GlossaryKind of term: Manufacturing termTool access
What is tool access?
Tool access is whether a tool can machine a feature without the tool, holder or spindle colliding with the workpiece or the workholding.
The question is asked per setup and per available tool: the cutting edge has to reach the feature, and the shank, spindle nose or head have to stay clear too. The question is not whether the feature can be made at all, but whether it can be reached from this orientation with enough stiffness. The same feature can be out of reach in one setup and easy in the next.
What does tool access depend on?
Access depends on the depth and width of the feature, its internal radii, the length and diameter of the tool, the shape of the holder, the orientation of the part, the kinematics and tilt ranges of the machine, the workholding and what earlier operations have already removed. Stiffness is part of the question. In the simple cantilever model, the deflection of a cutter under the same force grows with the cube of its overhang and falls with the fourth power of its diameter. A feature that is only just reachable may therefore be machinable only with low cutting data and a modest finish.
How does tool access work in practice?
An example: in a pocket 40 mm deep with 3 mm internal radii, the corners take a cutter of ⌀6 at most, in practice often a smaller one, and it has to stick out more than 40 mm. The rest of the pocket can be cleared with a larger cutter; the corners still need the slender one. It is prone to chatter and needs smaller cuts and a lower feed, so more machining time. If a feature cannot be reached from the current orientation, the options are a long-neck cutter, a slimmer shrink-fit holder, an angle head, another setup or a machine with more axes. Which is cheapest depends on quantity, the tools already in stock and rates. Sometimes the better course is to ask the customer whether the radius or the depth can change.
What is tool access often confused with?
Tool access is not manufacturability: a feature can be reachable and still carry a tolerance or roughness that cannot be held in that situation. Nor is it the work envelope, which says whether the whole part fits within the machine's axis travel; access concerns one feature with one tool. And it is not the machining direction, which says from which direction a feature is approached; access says whether that approach actually works.
Frequently asked questions
Can I fix an unreachable feature with a different tool?
Sometimes, with a long-neck cutter, a slimmer holder or an angle head. If that does not give enough stiffness, the remaining options are another setup, another machine or a conversation with the customer about the radius or depth.
Why do deep, narrow features cause trouble?
A cutter slim enough for the feature sticks out a long way and so deflects a lot. To avoid chatter, depth of cut and feed come down and machining time goes up, and wall dimensions and roughness near the floor become harder to hold.