Project 3: Square Block

For some prismatic shapes it is preferable begin by machining a block of material to a specific size. This can be done by jogging the machine using the hand wheel on the control. The process of squaring a block is also helpful for understanding concepts of flat, square and parallel as they relate to the CNC machine axes.

1. Prepare Part for Machining

Begin with sawed raw material large enough to be machined on all sides: usually at least .050 inches over-sized in each dimension.

Stock walls must be sufficiently flat and opposite sides parallel to be safely gripped by the vise. Use common sense; if the part can be moved by hand in the vise, it will loosen under cutting pressure and could move or be ejected from the vise.

Faces are machined in the sequence shown in Figure A.4 below. Figures on the following pages indicate the Top face in color grey, making it easier to see how the part is flipped for each operation.

Figure A.4: Saw Cut Stock and Machining Sequence

2. Set Tool Position

The machine spindle must be off. Manually jog the tool so it is about one inch above the Top face. Move the machine down in Z in .1 inch increments. After each move carefully slide a 1-2-3 block between the top surface and the tool, until the block makes contact.

Switch the jog increment to .001 and raise the tool until the block just slides underneath. This sets the tool exactly 1.00 inch above the face of the stock.

Figure A.5: Set Tool Position

3. Machine Top Surface

Estimate the amount of material to remove with the first cut, and then jog the machine down 1.00 inches plus this value. For instance, to remove about .010 inches of material, jog the machine down 1.010 inches.

Set the jog control to the X-axis, turn on the spindle CW, and use the hand control to machine the top face. When complete, turn the spindle off and move the tool clear of the work area.

Figure A.6: Machine Top Surface

4. Machine Front Surface

Flip the part about the X-axis as shown in Figure A.7 below so the top surface machined in the previous step rests against the fixed vise jaw. Be sure to first clean the work area with a paintbrush to ensure the part does not rest on any chips or debris.

Because the surface against the movable jaw is rough, insert a solid brass rod as shown below. This forms a fulcrum that lets the part pivot, ensuring the top surface rests flat against the back fixed vise jaw.

Figure A.7: Machine Front Surface

5. Machine Bottom Surface

Flip the part about the X-axis as shown in Figure A.8 placing the top surface against the floor of the vise or parallels. Again use the brass rod to ensure part lays flat against the fixed jaw, clear chips, and ensure there is no small gap between the top face and vise floor.

Rough and finish the bottom side as required to establish the finish dimension between the top and bottom faces.

Figure A.8: Machine Bottom Surface

6. Machine Back Surface

Flip the part about the X-axis as shown in Figure A.9 so the top surface now rests against the moving jaw. Do not use the brass rod. Clear all chips and tap down the part.

Rough and finish this side as required to establish the finish dimension between the front and back faces.

Figure A.9: Machine Back Surface

7. Machine Left Surface

Next, rotate the part counterclockwise about the machine Y-axis standing it on end. Use a machinist's square to set the machined surface perpendicular to the vise base.

Figure A.10: Machine Left Surface

8. Machine Right Surface

Finally, rotate the part again about the machine Y-axis 180 degrees so that the left surface is now against the machine base. Clear chips and tap down the part. Machine the right face to establish the finish dimension between the left and right part faces.

The part is now the precise size and all sides are flat, square, and parallel.

Figure A.11: Machine Right Surface