how do I prepare bamboo to make it flat, to glue it?

[Osip]

I have a piece of bamboo that I want to glue to a red oak board, which is flat. How do I prep the bamboo slat to make it flat, without access to a machine planer?

[PatM]

A rasp and some coarse sandpaper stuck to a very flat board.

[Kidder]

The easiest method involves the use of power tools. I trace on the profile of the belly onto the bamboo and then cut it out on the bandsaw. I then flip it on its side and cut the thickness profile down a ways.  I then use a belt sander to thin it and flatten it. Not the most primitive methods, and I know it can be done with hand tools, but I don’t have the patience for that, especially when the power tools are staring at me.

[Osip]

some coarse sandpaper stuck to a very flat board.

ah, genius

[Del the cat]

Here's a post from my blog showing how I do it.
It can help to take off any excess from the edges with a band saw first, similar to cuts 1 & 2 in this sketch (which was to illustrate chopping out the belly from a half log, but hopefully you get the idea)
https://bowyersdiary.blogspot.com/2014/11/bamboo-backing-build-along.html
Del

[Eric Krewson]

There is more to making it flat if you want to glue the slat on a bow, you have to thin and taper the slat.

After you do your initial flattening draw out your bow pattern on the belly of your now flat bamboo, make this drawing as exact as you can with tapering to the tips and all.

Get out your sanding block and continue flattening the bamboo until every edge is 1/16" thick, this will naturally taper your slat from handle to the tips.

When you finish this secondary thinning you are ready for your glue-up.

You should end up with a piece like this;

[Bamboo-Bows]

You can use a normal drawknife or spokeshave. Use a smaller woodboard to support the bamboo. Flip the bamboo so the backingside in on the board and the innerside is facing you. Clamp it on one side with 2 woodclamps and shave the inner surface. Skip the places where the nodes are, you can file them down with a rasp or with the spokeshave. Carefully trying to prevent cutting to deep into the backing.

[Tradslinger]

I usually leave the back of the bamboo natural with the nodes. I use my belt sander to get the belly side flat. normally because my home grown bamboo is not as thick as some from Asia, I end up with the butt end being thicker unless I address it while sanding. Then I prep both gluing surfaces with first: using a hacksaw blade to rough the surfaces then applying glue to both surfaces and allowing it to soak into them for several minutes. Then using a little more glue, I clamp them together. I use TBIII. I have done with several bows including a Red Oak bow. The red oak and bamboo bow ended up 48# and shoots very nicely. I use some steel wool to lightly sand the back side of the bamboo for the stain to work then use TruOil. I used the bamboo to salvage a not so good piece of red oak and it has been a great bow. I glued the bamboo on first then trimmed or sanded the edges down flush to the red oak. The bamboo with nodes on and stained looks awesome to me. Good luck