When designing mechanical components, a system of standardized tolerances called International Tolerance grades are often used. The standard (size) tolerances are divided into two categories: hole and shaft. They are labelled with a letter (capitals for holes and lowercase for shafts) and a number. For example: H7 (hole, tapped hole, or nut) and h7 (shaft or bolt).
H7/h6 is a very common standard tolerance which gives a tight fit. The tolerances work in such a way that for a hole H7 means that the hole should be made slightly larger than the base dimension (in this case for an ISO fit 10+0.015−0, meaning that it may be up to 0.015 mm larger than the base dimension, and 0 mm smaller). Tolerance of magnet usually with +/-0.05 mm like neodymium magnet, but accurate tolerance still depends on the shape, grade and material of magnet.
Like disc magnet, the minimum we can manufacture is sintered neodymium magnetic materials and bonded magnetic materials, out dimension is easy for machining process except hole or countersunk hold inside of magnet, so we might change the standard tolerance, which is also known as Limits and Fits and can be found in ISO 286-1:2010 (Link to ISO catalog).
The table below summarise the International Tolerance (IT) grades and the general applications of these grades:
|Fits||Large Manufacturing Tolerances|
An analysis of fit by Statistical interference is also extremely useful: It indicates the frequency (or probability) of parts properly fitting together.
Normal magnetic dimension inspection report for each production lot:
Due to guarantee the standard tolerance of magnet, KM Q&C dept inspects magnet by sampling survey, if you are crucial with tolerance, our technical dept support automatically by our designed tolerance inspection machine.
Although the process is extremely elegant, and would appear to be very simple, translating this into a full scale production process with careful Q&C control and monitoring systems is a major engineering feat, then can keep the tolerance of magnet accurately for specific project, to meet the high standard specification quality requirements.