Leslie:
As Tim has mentioned it could be that the lead screw is getting filled up with wood fibers and not clearing properly, meaning that it could be the wood and not the bit.
You can look at the threads and see if they are damaged and need cleaning.
Understand how to sharpen your bits is also important.
You can use a special "bit sharpening file" to sharpen it.
These files have cutters on the sides on one end, and cutters on the flats on the other end, so that when you are filing your bit you don't "over file" some place other then where you actually want to file.
And never file the outside of the wings, as this would change the diameter of the hole you want to bore. Only file the inside of the wings.
Good luck.
Jim Rogers
