Router rabbetts infeed deeper than outfeed

[Dave Anthony]

The other day I was cutting rabbetts using a straight bit on the router table. This was for box lids, and I noticed the leading edge of the cut was slightly deeper than the trailing edge, resulting in a slight ridge at the corners. If you looked at the bottom of the lid the low/high ridges would look like this:

L/H------------L/H
| |
| |
| |
H/L------------H/L

I routed the ends 1st, then the edges to minimize tearout. The ridges are very small, and I just sanded them out. It seems that for any given cut it was slightly deeper at the leading edge. Then I got to wondering what caused them. Any ideas?

[Salem Ganzhorn]

If the out feed is higher than the infeed you would get this type of cut right? Is your insert perfectly flush and is your table actually flat?

Good luck!
Salem

[mickey cassiba]

For what it's worth, If you are using a small shank, or a a high feed rate, you could be flexing the bit backwards, causing the the leading edge to cut a little deeper. Is the bottom of the cut radiused?

[Dave Anthony]

The insert isn't perfectly flush, though it doesn't seem off by much. The boxes were pretty small, so most if not all of the wood was on the insert, not the table. 1/2" shank bit, using the fence to guide the piece. At first I thought maybe I was pushing down harder on the leading edge, but I think it's something else.

[Alex Shanku]

sawdust getting trapped underneath?

[pat warner]

Table and insert not flat and even or the work is bowed/cupped.
Will it rest without rocking, say on a jointer table?

[Matt Armstrong]

Pat's answer is right - but this is generally true - cuts that are slightly off, tapered, bowed, etc, will generally have a corollary on either the workpiece or the tool. As an example, I was trying to route quarter-rounds on some cedar... some pieces had a nice bullnose once routed on both sides, but some were squared off a bit. The problem was the wood not being perfectly square...

[Josiah Bartlett]

How are the bearings on your router? Is the shaft sliding in and out? Is the bit slipping in the collet and walking up?

[Simon Dupay]

Sounds like your fence isn't straight or one side is offset.