FitterMaster Miter bend calculator: cut angles, piece lengths and a 16-point template
For a miter bend, each cut is at total angle ÷ (2 × (pieces − 1)) from square. A 3-piece 90° miter has two cuts at 22.50°; on 6" pipe with a 9" centreline radius the end pieces are 3-3/4" and the middle piece 7-7/16" on the centreline. FitterMaster's Miter screen gives those and the 16 cutbacks to lay out.
When does a miter bend make sense?
A segmented (miter) elbow is built from straight pipe when no fitting is available, on large diameters, or when the bend radius must be bigger than a standard ell. The more pieces, the smoother the bend and the smaller each cut angle. Laying one out by hand can take a few tries to get the stations right; the app skips straight to the numbers.
What is the miter bend formula?
- Cut angle α = total angle ÷ (2 × (pieces − 1)).
- Number of cuts = pieces − 1.
- End piece length (centreline) = Rc × tan α; middle piece = 2 × Rc × tan α, where Rc is the centreline radius.
- Ordinate at each station = (OD ÷ 2) × tan α × cos φ, at 16 stations 22.5° apart. The cutback is the longest ordinate minus each one.
How do you lay out a miter bend in FitterMaster?
- Open Miter under Calculate (Pro).
- Under Pipe, pick the Size. The OD comes from the pipe table.
- Under Bend, set Total Angle (15° to 135°), the number of pieces with the pieces stepper (2 to 8) and type your Centreline Radius. It starts at 9".
- Read Cut Angle (each) and Number of Cuts under Miter Cuts, plus the end and middle piece lengths in the note.
- Use the Wrap Template: 16 stations around the pipe, marked back from station 1, the longest.
Worked example: 3-piece 90° on 6" pipe
6" pipe (OD 6.625"), Total Angle 90°, 3 pieces, Centreline Radius 9": Cut Angle (each) 22.50°, Number of Cuts 2, end pieces 3-3/4", middle piece 7-7/16".
| Station | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |
|---|---|---|---|---|---|---|---|---|---|
| Cutback | 0" | 1/8" | 3/8" | 7/8" | 1-3/8" | 1-7/8" | 2-5/16" | 2-5/8" | 2-3/4" |
Stations 10 to 16 mirror 8 back down to 2: 2-5/8", 2-5/16", 1-7/8", 1-3/8", 7/8", 3/8", 1/8". Station 9 is the short side, directly opposite station 1.
More pieces, smaller cuts
| Pieces | Cut Angle (each) | Cuts | End piece | Middle piece | Largest cutback |
|---|---|---|---|---|---|
| 3 | 22.50° | 2 | 3-3/4" | 7-7/16" | 2-3/4" |
| 4 | 15.00° | 3 | 2-7/16" | 4-13/16" | 1-3/4" |
| 5 | 11.25° | 4 | 1-13/16" | 3-9/16" | 1-5/16" |
Transferring the template to the pipe
- Divide the circumference into 16 equal parts with a wrap-around and number them from the longest point.
- Draw a square reference line round the pipe, measure each cutback back from it, and join the points with a smooth curve.
- Nothing is printed: the numbers are on screen, and you lay them out yourself.
- The centreline radius is your choice. The app does not derive it from the pipe size, so type the one on your drawing.
Questions and answers
What is the cut angle for a 3-piece 90 degree miter?
What is the cut angle for a 4-piece 90?
Can I print the miter template?
What range does the Miter screen cover?
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