What's inside
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A mortise gauge is useful when a tenon needs two parallel cheek lines, one on each side of its thickness. The tool does not decide the tenon size for you; it transfers a setting from a reference face or edge. That makes the quality of the fence, the sharpness of the pins and the way you hold the stock more important than a long list of features.
For most bench work, a sound traditional mortise gauge is enough. A combination gauge earns its keep if you also mark shoulders and general layout lines. For repeated work or awkward stock, a dual-screw or wheel-style gauge can be easier to control, but it costs more and still needs careful setup.
What to look for in a mortise gauge
Start with the fence. It should sit firmly against the reference face without rocking, and its clamping arrangement should hold the beam without slipping when you press the pins into the wood. A loose fence can shift the setting by a fraction of a millimetre—enough to make a tenon too thin or leave one cheek wider than the other.
Check the marking points as well. Traditional gauges use two fixed pins: one marks the mortise width, the other the tenon cheek. The points should be fine and secure, not blunt, bent or so sharp that they tear the grain. Some designs let you adjust the spacing between the pins; others fix that spacing and move the fence to set the gauge.
A wheel-style gauge uses a small cutter instead of a pin. It often produces a clean line across end grain and is less likely to follow the grain, but it makes a narrow cut rather than a light scratch. That is helpful for layout, though it can be less convenient if you want a faint line that is easy to erase or move.
Mortise gauge types compared
| Type | Best use | Main trade-off |
|---|---|---|
| Traditional two-pin mortise gauge | Occasional mortises and tenons; straightforward bench work | Pin spacing may be fixed or awkward to adjust; pins can follow grain |
| Adjustable-pin mortise gauge | Changing mortise widths or matching different chisels | More adjustments to check and more opportunity for settings to shift |
| Wheel-style marking gauge | Clean, controlled lines, including across end grain | Usually a single cutter; not a substitute for two independently spaced pins |
| Combination gauge | One tool for mortise lines and general marking | Versatile, but may be slower to set precisely than a dedicated gauge |
Which one should you buy?
If you cut a few mortise-and-tenon joints a year, choose a basic, well-made two-pin gauge with a dependable fence. There is little benefit in paying extra for multiple scales or elaborate adjustment if you will set it once, test it and mark a batch of parts. A traditional two-pin mortise gauge is the sensible starting point.
For a small shop where one gauge handles most layout, consider a combination gauge with a movable pin or cutter. It can mark shoulders and offsets as well as tenon cheeks, saving space. The compromise is that a general-purpose design may be less convenient to reset repeatedly than a dedicated mortise gauge. Look for a fence that locks positively and a beam long enough to stay stable against your workpiece.
If you make repeated joints, or need to set the two lines to a particular chisel width, an adjustable-pin model is worth considering. Its extra adjustment is useful only if the pins lock securely and can be brought back to the same spacing. A gauge with adjustable pins offers flexibility, but check that the adjustment does not creep when marking.
Wheel-style gauges are a good choice when clean cuts matter more than having two points on one tool. They work well for marking a single line or shoulder, but you need two cutters or another gauge to lay out both cheeks at once. A wheel marking gauge is therefore a complement to, rather than a direct replacement for, a two-pin mortise gauge.
Set it from the reference face
First choose the face and edge that will guide the joint. Plane them square if the work requires it, then mark them clearly. Keep the gauge fence against the same reference face on both sides of the mortise or tenon. If you flip the stock and reference from opposite faces, small thickness differences can move the cheek lines off centre.
Set the pin spacing to match the mortise chisel, if the gauge allows. For example, a 6 mm chisel calls for lines about 6 mm apart; a 10 mm chisel calls for about 10 mm. The mortise may need a little clearance for the tenon, so test the fit in scrap rather than assuming the gauge setting alone guarantees a perfect joint. On a tenon, the outer pin establishes one cheek and the second pin establishes the other relative to the fence.
Before marking the actual piece, make a short test on offcut material of similar hardness. Check that both lines are parallel to the edge and that the spacing is right. If the lines converge, the fence may be tilted or the workpiece edge may not be straight. If one line is faint, inspect the point and use steady pressure rather than bearing down harder.
Marking without spoiling the layout
Hold the fence flat against the reference face and draw the gauge in one controlled pass. A light first pass is safer than a heavy stroke: it lets you confirm the path before deepening the lines. Keep the tool square to the stock rather than leaning it toward or away from the fence. On long pieces, support the work so it cannot roll or sag as you draw the gauge.
Common failures are simple. A fence that rocks produces wandering lines. Loose pins change the spacing mid-stroke. A blunt pin crushes fibres instead of marking them, while an overly aggressive pin can tear out at the edge. Wiping the beam or fence against the work can also move the setting if the lock is not secure.
After each setting change, lock the gauge and check the distance again with a rule or calipers. If the tool has graduations, treat them as a quick reference, not a guarantee: verify the actual pin-to-fence distance on scrap. Store the gauge with its points protected, and keep pins sharp enough to score cleanly without forcing the tool.
A practical buying checklist
Before ordering, check the gauge’s usable beam length, fence stability, pin adjustment range and replacement-point availability. A compact gauge may be awkward on wide stock; an oversized one can be clumsy for small cabinet parts. For ordinary furniture work, a stable fence and repeatable setting matter more than fancy materials or engraved scales. Buy the simpler tool if it locks securely, then spend the saved money on a sharp chisel and accurate stock preparation—the parts that determine whether the tenon actually fits.