Design a sheet metal bracket from the bolts and the load outwards: choose the simplest shape that connects the two surfaces, a thickness that won't flex, then place holes clear of the bends and give each flange room to fold. Most bracket problems we see come from doing it in the opposite order.
Brackets look like the easiest part on any job, so they get drawn in five minutes and sent back. A hole sits on a bend, a flange is too short for the die, or the bracket bends like a diving board under load. Here's how to pick the shape and thickness, a worked example in millimetres, and the details that make a bracket quick to make.
Pick the simplest shape that works
Nearly every bracket is a variation on a handful of shapes. Each extra bend adds a setup on the press brake, a little more variation in the final dimensions, and one more thing to check.
| Shape | Bends | What it does | Watch out for |
|---|---|---|---|
| Flat plate | 0 | Spacer, mending plate, base plate | Stiffness, since there are no bends to help |
| L (angle) | 1 | Joins two surfaces at 90° | Flexes at the bend under heavy load |
| Z (offset) | 2 | Joins two parallel surfaces at different heights | The step between bends must be long enough to bend |
| U (channel) | 2 | Clamps or straddles a tube or panel | Inside width vs outside width on the drawing |
| L with gusset | 1 plus a welded plate | Heavier loads, shelf brackets | Needs welding, so costs more |
| L with return flanges | 3 | Stiffer L without welding | Bend relief where flanges meet |
If an L does the job, use an L. If it's not stiff enough, add return flanges before reaching for a welded gusset. Folding is usually cheaper than welding, and there's no heat distortion to deal with.
Thickness: stiffness first, then strength
Brackets rarely break. They bend, sag, or vibrate. So think about stiffness before ultimate strength.
A useful bit of physics: a flat plate's resistance to bending grows with the cube of its thickness. Go from 2 mm to 3 mm and the plate gets roughly 3.4 times stiffer (1.5 × 1.5 × 1.5). Double the thickness and it's about 8 times stiffer. That's why a small jump in thickness transforms a floppy bracket.
But thickness isn't the only lever, and it costs weight and money. Before going thicker, try:
- Shortening the lever. A bracket that sticks out 150 mm bends far more than one that sticks out 75 mm. Keep loads close to the mounting face.
- Adding a return flange along the free edge of each leg. It turns a flat leg into a shallow channel, which is much stiffer.
- Adding a gusset across the bend for heavy, static loads.
- Using a wider bracket. Width adds stiffness in direct proportion, and it's free on the laser.
For guidance on what thicknesses are common and how gauge numbers translate to millimetres, see our sheet metal thickness guide.
Worked example: a 3 mm mild steel L-bracket
Say you need a bracket to hold a small pump housing to a wall, using M10 bolts. You choose 3 mm mild steel, an L shape, 60 mm wide, with outside leg lengths of 60 mm and 40 mm.
Bend radius. For mild steel, about 1× thickness is a sensible starting point, so R3. Our guide to sheet metal bend radius explains where that comes from.
Flange length. The rule of thumb is at least 4× thickness, or 4T + R for comfort: 12 to 15 mm. Both legs are far longer than that. Fine.
Hole size. An 11 mm clearance hole is a common choice for M10. That's well above the starting rule of a hole at least equal to the thickness.
Hole distance from the bend. Rule of thumb: at least 2.5T + R from the bend line to the hole edge. That's 2.5 × 3 + 3 = 10.5 mm. Add half the hole (5.5 mm) and the hole centre needs to be at least 16 mm from the bend line. On the 40 mm leg, a centre around 22 to 25 mm out leaves plenty of room. See how close a hole can be to a bend for more.
Edge distance. Keep the hole edge at least one thickness from the end of the leg. With the centre at 25 mm on a 40 mm leg, there's well over 3 mm to spare.
Five quick checks, and the bracket is ready to cut and fold with no queries.
Holes, slots, and adjustment
Brackets almost always meet something that isn't perfectly where the drawing says it is. A wall, an existing frame, a machine casting. Build in adjustment where you can.
- Use slots instead of round holes on at least one leg. A slot 6 to 10 mm longer than the hole lets the bracket move to line up.
- Slot in different directions on the two legs, one horizontal and one vertical, so you get adjustment in both.
- Keep matching holes on the same flange. Holes on one flat face are cut together and stay accurate to each other. Holes on two different legs depend on the bend as well.
- Dimension holes from the nearest bent face, not from the far end of the part.
Material and finish
Mild steel is the default bracket material: strong, cheap, easy to bend and weld. Coat it if it's going anywhere damp. Powder coating or painting gives it a long life indoors and inland.
For wet, outdoor, or industrial sites, consider 3CR12 (coated where looks matter) or stainless. Aluminium makes sense when the bracket is joined to aluminium or weight is critical, though it's less stiff than steel at the same thickness, so it often needs to be thicker or have return flanges.
One caution for mixed materials: bolting a bare aluminium bracket to stainless or mild steel in a wet environment can cause galvanic corrosion of the aluminium. Insulating washers, a coating, or matching materials avoid it.
Sending your bracket for a quote
Send a STEP model or a dimensioned sketch or PDF of the bent bracket, with material, thickness, quantity, and finish. If it's a copy of an existing bracket, photos with a ruler in the frame work well.
Our CNC bending service cuts and folds brackets from one-offs to production runs on the same quote form, and powder coating can go on the same order. Start a quote for CNC bending.