Choosing Sheet Metal for a DIY Fire Pit or BBQ Grill

Most DIY fire pits and grills that disappoint do so for one of three reasons: the steel rusts through, thin sheet warps in the heat, or slot-together parts won't fit because the sheet doesn't match the drawing. Here is how to choose the material and set up the cut so none of that happens.

Which steel to use

• 304 stainless steel resists rust, which suits portable gear that gets packed away damp. It costs more, and it changes colour near the fire; the heat tint is cosmetic.
• Mild steel is the cheapest and easiest to cut. It rusts, so it suits a backyard fire pit where some patina is fine. Use high-temperature paint on the outside if you want it to stay dark, and oil cooking surfaces like cast iron.
• Weathering steel (often sold as Corten) forms a stable rust layer and needs no paint, but its run-off stains stone and decking underneath.
• Avoid galvanized, zinc-coated or painted sheet. Coatings burn off in a fire, and zinc fumes can make you ill.
• Aluminium is not suitable for anything that holds a fire. It melts at about 660 °C, and a wood fire can get hotter than that.

How thick

• Portable and camping gear: 1 to 2 mm stainless keeps the weight down. Our Card-Type BBQ Grill is 1.7 mm 304 stainless, and our Triangle Fire Pit weighs 600 g.
• Backyard fire pits: thicker mild steel, around 3 to 6 mm (roughly 1/8 to 1/4 inch), lasts longer and warps less in a big fire.
• Grates and fire bowls take the most heat. If anything is going to sag or warp, it is these, so go a size thicker there if the design allows.

Thin sheet can still work in a hot fire if the design gives it shape. Parts that brace each other, ribs and folds are much stiffer than a flat panel of the same thickness.

Slot-together designs: thickness and slot width

Flat-pack designs such as our Collapsible Fire Pit hold together with slots, so the sheet thickness has to match the slots in the drawing.

• Leave clearance. Make each slot a little wider than the sheet: a few tenths of a millimetre on a laser, more on plasma, because plasma edges come out slightly bevelled.
• Allow for heat. Steel expands when it gets hot. A little extra clearance means you can still take the parts apart after a fire.
• Change the slots, not the scale. If your sheet is thicker or thinner than the drawing was made for, edit the slot widths in CAD. Scaling the whole drawing changes every part, and the slots still won't match.

Laser, plasma or waterjet

• Fibre laser: clean edges, a narrow kerf and fine detail such as small holes and star cut-outs. Best for thin stainless.
• Plasma: cheaper and happy with thick plate, but the kerf is wider and the edges need the dross cleaned off. Holes much smaller than about 1.5 times the sheet thickness tend to come out rough or tapered, so check the small features first.
• Waterjet: no heat, so no warping or heat tint at the edges, but it is slow and usually the most expensive.

Checklist before you cut a DXF

1. Import in millimetres and measure one part to confirm the scale.
2. Check the sheet thickness against the slot widths.
3. Set kerf compensation: outside the line for profiles, inside for holes and slots.
4. Put lead-ins in the waste, away from slot edges and tabs.
5. Cut a test part from scrap and check the fit.

Wear eye protection rated for your cutting process and keep the area ventilated: laser and plasma cutting both produce fumes.

Looking for a design to cut? Browse our DXF cut files, or see the finished fire pits and grills. For a step-by-step example, read how to cut and assemble the Card-Type BBQ Grill.