Reference Tables for Machined Motor Parts
The numbers we kept looking up, put in one place. Free to use, free to link to, no email wall and no account.
Bearing seat fits for motor housings
H6, H7 and H8 bore limits for any diameter from 1 to 500 mm, taken from ISO 286. Includes a calculator for how much an aluminium housing opens up at running temperature, which is the number that usually decides whether the outer ring stays put.
ISO 286Rotor balance grades for electric motors
Turn a G grade into a real limit. Enter rotor mass and service speed to get the permissible residual unbalance in gram millimetres, and the equivalent mass on the rim. Plus what the machine shop can and cannot control.
ISO 1940-1
Why these are free
Because a table behind a form is a table nobody cites. If these pages are useful, use them, screenshot them, put them in a design review. A link back is welcome and is the only thing we ask.
Every figure is either definitional, computed from a published formula, or labelled as typical practice. Where a source disagrees with itself we leave the number out and say so rather than pick one. The reasoning behind that is on the about page.
Coming next
Surface finish against process for motor journals and seats. Material comparison for housings and shafts. A drawing checklist you can run before an RFQ goes out.
Missing something you look up often? Tell us at and it goes on the list.