Tacking it

Front Triangle

As you miter your going to want to start tacking the frame together.

Here is the order that I used:

1) Seat tube to bottom bracket. Be careful that you account for the natural bends in the bamboo in this case I allowed it to natural bend slightly backwards towards the rear wheel. Make sure to sand the metal and bamboo parts. Apply a thin layer of epoxy to the metal, let it dry and then sand before attaching the tube. For the bamboo sand till dull and then rub with a small amount of acetone (or acetone alternative) 15 mins before bonding, see materials blog for more info. Also, during this whole process make sure that you are using a respirator w/ an organic vapor filter. If you start getting a headache, its probably just your brain melting.

2) Then I mounted the head tube in the jig and mitered the top tube into place. Again this is where having a frame to copy comes in handy you can hold it up to compare angles, heights etc. When tacking the joints use more epoxy than you think necessary, add microfiber filler to thicken so it doesn’t just run off. It also likely helps to wet down the inside of the mitered joint to help adhesion. Add more epoxy than shown above, cover the whole mitered area if you can.

One nice thing about this jig design is the ability to microtune it. The picture above shows me dialing in the correct angle, making sure everything is straight.

3) Next step was the down tube. I started by mitering the bottom bracket joint first. When that was set I slowly mitered down (using sand paper laid on top of a wide pole, see mitering post) the head tube – bottom tube joint. This worked quiet well because it allowed me to get the angled miter to the head tube correct, since the bottom bracket miter can swivel.

Rear Triangle

4) Next is was the chain stays. Things to keep in mind. Seems obvious but its worth mentioning. You need your wheel on straight. There is probably a better method but here is what I did. First I drew a straight line from the middle of the bottom bracket to the middle of where the hub will be. I hung a straight piece of metal from the carriage bolt (shown below… its a hacksaw blade). I then measured the hub spacing from my metal frame and fixed that distance on between the washers and centered the hacksaw blade in the exact measured middle point. This is important because it allows you to eyeball it much easier. Then trust your eye. Make sure everything is inline, including you seat post and head tube.

The hardest part here was mitering and setting the poles in such a confined space. Again use the techniques described in the mitering post on this blog. Be very incremental, small changes make are a big deal here. I tried to keep the joints far out on the bottom bracket to free up extra space for tire clearance. Also always look at each poles characteristics and try to use it to your advantage, use slight bends to free up tire space etc. Also keep in mind that bamboo nodes are the weakest link in you bamboo pole avoid depending on them if possible.

Before you tack your chain stays in place make sure you have enough clearance for you wheel and tire, and also make sure that you have you dropouts set in a place that will allow you to get the correct angle for your seat says. Use a lot of epoxy for this tack because its a long lever arm and its holding up your heavy ass dropouts.

NOTE: My intuition is that your epoxy and hemp fiber will not be enough to hold the dropouts in place. For this reason when I tacked the frame together I only applied glue to the hub-side of the dropouts. This keep a nice open hole on the outside which you can better fill with thickened epoxy or fiber/epoxy later.

5) Seatstays
After your epoxy from the chainstays has hardened, you can start touching it again. Here I used the online miter pattern tool and alot of slow progressive sanding to get everything in place. After the upper part of tube was mitered I trimmed, mm by mm, the lower part of the tube till it was flush and striking the right place. Then I applied some epoxy and let it dry.

Next I tacked the dropout side of the seat stay. NOTE: I regret not taking more time to make sure the clearance was good for the rear wheel. Unfortunately I do not think that I will be able to run with a disk brake in the rear any more… just not enough clearance. Also the gear-side chain stay does not have as much clearance for a 9 speed cassette as I had hoped, but it looks like it will work.

The next step was to properly fill the rearmost (dropout side) openings of the seat and chain stays. Here I worked a whole crapload of thickened (mayonaise-like) epoxy into the tubes ( I was trying to fill them as much as possible. You might even consider cramming some hemp fiber down in order to prevent the epoxy from fracturing. Each pair of tubes I used one batch of epoxy as measured by the West System pumps. I believe that this will help to hold the dropouts in place and avoid getting cracks in any of the tubes. I then used my torch to harden the epoxy on the outside and hung the frame from the head tube, thus encouraging the epoxy to work its way back around the dropouts. You can see the slightly burnt epoxy that was holding in the liquid epoxy inside the tube above.

NOTE: I have found after some trial with both that the West System 404, high density filler is easier to work with. It more easily disolves (microfiber filler gets very clumpy but does seem to thicken more rapidly) and should provide better load-bearing properties.

That’s it!