Most jobs start with a sketch. It might be a pencil drawing on the back of a delivery docket, a photo with some arrows on it, or a few lines in an email. That is a perfectly good place to start. The problem is that a sketch only has to make sense to the person who drew it, while a manufacturing drawing has to make sense to someone who has never seen the part and can’t ring you at 2pm on a Tuesday.
This post is a checklist of what to gather so your sketch can become a drawing a workshop can build from. You don’t need to get everything perfect. Knowing what is missing is the useful part.
Dimensions: the ones that matter
You don’t need to dimension every edge. You do need the dimensions that control whether the part fits and works. Start with these:
- Overall size: length, width and height (or diameter and length for round parts).
- Hole positions and sizes: measure from a consistent edge or centreline, not from hole to hole to hole. Chained measurements stack up errors.
- Thickness: of plate, tube wall, or sheet. Say whether it is measured or assumed.
- Mating features: anything the part bolts to, slides into or sits against. These are often more important than the part itself.
- Angles and bends: include the direction of each bend and whether the dimension is inside or outside.
Say which units you are using, and be consistent. If a measurement is approximate, write “approx.” next to it. An honest estimate is more useful than a number that looks exact but isn’t.
Material and finish
If you know the material, write it down. If you don’t, say what it is made from in plain terms: mild steel, stainless, aluminium, plastic, cast iron. Even that narrows things down a lot.
Also note:
- Whether the part is currently working or failing. If it keeps breaking, the original material or section may be the problem, and a straight copy would just repeat it.
- The environment: outdoors, wet, coastal, food contact, chemicals, heat, washdown. This affects material and coating choices.
- Finish: raw, painted, galvanised, powder coated, anodised, polished. If you don’t have a preference, say so and we can suggest something suitable.
- Welding or machining requirements: for example, whether welds need to be ground flush for appearance or safety.
If you are not sure of the grade, that is fine. Don’t guess a grade just to fill in a box. A workshop can often identify a material, and the drawing can say “to match existing” until it is confirmed.
Quantities, tolerances and how the part is used
Quantity changes how a part should be designed. One off can be cut, bent and welded by hand. Fifty might justify a jig, laser-cut profiles or a different joining method. Tell us how many you need now, and how many you might need later. “One now, maybe ten next year” is a useful answer.
Tolerances are where sketches usually go quiet. Tighter tolerances cost more, so they should only be applied where they matter. As a rough guide:
- Fit-up surfaces, bearing seats, shaft diameters and sliding parts usually need tighter control.
- Brackets, guards and general fabrication usually don’t.
If you don’t know what tolerance you need, describe the fit instead: “this must slide freely into that,” or “this is a press fit on the shaft.” That gives enough to set sensible tolerances on the drawing.
Finally, tell us what the part does. Loads, speed, how often it moves, who touches it, what could go wrong. This matters for function and for safety. If the part is part of a machine that people operate or work near, safety in design questions come into it, and any structural or pressure-related sign-off must be done by an appropriately qualified person. A drawing is not a certification.
Photos and what else to send
Photos save a lot of back and forth. Good ones show:
- The part from several angles, including the underside and any hidden faces.
- The part in place, so we can see what it connects to and what is around it.
- A tape measure or ruler in the frame for scale, with the markings readable.
- Close-ups of wear, cracks, welds, stamped numbers, labels or part numbers.
Take photos square-on where you can, in decent light, rather than at an angle that distorts the shape. [CHECK: confirm Drafting Central is happy to start from phone photos plus a tape measure for simple parts, and whether you prefer a site visit or the part posted in for anything more complex]
Beyond photos, a handy package to send includes:
- Your sketch, even if it is rough or messy.
- Key dimensions, marked as measured or estimated.
- Material, finish and quantity.
- A short note on what the part does and where it goes.
- Any existing drawings, manuals, supplier datasheets or part numbers.
- Your deadline, and whether it is firm or flexible.
If the part is complex, curved, worn or difficult to measure by hand, it may be better to scan it than to measure it. 3D scanning and reverse engineering can capture the real geometry, and the drawing is then built from that. It is worth asking about early, before anyone spends an afternoon with a tape measure and a pair of calipers.
Where to start
Don’t wait until your sketch is tidy. Send what you have, and be upfront about what you don’t know. Missing information is normal. Guessed information that looks certain is what causes trouble later.
A sensible first step is to work through the checklist above and mark each item as known, estimated or unknown. From there it is usually clear whether you need a simple workshop drawing, a 3D model, or a site visit to measure things properly. You can see the sort of work we do on our services page.
When you are ready, send us your sketch, photos and notes and we will tell you what else is needed and how we would approach it.
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