When machining raw blocks of material to be precisely square, the key is to only ever reference flat and square faces of the stock. Before starting, you also want to deburr your raw material to ensure the burrs do not interfere with holding onto your part as squarely as possible, as well as ensure all parts and pieces are thoroughly clean of all loose debris.

1. Side 1: Starting with raw stock, this means holding onto the most square faces of the stock (not saw cut edges), then facing the top-facing side of the part (Side 1), removing only enough material to clean up the entire face from its original stock surface.

   • Deburr/break all edges before proceeding

   • Thoroughly clean all parts and pieces before proceeding

   • Ensure the part is clamped securely before making any cuts

2. Side 2: Once you have at least a single surface that has been machined flat, you can no longer reference any other surfaces of the material unless they are machined. You can isolate these non-referenceable surfaces using a round piece of wire/rod. Additionally, you should always utilize the most consistent feature(s) of whatever workholding device you are using - most often the rigid jaw of a vise. With your first machined surface against your vise's rigid jaw and all other surfaces of the block isolated, you can cut the top-facing side of the part (Side 2) square to your first side, removing only enough material to clean up the entire face from its original stock surface.

   • Deburr/break all edges before proceeding

   • Thoroughly clean all parts and pieces before proceeding

   • Ensure the part is clamped securely before making any cuts

3. Side 3: With two sides now machined, you will want to rotate the block to orient it such that one machined side is against the rigid jaw of the vise and the other is resting flat on top of  two parallels, seated at the base of the vise between the jaws. All other non-referenceable surfaces should be isolated, with a piece of wire/rod. You can then cut the top-facing side of the part (Side 3), removing only enough material to clean up the entire face from its original stock surface. After this face has been cleaned up - and without either removing the part from the vise or moving the tool in relation to the Z Axis - you can measure the dimension between the bottom and top faces, determine how much material is left to remove to reach your target/nominal dimension, and take cut(s) until the dimension is within tolerance. It is recommended you take at least two passes for most parts - the first being a "roughing" pass, designed to remove the majority of unneeded material efficiently, and the second being a "finish pass", designed to remove the last, minimal remaining material and achieve an ideal surface quality/finish on the surface. For most parts, it would be recommended to do roughing passes until you are at or just above the high range of your dimension's tolerance, and finish passes to bring it within tolerance/to your target dimension.

   • Deburr/break all edges before proceeding

   • Thoroughly clean all parts and pieces before proceeding

   • Ensure the part is clamped securely before making any cuts

4. Side 4: With three sides now machined flat and square to one another, you now have enough sides to be able to reference all three "sides" of a vise - the rigid jaw, the parallels, and the moveable jaw - without the need for isolation. From here, you can perform the same procedure as with the previous side (Side 3), first cleaning up the top face of the part, then measuring, and finally bringing it within tolerance or your target dimension, to complete Side 4.