Wood – How to make 1/4 inch beveled edge on unfinished walnut countertop

Sorry. My first answer mis-understoood the question. Based on the updated question, there are many ways to create a shape of the desired profile, based on what tools you have or can find/buy/etc.

• Rip the edges with an angled tablesaw blade.
• A handheld power (circular) saw, with the blade at an angle. A fence will help you get a straight edge.
• A jointer.
• A handheld power jointer.
• A hand plane. A good craftsman with a sharp jointer plane can do this easily.
• A router table.
• A handheld router.
• A millwork shop can easily turn this profile out, so you can always buy it ready made, for a price.
• If you have a friend with any of the above power tools, I'll bet they can be bought off for the price of a pizza.

Very much depends on what tools you have, how much money you want to spend. You can use it to justify buying a specific tool, if you have a use for one of the tools I've mentioned. They are all useful.

A tablesaw or a router are both terribly useful tools, but if this is a one time job and you have no interest in woodworking, then I'd look for a friend who can help you out. If you insist on doing it yourself, and might have an occasional use for a hand held circular saw, then go that route. A circular saw will be often enough of use even to someone who is not an avid woodworker.

Attach your board to a straight piece of wood to use as a fence. Then angle the blade, and rip the edge as you want it. I'll argue this is the cheapest solution that will give you a good edge. (A hand held jointer plane might be even cheaper, since you can get them quite inexpensively from an antique shop. But a jointer plane will take some practice to do this job well.)

Yellow line is where you need to go, make the form slightly longer on the meeting edges so the ends can be recut to a clean joint. the reason being, moisture loss in concrete will change the look of the slab were it looses it rapidly. This means at any joint in the form where water can leak out will force the concrete to cure differently. Caulking the corners will help fix the problem an will also radius the edges a little or more if you choose, when done in the right spots. This should be done on the meeting joint, but of course you don't want a radius where they meet, hence the recut. Have some 1/4" stainless steel rod to drop into the wet mix at the sink front to strengthen those ends. If you put any on the back edge, be sure you steer clear of the area where the faucet is drilled.

You may be aware of this already, but I need to mention this. Concrete slab tops are honed/polished like natural stone is. A stain can be added to the surface prior to honing to add a variation in color too. Melamine will give a good start, but the honing and polishing will give a fine finish.