How to build a steel fire pit from plate

🔥 Build a Durable Welded Steel Plate Fire Pit

How do you build a tapered steel fire pit from plate?

This guide covers fabrication of a square, tapered fire pit using 3 mm mild-steel plate, a 5 mm base, and welded steel legs. The finished pit is approximately 700 × 700 mm at the top, 450 × 450 mm at the base, and 400 mm high including legs.

The design suits backyard entertaining areas, but it must only be used on a non-combustible surface and when permitted by your local council, fire authority and current fire restrictions. Never operate a solid-fuel fire pit during a Total Fire Ban.

What skill level is required to fabricate a steel fire pit?

Basic MIG welding and grinder experience is recommended. DIY fabrication generally does not require welding certification, but complete an introductory welding course or supervised practice before attempting the project.

The fire pit itself is not intended as a load-bearing structure. Any load-bearing frame, permanent installation or integration into a deck or structure must comply with AS/NZS 1554.1 Structural Steel Welding and may require a qualified welder or engineer.

What tools and welding equipment are required to build a steel fire pit?

🔧 Equipment Required

Materials Required

Do not use galvanised steel, painted scrap, chemical drums, gas cylinders or unknown coated plate. Heating these materials can release toxic fumes or create an explosion hazard.

Safety Requirements

⚠️ Safety

Step-by-Step Guide

Step 1: Confirm the Design and Location

1️⃣ Choose the finished dimensions

This guide uses a tapered square bowl with:

The tapered sides direct heat upward and make ash removal easier than a deep vertical box.

Before cutting steel, choose the operating location. Confirm that it is level, non-combustible, clear of vegetation and compliant with local fire rules.

Do not design the pit for use on a combustible deck. A thin sheet of steel underneath is not adequate thermal protection.

Step 2: Mark the Four Side Panels

2️⃣ Lay out identical trapezoids

Mark four trapezoidal side panels on the 3 mm mild-steel plate. Each panel should have:

Use a steel rule, framing square and scriber rather than a thick permanent marker. Check both diagonals and confirm that all four panels match before cutting.

Arrange two panels per row on a 1500 × 750 mm sheet. Allow approximately 3–5 mm between pieces for the cutting kerf.

💡 Make one accurate cardboard or thin-plywood template first. Use it to mark all four panels consistently.

Step 3: Cut and Dress the Plate

3️⃣ Cut accurately and remove sharp edges

Cut the panels using a plasma cutter, steel saw or thin grinder cutting disc.

For a 40 A plasma cutter on 3 mm mild steel, begin around:

If using an angle grinder, support the plate securely and allow the disc to cut without twisting or side-loading.

Dress all cut edges with a flap disc. Remove slag, burrs, mill contamination and plasma dross from at least 20 mm on either side of every weld.

Slightly bevel the side seams to approximately 20–30° if the fit-up is completely closed. Leave a 1 mm root gap where practical to promote fusion through the 3 mm plate.

Step 4: Prepare the Base and Drain Hole

4️⃣ Cut the firebox floor

Cut the 5 mm mild-steel base to 450 × 450 mm. Check that it fits the lower opening formed by the four panels.

Drill one 12 mm drain hole in the centre to prevent rainwater collecting in the pit. Deburr both sides of the hole.

If fitting a removable ash tray, leave enough access beneath the drain and avoid locating a leg directly under it.

Do not add large ventilation holes near the bottom of the side panels. They can allow embers and hot ash to escape.

Step 5: Tack the Side Panels Together

5️⃣ Assemble on a flat surface

Stand two side panels together and align their tapered edges. Use magnets or clamps to hold the corner.

Place tack welds approximately 15–20 mm long at:

Add the remaining panels, then check:

Both top-opening diagonals should be within approximately 3 mm of one another before final welding.

Recommended starting settings for 3 mm mild steel with 0.9 mm ER70S-6 wire are:

Settings vary by welder, joint gap and travel speed. Run test welds on offcuts from the same plate before welding the fire pit.

Step 6: Weld the Side Seams

6️⃣ Control heat and distortion

Weld the seams in short sections rather than completing one entire corner at once.

Use the following sequence:

Use a slight push angle of approximately 10–15° and keep the wire near the leading edge of the weld pool. Aim for full fusion without excessive reinforcement.

For a cleaner exterior, make the main weld on the inside and add only enough exterior weld to close gaps or reinforce uncertain areas. Avoid aggressive grinding that reduces the parent metal below 3 mm.

💡 If the plate begins pulling out of shape, stop welding. Clamp it square and allow it to cool naturally. Do not quench hot welds with water.

Step 7: Fit and Weld the Base

7️⃣ Seal the bottom of the bowl

Turn the assembly upside down on the welding table. Position the 450 × 450 × 5 mm base plate against the lower opening.

Tack each corner, then add intermediate tacks. Recheck that the plate remains centred and flat.

Recommended starting MIG settings for the 3 mm to 5 mm joint are:

Use a series of 40–60 mm welds in an opposing sequence. The finished joint should be continuous enough to retain ash and prevent hot embers escaping, except for the intentional drain hole.

Where a small gap exists, direct slightly more heat into the 5 mm base plate and wash the weld pool onto the thinner 3 mm side panel.

Stick welding is an alternative. Use a 2.5 mm E6013 electrode at approximately 75–95 A, practising first to avoid burn-through.

Step 8: Fit the Legs

8️⃣ Provide stable ground clearance

Cut four lengths of 40 × 40 × 3 mm SHS at 150 mm. Deburr the ends and clean the weld areas to bright steel.

Position one leg near each corner, inset approximately 40–50 mm from the outer edge. Ensure the drain hole remains clear.

Clamp the legs square and tack each one on two sides. Turn the pit upright, place it on a flat surface and check for rocking. Adjust before final welding.

Weld each leg in a balanced sequence, moving diagonally between corners. A 40–50 mm fillet weld on two or three sides of each leg is generally adequate for a portable fire pit.

Cap or seal the lower SHS ends to prevent them filling with water. If welding caps, include a small vent hole during welding so heated trapped air cannot pressurise the tube.

This leg arrangement is only for supporting the fire pit. It is not a structural stand for seating, climbing or other loads.

Step 9: Add the Top-Rim Stiffener

9️⃣ Strengthen the opening

Cut four lengths of 25 × 3 mm mild-steel flat bar to suit the top edges. Mitre the corners at 45° for a neat frame, or butt the strips together if using basic tools.

Clamp the flat bar around the outside of the top edge, with its upper surface flush or slightly above the plate edge.

Tack at each corner and at approximately 100 mm intervals. Stitch-weld in 30–40 mm sections, alternating around the pit to control distortion.

The rim improves rigidity, covers the sharp plate edge and provides a stronger lip for an optional spark guard. Round all exposed corners with a flap disc.

Step 10: Inspect and Finish the Welds

🔟 Check fusion and remove hazards

Inspect every joint under good lighting. Look for:

Repair defects before grinding. Grind only where necessary for appearance or safety; intact weld reinforcement is stronger than an over-ground seam.

Round exposed edges and corners. Remove spatter and wipe the exterior with wax-and-grease remover.

Do not use automotive body filler on the firebox. It will fail when heated and may emit hazardous fumes.

Step 11: Apply the Exterior Coating

1️⃣1️⃣ Protect the outside only

Leave the inside of the fire bowl as bare steel. Most paints are not intended for direct contact with flame, coals or cooking surfaces.

Apply a high-temperature coating to the exterior according to the product instructions. Typical preparation includes:

Mask the drain hole and avoid heavy paint buildup around leg contact surfaces.

If the fire pit will be used for cooking, use only purpose-designed, food-safe components above the fire. Do not assume ordinary high-temperature paint is food-safe.

Step 12: Conduct a Controlled First Burn

1️⃣2️⃣ Test outdoors under safe conditions

Move the pit to its final non-combustible location. Confirm that no fire restriction or Total Fire Ban applies.

Start with a small hardwood fire. Do not fill the pit with timber on its first burn. Watch for:

Keep the extinguisher and hose ready. Allow the pit to cool naturally before touching, moving or inspecting it.

Dispose of ash only when completely cold. Place it in a non-combustible metal container with a lid, as buried embers can remain hot for days.

Common Mistakes to Avoid

Steel below approximately 3 mm can distort, burn through during welding and deteriorate rapidly under repeated heating.

Galvanised coatings release hazardous zinc oxide fumes when welded or heated. Chemical drums and gas cylinders may also contain explosive or toxic residues.

Concentrated heat pulls the bowl out of square. Use short welds in an opposing sequence.

Ordinary and many high-temperature paints are unsuitable for direct flame exposure.

Radiant heat and falling embers can ignite timber, composite boards, mulch or dry grass. Always verify local rules before lighting.

Pro Tips

Recommended Tools

For welding machines or plasma cutters costing over $1,000, equipment finance may be available through Local Knowledge Finance; compare the total cost, fees and repayment terms before purchasing.

🔧 Recommended Equipment: Search for a 180–200 A inverter MIG, 0.9 mm ER70S-6 wire, a 40 A plasma cutter, and an AS/NZS 1338.1-compliant auto-darkening helmet.