I laminated several sheets of rectangular 1/2" marine plywood sheets together to form a 3 1/2" thick slab. The first goal is to clean up the vertical edges with a 1/2" carbide end mill with two flutes. I want to create a clean block with true vertical faces on all four sides so I can flip mill it with accuracy. This is my first experience using more than the first 7/8" of a bit and it didn't go so well. I oversized the stock about a 3/16" +/-on all four sides and thought the 1/2" bit would have no trouble trimming out the block as it dropped 1/2" per pass and ate about 3/16" into the wood as it cut rectangular toolpaths around the perimeter of the stock. I ran the router at 18000 rpm using my 2.5 HP spindled PRS Standard machine. Here is a picture of the block after the procedure and another block before being trimmed:
Trimmed Piece.jpgPretrimmed piece.jpg
The bit only had 2 1/2" of actual blade so I didn't cut all the way down the side of the block and cleaned up the remaining material with a flush trim bit in my router. In the attached picture you can see the rippled face where the shopbot milled it and the smooth face where the router bit surfaced it.
Maybe this procedure is inherently loud because the bit is eccentrically loaded in a trimming operation but from the very beginning of the tool path the bit was loud trimming out the material and by the time it was almost done the bit was really loud. It finished the routine but the bit wound up sitting on the part at the end of the process. It was still in the collet but it turns out it had wiggled loose a bit. I'd like my next results to be more like that router bit and a lot safer . Maybe the answer is self explanatory. I need to tighten up the bit more when I play with a 1/2" bit instead of my usual 1/4" fair?! Maybe longer router bits also just produce a less quality cut because they have to extend so far out from the spindle? I'm really hoping this kind of performance is not something I should get used to. The large bits are expensive and I'd like to produce something with more accuracy. I wound up tossing the collet and the bit. The bit was chipped on the end.
I've purchased another bit. Can anyone give any advice on how to do this right? Maybe make toolpath passes in smaller vertical increments? 1/4"? Maybe I just need to make sure that collet nut is tight? Any help is greatly appreciated.