How much bike to use

Today's question is: do I cut off the entire rear triangle of the salvage bike, or do I only use half of it? That steel is heavy! Moreover the connection into the main bike is tricky, since I foolishly did not leave a long tail on the lower pole, and the bracing poles interfere with connection parts.

I have long tails on the upper two bars. This is what I leaning toward: I will use half the lower bar of the triangle, connecting the cut-off ends to a bamboo fork I can splice into the main frame. I will use the entire rear bar of the triangle, to have the mounting space for brakes and other items. The tails of the upper bamboo can make nice lap joints with the rear triangle bar. The bamboo, with a little shaving, can fit into the cut ends of the lower bar. A little diagonal bracing and this should be a strong mount.

On the Other Hand

Maybe a hacksaw is better. I'm always checking and trying things. Had a tight space where the 1" wide dremel cutting wheel didn't really fit. So I used the metal cutting blade on a keyhole saw and quite easily finished the cut. So for the next tube, I tried the hacksaw, and went faster with less dust.

Caveat: I didn't check the blade before I started, but it was ruined when I was done. 3" of teeth were worn away. If this holds true, I'm going to prefer to go through 2-3 dremel wheels (15c each) rather than 1 hacksaw blade.

The incomparable dremel

I had assumed that I would have to use a hacksaw to cut up the bicycle, and was not relishing the thought of the time spent going ree-ree ree-ree on hardened steel. If a hacksaw could even cut hardened steel. I have a scroll saw with a metal blade, but that was a slow screaming terror when I tried to use it on aluminum.

Behold! The indefatigable dremel cuts through hardened steel using only its ordinary emery board cutter. The cutters wear out fast, but they are working!

Destruction!

Part of my plan includes using bicycle parts. I plan to use the aft section of a bicycle to hold the rear wheel, and the steering hub and fork of two kiddie bikes to hold the fore wheels. I've got the adult bike, so today I started disassembling it. What fun. Had to break the chain to get it off, but I figure I'll have to link two-three chains to deal with the longer length, so, no big deal their. But getting off all the fancy new components (bicycles have changed a lot since I was a kid) was a treat.

Progress

As you can see in the photo below I have added the supports for the third pole so I will have a strong, triple poled frame. I built these braces a little differently than the first, as you can see from the close-up below.
I cut each brace pole on a 30deg angle, and drilled their mortises at a similar angle around the main poles, so that they meet in the middle snuggly. Only one of them required any real trimming to make snug. Then I make three oval holes in the third pole, set it down over these braces, and secure with a single pin through both braces. This oval hole is on the large side. To keep it from getting too large, and weakening the pole, I notched the peak of the braces.

It all worked very nicely. I don't have pictures of the main frame assembled, yet, but it is almost done. Next will come building the support for the front wheels.

Tools

These are all the tools I found I needed in my work. I'll try to keep this updated, and not include any tools needed for things I tried but didn't use.

• Power Drill, inc. 1/2" speedbore bit
• Dremel (rotary cutting tool), inc. cutting wheel, and large and small sanding drums
• miter saw
• wood chisel, 1/2" or so
• mallet or hammer
• coarse sandpaper
• machine screws (bolts) with locking washers and nuts, 8/32, several 2", some 1", 1&1/2", and a couple 2&1/2"
• screwdriver
• wrench
• hacksaw
  
• keyhole saw with metal-cutting blade.
  

Bracing the frame

I've been adding diagonal braces to the frame poles. It took some experimenting to determine the best way to do this, but this is where I settled:

1. I use a mitre saw or coping saw to cut two 45deg cuts opposing each other on the inside of the poles, at each end of each brace. These cuts go down only a 1/16th of an inch, not even enough to go through the bamboo wall.
2. I use a 1/2" chisel to cut out the opening.
3. I use a dremel or rotary cutting tool with the drum sander to shape one side to the shape of the brace pole. The other side, which takes the end of the brace, is kept flat.
4. When I have two good openings like this at the proper places on the two poles, I measure and cut the diagonal brace from 1/2" bamboo.
5. I firmly hold the brace in place, and drill through the frame and brace at a slight angle.
6. I insert a 2" machine screw (bolt) through the hole and bolt it together.

The use of bolts unfortunately adds a noticeable amount of weight, but appears required. I suppose I could mortise this joint as well, and secure with a pin, but drilling at a 45deg anle into the bamboo would be challenging, and there would be complications, such as the difficulty of getting the brace in between the poles, or of passing it through the poles.

The frame is started!

I have constructed the first piece of the frame!

This is the two lower poles that for the main part of the frame, which will make a triangle-beam with a third pole. The 1" bamboo poles are joined by short lengths of 1/2" bamboo, mortised and pinned, as shown in this photo:

The wire is 18 gauge galvanized steel I wrapped around the bamboo to prevent/repair splitting when the snug crosspole is inserted (an issue). The pin is a 3/16" hardwood dowel that prevents the crosspole from coming out.

This entire construction has nothing to do with my plans, and indeed contradicts advice I gave elsewhere: a speedbore can be used successfully on bamboo, if the bamboo is prevented from vibrating with a firm parrallel clamp. I decided to go with this joinery option, thinking that I would use several half-inch bamboos for triangulation anyway. Other sites described this sort of motising as a strong joint, and it appeared to be the simplest and least fussy option. Here I go!

The Model

I said I had made a model. Here are the photos. Note that I made a number of changes to the design after making this model. Which I will note after the pictures:

The most significant change I made was to invert the triangle formed by my three poles. That is to say, I put one pole on top and two along the bottom. Why?

It's hard to see in this photo, but the rear axle is at a noteworthy angle from perpendicular. Because there is no continuous bar from the main frame to the axle, there is a large amount of play, and a slight inaccuracy in the length of the poles or squareness of the joints easily become noticable errors in alignment. By using two poles along the bottom, these become straight by definition, and the number of variables is reduced.