Definition
Accessibility describes whether a given cutting tool, at a given length and orientation, can physically reach a feature to machine it, without colliding with the part itself, the fixture, or the machine's own structure. A feature can be geometrically well-defined and still be effectively unmachinable if nothing can reach it.
Why accessibility isn't a fixed property of the feature alone
Accessibility depends jointly on the feature's geometry, the available tool lengths and diameters, and the chosen setup and machine, which is why the same feature can be trivially accessible in one setup and unreachable in another.
How accessibility is actually assessed
Not stated directly; it is inferred by checking a feature's geometry (depth, surrounding walls, internal corners) against the reach of available tooling for a given setup.
Common mistakes
Treating accessibility as solely a function of the feature's own dimensions. The same hole can be accessible or not depending on what else is already machined nearby and which setup is chosen.
Accessibility depends jointly on the feature's geometry, the available tool lengths and diameters, and the chosen setup and machine, which is why the same feature can be trivially accessible in one setup and unreachable in another.
See how Blake reviews a partFrequently asked questions
Is accessibility the same as manufacturability?
Accessibility is one input to a manufacturability judgment; manufacturability also weighs tolerance, material and other factors together.
Can a feature become accessible just by choosing a different tool?
Sometimes, if a shorter or differently shaped tool exists; otherwise it may require a different setup or orientation.
Why do deep, narrow features often have accessibility problems?
Because a tool long and thin enough to reach the bottom is also more prone to deflection and vibration, which limits practical reach.