Rotary Broaching a Keyway on the Lathe with simple materials you have in the shop

[thehomeengineer]

It is possible to do on a mill. The spindle obviously rotates and the tool and workpiece both stay stationary. (I say the tool stays stationary!) The tool holder has a chuck type holder but the tool shaft is set in bearings so the spindle rotates but the tool doesn’t (due to tool shaft in bearings) The tool shaft is not at 90 degrees to the main spindle and is at an angle no bigger than a degree. As the spindle rotates the tool is forced to move back and forth and with applied pressure from the mill quill or raising the mill table allows the tool to broach the desired form of the tool while not rotating but more of an oscillating action being used. The tool bit is ground with clearance on the side and slightly dished at the bottom to create clearance and a clean sharp cutting edge. The cutting tool does require a hole the same size or bigger than the A/F of the cutting tool (if cutting squares, hexagons etc) or in the case of a keyway the tool holder would be supported by the bore but would need to be able to move in the bore to allow the cutting tool to move in the same oscillating movement to cut. This could be achieved by having a bead radius on the end of the tool holder the same size of the bore but allowing the tool holder to mov. (I have never cut a keyway using this method hence the interest in your video and post) I will see if I can find a video of the cutting action and post on HMT
I hope this makes sense and would be very interested in your views and others. Just incase I am totally barking up the wrong tree.
The Home Engineer