ART
BEAUTÉ ET BIEN-ÊTRE
ARTISANAT
CULTURE ET HISTOIRE
DIVERTISSEMENT
ENVIRONNEMENT
NOURRITURE ET BOISSONS
INGÉNIERIE INVERSE
SCIENCES
SPORTS
TECHNOLOGIE
TECHNOLOGIE PORTABLE
Fits: Clearance, Transition and Interference — the Difference Is Microns
A shaft that slides into a hole and a shaft that has to be pressed in can differ in diameter by less than the thickness of a human hair. Which of those you have is decided by a few microns, and the difference in behaviour is total.
A CLEARANCE fit always has a gap: the parts assemble by hand and can move. An INTERFERENCE fit always has the shaft larger than the hole: the parts must be forced together and then grip each other permanently. A TRANSITION fit may be either, depending on where the two parts happen to fall in their tolerances.
This is why a bearing can spin on its shaft, or crack its outer ring, or work perfectly — all from the same drawing and the same parts bin. The fit is the design decision, and it is made in numbers before anything is cut.
Intermédiaire
3 hours
Consignes
1
1
Measure both parts, and measure them properly
Measure both parts, and measure them properly
You cannot choose a fit without knowing what you have. Measure the shaft and the bore with a micrometer or a good caliper, at several places along their length and at several angles round them.
Several angles matters because nothing is perfectly round. A shaft that reads 19.98 mm one way and 20.02 mm at ninety degrees is out of round by 0.04 mm, which is larger than most fits — and averaging the two hides it.
Let both parts reach the same temperature first. Steel expands about 11 microns per metre per degree, so a 50 mm part handled for a minute can grow by more than the fit you are trying to measure. Warm hands are a real error here.
Matériaux pour cette étape :
Arbre en acier de 30 mm1 pièceOutils nécessaires :
Pied à coulisse
Pied à coulisse numérique 6 pouces2
2
The arithmetic, and what each fit is for
The arithmetic, and what each fit is for
Chargement du notebook Jupyter…
Matériaux pour cette étape :
Arbre en acier de 30 mm1 pièce
Ball Bearing - Non-Flanged (8mm Bore, 22mm OD)1 pièceOutils nécessaires :
Pied à coulisse
Ordinateur de bureau
Calculatrice3
3
Temperature is a tool, not just an error
Temperature is a tool, not just an error
Heat the outer part and it grows; chill the inner part and it shrinks. Do both and an interference fit can be assembled by hand, then locks as the temperatures equalise.
Steel expands about 11 microns per metre per degree Celsius, so a 100 mm bore heated by 100 degrees grows roughly 0.11 mm — far more than any normal interference. An oven at 120 degrees, or a freezer for the shaft, is usually enough.
Never heat a bearing above about 120 degrees. Above that the hardened rings begin to temper and lose hardness permanently, and a blowtorch anywhere near a bearing ruins it in seconds. Induction heaters and hot oil baths exist precisely because the temperature has to be controlled.
Matériaux pour cette étape :
Arbre en acier de 30 mm1 pièceBall Bearing - Non-Flanged (8mm Bore, 22mm OD)1 pièceOutils nécessaires :
Pied à coulisse numérique 6 pouces
Gants en nitrile4
4
Surface finish and roundness are part of the fit
Surface finish and roundness are part of the fit
A measured diameter is an average over a surface that has peaks and valleys. Press two rough surfaces together and the peaks flatten, so the effective interference is less than the measured one — often by 2 to 5 microns on ordinary turned work.
That is why bearing seats are ground rather than turned. It is not fussiness: a rough seat loses a significant fraction of a 15 micron interference to flattened peaks the first time the joint is loaded, and then the bearing creeps.
Roundness matters as much. A bore that is 0.03 mm oval will grip a round shaft at two points and leave gaps at ninety degrees, so the pressure is concentrated rather than shared — which distorts the bearing ring and takes the internal clearance with it.
Matériaux pour cette étape :
Arbre en acier de 30 mm1 pièceOutils nécessaires :
Comparateur à cadranPied à coulisse
Jeu de cales d'épaisseurMatériaux
2- 1 pièceEspace réservé
- Ball Bearing - Non-Flanged (8mm Bore, 22mm OD)10 % de commission1 pièce€1.11
Outils requis
7- Espace réservé
- Espace réservé
- Espace réservé
- Espace réservé
- Espace réservé
- Espace réservé
- Espace réservé
Total estimé
Ce que le maker a acheté. Les matériaux sans prix se trouvent là où vous les achetez.
Blueprints liés
Ces blueprints partagent des connaissances — techniques, matériaux ou principes
CC0 Domaine public
Ce blueprint est publié sous CC0. Vous êtes libre de copier, modifier, distribuer et utiliser ce travail pour tout usage, sans demander la permission.
Soutenez le Maker en achetant des produits via son Blueprint où il perçoit une Commission Maker définie par les Vendeurs, ou créez une nouvelle itération de ce Blueprint et incluez-le comme connexion dans votre propre Blueprint pour partager les revenus.