Printed parts that fit: test the interface before the whole object

By the Lindenmaker team. Sources checked in October 2026.

Before printing a whole box, try the lid's mating edge. Before printing a large holder, try the opening that must fit the object. A small representative sample turns a big, slow print into a manageable design question.

Define the fit before choosing a gap

Should the parts slide, locate or clip together? Prusa's design guidance says there is no single universal value for a fit: it depends on factors such as size, orientation, geometry, calibration, settings and material. It recommends test prints before you treat a design as final, and suggests saving versions as you go. See Prusa: modelling for printing.

Write a plain acceptance condition, such as "the lid slides on by hand and can be removed without tools". That is a project goal, not a dimensional guarantee.

Say whether your clearance is total or per side

Take an invented round peg and hole. If the hole's diameter is larger than the peg's by some allowance, that allowance is a difference in diameters. If the peg sits perfectly centred, the gap on each side is half of it.

That arithmetic describes the drawing, not what your printer will deliver, and it is not a recommended clearance. Label the CAD parameter explicitly, for example diameter-difference-mm, so you never double or halve an allowance by accident.

Keep the sample representative

Keep the important mating geometry, the material, the orientation and the relevant process settings. Note anything you simplified. Prusa lists these as factors that affect fit, so a sample printed differently from the final part needs cautious reading.

Change one chosen variable between trials and keep the previous files. This is Lindenmaker's suggested record structure:

Trial	File and profile version	One change	Intended dimension	Measured result	Fit observation
A		Baseline
B
C

Record the measuring tool and its limits alongside each result. Decimal places in a CAD file do not establish measurement accuracy.

Check whether the first layer is the problem

Prusa explains that the first layer is squished against the heated bed and is usually a little wider than it should be, often called elephant's foot. Its slicer compensation shrinks that layer. If binding is confined to the base, look at that feature before deciding the whole model is the wrong size. Follow the documentation for your slicer and version, because a setting described for PrusaSlicer does not automatically carry over to another program. See Prusa: elephant-foot compensation.

Keep the test within your safe setup

The University of Edinburgh publishes guidance on printer emissions, fire precautions, manufacturer information and material safety data sheets. It is institutional guidance, not a home-workshop certification. Use it to find questions to ask about your own setup rather than as a ventilation prescription. See University of Edinburgh: printer guidance.

A successful fit does not show strength, heat resistance or safety for medical, protective or load-bearing use. Keep this approach to ordinary low-risk prototypes unless the application has had a proper design assessment.

Save the accepted sample, the source model and the settings together, so you can repeat the result later.