A simple spacer makes a useful learning exercise because three dimensions define its main form: outside diameter, hole diameter and height. Keep this exercise non-load-bearing and inspect the export as a new file. It is not a design for structural, electrical or safety use.
Download the English project worksheet. Open it as UTF-8 CSV, replace the guide context with your project inputs and record observations separately from acceptance decisions. Blank cells do not indicate a passed check.
Define the purpose and three dimensions
Record what the spacer separates, units and a reference face. In the stored digital exercise, the bottom is Z = 0 and the axis follows Z. Stop if your application needs more than a simple ring.
Measure outside diameter, hole diameter and height, recording their source and the instrument. The nominal radial wall is half the difference between diameters. For 20 mm outside and 10 mm inside, (20 − 10) ÷ 2 = 5 mm. The 10 mm difference spans two opposite walls. This is geometry, not strength evidence.
For a hole that slides over another part, distinguish clearance and manufacturing tolerance. Use reference-face measurement when copying an existing component.
Build a concentric ring and inspect the hole
Draw two circles with the same centre and explicit diameters. The inner diameter must be smaller so the wall is positive. Extrude the ring to the selected height and check direction and flat ends. Do not add fillets or fit allowances without recording new dimensions.
Check the difference between a circle and its polygon
The stored fixture approximates both circles with 64 segments. Inner vertices lie at radius 5 mm and outer vertices at radius 10 mm. Straight chords connect them, so the smallest clear diameter across opposite inner faces is approximately 9.987955 mm, slightly below the 10 mm vertex diameter. Sixty-four segments is a fixture choice, not a universal quality setting.
Inspect the recorded digital example
Open the reference STL locally and measure its outside, hole and height separately.
| Feature | Recorded digital value |
|---|---|
| Outside diameter | 20 mm |
| Nominal hole / diameter across vertices | 10 mm |
| Smallest polygon opening | Approximately 9.987955 mm |
| Height | 6 mm |
| Nominal radial wall | 5 mm |
| Facets | 512 |
| Vertex records reread | 1,536 |
| Open edges, non-manifold edges, winding differences | Zero |
The script checked both vertex radii, distance to inner edges, height and axis limits. No CAD interface, slicer, physical print, fit or load was tested.
Reopen the export separately
Check its bounding box, open centre, flat ends and facets. Record millimetres separately because STL does not declare a standard unit. A correct 20 × 20 × 6 mm envelope can conceal a missing or undersized hole. The inner polygon's apothem is why the fixture checks its smallest opening as well as its vertices.
Reject the wrong hole even when the outside is correct
A hypothetical rejection illustrates the difference: outside diameter 20 mm and height 6 mm are correct, but the minimum opening is 9.6 rather than the requested 10 mm. The radial wall at that section is (20 − 9.6) ÷ 2 = 5.2 mm. The envelope is unchanged while the functional opening differs by 0.4 mm. Investigate source, export and fit requirements instead of approving from the outside dimensions.
Take a measured design to the next step
Stop for an unknown mating diameter, missing clearance, eccentric hole or structural application. A real fit needs a project-specific trial and acceptance criterion.
When your own exported geometry is correct, send its revision, units and mating-part dimensions to the 3D printing service. Do not use the exercise's dimensions as default product dimensions. For an eccentric hole, extra connections or a different function, request modelling with a marked sketch. Use the prototype assessment to distinguish a digital dimension from measured physical fit.