Key takeaways
- Hold the frame diagonal to ±1.5 mm over 1,200 mm and check flatness with the frame standing on its own feet; a frame that is square on the bench can still rock on a tiled floor.
- On 25 × 25 × 1.6 mm tube, 110 A with 0.8 mm wire at 5 mm/s puts about 0.32 kJ/mm into the joint, which is enough to fuse without blowing through the wall.
- A 1.6 mm bracket blank weighs 12.6 kg/m², so a 300 × 200 mm bracket is 0.75 kg; that mass on a 1.6 mm tube wall is a fatigue detail, not a cosmetic one.
- Stitch welds at 25 mm on 100 mm pitch hold a furniture frame without the wave that a full seam puts into a visible face.
- Ganesh stamps brackets on 20–300 T presses, cuts on the 12 kW laser, welds in fixtures on three CLOOS cells or at 30+ manual stations, and coats on the seven-tank line.
Metal furniture frame manufacturing succeeds or fails on two things that have nothing to do with how the frame looks in a photograph: whether it rocks on a flat floor, and whether a bracket joint on a 1.6 mm tube wall survives. Both are manufacturing outcomes, and both are decided by the fixture and the weld sequence rather than by the drawing.
The numbers that govern the part are small. A chair or table frame in 25 × 25 × 1.6 mm tube has a wall thin enough to blow through at 130 A, and a diagonal that has to stay within ±1.5 mm over 1,200 mm for the frame to sit without a wobble. A quarter-millimetre of weld shrinkage at each of eight joints, unbalanced, is 2 mm of twist.
This walk-through covers the route from tube and coil to a coated frame, the fixtures and inspection points that hold it, and the four mistakes that send frames back for rework.
What makes a furniture frame different from a machine frame?
Three things: it is visible, it stands on a floor, and it is usually a mixed batch rather than a single part number.
Visibility raises the standard on the weld and the finish. A 1 mm undercut on a machine base is a note on an inspection report; on a chair frame it is a reject, because the user sees it and the coating will not cover it.
The floor is the real specification. A four-leg frame touches the ground at four points, and if those four points do not sit in one plane, the frame rocks. On a tiled floor a 1 mm rock is obvious. That is why flatness is checked with the frame standing on its own feet, not lying on a bench.
Mixed batches change the economics. A furniture programme may run a chair frame, a table frame and a shelving upright in the same week, each in three finishes. That favours laser cutting and press tooling that can be changed quickly over a dedicated line, and it puts a premium on fixture design that can be reused across a family of frames.
Metal furniture frame manufacturing, step by step
- Cut tube to length and notch the ends to fit the mating tube, so the joint closes without a gap that the welder has to bridge.
- Cut or stamp the brackets, gussets and top plates. Sheet parts at 1.6–3 mm come off the laser for low and medium volume, or off a press tool once the annual quantity justifies it.
- Form the brackets and any sheet panel on the press brake, to the radius the coating can cover.
- Deburr every cut edge and every notch before welding. A burr under a clamp holds the part off the fixture by 0.3 mm, and the frame inherits the error.
- Weld in a fixture, locating on the datum faces and the bracket holes, with the sequence set so shrinkage is balanced.
- Cool in the fixture below about 50 °C, then release and check the diagonal.
- Blast and pretreat on the seven-tank line, then powder coat at 60–80 µm and oven cure.
- Assemble glides, inserts, hinges or fasteners after coating, with threads masked through the line.
The order matters more than any single step. A frame that is welded before its bracket holes are used as datums will be square to the outside edges and out of position at the holes, which is the error that shows up at assembly when the seat or the shelf will not bolt on.
Frame specification and the limits we hold
| Feature | Typical specification | Ganesh limit or note |
|---|---|---|
| Tube section | 25 × 25 × 1.6 mm | 1.2 mm minimum wall; 2.0 mm at load-bearing joints |
| Tube mass | 1.18 kg/m at 25 × 25 × 1.6 | A 12 m frame is about 14 kg of tube before brackets |
| Bracket material | 1.6–3.0 mm CRCA | Laser cut or stamped; 2.0 mm where a thread is welded in |
| Bracket mass | 0.75 kg at 300 × 200 × 1.6 | 12.6 kg/m² for 1.6 mm sheet |
| Bend radius | 1.0–1.5 × t | 1.5 mm inside radius on 1.6 mm; 2 mm on 2 mm |
| Weld | Stitch 25 mm on 100 mm pitch | Full seam only where the joint is visible and dressed |
| Weld quality | ISO 5817 level C | Level B where the frame is a visible premium product |
| Heat input | 0.3–0.5 kJ/mm on 1.6 mm | 0.32 kJ/mm at 110 A, 18 V, 5 mm/s |
| Frame diagonal | ±1.5 mm over 1,200 mm | Measured standing on its own feet, after cooling |
| Floor flatness | 1 mm across four feet | Checked on a surface plate at the foot pads |
| Coating | Powder 60–80 µm | 80–120 µm for outdoor or washdown use |
| Adhesion | Cross-hatch ISO 2409 class 0–1 | Recorded per lot on a coated sample |
| Frame mass | 16–22 kg for a chair frame | Confirm before specifying castors or glides |
Stamping the brackets that carry the joints
The brackets do the work that the tube cannot. A 300 × 200 mm bracket in 1.6 mm CRCA weighs 0.75 kg, and it is usually the part that carries a thread, a hinge or a levelling foot. That means the bracket gets a weld nut or a clinch insert, and the insert has to survive the coating line.
Two routes make sense. At low and medium volume the bracket is laser cut from flat, formed on the brake and fitted with a weld nut at the fixture. At higher volume a press tool blanks, pierces and forms the bracket in one or two strokes, which is faster and more repeatable but needs a tool and a die maintenance plan. The crossover is the same one described in the tooling cost versus piece price guide; the number is annual quantity, not batch size.
Whichever route is used, the bracket hole that locates the frame in the fixture has to be pierced in the same operation as the mating hole, or the pair will drift. A bracket with two holes pierced in separate hits is a bracket that will be 0.2 mm out, and on a frame with a bolted top that shows up as a hole that will not line up.
Deburring belongs here, not at the end. A laser-cut bracket has a hard dross edge on the underside, and a 0.2 mm burr under a clamp is enough to tilt the bracket in the fixture.
Fixtures: the difference between a frame and a pile of tubes
A furniture frame fixture does three jobs: it sets the tube spacing, it sets the height of the bracket faces, and it holds all of that while the welds cool.
Locate on the surfaces that the customer will use. For a chair frame, that is the seat mounting plane and the two front leg faces. For a table frame, it is the top rail plane and the leg bolt pattern. Clamping on the outside of the tube looks convenient and is wrong, because tube outside dimensions vary by mill tolerance and the frame inherits that variation.
Pin the tube ends rather than butting them against a stop. A pin through a drilled hole in the fixture holds the tube in two axes; a stop holds it in one. On a frame with eight joints, the difference is the difference between ±0.5 mm and ±2 mm on the diagonal.
Clamp every joint that will be welded, at about 300 mm spacing, and leave the clamps on until the frame is cool. Removing a clamp at 150 °C to save a fixture is how a frame gets a 1.5 mm bow that nobody can explain later.
Welding 1.6 mm tube without blowing through
The wall is the constraint. At 1.6 mm, the current window between "fuses" and "burns through" is narrow: 90–120 A with 0.8 mm wire, 18 V, and 80/20 argon-CO₂ at 12–15 L/min is the working range on a manual station. Travel speed around 250–350 mm/min gives a heat input of roughly 0.32 kJ/mm at 110 A and 5 mm/s.
That heat input number matters because it predicts distortion. Doubling the current to 180 A to "get penetration" doubles the heat and roughly doubles the shrinkage, and on a visible 1.6 mm joint it also produces a wider heat-affected zone that shows through the powder as a faint line.
Three practical rules:
- Notch and fit before welding. A 1 mm gap at a tube joint needs bridging, and bridging means a weld that is thicker, hotter and more distorted than the drawing asked for.
- Tack in the fixture, weld in the fixture, cool in the fixture. Tacking outside and welding inside is how a frame gets two datums.
- Weld the least visible joints last. The first weld on a cold frame is the one most likely to pull, so put it on a joint that the eye will not find.
The robotic cells are used where the frame family repeats and the joint access is consistent. A three-sided tube joint with a bracket in the way is a manual job, and forcing it into a robot cell adds a fixture and a programme without improving the weld. The robotic versus manual welding cost comparison sets out where the crossover sits.
Coating a frame that has threads, glides and sliding faces
Powder over seven-tank pretreatment at 60–80 µm is the default finish. The pretreatment is what carries the warranty: a frame that is degreased and phosphated properly will hold powder through a scratch test, and a frame that is wiped and sprayed will not, whatever the powder.
Masking is the part that gets missed on a furniture drawing. A frame usually has weld nuts for a seat, inserts for glides, and sometimes a sliding interface for a drawer or a shelf. Every one of those has to be plugged or taped before the line, because cured polyester in an M6 weld nut is a tap, a touched-in thread and a colour mismatch.
Cure temperature is the other constraint. Polyester powders cure around 180–200 °C, which is above the softening point of many nylon glides and some rubber inserts, so those parts go on after the oven. A design that moulds a plastic insert into a steel tube before coating is a design that will see the insert sag.
Finally, the coating adds thickness at every joint. A bolted bracket face gains about 0.14 mm at 70 µm per side, which is harmless on a furniture frame and not harmless on a close-tolerance sliding fit. Specify a masked face where the fit is tight.
Four mistakes that send frames back
Welding after coating. A bracket added after the oven means a bare weld and a patch. Every welded item goes on the drawing before the first lot.
Fixture built on the outside of the tube. Mill tolerance on 25 mm tube is enough to move the frame 0.5 mm per leg, and the diagonal absorbs all of it.
Coating before the threads are checked. A go/no-go gauge on every weld nut before the line takes seconds; after the line it is a tap and a touch-in on every frame.
Flatness checked on the bench. The frame has to be checked upright, on its feet, at the foot pads. A bench check passes frames that rock.
Inspection that proves the frame will stand
The inspection plan is short and physical. Measure the diagonals with the frame upright, on a flat surface, and record the difference rather than the two lengths. Check the foot pads on a surface plate, with the frame supported as it will be in service, and look for a 1 mm gap.
Weld inspection is visual to ISO 5817 level C on the joints the drawing names, with particular attention to the toe of any bracket weld on a 1.6 mm wall. A crater at the end of a stitch weld is a crack starter on a chair frame that gets dragged across a floor.
On the finish, measure DFT on a flat face and on an edge, and run a cross-hatch test to ISO 2409 on a sample from each lot. Class 0–1 is the expectation on pretreated CRCA. Then assemble: glides, inserts and fasteners at the specified torque, and a static load test to the customer's figure, typically 1.5 times the working load.
Traceability follows the same logic as any welded assembly: heat or coil number for the tube and sheet, coating batch, and the inspection record against the frame serial or lot. The welding inspection and traceability guide covers the record set.
What to put on the frame drawing
- Tube section, wall and grade, with the mill certificate requirement.
- Bracket material and thickness, and which holes are the fixture datums.
- Joint details with weld symbols to ISO 2553, stitch length and pitch, and the ISO 5817 quality level.
- Squareness and flatness, with the measurement method: diagonal on the feet, flatness at the pads.
- Coating system and DFT, plus a masking schedule for threads, inserts and sliding faces.
- Assembly items that must not go through the oven, and who fits them.
- Load and use, so the fixture and the weld detail can be matched to the duty rather than to the drawing alone.
The railway parts range covers seat frames, luggage racks and coach furniture, and the metal furniture parts range covers chair, table, shelving and locker frames. Both sit under the railway, furniture and infrastructure hub, and the press route behind the brackets is on the sheet metal stamping capability page.
When welding is the wrong route
A welded frame is right for a fixed shape that ships assembled, in a batch large enough to justify a fixture. It is wrong for a knock-down product where freight volume is the dominant cost, and it is wrong for a frame that has to be adjusted on site.
It is also wrong where the joint has to be invisible. A welded and coated tube joint always shows a slight line at the weld, and a premium furniture product may need a machined collar, a die-cast joint or a concealed connector instead. We weld and coat; we do not cast connectors or mould plastic parts.
Finally, a frame that has to pass a structural test to a furniture standard needs the test house, not the fabricator. We build to drawing and inspect to the drawing, and the load test is a check on the lot, not a type approval.
Send the frame drawing with the joint details, the datum holes and the masking schedule through the RFQ route. Those three items decide the fixture, the weld sequence and the price, and they are the ones that are missing from most furniture enquiries.
Frequently asked questions
How is a metal furniture frame made?
Tube is cut to length and notched, sheet brackets are stamped or laser cut, and the parts are located in a fixture and welded. The frame is then deburred, pretreated on a seven-tank line, powder coated at 60–80 µm and oven cured before assembly. The fixture, not the welder, sets the squareness.
What tube thickness is used for a furniture frame?
1.6 mm wall is the common default for chairs, tables and shelving uprights in 25 mm square tube, with 2.0 mm at joints that carry a person's weight or a stacked load. Thinner than 1.2 mm is hard to weld without blowing through and hard to keep straight after welding.
Why does a welded frame distort, and how is it controlled?
Welding shrinks metal as it cools, and an unbalanced sequence pulls the frame out of square. Control it by locating on the datum faces in a fixture, welding diagonally opposite joints in turn, and leaving the frame clamped until it is below about 50 °C. A 1.6 mm tube frame welded freehand can bow 1–2 mm over 1,200 mm.
Should furniture frames be welded or knock-down?
Weld when the frame ships assembled and squareness has to survive handling. Go knock-down when freight volume dominates: a table frame ships flat in a fraction of the space, but the corner joint then carries the squareness, so the bracket and the fastener torque become the critical specification.
What coating is used on metal furniture?
Powder over seven-tank pretreatment at 60–80 µm is the default, and 80–120 µm where the frame is used outdoors or in a washdown area. Threads, weld nuts and any sliding interface are masked, because powder in a thread is a tap and a rework ticket.
How is a furniture frame inspected?
Diagonal measurement with the frame standing on its own feet, flatness on a surface table at the mounting points, weld visual to ISO 5817 level C, DFT on the coated faces and a cross-hatch adhesion test to ISO 2409. A static load test follows the customer's figure, typically 1.5 times the working load.
Sources and further reading
- ISO 5817:2023 — Fusion-welded joints in steel: quality levels for imperfections · reviewed 3 Nov 2026
- ISO 2409:2020 — Paints and varnishes: cross-cut test · reviewed 3 Nov 2026
- IS 513 — Cold reduced carbon steel sheets and strips (BIS catalogue) · reviewed 3 Nov 2026
Have a furniture frame drawing?
Send the tube sections, the joint details and the finish. We will confirm the fixture, the weld sequence and the coating plan before quotation.
Send a drawing