Although crude horizontal boring machines driven by water power were at first used, these appear to have been superseded in the 18th century by a vertical variety driven by horses. However, in the vertical machine in which the drill rotated while the descended by its own weight, precise alignment of the drill with the axis of the piece was difficult to maintain, so it was eventually decided to revert to the horizontal type. The latter, in which the gun rotated while the drill or boring bar remained steady, could be set up on a much firmer foundation, and therefore produced a more precise job. As a further advantage the horizontal machine enabled the outside of the piece to be machined at the same time as the bore. Boring and turning completed, the vent was then drilled by two men with a hand-operated drill.

After venting, the trunnions were machined. The gun was positioned with its trunnions vertical, after which about a quarter of an inch (6.35 mm) of the uppermost trunnion was brought to the proper size by file and chisel. Upon it was then placed a circular box with a cutter fixed on its underside, while on the upper part was fixed a vertical spindle with a heavy weight pressing down upon it. Levers were then attached to the spindle, and two men kept walking round and round rotating the box until the length of the trunnion had been machined, the end being finished with file and chisel. The men then repeated the performance on the other trunnion - and hoped the axes of the two were somewhere near being in the same straight line, and that this line was at right angles to the axis of the piece! With the coming of steam power (1845 in Woolwich), the hand-finishing of trunnions ceased with the introduction of a special trunnioning machine which ensured their accuracy in all respects. Power drills, eg for drilling vents, were also introduced. The 'think big' guns described earlier were not machined, merely cleaned up after casting.