamboo skewers from grocery aisles are all that is needed, and have the advantage of being a consistent size. I think they are too small for my purposes, however.

I neglected to include in this illustration that you ought to first cut the crosspole end into the shape of the bamboo mainpole (see Bamboo Joinery 2, below).

Bamboo Joinery 2

Making a T joint:

1. Cut the end of the side pole into a curve closely fitting the cross-pole, using a coping saw.
2. Take a 1" length of a hardwood dowel that fits snugly into the bamboo cavity, apply a strong, weatherproof glue such as Weldbond Outdoor wood glue, and insert into the end of the side pole.
3. Bore a hole into the dowel in the side pole (use a bit the diameter of the shank of your hanger bolt screw-side) and another through the side of the cross-pole (use a larger bit, the diameter of the threads of the hanger bolt bolt-side).
4. Drive the screw end of the hanger bolt into the dowel, and insert the bolt end into the cross-pole.
5. Secure the bolt with a washer and nut.

The Motor

Many of you may be wondering about the motor:

That part is simple. I buy a wheel with a motor attached, put it on the bike, and I'm good to go. A number of good motors are made:

Bionx
Electric rider

I think I'm going for the Phoenix Cruiser from Electric rider, because it is fast (30mph), but has more power for hills (important in Vermont) than their faster Racer model.

The Bionx system has regenerative braking, which I like, but it also has a system to prevent the bike from exceeding 20mph, which is the legal maximum, yes, but... when's the last time you bought a car that couldn't go faster than 65?

Bamboo Joinery

The official way I read about doing bamboo joinery is with bins and hooks and bolts. Say, to make a T-joint, you would put a pin through the stem of the T, bend one end of a threaded rod into a hook, insert the hook into the end of the stem and hook the pin, then put the other end of the threaded rod through a hole bored in the cross bar and secure with a nut.



The problem is, my bamboo is so narrow there is no hook can be inserted into the hollow.

My solution: cut 1" pieces of 1/2" dowel (or other size that fits snuggly inside the bamboo cavity. Glue one piece into each end of the bamboo with a strong, weather-proof adhesive, such as Weldbond's outdoor wood glue. Bore a hole into the butt end of the dowel, and insert a hanger bolt (one of those bolts with a screw on one end and the bolt on the other. Bore a hole through the piece you want to join to it, put the bolt through, and secure with a nut.

This method should be equal to the official in sheer or compression. If pulled apart, the joint is dependent on the strength of the glue. I think I might use an epoxy between the two part, such as JB Weld, to help. This would make two distinct glue joints which each support each other: this chain is as strong as its strongest link.

Simplify

Okay, on second thought, the hole saw doesn't work. Spent $25 on a new hole saw the right size (1"), just rip the bamboo apart.

New approach: the coping saw. I use one of my successful hole saw bamboos as a template, trace it, and cut the next one out by hand. It goes really fast, doesn't require pre-drilling or extension cords, and NEVER splits the bamboo.

Working Bamboo

This is my insightful discovery: bamboo is different than wood.

Bamboo is very strong in terms of bending and load bearing. But let something sharp strike it across the grain, and WATCH OUT!

Bamboo handles like a bundle of silk threads running the length of the pole. It is prone to splitting.

• Don't use a speed bore on bamboo. The moment that spinning blade touches the bamboo, POW! split if not shatter.
• Be careful using a large-bore (3/16"+) drill bit. A very gentle touch works, but push too hard and it splits.
• Predrilling with small bore bits helps. Ironically, the spear point on a speed bore has never caused trouble for me, and I use it to pre-drill. Just have to stop before the blade touches.
• Use small-tooth saws. I used a mitre saw.
• I wouldn't dare nail it.

Don't know if this will work, or if I'm off on the wrong direction. We'll check in again.

Poles Poles Poles

Just received my shipment of bamboo poles. I ordered 6'x1" tonkin poles. I'm really excited, but I have to say: cylindrical things always look a lot thinner than they measure. I'm wishing I'd order 1&1/4, or even 1&1/2.

On the upside, my daughter and I could sit together on two poles, and even wiggle a little, so I think it will work with my 3 pole design.

I ought to put three poles together and jump up and down on them, but I can't bring myself to try it.

Steering mechanism

Another decision was how to rig the steering when your technical skills are limited. Most Tadpole Trikes (two front wheels) use a design where the crossbar of the frame heads out toward the axle, then has a hinge. This is clearly the superior design, but I don't know how to find such a hing. I don't think door hinges will work. So my thought was to take the front end of a pair of kid's bikes, and have the crossbar connect to the cylinder.

• Use a bike with a small front tire, say 16", so your bike doesn't look like this:

The downside is this involves a bamboo-metal connection, but we'll deal with that in a bit.

Trike: one in front or one in back?

I knew I wanted a trike so I felt safe on slippery roads, so it felt more car-ish. I bike is simpler but I wanted a trike. However, trikes do have a stability problem. The traditional trike design, called a "delta," with one wheel in front, can easily flip at high speeds. This illustration shows why:

A. Trike moving forward. Blue arrow indicates interia keeping it moving forward.

B. Front wheel is turned, creating a deflection force (pale blue) for the front of the trike.

C. The trike starts to turn. Inertia still wants the trike to move forward, the wheel is still deflecting the trike front to the right. Notice that inertia is now moving across the line between the front wheel and the rear left wheel. This line become a fulcrum for the bike to tip over. In a car, the weight of the car is shift to the front left wheel. In a delta trike, this wheel doesn't exist.

D. Inertia keeps the bike moving forward, by adding a simple torsion to the bike mass, known in highways safety lingo as a roll-over, or just a crash.

In a trike with one rear tire and two front tires (called a "tadpole"), the left front tire does exist, and the rollover is prevented.

Other factors, pro and con:

• A delta trike requires a more complex power train, some sort of differential to allow the rear tires to spin at different rates in a turn, and or a single axle to transmit power to both tires.
• A tadpole trike requires a more complex steering mechanism, so the front wheels turn in unison.
• One poster has said that tadpoles are more inclined to fishtail.
• The majority of trike designs available from more technically informed people are tadpoles.
• Tadpoles look cool.

I'm gonna make a tadpole.

Frame Design

I really know very little about bamboo as a building material. Exactly how thick a pole of what species do I need? My cursory research didn't reveal "how strong is bamboo" so I did what Idle Dads do, which is to get some and see. I need to keep costs down, but I figured that, depending on what I found, I could probably adapt the design. I ordered 1" dia. tonkin poles from http://bamboofencer.com/, which doesn't have surcharges for small orders and ships from nearby Massachussets.





Here are the three basic frame designs:

The Single Pole, or cross design, is what to use if the bamboo proves very strong and sufficiently rigid. In the picture above, the rear wheel is on the long end of the cross, the front wheels on the ends of the crossbars, and the crank and pedals on the bent tip (the crank needs to be above the seat, for various reasons).

The Double Pole design should be much stronger, and stiffer in the vertical dimension. Not shown in this sketch are short lengths of bamboo connecting the two principal poles. The weakness of this design is that there is no stiffening in the horizontal direction, nor from twisting. This means loss of some of the shock absorbency of bamboo, and some wiggle in steering. It is possible to put the two poles side-by-side instead of over-and-under, which would restore the shock absorbency and stiffen the steering, but the trade of would be loss of strength in the vertical direction. Since this is the direction of stress from a pothole hit at 30mph with 180lbs of Idle Dad aboard, it would seem to be the primary need for extra reinforcement.

The Triple Pole design is stronger in all directions. I can't imagine that it won't be strong enough. It loses some shock absorbency, and it is significantly more complex to build than the others, but is the assurance that my 1" poles will be adequate. The picture above may be tricky to see, but I am finishing a model that I will post soon.

Metal, Plastic, or Bamboo

Everyone else makes them out of metal. But to do metal you need to weld or "braze" pipe together. Before I started this project I'd never even heard of "brazing." Another posibility is ABS pipe, like water pipes are made of nowadays. I decided against plastic for several reasons:

• I don't like plastic
• It gets brittle in cold weather and I live in Vermont
• I've heard complaints about how it weathers

I wasn't sure if the bonding in plastic weld--adequate for carrying water--would be adequate for carrying 180# of Idle Dad 30 mph over potholes.

Bamboo suggests several advantages to me.

• It looks cool
• It's natural flexibility will provide shock absorbancy over frost heaves.
• I read about how to do bamboo joinery and--unlike brazing--it sounds like something an Idle Dad can do.
• It is a renewable resource and doesn't offgas solvent vapors
• I've always liked bamboo

As you can see, my resources are all based in good engineering and sound logic

Do You Need Fast and Free?

Is this you?

• You can't afford a Prius
• You can't afford gas
• You aren't an engineer
• You don't have the gumption to bike around town
• You like to fiddle with things

If so, you're like me. And then maybe you, like me, are intrigued at the possibility of electrically-assisted bicycles. Vehicles that can travel 30 mph without any effort, even faster if you get exercise while you travel. They can have three wheels to be stable in slippery conditions, and even be enclosed to be dry in the rain. They don't burn a drop of gasoline.

There are a number of places to buy such things. Electricrider.com, exertrike.com. But I'm poor, and I like projects. So I decided to build one.