Calibrate the enclosure for your printer

Every printer makes holes a little smaller and parts a little larger than modelled. The Printer profile tab of the Board & enclosure dialog corrects the enclosure for your printer.

The printer profile

Its four values are saved with the project; all at 0 give the uncalibrated typical sizes:

• Hole compensation (mm): added to every round hole diameter (screw, pilot and insert holes).
• XY clearance (mm): added per side to connector openings and lid windows.
• Lid fit offset (mm): added to the gap between lid lip and wall.
• Insert hole, measured (mm): the insert hole that worked on the coupon; 0 uses the typical insert size plus the hole compensation.

Print the fit-test coupon

You read these values off a small test print. Open Instruments → Board & enclosure…, choose the Printer profile tab and press Generate the coupon. For M3 heat-set inserts (the screw size and fixing come from the Enclosure tab) the status reads Coupon 77.2 × 39.5 mm ready: all 5 checks passed. The coupon is a 3 mm plate with seven holes (3.4 to 4.0 mm), seven slots for a loose 6 mm test peg (6.0 to 7.2 mm), five standoff samples with insert holes from 3.6 to 4.4 mm, and the peg itself. Instead of text, each sample has 1 to 7 embossed tick marks; the drawing Fit-test coupon, top view shows the size behind each count. Press Download the coupon (STL) and print it flat with the material, nozzle and slicer settings you will use for the enclosure.

Read the coupon and apply it

Then test the print and enter what you found under Read the printed coupon:

• Smallest hole your screw passes freely: for example 3 tick marks (3.6 mm, 0.2 mm larger than modelled).
• First slot the peg drops into freely: for example 5 tick marks.
• Slot with a firm push fit: for example 4 tick marks.
• Standoff sample that held the insert best: for example 4 tick marks (4.2 mm).

Press Apply to the printer profile. The message 4 printer profile values updated from the coupon. confirms it, and the fields now read 0.2, 0.4, 0.1 and 4.2 mm. Press Generate the enclosure. For the example sensor board the box keeps its size of 76 × 56 × 24.6 mm and all 18 checks pass, but the Verification list now says the openings match each connector plus 0.9 mm clearance instead of 0.5 mm (0.5 + 0.4), the standoffs have a 4.2 mm hole instead of 4 mm and the lid lip sits 0.3 mm from the wall instead of 0.2 mm.

When to print it again

Print the coupon again whenever you change the printer, material, nozzle or slicer settings. For the board itself see Design a 3D-printed enclosure for your board. The ohmforge-enclosure-generator tool has the same four fields and prints the same coupon when you set Output to the fit-test coupon.