Welded workbench: cutting-list calculator
Give three dimensions and a section, and you get the cutting list, the steel to buy, the length of welds and the current. The drawing redraws with the numbers; the list prints, downloads or saves as a link.
A worked example: 1500 × 700 × 850
The version most people start from: a 1500×700 mm top at 850 mm, a frame of 40×40×2, a 4 mm plate and a bottom shelf.
| Item | Section | Length, mm | Qty |
|---|---|---|---|
| Legs | 40x40x2 | 846 | 4 |
| Top frame, long side | 40x40x2 | 1500 | 2 |
| Top frame, short side | 40x40x2 | 620 | 2 |
| Cross member under the top | 40x40x2 | 620 | 1 |
| Bottom frame, long side | 40x40x2 | 1420 | 2 |
| Bottom frame, short side | 40x40x2 | 620 | 2 |
Mass is worked out without the corner radii of the section, so it comes out two to three per cent below the standard tables. No allowance is added for saw kerf or cutting errors: when buying, add one commercial length.
That comes to about 12.3 m of section (three commercial 6 m lengths), 29 kg of frame and 33 kg of top — a little over 60 kg of finished bench.
The order that keeps the frame straight
A bench goes out of square not from bad welding but from the order of work. Heat put in from the same side every time pulls the frame that way, and you only see it once everything has cooled — when straightening is hard.
- Cut everything and sort it. The four legs must be exactly the same length: 2 mm of difference is a bench that rocks. Cut them as a bundle in one go.
- Assemble the top frame flat and measure both diagonals before tacking. Equal diagonals are the only proof the frame is rectangular — a square will not show it over 1.5 m.
- One tack per corner, check the diagonals again, and only then add the rest.
- Weld the legs with the frame upside down on a flat floor: the legs then set themselves in one plane.
- Weld corners alternately, diagonally opposite, each with a short run rather than all the way round at once.
- The top goes on last, stitched every 200–300 mm. A continuous weld round a 4 mm plate dishes it, and that does not come back out.
Welding settings
A 2 mm wall is already thin material: the current you normally use burns a corner away in a second. The values are the same as on the welding square tube page; the calculator above shows the row for the wall thickness you chose.
| Wall, mm | Section | MIG/MAG | MMA |
|---|---|---|---|
| 1.2 | 20×20, 20×40 | 0.8 mm · 50–70 A · 16–17 V | 2.0 mm · 50–65 A, stitch welding |
| 1.5 | 40×20, 40×40 | 0.8 mm · 70–90 A · 17–18 V | 2.0 mm · 55–70 A, stitch welding |
| 2.0 | 40×40, 60×40 | 0.8 mm · 90–110 A · 17–19 V | 2.5 mm · 70–90 A |
| 3.0 | 60×40, 80×40 | 0.8–1.0 mm · 120–140 A · 19–21 V | 3.2 mm · 90–120 A |
| 4.0 | 80×40, 100×50 | 1.0 mm · 140–170 A · 19–21 V | 3.2 mm · 110–140 A |
What usually spoils the job
| What went wrong | Cause | How to avoid it |
|---|---|---|
| The frame twisted | Welds run one after another on the same side | Alternate corners, weld in short runs |
| The diagonals came out unequal | Nobody checked them before tacking | Measure both diagonals twice |
| Burnt through the wall | Too much current for 1.2–1.5 mm | Turn it down, stitch it with pauses |
| The corner welded on one side only | Saving time | Weld both sides wherever the joint takes load from two directions |
| Rust from the inside within a year | Open ends | Caps, or weld them shut |
Frequently asked questions
What height should a workbench be?
For standing work it is measured from the elbow: the top 10–15 cm below the bent elbow. For most adults that comes out at 850–900 mm. For welding and sawing, lower is better; for assembling small parts, higher.
What section for the legs?
40×40×2 is enough for a bench up to 1.5 m with a 4 mm top. Beyond 1.5 m, or under a vice and a hammer, go to 50×50×2 or 50×50×3. Below 2 mm of wall there is no point: the saving is small and it is very easy to blow through when welding.
Steel top or timber?
For welding, steel only: sparks and hot offcuts leave no choice. 4 mm is the minimum to stop the top drumming; 6–8 mm stays flat for years. Timber is fine on an assembly bench, but do not weld on it.
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