1. Choose set-on or set-in
Set-on: the branch rests on the outside of the main pipe. This tool uses branch inside diameter, calculated as OD minus twice the branch wall thickness, for the nominal passage outline. The existing branch-end notching calculator is a separate tool.
Set-in: the branch enters the main. The effective diameter is branch OD plus the specified diametral clearance. A 1 mm diameter difference is 0.5 mm per side in the branch cross-section; it is not a uniform 0.5 mm offset of the unwrapped curve. Clearance is not a weld-gap or kerf setting.
2. Know what the template represents
The output is the intersection of the effective branch cylinder with the OUTSIDE of the main tube, unfolded using main-surface arc length. It is not a circle or a flat-plane ellipse pasted onto a curved tube.
It marks the outer surface only. Main wall thickness, an inside-face contour, branch insertion depth, root opening, bevel and cutting tool orientation are not calculated. An angled opening cut radially through a thick main wall may need additional finishing to clear an inserted branch. Do not treat this DXF as a finished CNC toolpath.
For this version the effective diameter must be strictly smaller than the main OD and at least 1 mm. Included angle is 15–90 degrees, with intersecting centerlines and no offset. Equal-size or wrap-through openings need a different layout and are rejected.
3. Mark the center and the direction
The center is where the branch axis meets the main OUTER surface, not where the two tube centerlines meet inside the main. Measure its axial distance from the selected pipe end. Default values are examples; enter your actual drawing dimensions.
Draw a reference generator along the main tube and call it 0 degrees. Looking into the selected pipe end, measure clock position clockwise. The displayed arc from 0 degrees equals main circumference multiplied by clock angle divided by 360. Wrap a tape square to the main axis to transfer it.
Place the template cross at this mark. Its vertical axis runs along the main tube; down on the page means away from the selected end. The branch leans toward that same away-from-end direction. If the required branch leans toward the end, use the other end as the reference and remeasure distance and clock position.
4. Print and transfer the closed loop
Choose a supported paper size, print at 100% and measure both rulers. For multiple sheets, match the template code and both A/B targets on every join after trimming the indicated left/top edges. Do not butt paper edges.
The patch covers the opening, not the whole circumference. Mark the center before cutting the paper. Trace the closed solid loop; remove the INSIDE. Dash-dot axes and circled registration marks are references only.
DXF is in millimeters with its origin at the marked center: X is circumferential arc and Y is axial distance away from the selected end. HOLE_PROFILE is a closed polyline. REFERENCE_DO_NOT_CUT contains reference axes.
5. Check the physical fit
The tool checks that the outline does not pass the selected pipe end, but it does not know the total main-pipe length or nearby holes. Check the far end and surrounding features yourself.
Confirm the stock dimensions, paper scale and actual fit on a test piece. Welding preparation, structural suitability and pressure design are separate decisions. The branch-end tool does not calculate a set-in branch insertion length or an inner-wall end profile.