Dogbone Fillets for CNC-Cut Wood Joinery

Separate two fit problems

Slot width controls side clearance; corner relief controls whether a square corner can enter. Enlarging the entire slot to solve an internal radius creates unnecessary looseness. First establish fit with a straight coupon, then add local relief for the corners.

Dogbone and T-bone geometry

Vectric describes dogbone relief as a circular extension positioned around the corner and T-bone relief as an extension to the side, useful in particular width/tool relationships. Names and implementations vary across CAD/CAM tools, so inspect generated vectors and toolpath rather than relying on the label.

Use actual tool geometry

The relief must accommodate the cutter path and mating part, including runout and intended assembly clearance. Changing cutter diameter without regenerating the joint can leave insufficient relief or create a large visible notch. Parameterize cutter diameter and material thickness where practical.

Protect strength and appearance

Relief removes material beyond the nominal corner. On a narrow tab, near a fastener or in visible furniture, its location can weaken or distract. Rotate or relocate the relief, change joint style or use a smaller suitable cutter when the design cannot tolerate the notch.

Test an assembly coupon

Cut several slots and tabs with small controlled fit changes in representative material. Label each before removing it from the sheet. Test by hand without hammering, then inspect veneer damage and corner contact. Use the chosen value in the project model and retain the coupon record.

Start from assembly intent

Identify which external corner must enter each internal corner and where extra clearance is acceptable. A dogbone is a functional relief, not decoration. Its direction affects appearance, edge strength and tool access, so choose the style in context and inspect the assembled joint rather than judging the profile alone.

Keep cutter assumptions synchronized

Relief geometry must match the cutter used to make it. If the CAM tool diameter changes while the drawing remains fixed, the joint can become too tight or unnecessarily open. Store the tested cutter, measured material thickness and clearance with the project, then recut a coupon whenever one of those inputs changes.

Decision table

Practical checklist

1. Confirm actual cutter diameter.
2. Separate fit allowance from corner relief.
3. Review strength and visible surfaces.
4. Cut and label an assembly coupon.

Frequently asked questions