I am not understanding exactly what you are trying to do. Is the taper totally straight or are you matching an irregular wall? Are you planing the face of the board or the 3/4” edge? The board is 3/4 x 30 x what?

Hot melt glue a fence to your planer at a 90* angle to the cutter.

@Seabornman, I don't think I can judge I that I'm holding it steadily. After I do a pass, the surface is all wavy. I borrowed the planer from a friend. No accessories.

@mononhemeter I'm trying to taper just one end to match an irregular wall. The wall tilts in by 3/16 from top to bottom, so I'm trying to plane off 3/16 at the bottom end and feather back to 0. I'm planing the 3/4" edge of the board. The board is 5"x3/4"x30". I have clamped to my work table to plane the edge. I start at the end and follow my pencil mark till it trails off, but I can't see what's going on underneath the planer. It feels so wobbly riding on that narrow edge. I end up with a wavy mess. If I go too slow, the planer burns the wood.

@Joseph Corlett, LLC, can you suggest what I use for a fence?

Are you cutting across the grain or along the grain? Could you try using a bandsaw (or even a jigsaw with a fence). Or a router with a straight bit and a piece of wood used for the fence?

@mononhemeter I'm cutting along the grain. I have a jigsaw, but no fence. It's hard to cut a flat angle that tapers to 0 with a jigsaw. I'm afraid it would look chewed up as I try to skirt along the edge. I don't have a router or a table saw. :(

A small piece of plywood would make a fence.

You could try using the jig saw on a test piece of cheaper wood. Clamp the plywood as Joseph mentioned above to the wood so that the side of the jigsaw rides against it. Then sand it.

I have always been frustrated with my power planer. I've rigged fences, clamped the material, taken shallow cuts, but It's a very temperamental tool. Very good for wide things like doors. If it's only 3/16", buy a small hand plane.

Here is a video about using a fence with a jigsaw. https://m.youtube.com/watch?v=TEb7IdWbWKI

@Joseph Corlett, LLC

@Seabornman

@mononhemeter

Thanks, guys! I will watch the video and practice using a fence on scrap wood. If I can't do that well enough I will try a hand plane. I inherited one from my dad. Need to look in the garage for it. The blade might need sharpening - had some nicks if I recall.