Common conduit bending mistakes
The common conduit bending mistakes are shrink forgotten, a rise measured edge to edge, the wrong take-up, a dog leg and a kink — and every stick of scrap I have made came from one of the mistakes on this page, most of them from the first four. They sort into three kinds: the layout was wrong before the bender touched the pipe, the bender was read wrong, or the pull went wrong. For each one: what you see on the finished pipe, why it happened, and what to do so it does not happen on the next stick.
Layout mistakes — wrong before you bend
Shrink forgotten
What you see: a clean offset that stops 1" (25 mm) or 2" (51 mm) short of the fitting. The rise is right; the length is not.
Why: the stick was cut to the flat distance and the two bends pulled the far end back by the shrink.
Fix: add the shrink to the overall length before you cut — the shrink calculator gives it for any rise and angle. Moving mark 1 does not buy it back: that stretch of pipe is straight and never changed. On a 45° offset the shrink is nearly half the rise.
Rise measured edge to edge
What you see: the offset is bigger than it needed to be by about one pipe diameter, and the run lands high.
Why: the rise was taken from the bottom of the pipe where it is to the top of where it should be. The pipe's own thickness got counted.
Fix: centre to centre, always — or bottom to bottom, which is the same thing. Every calculator here wants the centreline rise.
Measured from the wrong end
What you see: the bend is in the pipe at the right distance from the end you did not measure from, which is to say the wrong place entirely.
Why: the mark was measured from one end and the bender hooked from the other, or the stick was flipped between marking and bending.
Fix: write the figure on the pipe next to the mark with an arrow to the end it came from. It takes two seconds and it has saved me more sticks than any other habit.
Mark only on one side
What you see: the bend is 1/8" (3.2 mm) to 1/4" (6.4 mm) off, and it varies stick to stick.
Why: a tick on one side of the pipe is hidden under the shoe, so the arrow gets lined up by eye from above.
Fix: draw the line all the way round. A short piece of angle iron, or the shoe of the bender, is a straight edge to wrap it.
Wrong multiplier
What you see: the rise is wrong but the run is level — both bends are clean and the same, the pipe is just the wrong shape.
Why: the shop rule for one angle used with the chips set to another: ×2 with 45° pulled, say. The between-marks distance and the angle have to agree.
Fix: take the between-marks figure and the angle from the same line of the multiplier table, or from the calculator, which cannot mix them.
Bends in the wrong order on a saddle
What you see: the hump is there but it leans, or the outer bends are not where the marks were.
Why: an outer bend was pulled first, and then the pipe would not sit in the shoe for the centre.
Fix: centre first, always, on the notch — then the outers, each on the arrow, each the opposite way. The order is in the saddle calculator's "Do it" list.
Bender mistakes — the tool read wrong
Wrong take-up
What you see: every stub lands tall (or short) by the same amount.
Why: the take-up is for a different shoe, a different pipe, or a stamp that no longer matches a worn shoe. A consistent error is always a figure.
Fix: one test bend, on measure your bender. Save the real figure and the calculators use it.
Arrow used where the star was wanted
What you see: a clean U whose distance between the backs is wrong — and wrong by the same amount on every stick you bend.
Why: the second 90 was bent with the arrow on the mark. The arrow places the start of a bend; the star places the back of it. The second mark of a back-to-back is a back, so the U comes out wrong by the distance between those two marks on your shoe. That distance is a property of the tool, like take-up — it is not the gain and it is not the take-up.
Fix: star on mark 2, hook facing the first bend. No star on your shoe? Lay one U out on a scrap, bend both 90s on the arrow, measure back to back: the difference from what you laid out is that shoe's arrow-to-star gap, in the direction the scrap shows. Apply it to the second mark from then on.
Notch that is not a centre
What you see: the saddle's hump is a little to one side of the obstruction, on every saddle, by the same amount.
Why: the rim notch on this shoe is not exactly at the centre of a 45, or the centre bend went on the arrow.
Fix: test 3 on the measure page gives the notch offset; shift the centre mark by that much.
Hook facing the wrong way
What you see: the stub is the long end of the stick and the run is the short one.
Why: the end you measured from was under your foot instead of on the hook side.
Fix: the end you measured from goes on the hook side — it is the end that rises. Say it out loud until it is a habit.
Degree line read from the wrong side
What you see: bends a few degrees over or under, though you stopped on the line.
Why: the scale is read where the pipe's tangent crosses it, and from above it is easy to read the wrong edge of the pipe against the mark.
Fix: read it from the side, level with the shoe, and check the first few bends on a new bender with a protractor or a level app.
Different pipe, same figures
What you see: the offsets are fine but the 90s are off — after switching from EMT to rigid, or from one size to another.
Why: multipliers and shrink are pure angle and do not care what the pipe is. Take-up and gain belong to the shoe and the pipe, and both changed.
Fix: a take-up per pipe size and type, each from its own test bend. The conduit types page has what changes with each.
Mistakes in the pull
Dog leg
What you see: the pipe rocks on the floor; the far end is off to one side though the rise is right.
Why: the second bend of an offset (or the outers of a saddle) was pulled with the pipe rolled a few degrees from the first.
Fix: sight down the pipe before every second pull. A pencil line along the top of the pipe between the marks shows any roll at a glance. Small dog legs can be twisted out with the bender on the second bend — fixing dog legs and kinks shows how.
Kinked
What you see: a flat spot or a crease on the inside of the bend, a bulge on the outside; the pipe is ruined.
Why: the handle was pulled without weight on the pedal, so the pipe lifted out of the groove and folded instead of wrapping the shoe.
Fix: foot pressure first and throughout, one steady pull. If a bend needs more force than that, the pipe is too big for a hand bender.
Springback ignored
What you see: every bend a degree or three shy; offsets whose far leg climbs; a 90 that is not square.
Why: the pull stopped on the line and the pipe relaxed back off it. Rigid and IMC do this more than EMT.
Fix: pull a touch past every line — test 4 on the measure page tells you how much for your pipe. Same touch on both bends of an offset.
Pipe creeps before the bend
What you see: bends land a little late — further from the end than the mark — and not always by the same amount.
Why: the pipe slid in the shoe as the pull started, before the hook took hold.
Fix: take up the slack: lean into the handle gently until the hook bites, check the arrow is still on the mark, then pull.
Second bend the same way
What you see: instead of an offset, two bends in the same direction: the pipe curls up and does not come back level.
Why: the pipe was not rolled a half turn between the two bends, so the second bend added to the first.
Fix: after the first bend, slide the pipe forward in the groove, roll it half a turn so the bend points the opposite way, then line the arrow on mark 2.
Too many degrees on a segmented bend
What you see: a sweep that closes up tighter than the radius asked for, or one that is lumpy.
Why: each small bend a degree over, times ten; or the spacing varied from bend to bend.
Fix: a protractor on every segment, not the shoe's scale, and marks laid out from one end at the calculated spacing — never each from the last.
The checklist
Before the pull, the questions I ask, in order. They catch nearly everything above.
- Is the rise centre to centre? Not edge to edge.
- Is the shrink added to the length? Every offset, saddle and kick eats run, so the stick has to start longer. It does not move mark 1 — the pipe before the first bend is straight. The one mark that does carry a shrink is a three-point saddle’s centre mark C, and that is one offset’s worth at the outer angle.
- Do the multiplier and the angle agree? Both from the same line of the table.
- Is the take-up mine? For this shoe, this pipe — measured, not remembered.
- Which reference? Arrow for starts of bends, notch for the centre of a saddle, star for the back of a 90.
- Which end is on the hook? The one I measured from.
- Is the line all the way round the pipe? A tick on one side hides under the shoe.
- Foot on, then pull. A touch past the line, and the same touch on the second bend.
- Sight down it before the second bend, and lay it on the floor after.
Questions
- I did everything right and it is still 1/4" (6.4 mm) off. What now?
- A consistent error is a figure, not a technique: the take-up you are using is off by that much for that shoe and pipe. Do the test bend on the measure-your-bender page and save the real number. If the error is not consistent, it is technique — usually the pipe creeping in the shoe before the bend starts, or the arrow lined up from a different side each time.
- Can a bent stick be saved?
- Sometimes. A bend that is a few degrees short can be pulled further. A dog leg can be rolled straight if it is small — put the bender back on the second bend, and twist while you take it slightly further (the fixing dog legs and kinks page walks through it). A bend that is over, or in the wrong place, generally cannot: you can cut the bend out and use the two straight pieces with a coupling if the design allows, or it is scrap. Scrap is the cheapest lesson in the trade.
- Which mistake costs the most pipe?
- Forgetting shrink on a long run of parallel offsets: four sticks, all laid out from the box, all landing short by the same amount. Second is a back-to-back bent on the arrow both times, because you do not find out until the U is finished.