Parallel offset calculator for concentric bends
Enter the centre-to-centre spacing of the runs and the bend angle. You get how far to shift each next pipe's marks so a rack of offsets stays parallel.
Enter your measurements
Shift each next pipe's marks by
9/16in
Exact geometry
Every result is in Truemark
The free web version shows the main result and the drawing. Truemark gives you every mark and measurement, and exports a cut sheet. It is free to download.
How to lay it out
Lay out the first pipe
Mark the first pipe as a plain offset. It is the reference and its marks do not move.
Measure the spacing
Measure the centre-to-centre spacing between the pipes in the run, as they will sit on the strut.
Shift the next pipe's marks
Copy the marks to the next pipe and move both marks by the shift shown. The pipe on the inside of the first bend has its marks closer to the end.
Repeat across the rack
Each further pipe moves one more shift. The third pipe moves twice as far as the second.
Bend every pipe the same
Bend all pipes to the same angle and depth, so the finished offsets nest with even spacing.
Good to know
- FabLayout runs the same code as Truemark; the result is exact geometry.
- Source: ToolGrit conduit bending guide (shift = spacing × tangent of half the bend angle; example: 30° offsets at 2″ spacing, about 0.54″)
Method and formula
When several conduits run side by side and all offset together, bending each one with the same marks makes the run fan out or pinch. The bends have to nest, so each pipe's marks move a little along the pipe.
- Shift = centre-to-centre spacing × tan(θ ÷ 2).
The shift comes from the tangent lengths of two bends that share a centre: two paths spaced apart by S differ in length by S × tan(θ ÷ 2). The shift does not depend on the bend radius. It adds up pipe by pipe, so each further pipe moves one more step than the one before.
Worked example
The page defaults: pipes 2″ apart, 30° bends. The shift is 2 × tan 15° = 0.5359″ between the marks on successive conduits. This matches the published example: for 30° offsets with 2″ spacing, the adjustment is about 0.54″.
Questions
Which way do I shift the marks?
For the first bend, the pipe on the inside of the turn has its marks closer to the end of the pipe. The shift does not change the offset depth or the angle.
Does the bend radius matter?
No. The shift depends only on the spacing and the angle, as long as the radius is larger than the full width of the rack.
What if the pipes are different sizes?
The spacing between centres changes from pipe to pipe. Work out the shift for each gap and add them up from the reference pipe.
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