This is merely a refinement on the "dowel through a block" gauge, having the benefit of a smooth easy action together with a simple jamb lever which minimises the possibility of movement between taking and transferring the measured depth.

The sketch below shows the essential features of the gauge. However any of the dimensions can be adjusted to suit the intended application.

The rod for example, can be of any length with a diameter of say 3 - 10 mm. I used a stainless steel rod about 250 x 6 mm which happened to be available but a length of galvanised wire, a brazing rod or an old knitting needle could be used, providing it is straight and uniform in diameter .

The cross-bar must also be straight and big enough to span the widest diameter of the bowl or recess to be measured. The thickness of the bar should be about three times the diameter of the rod to ensure that they remain at right angles. The hole should have just enough clearance to provide an easy fit, if necessary by application of oil or another lubricant.

The locking lever, say of brass or aluminium, should be fitted so that it jambs at an angle of about 5 degrees or at a slope of about 1 in 10 as shown.

A screw and spring complete the assembly.

To take depth measurements, release the lock, extend the rod and plunge it into the cavity. The lever will allow the rod to adjust to the required depth and will lock it in position for subsequent measurement.

John Randall