Tube Notch Troubleshooting — Root Gaps, Wrap Errors & Fragile Horns

Quick Diagnosis Table

Gap at the Root of the Joint

The generator cuts on the outer surface (thin-wall assumption). Thick-wall tube has a different inner intersection — the ID wants a slightly different profile. A light bevel toward the root usually closes the gap enough for a sound weld. If the gap is uneven around the saddle, the axes are probably not centered or not coplanar in the real fixture even though the drawing says they are.

Template Does Not Wrap True

Almost always printer scaling. If you did not verify the 1 in / 50 mm square, the strip will be short or long and the ends will not meet. Reprint at 100% Actual Size and re-measure the square before blaming the math. Second cause: nominal OD instead of measured OD — especially on painted, plated, or out-of-round tube.

Fragile Horns at Near-Equal Diameters

When branch OD equals run OD at 90°, the notch is a full-depth fishmouth. The thin tips (“horns”) are geometrically correct and mechanically fragile. Support them while grinding, avoid aggressive cut-off wheels at the tip, and consider a dedicated notcher or CNC laser if you make many equal-diameter joints.

Angle Measured Wrong on the Fixture

Entering 90° when the fixture is really 75° produces a template that looks fine on paper and fails on dry-fit. Measure the angle on the clamped assembly, not from memory. Shallow angles (<~35°) make long templates that amplify small angular errors — the tool warns on those inputs for a reason.

Still choosing between a printed template, hole saw, or dedicated notcher? See Template vs Hole Saw vs Notcher. Related bend geometry: Tube Bending Calculator and Tube Bending Guide.