How do you capture an odd-shaped flat part for CAD without measuring it?
A saw blade tang. Curves, a taper, and holes in what look like random spots. You could spend an hour with calipers and still miss the one dimension that matters. A phone photo looks like a shortcut, but the lens bows straight edges and blows up whatever's closest. Dan Crafted puts it on the printer's scanner bed instead.
Applies to
- Process
- Reverse engineering for 3D printing; also laser and CNC templates
- Parts
- Flat or flat-backed parts: blade tangs, brackets, gaskets, plates with holes
- Setup
- Flatbed scanner or all-in-one printer, a sheet of standard paper, CAD with image import and calibrate
- Software
- Creator uses Fusion's Canvas → Calibrate; most CAD has an equivalent
- Not for
- Thick or curved parts. Only the face on the glass scans true
Why it matters
Measuring an irregular part with calipers is slow, and every missed dimension shows up later as a bad fit. Curves are worst. You end up measuring twenty points and guessing at the arcs between them.
A photo is faster but lies. The lens bends straight edges and enlarges whatever sits nearer the camera, and the clip shows exactly that with a reality-versus-photograph graphic.
A flatbed scans the glass at 1:1.
So once you set the scale from something you know, the scan is a full-size drawing of the part. Holes land where the holes are.
What good looks like
- The calibrated paper edge in CAD reads the paper's real size
- A hole or length you check with calipers matches the trace
- The traced outline drops onto the real part with no offset at the ends
- Holes in the test print line up with the real holes
How to apply it
- Lay the part flat on the scanner glass.
- Add a sheet of standard paper so at least one full edge, ideally the long one, is in the scan.
- Scan it and save the image. 300 dpi is plenty for print-fit work; that's about 0.08 mm per pixel.
- Look up the paper's exact size if you don't know it. A4 is 297 mm on the long edge.
- Import the scan into CAD as a canvas or reference image and calibrate it against the paper edge.
- Sketch over the image to trace the outline and the holes, then model around the sketch.
- Print a small section first, the part with the holes, and test it on the real thing before you print the whole part.
Test it on your setup
- Scale check: after calibrating, measure one real feature, like a hole diameter or the overall length, with calipers and compare it to the trace. Within about 0.2 mm (0.008 in) is a good result.
- Second-axis check: measure the paper's short edge in CAD too. If it's off while the long edge is right, the scanner stretches one direction and you'll need to scale that axis separately.
- Fit test: print just the hole region and drop it on the part.
Exceptions & tradeoffs
Thick parts sit off the glass, so their top edges blur and cast shadows. Trace the face that's touching the glass and measure the thickness with calipers.
Some scanners stretch slightly in one direction. Calibrating on one edge won't catch it, which is why the second-axis check exists.
Part too big for the bed? The creator suggests calibrating off any known dimension on the part itself instead of the paper, though he hasn't tested it. Use the longest one you can measure.
Mind you, a photo can work if it's shot square-on from far away with a zoom, and the reference sits in the same plane as the part. It's never as clean as a scan.
Common mistakes
- Shooting a phone photo from a foot away and tracing thatScan it, or shoot from distance, square to the part, with a reference in the same plane
- Calibrating on the paper's short edge, or a tiny featureCalibrate on the longest known dimension; a small picking error matters less over a long span
- Printing the whole part firstPrint the hole and fit area as a test piece
Frequently asked questions
- How do you scan a part for CAD?Lay it flat on a flatbed scanner with a sheet of paper of known size, scan it, and import the image into CAD. Calibrate the image to the paper's long edge (297 mm for A4, 11 in for US Letter), then trace the outline and holes.
- How do you calibrate a canvas in Fusion 360?Insert the image as a canvas, right-click it in the browser and choose Calibrate. Click two points on a known edge, like the two ends of the paper's long side, and type the real length. Fusion rescales the image to match.
- Is a scanner better than a photo for tracing parts?Yes, for flat parts. A flatbed images the glass at true scale, while a phone lens bends straight edges and enlarges whatever is closer to the camera. A photo only gets close if it's shot square-on from a distance.
- What resolution should I scan a part at for tracing?300 dpi is plenty for 3D-print fits. That's about 0.08 mm (0.003 in) per pixel, finer than a printer can reproduce. Go higher only for very small parts.
Photo-versus-reality distortion (0:18), scanning a blade tang alongside a sheet of paper (0:24), calibrating in Fusion and modelling a handle around the trace (0:32), and test-printing a subsection (caption) — Video by dancrafted_ (Instagram reel) ↗ at 0:18–0:32.
Summarized and independently edited by Start Here from Dan Crafted's Instagram reel, frames and caption only, no audio. Scanning with a reference sheet, calibrating in Fusion, tracing and test-printing a subsection are his. The calibration value is only half-typed in the frame ("29…"); I've read it as 297 mm, the A4 long edge, which matches the sheet in the scan. The scan resolution, the accuracy target, the second-axis check and the thick-part caution are mine.