Calculator Inputs
Example Data Table
| Branch OD | Main OD | Angle | Points | Use Case |
|---|---|---|---|---|
| 50 mm | 100 mm | 90° | 24 | Standard tee notch |
| 76 mm | 114 mm | 45° | 36 | Angled brace joint |
| 2 in | 4 in | 60° | 32 | Frame support pipe |
Formula Used
Wrap Length = π × Branch OD
Step Spacing = Wrap Length ÷ Number of Points
Estimated Notch Depth = Radius × cos(angle) + curvature factor + clearance + half kerf
This calculator gives a practical layout estimate. Always verify marks with a test wrap before final cutting.
How to Use This Calculator
- Enter the outside diameter of the branch pipe.
- Enter the outside diameter of the main pipe.
- Add the joint angle in degrees.
- Choose the number of layout points.
- Add kerf and clearance values.
- Press calculate and mark each point around the pipe wrap.
Fish Mouth Pipe Layout Guide
What the Calculator Does
A fish mouth pipe cut helps one round pipe fit against another round pipe. The cut shape looks like a curved saddle. It is common in handrails, frames, braces, exhaust work, and tube fabrication. This calculator estimates wrap distance, point spacing, and cut depth.
Why Accurate Marks Matter
Small pipe layout errors can create gaps. Gaps weaken welds and increase grinding time. A clear wrap pattern helps you mark the pipe before cutting. It also helps you compare different branch sizes and joint angles.
Planning the Cut
Start with accurate outside diameters. Do not use nominal pipe size unless it matches the measured outside diameter. Then select a practical number of points. More points create a smoother curve. Fewer points are faster, but less detailed.
Kerf and Clearance
Kerf is the material removed by the cutting blade or wheel. Clearance gives space for fitting, beveling, or weld preparation. A small allowance can make the pipe easier to seat. Too much allowance can create a loose joint.
Using the Pattern
Measure the wrap positions around the branch pipe. At each position, mark the listed cut depth from the pipe end. Connect the marks with a smooth curve. Cut slightly outside the line. Then grind slowly until the fit is clean.
Best Practice
Use this tool for planning and layout. For pressure systems, structural work, or certified welding, confirm the pattern with approved shop methods. Material thickness, bevel angle, and welding procedure can change the final preparation.
FAQs
What is a fish mouth pipe cut?
It is a curved notch that lets one round pipe fit against another round pipe.
Can this calculator handle angled joints?
Yes. Enter the joint angle, and the calculator adjusts the estimated notch depth.
Should I use outside diameter?
Yes. Use measured outside diameter for better layout accuracy.
What does wrap length mean?
Wrap length is the distance around the branch pipe circumference.
Why add kerf allowance?
Kerf allowance accounts for material removed by a saw, grinder, or cutting wheel.
How many points should I use?
Use 24 to 36 points for a smoother hand layout pattern.
Is this suitable for welding preparation?
It helps with layout, but certified welding work needs approved shop checks.
Can I download the results?
Yes. Use the CSV or PDF button after calculating the layout.