Machine Design

Scanning for Ideas: Power drawbar holds tool despite loss of hydraulics

Power Ott Jakob drawbars from Advanced Machine & Engineering, Rockford, Ill. (ame.com), use hydraulics in a modular system to hold cutting tools securely in place.

The device lets users quickly change tools by putting no load on the spindle and reducing the amount of forced needed to release the previous tool. The compact drawbar has minimal rotating mass. Its gripping fingers hold tools in place. These fingers are pulled into the taper with a spring pack.

When a tool is being clamped, the spring acts on the clamping sleeve to push balls outward, with the angle of the clamping ring and cylinder shoulder increasing the spring force by a factor of three. A cam inside the spindle closes the fingers, thus securing the tool. To release the tool, pressure is supplied through the rod to the hydraulic piston, pushing the clamping sleeve down to reduce the spring force. After clearing the cam, the fingers open and the face of the holder ejects the tool with a controlled stroke. This means loss of hydraulic pressure will not release the tool.

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