Parts that receive standard consumables: microplates, cuvettes, tubes, slides, dishes.
The governing principle: where a published standard exists, design to the standard; where it does not, require a measurement. Microplate footprints are standardised. Well geometry, skirt profiles, tube dimensions, and lid fits are not.
Verified dimensions live in assets/standards.json. Query them rather than copying numbers:
python scripts/check.py standards --show slas-microplate-footprint
Four documents split the plate geometry. All are ANSI-approved and were reaffirmed in 2012.
| Document | Governs | Key numbers |
|---|---|---|
| ANSI/SLAS 1-2004 | Footprint | 127.76 x 85.48 mm ±0.25; corner radius 3.18 ±1.6 mm |
| ANSI/SLAS 2-2004 | Height | 14.35 ±0.25 mm, resting plane to top of perimeter wells |
| ANSI/SLAS 3-2004 | Bottom outside flange | Short 2.41, medium 6.10, tall 7.62 mm, each ±0.38 |
| ANSI/SLAS 4-2004 | Well positions | 96-well: 9.0 mm pitch, A1 at 14.38 mm from left, 11.24 mm from top |
Three traps, in the order people fall into them.
1. Design to maximum material, not to nominal. A plate at the top of tolerance is 127.76 + 0.25 = 128.01 mm. A pocket cut at 127.76 + clearance will jam on roughly half the plates you try. Compute:
plate_l_mm = 127.76 # ANSI/SLAS 1-2004 nominal
plate_tol_mm = 0.25 # ANSI/SLAS 1-2004
fit_clearance_mm = 0.40 # per side; FDM, see fabrication-limits.md
pocket_l_mm = plate_l_mm + plate_tol_mm + 2 * fit_clearance_mm # 128.81
2. The corner radius tolerance is enormous — and it bounds the pocket radius from above, not below. 3.18 ±1.6 mm means a real plate corner is anywhere from 1.58 to 4.78 mm. Get the direction right: a plate corner is convex, a pocket fillet is concave material bulging inward, so a sharp internal pocket corner always clears a rounded plate — the unused corner is empty space. It is a pocket fillet larger than the plate's corner radius that binds: the bulge occupies space the plate needs. Sizing the fillet to the plate's maximum corner radius is therefore exactly backwards — it binds every plate except those at the top of the corner tolerance.
The safe options, best first:
R ≤ r_min + ~3.4 × per-side clearance — the geometry only recovers the
intrusion when the plate stays roughly centred, so treat this as a last resort and say so.with BuildPart() as pocket:
# ... pocket geometry ...
# relief bores just outside each pocket corner: clears any conforming corner radius
with Locations(*corner_relief_centres()):
Hole(radius=2.0)
3. Height depends on the flange, not just the plate. ANSI/SLAS 3 standardises three flange heights. A carrier that grips the flange must be told which one. Ask; do not assume medium.
For a part that must reach individual wells — a magnet block, a lid with access holes, a light guide — lay out from the plate's outline corner, not from the plate centre:
a1_x_mm, a1_y_mm, pitch_mm = 14.38, 11.24, 9.0 # ANSI/SLAS 4-2004, 96-well
locations = [
(a1_x_mm + pitch_mm * col, a1_y_mm + pitch_mm * row)
for row in range(8) for col in range(12)
]
The standard's positional tolerance is a 0.70 mm diameter zone around each nominal centre, not a ±0.70 mm band. A feature that must clear every well needs at least 0.35 mm of radial margin on top of your own process tolerance.
384-well pitch is 4.5 mm and 1536-well pitch is 2.25 mm. The A1 offsets for those formats in
standards.json are marked unverified — they were derived, not read from the document. Read
ANSI/SLAS 4-2004 before relying on them.
Well diameter, well depth, well bottom shape (flat, round, conical), skirt height, lid geometry, optical bottom thickness, and deep-well plate height. All vary by manufacturer and product line. If the part touches any of these, get the vendor drawing or measure it.
The standard macro cuvette is a convention rather than a published standard, but it is close to universal: 12.5 x 12.5 mm external, 45 mm tall, 1.25 mm wall, 10 mm optical path.
Design notes:
Tube dimensions are not standardised and differ measurably between suppliers, and often between product lines from the same supplier. Approximate outside diameters near the tube rim:
| Tube | Approximate OD | Note |
|---|---|---|
| 0.2 mL PCR | 6 mm | Often supplied in strips or as a 96-format plate |
| 1.5 mL microcentrifuge | 11 mm | Rim is wider than the body; the body tapers |
| 2.0 mL microcentrifuge | 11 mm | Same rim as 1.5 mL, taller body |
| 15 mL conical | 17 mm | Cap is wider than the tube |
| 50 mL conical | 30 mm | Cap is wider than the tube |
Treat every number in this table as a starting point for a first article, not a design input. Ask the user for the supplier and catalogue number, or ask them to measure with calipers. Then design a rack that holds the tube by the rim or the cap, which is dimensionally stable, rather than by the tapered body, which is not.
For a rack, the useful pattern is a through-hole sized to the body plus clearance and a counterbore that catches the rim, so the tube hangs rather than bottoms out.
Standard slide: 75 x 25 mm, 1.0 mm thick (ISO 8037-1 covers slide dimensions; thickness classes vary, and 1.0-1.2 mm is typical). Coverslips are specified by thickness number, not dimension:
Objective working distance is unforgiving. A holder that adds even 0.2 mm under the slide can put the sample outside a high-NA objective's working distance. Design slide holders so the slide registers directly against the stage datum, with the holder clamping from above.
Standard dish outside diameters are approximately 35, 60, 90, and 100 mm, but the flange profile and lid fit vary. Dishes are also slightly out of round. Locate on three points rather than a continuous circular pocket: a three-point nest is insensitive to ovality, a close-fitting bore is not.
For stage inserts, the interface that matters is the microscope stage opening, which is instrument-specific and must be measured. Many stages accept a standard SLAS-footprint insert; confirm before assuming it.
Declare the pocket in the model's interfaces() and let the check read it:
python scripts/gen.py carrier_model.py --outdir out/
python scripts/check.py interfaces out/carrier.manifest.json
Do not point check.py fit at the carrier's STEP. fit measures the outer bounding box, which
for a carrier is the outside of its walls — 6 mm larger than the pocket here — so it fails against
the plate footprint no matter how correct the pocket is. The dimension that matters is internal, so
it has to be declared, not measured from the envelope.
To check the number by hand instead:
python scripts/check.py fit --standard slas-microplate-footprint \
--intent envelope --clearance 0.8 --value footprint_length=128.81
--intent envelope checks one-sided against maximum material condition, and --clearance is the
total intended clearance: 0.40 mm per side is 0.80 mm. Passing means the pocket is the size you
intended, not that the plate fits — only a test print shows that.
Then always run snapshot.py and confirm the pocket is on the face you meant.