Three-point saddle calculator
A three-point saddle carries a run over a round obstruction with one centre bend and two outer bends half its angle. Enter the depth you need to clear and the centre angle; the calculator gives the distance from the centre mark to each outer mark, the shrink to add so the far end still lands right, and the three lines to follow at the bender.
On the bender
A three-point saddle is one centre bend and two half-angle outers pulled the opposite way. The marks come from the calculator; the order and the references are below.
- Measure. From the end of the stick to a point directly over the crown of the obstruction — the centre measurement. The depth is how much the run has to lift to clear it, centre of pipe to centre of pipe, plus the clearance you want.
- Mark. The centre mark C goes at the centre measurement plus the shrink — the one place on this site where a shrink figure moves a mark, because the crown you measured to ends up that much back along the bent pipe. Marks 1 and 2 go the centre-to-outer distance either side of C. Three lines right round the pipe. The saddle eats twice that figure out of the run, so add that to the overall length.
- Line up. Centre mark C on the notch (the saddle mark on the rim of the shoe), not the arrow. Bend the centre angle — 45° on the usual saddle — first.
- Bend. Slide to mark 1, roll the pipe a half turn so the outer bend goes the opposite way, put mark 1 on the arrow, and pull half the centre angle (22.5° for a 45 saddle). Do the same at mark 2. Keep all three bends in one plane — sight down the pipe between each.
- Check. On the floor, both ends flat and the hump standing the depth above them, with its peak at the centre measurement from the end. A hump that leans has one outer angle bigger than the other; re-check the degree line and pull the short one a touch more.
Worked examples
A 2" (51 mm) saddle over a 2" conduit, 45° centre
Say a two-inch conduit crosses your run and you need a 2" (51 mm) saddle over it at a 45° centre. The outer bends are 22.5°, whose multiplier is 2.613, so each outer mark sits 5 1/4" (133 mm) from the centre mark (2 × 2.613 = 5.23). The centre-mark correction is the 22.5° shrink figure applied to the depth, about 2 × 0.199 ≈ 3/8" (10 mm) — and it has to be used. Measure from the end of the stick to a point over the crown, then put C 3/8" (10 mm) further along than that: the bent pipe carries its peak back by exactly that much. Marks 1 and 2 go 5 1/4" (133 mm) either side of C. Bend the centre 45° first, then each outer 22.5° the opposite way. The saddle also eats twice that correction out of the run — 2 × 0.398 ≈ 13/16" (20 mm) — which goes on the overall length, not on any mark.
A 50 mm saddle at 45°, metric job
A pipe crossing needs the run lifted 1 15/16" (50 mm). With a 45° centre the outers are 22.5°, so each outer mark sits 50 × 2.613 = 130.7 → 5 3/16" (131 mm) from C. The centre-mark correction is 50 × 0.199 = 9.9 → 3/8" (10 mm): put C that much past your measurement to the crown. The saddle takes twice that, 13/16" (20 mm), out of the run — add it to the overall length before you cut.
Try one — a saddle
Work it on paper, then type the marks. A sixteenth either way counts — that is as close as a tape reads. Two millimetres either way counts.
Loading a bend…
Tapez des pouces comme 12, 1 5/8 ou 1' 3 1/2".
What went wrong
Saddles are the bend a first-year ruins most, and it is nearly always one of three things. Each is a three-line diagnosis and the fix.
The hump lands beside the pipe, not over it
What you see: a good-looking saddle with the obstruction sitting under one of the outer slopes.
Why: the centre mark was measured to the near edge of the obstruction, or from the wrong end of the pipe, instead of to the crown.
Fix: measure to the centre line of what you are crossing, every time. Mark it on the floor or the wall first, then transfer it to the pipe — and remember the shrink goes on top.
A Z instead of a hump
What you see: the pipe steps up and stays up — an offset with a kink in it, not a saddle.
Why: one outer bend was pulled the same direction as the centre. It is the easiest mistake to make when the pipe comes out of the bender and goes back in without a look.
Fix: centre first, then flip the pipe end for end and pull each outer the opposite way to the centre. Before every pull, sight down the pipe and say which way the bend is going.
The crown is right but the end lands short
What you see: a perfect saddle, obstruction cleared, and the coupling 1/2" (13 mm) off the box.
Why: the shrink was not added to the centre measurement. The three bends took that length out of the run, and it came out of the far end.
Fix: the first line of the "Do it" list — centre mark at measurement plus shrink. Shrink is small on a shallow saddle and real on a deep one; on a 6" (152 mm) saddle at 45° it is 1 3/16" (30 mm).
The formula
The outer bends are half the centre angle, and the mark spacing is the depth times the outer multiplier:
outer angle = centre ÷ 2
centre to outer = depth ÷ sin(outer)
shrink = depth × (1 ÷ sin(outer) − 1 ÷ tan(outer))
Each half of the saddle is just an offset raising the pipe by the depth at the outer angle, so it obeys the same rise ÷ sin θ the offset does. The two halves meet at the centre bend over the crown. The triangle behind it is drawn on the formulas page.
Centre angle and its outers
The centre angle you pick sets the outer angle and therefore the mark spacing. A shallower centre spreads the saddle out and reduces shrink; a steeper one keeps it compact but pulls the end back harder. The shrink column is a ratio: multiply it by the depth, in inches or millimetres.
| Centre | Outer | Outer multiplier | Shrink × depth |
|---|---|---|---|
| 30° | 15° | 3,864 | 0,132 |
| 45° | 22,5° | 2,613 | 0,199 |
| 60° | 30° | 2,000 | 0,268 |
| 90° | 45° | 1,414 | 0,414 |
Which bender these numbers assume — and how to adjust
The geometry belongs to the angle, not the tool. What the tool changes — its reference marks, its take-up and gain, its springback — is yours to read off the shoe or prove on scrap, never a table here (the four test bends). For this bend:
The centre bend goes on the notch (the saddle mark on the rim of the shoe) and the two outer bends on the arrow. That is the pairing these numbers assume, because the notch marks the centre of a 45 on the shoes that have one, and the centre-to-outer distance is measured centre to start-of-bend. On a shoe with no notch, find where the centre of a 45 lands relative to the arrow with one test bend — the procedure is on measure your bender — and offset the centre mark by that amount before you line it up on the arrow.
Questions
- What angle is a three-point saddle bent at?
- The centre bend is the one you choose — 45° is the classic. The two outer bends are always half the centre, so a 45° saddle has 22.5° outers and a 60° saddle has 30° outers. The calculator uses the outer angle to work the mark spacing, because that is the geometry that clears the pipe.
- Where does the centre mark go?
- Not on the crown measurement itself — a little past it. Measure along the stick to the point over the centre of what you are crossing, then put the centre mark C that distance PLUS one offset's worth of shrink (the outer angle's shrink figure applied to the depth) along, because the bent pipe carries its peak back by exactly that much. This is the one place on the site where a shrink figure moves a mark. Then measure the centre-to-outer distance each way from C and bend the outers there. Bend the centre first, then the two outers, so the centre stays put.
- Does a saddle shrink the pipe?
- Yes, and by twice as much as people expect: the run loses TWO offsets' worth of the outer-bend shrink on the depth, because a saddle is two offsets in a row. That goes on the overall LENGTH of the stick — moving a mark does not buy the far end back. The centre mark is a separate correction and a smaller one: it moves along by ONE offset's worth, so the hump lands on the crown. Two different jobs for the same shrink figure; add the doubled one to the length and the single one to the centre mark.
- Three-point or four-point saddle?
- A three-point saddle goes over something round — a pipe or a conduit crossing yours. A four-point saddle is two offsets with a flat run between them, for going over something with a flat top like a beam or a duct. Use the four-point calculator for the flat case.