Dont know if Im explaining this right, Im not sure if they were there before we sanded floors, but what im looking at is looking at floor in standing position in the day light, where some planks meet each other it appears that one of the boards slope down about 4 inches just before it reaches the end. making it look like they have a dip, but you cant feel it. you only see it when poly is on the floor, I dont see it when its stripped. can anyone help!

Need you to post pictures. Or link to something like flickr or picasa.

I think I know what you are seeing. Did you sand the floors yourself? DId you cross cut the first pass on an angle? IN the mill the sawers are trained to cut the knots out thru the middle of the knot for maxim yield. What this does is leave a 1/2 or 1/4 of a knot on the but ends of boards. The knots are also very hard and dense making sanding them flat difficult with lightweight equipment or when you skip a lot of grits in the sanding. Your machine rides up and over the knots a leaves a slight wave in the floor. If Im right you need to 45 the first pass then with the same grit make your second one straight.

"one board slopes down 4 inches"



Racking my brain, I'm not seeing the picture. 4 inches is a lot not to see or feel.

i assumed they were talking about the length of the wave. couldnt be the depth.