A fabrication assembly drawing shows the finished assembly, lists every part in it, and tells the fabricator how the parts join, which dimensions matter, and how it should be finished. It's the one sheet that answers "what am I building?" when the individual part files can't.
Without one, a pile of DXFs is just a pile of flat shapes. The shop has to guess which way a bracket faces, which edges get welded, and whether that 450 mm is the outside or the inside. Guesses cost money and sometimes a remake. Below is what to include, a sample parts list, how to show welds without being a draughtsman, and the mistakes we see most.
When you actually need one
If you're ordering a single flat laser-cut part, you don't. A clean DXF with the material, thickness, and quantity is enough.
You need an assembly drawing as soon as parts have to be joined to each other. That includes:
- Anything welded, bolted, or riveted together
- Bent parts that fit together into a box or frame
- Parts with inserts, studs, or brackets attached
- Anything that will be coated after assembly, where masking matters
A 3D STEP model of the assembly does a lot of the same job, and if you have one, send it. But a model doesn't tell us which welds are visible, what finish you want, or which dimension must be spot on. A simple drawing on top of the model fixes that.
What a good assembly drawing shows
Here's the checklist we'd want on any fabrication drawing. Not every job needs all of it.
- Views of the finished assembly. At least a front, side, and top, or a clear isometric view. Show it the way it will be installed.
- Balloons or part numbers pointing to each component, matching the parts list.
- A parts list (bill of materials) with part number, description, material, thickness, and quantity.
- Overall dimensions of the finished assembly.
- Critical dimensions marked clearly: hole centres that must line up with something, openings that must fit a door, mounting positions.
- Weld information: where the welds go, whether they're continuous or stitched, and whether they're visible.
- Fasteners: bolt sizes, rivet types, inserts, and where they go.
- Finish: raw, brushed, painted, or powder coated, with the colour code, and any areas to mask.
- Revision letter and date, so we know we're quoting the latest version.
A sample parts list
The parts list is the most useful single thing on the drawing. Keep it simple. For a small bent and welded equipment stand, it might look like this:
| Part no. | Description | Material | Thickness | Qty per assembly | File |
|---|---|---|---|---|---|
| 01 | Top plate | Mild steel | 3 mm | 1 | stand-01-top.dxf |
| 02 | Side leg (bent) | Mild steel | 2 mm | 2 | stand-02-leg.step |
| 03 | Cross brace | Mild steel | 2 mm | 2 | stand-03-brace.dxf |
| 04 | Foot plate | Mild steel | 5 mm | 4 | stand-04-foot.dxf |
| 05 | M10 hex bolt and nut | Zinc plated | n/a | 4 | Bought-in |
Link every row to a file name. Then the order is: overall assembly quantity on the quote, and the parts list does the multiplying. If you're ordering 20 stands, we know that's 80 foot plates.
How to show welds if you don't know weld symbols
Proper weld symbols (the arrow, reference line, and triangle notation) are the clearest way if you know them. If you don't, plain notes are fine. A note that's clear beats a symbol that's wrong.
Useful plain-English weld notes:
- "Fillet weld all round, both sides"
- "Stitch weld 30 mm every 100 mm, inside face only"
- "Continuous weld, ground flush and brushed: visible face"
- "Tack only, customer to finish weld on site"
- "Seal weld: must be watertight"
Point each note at the joint it applies to. Then add one general note for everything else, such as "All other welds: 4 mm fillet, hidden, strength only."
If weld appearance matters, say it. "Visible" and "hidden" tell the fabricator more than a process name does.
Dimensions and tolerances that make sense for welded parts
Welding moves metal, so a welded assembly can't hold the same tolerance as a single laser-cut part. Drawings that apply ±0.1 mm to every dimension get one of two responses: a high price or a phone call.
A better approach:
- Dimension from the features that matter: mounting holes, the face that bolts to a wall, the opening a lid closes into.
- Mark which dimensions are critical and leave the rest at a general tolerance.
- Show where holes should be cut before welding and where they must be drilled after, if alignment across a welded joint is critical.
- Use a datum: one edge or face that everything is measured from.
Designing parts to locate themselves helps here. Our post on tab and slot design shows how slots and tabs hold parts in position for welding.
Common mistakes on fabrication drawings
- Mixed versions. The DXF says one thing and the PDF says another. Use one revision letter across all files.
- Dimensions to the wrong side of the material. On bent parts, say whether a dimension is inside or outside.
- No material for some parts. Every row in the parts list needs a material and thickness.
- Coating with no masking notes. Powder coating is thick enough to block threads and tight fits. Mark what to mask.
- Assembly quantity unclear. Is "qty 10" ten assemblies or ten of each part? Say which.
Sending your drawing (or a sketch, if you don't have CAD)
Upload your assembly drawing (PDF is fine), any STEP or DXF part files, and the quantity of assemblies.
If you don't have CAD, a hand sketch with dimensions, or a photo of an existing part with a tape measure in shot, is enough to start. Our guide to ordering a metal part from a sketch or photo explains what to include. If you're new to how fabricated parts are made, what is metal fabrication gives the overview. The quote form takes files up to 10 MB; bigger packs can go to ctrlcutsa@gmail.com. Read more about our fabrication service, or start a fabrication quote.