I want to buy a stationary belt sander. but I don't have one so this is how I do it. Block planes are kinda short but I guess will work. I use a jointer's plane that I got for $40 at an antique store. An extra HOCK (check the website) blade and 30 min of tuneup time and it's a work horse for me. I couldn't build bows with out it. the stock blade I reground to a VERY shallow crown. Skew the blade and take diagonal cuts and you have a gentle scrub plane for hogging off wood . . . kinda.
Back to boo flattening. I set the rounded blade to the widest part of the curve and set it pretty shallow then work it deeper in stages of like 1/64 till I'm happy.
I clamp the boo with a piece of bike tire tube under it. You should be able to get it for free from a bike mechanic. Or you could use two strips of the bike handle bar wraps laid side by side. Used is also free from bike mechanics. The crowns will cause high and low spots that wont sit still. I put a shim under the section I'm working on at the moment. Wax the sole of the plane to get a good slick glide with paste wax. Work slow and check often. I also precut the bow shape for the tips then re-thin and flatten those. There will be some tearout around the nodes unless your blade is "Scary Sharp" which I recommend (google that). I then use the disk from an angle grinder for sanding aluminum. 35 grit or something seriously coarse like that. Hand sand to get the plane facets out and blend out what little tearout you will have. I don't sweat a little tearout because I'll be using a grooving plane later anyway. Don't skimp on the glue. Get it in all the grooves and what little tearout you have.
If you have a belt sander then look up a website "poor folks bows" and read the bamboo backed Ipe build along.
