Most machining centers have an air blowing system within the spindle. During an automatic tool change, air will be blown from inside the spindle during the tool change. This keeps debris from getting into the spindle, but it could be a safety hazard as well. Here’s why:
Most machining centers allow the operator to manually remove tools directly from the spindle. The operator grabs on to the spindle tool with one hand and presses the un-clamp button with the other. With most machines, the air blowing system is not activated when the tool is manually unclamped so the tool will simply drop into their hand. Lastly, they press the clamp button.
There are, however, machines that will cause air to blow even when manually removing tools from the spindle. That is, as soon as the unclamp button is pressed, the air will blow. This added pressure has the tendency to blast the tool out of the spindle. So instead of gently falling into the operator’s hand, it comes out with much more force. An unknowing operator could be injured – either by straining their arm and hand trying to catch the tool, or by the weight of the tool if they drop it. I know of more than one operator who has been surprised by this function.
Note that some machining centers have an on/off switch labeled Air-Blow that is in close proximity to the clamp and unclamp buttons. When off, the air will not blow when the unclamp button is pressed. When this switch is on, the air will blow. Be sure operators know to keep this switch off when manually removing tools from the spindle.