This article on squaring stock is from Alan at Woody’s Workshop. The process is primarily designed to square a piece of stock ready for the cnc. However, it could be used for general machining as well.
Assume the stock can be represented by the following shape with each side numbered as shown. The numbering is important to help keep track of the process steps.
Inspect the stock and pick the side that has the surface that is the flattest and most appropriate for the end result you are looking for. Place this surface against the rear vice jaw. This eventually be machined to become Side 4 but for the moment just skim the top surface which will now become Side 1.
Note that there is no support to the workpiece but it is just placed as best to suit the top surface to be skimmed relative to the rear ‘rough’ face. If the front face is very rough and uneven a metal rod can be sandwiched against Side 2 to locate it more firmly against the front vice face but care is needed with this.
I use copper wire for the “rod” specifically because it will deform to match the face when squaring stock.Michael, Makers Forum
Rotate the block so that Side 1 now faces the back jaw and support it on a single parallel against the rear jaw and with a round pressure rod at the front jaw. Skim the top surface which will now become Side 2.
Rotate the block so that Side 2 now faces the rear jaw and support on a single parallel and with the pressure applied via the rod. Skim the top surface which becomes Side 3.
Rotate Side 3 to face the rear jaw so we now have three machined surfaces with the original best fit surface facing upwards. Support the block (Side 2 down) with two parallels. Machine the top surface which becomes Side 4.
You now have four machined surfaces which are parallel and each perpendicular.
Rotate the block in the vice by 90 degrees so that the surface 5/7 is uppermost. Clamp the block slightly off level and skim the top surface. No parallels or rod are needed. This becomes Side 5 and has a true edge (Red) but a tilted surface. The edge is the important part as this is perpendicular to Side 4 edges. Mark the edge to identify it.
Place Surface 5 face down in the vice with the true marked edge against the rear jaw and on a single parallel. Skim the top surface which becomes Side 6.
Invert the block to place Side 6 at the bottom on two parallels. Re-skim Side 5 so that is it now flat and true to all other sides. This face now become Side 7.
That’s it, you will now have a square piece of material.
Note: This clearly only works if the dimensions of each face are sufficiently large to ensure a good parallel grip action between machined faces.
This squaring stock process was written by Alan at Woody’s Workshop. Visit Alan’s website for a downloadable PDF version of this guide that can be posted onto the workshop wall.