Can you bend square tubing without a bender?

Yes, for light-gauge tube. Cut a V-notch through three walls at the bend, leave the fourth wall uncut, and fold. The uncut wall is the hinge on the outside corner. Weld the closed seams afterwards, because the fold alone won't carry load.

What angle do you cut the notch for a 90 degree bend in square tube?

A 90° V, which is 45° each side of the bend line. The notch angle always equals the bend angle, so a 60° bend takes a 60° V, 30° each side.

How deep should the notch be?

All the way to the inside face of the hinge wall: the tube's depth in the bend direction minus one wall thickness. On 1 in tube with a 1/16 in wall, that's 15/16 in (23.8 mm).

How do you make a rounded corner in square tube?

Split the bend across several smaller V-notches spaced along the tube, such as three 30° notches or four 22.5° notches for a 90° corner. Fold them closed a little at a time. Wider spacing between notches gives a bigger, flatter radius.

Is a notched and folded corner strong?

Not until it's welded. Folded, the corner hangs on one thin wall of bent steel. Weld or braze the seams on both side walls and across the inside corner for anything that carries weight.

JoineryMetal & Tube JoineryNotch-and-fold tube corner

How do you bend a corner in square tube without cutting it in two?

You need an L in square tube. The usual move is two pieces, two 45° cuts, a magnet square, and a lot of fiddling while the miter slides around under the first tack. There's a faster way to bend square tubing without a bender, and without cutting it in two: notch three walls, keep the fourth as a hinge, fold. Craft Hacks Studio does it in about ten seconds.

Cutting tube with an angle grinder: keep the guard on, use a cut-off wheel rated for the grinder's speed, and wear a face shield over safety glasses, gloves and hearing protection. Clamp the tube and stand out of line with the wheel; never hold the work in your hand to cut it. The notch edges and the wedge you knock out are razor sharp, so deburr before you handle them. Clear anything flammable from the spark path. Galvanized tube gives off zinc fumes when welded: grind the coating off the weld area and ventilate.

⚡ Rule of thumb

To bend square tube to 90° without a bender, cut a 90° V-notch through three walls at the bend line, stop at the inside face of the fourth wall, and fold until the notch closes. The uncut wall becomes the hinge on the outside corner. Split the 90° across several smaller notches for a rounded corner.

Starting point

90° V (45° each side), depth = tube depth − 1 wall · rounded: 3 × 30° or 4 × 22.5°

Measured

Depth from the open face to the inside of the hinge wall · V opening = 2 × depth × tan(bend ÷ 2)

Confidence

Creator technique

▶ Source video — Don't Weld Until You See This — Craft Hacks Studiowatch on YouTube ↗

Applies to

Process: Metal fabrication — frames, gates, brackets, furniture from tube
Materials: Light-gauge square or rectangular steel tube (the clip's is around 1/16 in / 1.5 mm wall)
Setup: Angle grinder with a cut-off wheel or a hacksaw, square, marker, hammer, welder
Orientation: Uncut hinge wall on the outside of the corner
Not for: Heavy-wall tube, or any corner that has to carry load before it's welded

Why it matters

Two loose mitered pieces have to be held square, gapped evenly and tacked without moving. A folded corner has done most of that already. The outside wall never comes apart, so the legs can't slide past each other, and the corner closes to the angle you cut.

The notch is the jig.

It also gets you a rounded corner without a tube bender. Several narrow notches side by side fold into a faceted curve, which the clip shows at about 0:06, closed up and checked against a rule.

What it doesn't do is hold. Until the seams are welded, the whole corner hangs on one thin wall of bent steel.

What good looks like

Both notch faces meet flush on each side wall, with no gap at the inside corner
The hinge wall bends along one crisp line, with no crack across it
The legs read 90° against a square before any weld goes in
On a rounded corner, the facets are equal and every notch closes the same amount

How to apply it

Mark the bend line square across the tube. Decide which wall is the hinge: it ends up on the outside of the corner.
On both side walls, draw a V with its point on the bend line at the inside face of the hinge wall and each leg at 45° to the bend line. Across the open (inner) wall the notch is 2 × its depth wide: about 1-7/8 in (48 mm) on 1 in tube with a 1/16 in wall.
Cut both legs of the V through both side walls and straight across the inner wall. Stop at the inside of the hinge wall. A light nick is fine; a cut through it is not.
Knock out the wedge and fold the tube until the notch faces close.
Check the corner with a square, then tack the seams on both side walls and across the inside corner.
Rounded corner: share the bend between several notches (3 × 30° or 4 × 22.5° for 90°). On that same 1 in tube a 30° notch opens about 1/2 in (12.8 mm) and a 22.5° notch about 3/8 in (9.5 mm). Space the notch points further apart than one notch is wide, and close them a little at a time.
Weld or braze every closed seam before the part carries any load.

Test it on your setup

Fold one offcut of the same tube first and put a square in the corner.
Closes past 90°: the V is too wide. Won't close to 90°: it's too narrow, or a sliver of side wall is still holding at the bottom of the cut.
Measure the outside of the folded legs against your drawing. The hinge wall stretches a little at the bend, so note how far off the offcut is and lay out the real part with that.

Exceptions & tradeoffs

Thick wall won't fold by hand, and it can crack along the hinge line when you force it. Mind you, the clip is light-gauge tube. Much heavier than that, cut two pieces and miter them.

Unwelded, the corner is a hinge. The fold locates it; the welds hold it.

Rectangular tube folds either way, but the notch depth is always measured in the direction of the bend. Bend 1 × 2 in tube the hard way (the 2 in side in the plane of the bend) and the notch runs nearly 2 in deep.

The first five seconds of the clip show a variation: a strip of wall left long on one leg pokes out through the other leg as the corner closes, then gets hammered flat over the outside face. It locks the fold before you weld. How that tongue and its slot are cut isn't on screen, so it isn't in the steps here.

Common mistakes

Letting the last grinder pass run straight through the hinge wallStop at its inside face; nick it at most
Leaving a sliver of side wall at the bottom of the V, so the fold jams short of 90°Cut both side walls all the way down to the hinge wall
Laying the notch out on the wrong face, so the hinge lands on the inside of the cornerMark the hinge wall before you cut; it goes on the outside
Calling it done because it's foldedWeld the seams on both side walls and the inside corner

Frequently asked questions

Can you bend square tubing without a bender?Yes, for light-gauge tube. Cut a V-notch through three walls at the bend, leave the fourth wall uncut, and fold. The uncut wall is the hinge on the outside corner. Weld the closed seams afterwards, because the fold alone won't carry load.
What angle do you cut the notch for a 90 degree bend in square tube?A 90° V, which is 45° each side of the bend line. The notch angle always equals the bend angle, so a 60° bend takes a 60° V, 30° each side.
How deep should the notch be?All the way to the inside face of the hinge wall: the tube's depth in the bend direction minus one wall thickness. On 1 in tube with a 1/16 in wall, that's 15/16 in (23.8 mm).
How do you make a rounded corner in square tube?Split the bend across several smaller V-notches spaced along the tube, such as three 30° notches or four 22.5° notches for a 90° corner. Fold them closed a little at a time. Wider spacing between notches gives a bigger, flatter radius.
Is a notched and folded corner strong?Not until it's welded. Folded, the corner hangs on one thin wall of bent steel. Weld or braze the seams on both side walls and across the inside corner for anything that carries weight.

Craft Hacks StudioSource & visual reference

V-notching three walls of square tube and folding on the fourth, plus the multi-notch rounded corner — Don't Weld Until You See This #metalworking #welding #tips ↗ at 0:00–0:14.

Summarized and independently edited by Start Here from Craft Hacks Studio's YouTube Short: frames and the video description, no audio, and the clip has no narration anyway. The notch-and-fold with one uncut wall and the multi-notch rounded corner are clearly on screen. The notch angles, depth and width formula are my geometry, not his numbers, and his wall thickness is my estimate by eye. He never shows how he finishes the joint, so the welding step, the strength caution, the test and the mistakes are mine. The locking tab in the first five seconds goes by too fast to see how it's cut, so I describe it instead of teaching it. Same clip as the slit-and-fold rail cap, which is a different joint: two pieces, not one.