Router Bit Tenon Depth & Groove Tolerance Chart

Tenon length and groove depth are different inputs

The rail tenon extends beyond its shoulders and enters the stile joint. Panel groove depth describes how far the center panel can enter the frame. Some cutter profiles make related dimensions, but equality must come from the actual profile and setup.

The calculator’s 3/8 inch value is an editable starting example. It is not an all-brand Freud, CMT, Whiteside or other manufacturer specification. A 1/2 inch choice does not certify a Domino or other loose-tenon joint as the same geometry as a cope-and-stick rail end.

Record the exact cutter identifier, stock thickness and setup. Use its instructions for permitted materials, configuration and safe operation. A product family name or a brand home page is not evidence for a tolerance.

Visible rail span = finished door width − 2 × stile width
Rail cut length = visible rail span + 2 × measured tenon length
Panel cut width = visible rail span + 2 × measured panel groove depth − total width allowance
Panel cut height = finished door height − top rail width − bottom rail width + 2 × groove depth − total height allowance

Reference table: vary only the measured tenon length

Assume an 18 inch finished door and two 2-1/4 inch stiles. The visible rail span is 13-1/2 inches. The table changes only tenon length; the panel groove remains 3/8 inch as a separate example input.

Freud’s manufacturer-authored Premier instructions RTD10000772AA illustrate a 13/32 inch stub tenon on PDF page 3. The 7/32–3/8 inch adjustment discussed on page 7 describes groove width and tongue thickness, not groove depth. The linked copy is hosted by a distributor; check the instructions for your exact cutter and revision.

The rail length difference between 3/8 and 11/32 inch tenons is 1/16 inch across the two rail ends. This is arithmetic, not a claim that bearing wear causes that error or that a particular joint will close correctly.

Check the actual profile on representative stock

Make a test joint using the intended cutter setup and representative stock, following the tool instructions. Record the tenon length from shoulder to end, groove depth to its root, groove width, actual panel-edge thickness and finished shoulder fit. Keep the tested setup with the cut list.

For example only, a measured 7/32 inch panel edge is 5.55625 mm, while a measured 1/4 inch groove width is 6.35 mm. Their difference is 1/32 inch (0.79375 mm). This does not establish acceptable fit or the thickness of all nominal 1/4 inch plywood.

A front-to-back thickness mismatch is different from the expansion allowance between the panel edge and groove root. Reducing the panel’s outline cannot fix a groove that is too wide through the stock thickness. Check each problem against its own measurement.

• Measure rail tenon length and panel groove depth independently.
• Measure panel thickness rather than relying on its nominal label.
• Check the cutter instructions for permissible shim changes; no universal shim formula is assumed here.
• Check rail shoulders and frame size, then verify panel retention and movement separately.

A fraction display is not a machining tolerance

The inch view can display the nearest 1/16 or 1/32 inch. Rounding is a reading choice, not permission to change an exact target. Keep the underlying decimal or millimeter dimension where a displayed fraction is coarser than the requirement.

There is no universal “Shaker bit tolerance” in this chart. Acceptable joint fit, cutter setup, finish requirements and stock movement depend on the actual tooling, material and project specification. Check the applicable instructions instead of treating a generic website or a sample dimension as a production limit.

For a broader bottom rail, subtract the actual top and bottom widths independently when calculating visible panel height. Do not alter the tenon length merely because rail width changes. Regenerate the cut list after any profile, stock or frame change.

Frequently asked questions

Continue your cabinet plan

Carry supported calculation inputs into the next tool, inspect the inherited dimensions, then calculate the next part of the job.