Yes, thanks Sam. I had guessed as much. I was trying to understand the cyclical nature of the fault and thought that a feed rate that was too high when combined with a high percentage of tool engagement (9mm on the face in contact with the workpiece) and the addition of conventional milling, would lead to some type of chatter.
The appearance of the fault looks as if the tool was constantly being deflected from and returned to its expected position at the workpiece. The speed of the feed rate was probably responsible for the repetitive phenomenon seen.
The deflection of the tool was likely the result of a high feed rate and high tool engagement percentage at the interface between the cutter and the workpiece. A blunt tool would not have helped this situation either and the torn rather than cut wood would suggest that the tool was due a replacement.
The tool rigidity initially did not strike me as an issue because wood and a 1/4 inch diameter 3 flute endmill (I believe that is what the #201 tool is) ought to be good together. The tool engagement with a large DOC of at least 3½ times the tool diameter with constant engagement of the cutting face, would easily be enough to induce deflection at the high feed rate used.
The collet on the Makita/Carbide router is tiny in relation to the job it is being asked to do here. The endmill loosening suggests that several factors need correcting before a satisfactory cut is obtained. I would clean the collet, nut and spindle taper after every job on my own machine. I don’t think that was being done here. The stickout may be too little if the endmill is butting up against the router spindle and potentially may cause deflections in the tool. it may be too much stickout if insufficient tool metal is held in the collet.
118 inches per minute is a high feed rate and I would use half that for my own softwood projects. I would not use a 9m stepdown on soft woods and the most I might get to is 1mm with a .5mm stepdown. The tool is suffering when you look at the wood, even assuming all was fine with the feeds and speeds, the cut edge of the wood looks to be torn rather than cut. I have not done any adaptive clearing in wood and I am only just learning about it. My understanding is that adaptive toolpaths save wear on the tool as well as time and expense and there is less tool breakage.
Perhaps all we are seeing is too fast a cut with a tool that was blunt. If the toolpath was appropriately calculated by the software, I am in no position to gainsay that.