Why does a plunge router leave a mark when it plunges into the wood?
Using a straight bit or a spiral bit, either one, I was routing out some long and wide, but shallow mortises earlier, and I had to hollow it out a row at a time. I would plunge the router in until the depth stop hit the turret and then lock it down. From there I would slide it along using an edge guide to keep the cut straight.
I tried each bit type to see what it would do, and I noticed that no matter which type I used when I plunge the bit into the wood it would leave a circular mark at the bottom of the mortise where it went in at. As I move the router along, it leaves a smooth bottomed path, but the point of entry always seemed to be slightly deeper than the rest of the groove was. It done this on each row, and even passing the bit over top of it did not clean it up. These mortises are part of the appearance in some wood trim I am making, so I will have to sand the circular marks out. I just wondered how the router can make a deeper cut at the point of entry than it does on the rest of the cut. I thought the depth stop would prevent this. At first I thought the router had plunged to the full depth and then backed off a little before being locked. But after seeing this several times I paid closer attention to that. The depth stop was in full contact with the turret but I still kept seeing the little circular marks at the point of entry. Do you suppose it is possible that the lever lock is retracting the plunge upwards very slightly as it locks? That's the only thing I can think of. It is a DeWalt DW618 plunge router.
Last edited by Duane Bledsoe; 06-25-2015 at 10:36 PM.