Do you have a moisture meter for checking the walnut? The reason I ask is that wood that has 20 to 25% or more needs to be dried more to use. 3/4 by 3/4 on some woods will shrink or warp after cutting, especially if green, which yours is not. However high moisture content will affect its end size after cutting down.
On green wood and on high moisture wood, I cut 1 x 1 blanks. Microwaving on "defrost mode" for 5 to 10 minutes dries it out and also causes it to shrink or distort from its original size and shape. Do NOT put it in a microwave on high for 2 minutes or more without watching it directly. It will burn, smoke and stink!
Drying in the oven on 150° for 30 minutes is also a possibility.
Remember this is for high content moisture wood cut to 1 inch. IF wood is in the 10% - 12% or less, 3/4 inch is OK.