Router bit depth keeps decreasing/slipping down, where is the problem?

Question

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!

Answer 1

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.

Answer 2

Generally you do not want to use a plunge router in a table. You should use a fixed base router when possible. A plunge router is used to start and stop router cuts when the cuts will not continue past the edge.

In normal operation of a plunge router after you plunge you can lock the height using a cam or some other handle provided but you still generally push down on the handles of the router ensuring that it will not creep up. Taking the springs out could help, blocking the router up from the underside could help as well but I think you would be best served by finding another router more suitable to the task.

Answer 3

One thing to check would be runout. Runout is the amount of eccentricity created by imperfections in the motor bearings. It manifests itself in a couple ways, one being excessive vibration which can cause the depth stops (and everything else) to wander around. Take your router and secure it somehow next to a stable platform that's the height of the bit. Attach a dial indicator to the platform and position it against the shaft of the bit or better yet against a centering dowel. Slowly turn the bit around and observe the changes on the dial indicator. The consensus is, if your differential is less than .005 you don't have a problem. Anything much greater than that and you'd do well to just pitch that router and invest in a Porter Cable or, my personal favorite, a Milwaukee.

Answer 4

I've seen tables where the height was set by a threaded or wedged platform pushing up against the back of the router, rather than counting on the router's own clamps to set and hold the height. You might need to consider that. (A more elegant version of the 2x4 answer.)

Also, of course, make sure that the router bit isn't slipping in the collet. If it is, you may need to either tighten down a bit more, or replace the collet (they do wear out eventually).

Answer 5

I have a Black&Decker BD66 router which I have only just tried to use because it was bought for me 20 years ago after I had finished a project using hand tools that would have been a very quick job if I'd had a router at the time. I found that the plunge depth slipped when trying to depth-clamp using the round screw-in clamping handles. The problem seems to be that the bolt ends of the clamping handles press against a flap of the plastic router mounting platform and squeeze it against the pillars. The plastic is too slippery to grip metal that has no surface texture cut into it. I have successfully template-trimmed about 40 feet of 15mm melamine board edge with no slippage at all after sliding a strip of cardboard between the plastic flap and the pillar on both sides! My daughter gets this material as 'A4 thick cardboard' for artist's use although it feels like it might be coated or impregnated with something to me. It might even be some sort of plastic sheet with cardboard-like folding characteristics for art use.

Answer 6

Most likely it is due to a light film of oil on the shaft of the router bit. Manufacturers routinely oil everything metal before packaging, because nobody will buy a tool that looks even a tiny bit rusty.

If you put such a router bit in the router, you then transfer some of that oil to the inside of the collet.

I suggest soaking a rag in denatured alcohol (or Windex if you don't have alcohol handy) and using that to wipe off the shaft of each of your router bits...then wrap some of the rag around a screwdriver shaft or similar and use it to clean the inside of the collet.

If the problem is due to the bit slipping (despite your efforts to tighten it), then this should solve the problem.

Answer 7

I have a Porter Cable router which I have mounted on a table. The depth keeps slipping. What I found was the fine adjustment knob turned once the power is on. I taped the knob and had fixed the problem. I needed to tape the knob each time I used it. Not the perfect solution, but a short fix. I hoped Porter Cable whould fix it.

Answer 8

You might want to look at his answer in the woodworking stack exchange.

It suggests that the problem could be caused by setting the bit tight against the face of the collet among other things. A nice thing about this solution is that it works without casting aspersions on particular products.

I have followed this advice and gotten rid of problems with the router bit working its way free of the collet.