AlignScan / Guides / Cylinder axis datum
Guide
Align a scan to a cylinder or axle axis
Flat faces are the usual datum for squaring a scan, but axles, shafts, pipes, hubs and other turned parts are better described by their centre line. On an assembly with brackets and mounts, the biggest flat face is often a bracket, not the thing you care about.
When to use a cylinder as the datum
- An axle, shaft or tube is the main body and brackets are bolted to it.
- A hub, wheel or bearing seat: the bore or spigot axis defines "straight".
- The biggest flat face is a mount or bracket that is not parallel to the part's real axis.
- You want the centre line of the part on an axis and through the origin, for example to model or revolve around it in CAD.
Automatic: cylinder priority
- Drop the scan into AlignScan.
- In the Align panel choose Priority: Cylinders & axles. The dominant cylinder axis (largest radius and length) becomes the datum and is squared to the nearest world axis.
- Recenter switches to Cylinder axis → origin: the axis line passes through the origin and the part is centred along it.
- The panel reports the measured radius and length, so you can sanity-check it against a caliper reading.
A cylinder only fixes two of the three rotations: the spin about the axle is free. AlignScan keeps that at the smallest turn and says so. If a flat face or a second cylinder is available, click it in Manual mode to lock the spin.
Manual: click the cylinder you mean
- Open the Manual tab and under "Click on a" choose Cylinder.
- Click anywhere on the shaft, pipe, boss or bolt. The tool follows the whole connected cylinder surface and fits its centre line and radius.
- Choose X, Y or Z to square its axis (smallest turn). Leave "Also put this axis through the origin" ticked if you want the centre line on the origin.
- Pick a flat face, or another cylinder, to fix the remaining spin about the locked axis.
How accurate is the axis?
The centre line comes from a robust fit to the whole cylinder surface, so it averages out scan noise. On a synthetic axle with a deliberately tilted bracket plate, the fitted radius came out at 12.00 for a true 12 and the length at 119.9 for a true 120. Always check partial scans: a cylinder that is only scanned along a short arc gives a less certain axis.
Skip the manual work: drop your scan into AlignScan. It runs in your browser and the file is never uploaded.
Open the aligner → Try a sample first