It seems to me that your main concerns will be from the plunge into the material as well as the side load from forcing the tool through the materials being welded. Your spindle should be able to be kept cool if you can consider a toolholder that will insulate your spindle.
I have made a FSW tool using a Bridgeport milling machine. 7hp with a CAT40 taper. The biggest problem I faced was the amount of side load on the spindle bearings from feeding the tool along the weld seam. The second biggest problem was isolating and delaying heat transfer from the tool itself to the holder and then to the spindle. |