I inherited a black and decker plunge router from my grandfather. From when I first tried it the bit has always slowly receded back decreasing the amount the bit protrudes from the router base. This has happened when using it freehand and in a upside down table configuration. The bit collet itself is gripping well enough onto the bit, the bit itself is not slipping down into the collet. No matter how tightly I tighten the height lock mechanism this always happens. I have even removed the plastic cam toggle handle as I read somewhere so I can tighten the lock nut itself even tighter with a spanner, this also does nothing.
The lock mechanism works with a bolt which basically seems to press against the rails/poles of the router to stop it from moving up or down. I loosened and flipped the entire base around so that the bolt would be pressing on "virgin" surface, because where the locking bolt repeatedly pressed on the original rail/pole it started to scratch a path into the surface. Doing this also did nothing. The depth decrease/slip issue only seems to happen once I begin routing. I've wondered if removing the springs could be a makeshift fix?
I have no idea what could be the problem. Is the locking mechanism bolt too smooth from being slightly filed smooth over the years? I can't do anything with the router because the bit height always decreases making it almost impossible and aggravating to do anything. Thanks!
Best Answer
I think that measurement is needed to determine what the problem is.
Load up the router with a bit, and measure how much the bit protrudes from the collet.
Lock the base in place. Measure the distance from the collet face to the base.
Measure from the base to the router body.
Now run the router until the bit sinks from the work.
Redo all those measurements, this will tell you which part is slipping. eg. If the bit is sticking out less from the collet, then the collet isn't holding the bit -- now you would have to figure that out -- is the lock nut tight, is the collet dirty or damaged.
If the distance from the base to the collet face is different then either the router body has slipped, or the depth adjustment has slipped. Then check the base to router body distance.
I have one old router that I can't trust the depth on - when it's on and upright the bit could choose to stick out 1/32 further than when it's upsidedown -- this router has an issue with the bearings and the shaft will wiggle up and down - this might also be an issue with your router, but it sounds like the travel is too far for this to be the problem.