How to bend a four-point saddle

A four-point saddle is two offsets with a flat between them: one up over the obstruction, a straight run across its top, one back down. Measure the depth and the width, put mark 2 where the flat starts (the near edge plus one offset's shrink), mark 1 and mark 4 the offset distance either side, mark 3 the width past mark 2, and bend up, down, down, up with all four bends in one plane. It is the saddle for anything with a flat top; for something round and narrow, see three-point vs four-point.

Measure the obstruction

• Depth — underside of the pipe where it runs now to where its underside has to be over the top (the obstruction's top plus clearance). Underside to underside is centre to centre; edge to edge adds a pipe diameter you did not need.
• Width — the widest thing across the top: seams, flange lips, tray rails. Add clearance at both sides; the flat can be longer than the obstruction, never shorter.
• Distance to the near edge — from the end you will mark from (the box, the coupling). Hook the tape on that same end when you mark.

Pick the angle

All four bends are the same angle. Each offset puts its two marks depth × the multiplier apart, and pulls the run back by depth × the shrink figure.

30° is my default: marks twice the depth apart, the arithmetic in your head. 22.5° when there is room — less shrink, an easier pull. 45° only when the room is tight; four 45s is a lot of bend, so count it against the limit in your code book between pull points.

Mark and bend

1. Measure. The depth to clear (underside to underside), the width across the top including flanges and lips, and the distance from the end of the pipe to the near edge.
2. Pick the angle. 22.5° or 30° for most saddles, 45° only when the room is tight. Multiplier and shrink from the same line of the table.
3. Mark 2. At the distance to the near edge, less your clearance, plus one offset of shrink (depth × the shrink figure). The flat starts here.
4. Mark 1. Back toward the end you measured from by depth × the multiplier.
5. Mark 3. Past mark 2 by the width plus clearance at both sides.
6. Mark 4. Past mark 3 by depth × the multiplier again. Lines all the way round, and a pencil line along the top through all four.
7. Allow the shrink. The saddle takes two offsets of shrink out of the run: add 2 × depth × the shrink figure to the overall length before you cut.
8. Bend the first offset. Arrow on mark 1, bend to the angle. Slide the pipe along to mark 2, roll it half a turn so the bend points the other way, arrow on mark 2, and bend the same angle back. That is an ordinary offset.
9. Bend the second offset. Slide the pipe on to mark 3 without rolling it: bend 3 turns the same way as bend 2. Then roll it half a turn for mark 4, which turns the same way as bend 1. Up, down, down, up.
10. Check. On the floor, both tails sit flat, the top is level, and the gap under it is the depth. If it rocks, a bend is out of plane.

Why mark 2 carries a shrink: the first offset pulls everything after it back toward you by one shrink, so mark 2 has to start that much further along to land on the near edge. The second offset's shrink comes off the far end, so the length gets both. The four-point saddle calculator lays the marks out from mark 1 instead; both ways put the bends in the same places.

Bend order and keeping it in plane

A degree of roll in each of four bends is a pipe that will not sit on the strap.

• Pencil line along the top. Through all four marks, before the first bend. If it wanders, so has the pipe.
• Rolls: yes, no, yes. Half a turn between 1 and 2, none between 2 and 3, half a turn between 3 and 4. Before each pull, say which way this bend takes it.
• Sight it after every bend. The bent part should stand straight above the line of the pipe, not lean off to a side.
• The same touch past the line on every bend. Two degrees between bend 1 and bend 2 and the flat is not level.
• Check the first offset before the second. If it rocks after bend 2, twist it true now — the dog-leg page has how.

A short flat is the awkward case: if marks 2 and 3 are closer than the shoe is long, the pipe will not seat for bend 3. Lengthen the flat, or if the thing is narrow, do a three-point saddle.

Worked examples

What goes wrong

Questions

How do you measure for a four-point saddle?

Three measurements. The depth the pipe has to lift, underside to underside (the same as centre to centre). The width across the top, flanges and lips included, plus clearance each side. And the distance from the end of the pipe to the near edge, which places mark 2.

Where does mark 2 go on a four-point saddle?

Where the flat should begin: the near edge less your clearance, plus the shrink of one offset, because the first offset pulls the pipe back by that much before it reaches the obstruction. Marks 1, 3 and 4 are then measured from mark 2.

Is the shrink on a four-point saddle doubled?

Yes, for the length of the run: two offsets, two shrinks. At 30° that is 2 × depth × 0.268, so a 4" (102 mm) deep saddle eats about 2 1/8" (54 mm). Only one of those shrinks sits before the obstruction, so only one moves mark 2.

What angle should I use for a four-point saddle?

30° is the easy default: the multiplier is 2, so the marks are twice the depth apart. 22.5° pulls easier and shrinks less but takes more room. 45° is for tight spaces; it shrinks the most.

Related

• Four-point saddle calculator — type the depth, width and angle, get all four marks and the doubled shrink.
• Three-point vs four-point saddle — when a peak does the job with one bend fewer.
• How to bend an offset — each half of this saddle, on its own.
• How to bend a saddle — the three-point version over a pipe.
• Conduit shrink calculator — one offset's shrink for any depth and angle.