How to measure a broken part so a maker can remake it

A maker can model a part from good photos, but measurements decide whether it fits. The aim is a short list of numbers, each with its unit, taken from the parts of the piece that are still intact.

Before you start

• Collect every piece. Fit the fragments together and hold them with tape so the original shape is visible.
• Clean the part. Grease and dirt add fractions of a millimetre to every reading.
• Zero the calipers. Close the jaws and press zero, or check that a dial caliper reads zero when closed.
• Work in millimetres. Write "mm" next to every number. If you measure in inches, say so once at the top of your notes.

Steps

1. Overall size. Measure the longest length, the widest width and the tallest height. Hold the jaws square to the part, not at an angle.
2. Holes. Use the inside jaws for each hole diameter. For the spacing, measure from the inside edge of one hole to the inside edge of the next, then add one hole diameter: that gives the centre-to-centre distance for two holes of the same size. Note whether a hole goes all the way through.
3. Wall thickness. Measure the thickness of each wall, rib and flange that you can reach. Thin walls are where a remade part needs the most care.
4. Clips and tabs. Measure the length and thickness of each tab, the height of the hook at the end and the gap it snaps into. Snap-fits only work within a narrow range, so these numbers matter.
5. Threads. Measure the outside diameter of a screw thread, or the inside diameter of a threaded hole. For the pitch, measure across ten threads and divide by ten, or use a thread gauge.
6. Gears. Count the teeth (mark the first tooth with a pen), then measure the outside diameter across the tips, the bore and the face width. Note what the gear meshes with.
7. The mating part. If the part clips onto a rail, slides on a shaft or sits in a slot, measure that too. It is usually less worn than the broken piece, so its numbers are more reliable.
8. A sketch. Draw the part roughly from two sides and write each measurement on it. A phone photo of the sketch is enough.

Worn, broken or warped parts

• Measure intact sections. A snapped edge is shorter than the original, and a crushed clip is thinner.
• Use symmetry. If one side of a symmetrical part is broken, measure the good side and say so.
• Measure three times and write down the middle value when readings differ.
• Flag wear. If a hole is worn oval or a gear's teeth are rounded, tell the maker. They can design from the mating part instead.

Why a maker may not copy it exactly

A UK government study of 3D-printed spare parts found that copying a traditional part's shape "without redesign is generally considered inappropriate": a printed part behaves differently from a moulded one, so wall thickness, ribs and print orientation may need to change [1]. Your measurements give the maker the fixed points (holes, clips, outside size). Tell them how the part is used, and let them adjust the rest. For moving parts such as gears and bushings, materials like nylon, which the Prusa Knowledge Base describes as "resistant to abrasion", are a common choice [2]; see the material guide.

What to send

Post your measurements and sketch together with the photos described in the photo guide, the model number and a line on how the part is used: indoors or outdoors, hot or cold, carrying a load or not.