Replies

1. 
   Dave45 | Jun 17, 2006 04:23pm | #1

   I would guess that you're getting into something like an "end grain" situation where the bit is tearing at the ends of the wood fibers in the curved section of the rail.  A spiral cutting bit may work better since it shears the fibers.

   Personally, I make arched rails (and panels) by cutting them on the bandsaw and leaving ~1/16" then using my oscillating spindle sander to sand to the line.

2. 
   hammer1 | Jun 17, 2006 04:34pm | #2

   With arches and similar shapes, the bit cuts with the grain on half the shape and against it on the other half. A typical method is to climb cut the half that is tearing out. This has some safety issues since you are moving the router in the direction of the rotation of the bit. The router will want to grab on to the stock and self feed. You eliminate this by taking small bites so that there isn't much 'meat' left behind the bit, always working the bit so that it finishes by cutting into an already cut area. I hope this makes sense. I have a picture of a convex arch. There are some arrows on the piece in dictating grain direction. As the piece is pictured, I start the cut on the very end. The piece will be moved from left to right in a series of small bites.

   Another way is to have two flush trim bits, one with a top bearing and one with a bottom. You just flip the piece over. This only works for a flush trim operation. With shapes, you have to climb cut.

   Beat it to fit / Paint it to match

   
3. 
   roscoe | Jun 17, 2006 04:37pm | #3

   Dustcollector,

   This doesn't answer your tear-out question but an easier and faster way to cut out the cathedral top rail is to put a guide busing on your router base and use a 1/4" spiral up-cut bit to cut out the rails. The guide busing will follow along the templates that you are using. How deep you cut each pass will be determined by the species of wood you are cutting. Using this method the rails will be perfect.

   Kerry