Set drill depths with a reliable depth gauge

Learning how to use a depth gauge for consistent drill bit depth removes guesswork from blind holes, dowel sockets and hardware recessing. The accessory provides a repeatable physical stop, so every hole reaches the same distance below the surface. That matters when a few millimetres separates a clean fit from a joint that is too tight, a hole that breaks through, or parts that no longer register with one another. Consistent depth also reduces handling and sanding after drilling.

A typical mechanical depth gauge is a sliding rod, sleeve or adjustable stop that links the drill spindle to a known reference surface. As the bit descends, the gauge reaches its stop and limits the travel. Some designs fit around the chuck, some attach to the machine column, and others use a collar on the bit shank. The operating principle is simple, but the best setting depends on the gauge, bit and machine being used.

Australia adds a few practical wrinkles. Most local drill bits, chucks and depth scales are metric, so read millimetres and keep imperial scales separate; one inch equals 25.4 mm. Bunnings, Mitre 10 and independent woodworking suppliers around Melbourne, Sydney and Brisbane are practical places to compare accessories and replacement bits, although choices vary by store. Sloan’s Woodshop carries drill and router bits and other craft accessories, but it ships within the United States and takes catalogue orders by toll-free phone rather than online checkout. Australian shoppers should therefore plan on local sourcing rather than an international parcel. If goods are imported, Australian Border Force may assess GST, duty and clearance charges.

Why the reference point controls the result

The reference is the part of the bit that actually cuts deepest. A standard twist drill usually ends in a point, while a brad-point bit, Forstner bit or centre-cutting bit has a different profile. If you measure from the shank, flute edge or a theoretical point, the stop setting will be wrong. Fit the bit, tighten the chuck with its key, and check that it has no sideways movement before setting any scale.

Even an accurate gauge cannot compensate for a moving workpiece, a wandering bit or a stop that slips. Clamp both sides of the work, use a sacrificial backing piece and feed at a steady rate. Dense Australian timbers such as jarrah and spotted gum benefit from sharp edges and frequent chip clearing, because heat and packed fibres can change how the bit enters the hole.

Select and fit the right gauge

Choose a gauge that matches the job and the machine. A spindle-mounted gauge follows the bit and is useful for batches at one depth. A fixed stop attached to the drill press is simple and positive but less flexible when the setup changes. Follow the maker’s fitting instructions; do not force an accessory into a chuck unless it is designed for that fit. Also check that the rod will clear the workpiece and that its scale can be read from a safe position.

Before setting the stop, lower the bit until its tip touches a flat scrap piece with the same thickness as the work. On a rod-style gauge, move the adjustable stop until the rod meets its reference surface at the desired bit travel. On a fixed stop, account for the distance between the bit tip and stop and for the stop’s position relative to the workpiece. For a laminated or stacked project, a woodworking layout plan can reveal how stock thickness and registration affect intended hole positions, helping you choose the right reference before cutting.

Lock every adjustment, then make a test hole before marking the workpiece. Read the scale in the same units used by the tool and record the reading beside the bit size. Australian chucks are commonly advertised in millimetres, with 13 mm the usual half-inch class; check the maker’s capacity range rather than assuming a 12.7 mm shank will be held identically. For an imported or second-hand drill press, check the 230–240 V rating, Type I plug and power lead, and use an RCD-protected outlet. A US 120 V machine is not suitable for local mains power.

Compare methods for different drilling jobs

No accessory is best for every situation. A spindle gauge gives convenient adjustment and readable feedback, while a rigid stop gives a hard physical limit. Less elaborate references are still useful for occasional work, provided their limitations are understood.

Method	Best suited to	Repeatability	Main limitation
Spindle-mounted depth gauge	Repeated holes at one depth	High when the rod and scale stay rigid	Must clear the chuck and workpiece
Fixed stop on the drill press	Long batches of identical holes	Very high once the stop is secured	Inflexible between setups
Collar on the bit shank	Occasional blind holes or a portable drill	Moderate	Can mark the bit and is easy to disturb
Masking-tape reference	One-off drilling	Low to moderate	Tape shifts, tears or hides the true depth

For repeat production, choose the method that minimises changes between holes, not necessarily the one with the most features. Change the workpiece height, bit length or reference surface, and the setting must be rechecked. If one method works well for a single template but drifts during a long batch, it is the wrong method for that production run. A short written setup record is often more valuable than another accessory.

Test the setting and correct common faults

Make a test hole in an offcut of the same thickness and measure from the top face to the deepest point of the hole. A depth gauge or vernier can confirm the result, although the conical point of a twist drill must be included rather than measuring only to the first visible sidewall. If the hole is shallow, reduce the indicated depth by the measured difference; if it is too deep, increase the setting by that amount. Drill a second test before changing the workpiece.

Most inconsistent results come from a loose chuck, a bent or dull bit, packed chips, an unfirm clamp or a gauge that was not locked. Check the bit for runout, clean the flutes and feed steadily enough to cut rather than rub. A pencil line on the bit is useful for checking, but it is not a positive stop and can shift under vibration. That registration principle is illustrated in Sloan’s guide to layered scroll-saw cuts: slight offsets become more obvious as layers accumulate.

If the first hole is correct but later ones vary, watch the work surface, clamp pressure and gauge position. A board that flexes or creeps upward changes the effective depth even when the machine setting stays fixed. Keep a sacrificial piece beneath thin stock to prevent breakout, and stop if the bit begins to wander. Recording the diameter, point style, depth and material makes the next setup quicker and more repeatable.

A repeatable workshop routine

Treat depth setup as a measured process rather than a last-minute adjustment. The workpiece stays still, the bit is clean and sharp, the gauge is locked and the first hole is checked. This sequence takes less time than correcting a batch of misaligned joints or filling oversized holes with filler and paste.

For repeat work, keep the setup beside the machine and note the gauge reading, bit and workpiece thickness. If the bit changes, check the reference again because a different tip profile may require a different scale setting. Use the same sacrificial board for test holes, and replace it once its surface becomes bruised or grooved.