flush trimming troubles

[harold brock]

I am building a crib for my first grandchild, but I am running into troubles trying to flush trim the arches. I am using a flush trim router bit on my table, but it is chipping the wood and taking out chunks of wood. Do I need to slow the bit down or what. Anyone got any ideas what my trouble is and how to fix it?

[Jamie Buxton]

The bit is probably cutting against the grain in the areas where you're getting chipping. One trick which sometimes helps is climb-cutting. You're likely moving the router "the right way" -- that is, the direction in which the cutting action acts to push the bit tightly against the pilot bit. Try going the other direction -- that's climb cutting. The bit will be trying to kick the router away from the edge you're trimming. That's not a big problem. Make several passes with the router, and make sure the last one has the bearing seated firmly on the wood. You can even make the last pass in the right direction. It will be just picking up little bits here and there, and will not likely chip out.

[Howard Acheson]

Jamie has the answer. You will run into trouble whenever you rout into the "uphill" direction of the grain. Instead, determine where that will happen by reading the grain and then routing in the "wrong" direction in those areas. Just be sure to take small cuts and hold onto the router tightly.

[Peter Quinn]

A few other thoughts?

1) Use an 1 1/8" pattern makers bit with shear angle tips, template below the work. Larger diameter means gentler exit angle and less chipping (slow down the bit speed a bit too).

2) Solid carbide spiral flush trim bit. Works better on difficult grain.

3) Cut those curves VERY close to the line and sand them flush with an OSS, clean it up with a flexible sanding strip. Unlike an arched door a crib rail doesn't generally have to meet another piece in a way that minor deviations will be particularly apparent, so no real need for the parts to be joint quality exact.

4) use your standard bit with very light passes, but cut VERY close to the line, within 1/16" maximum.

I do climb cut, even with the big pattern makers bit, but its not your only option and never my first choice unless the curve is very severe. A standard 2 flute straight flush trim bit is not your best weapon for arches, as regardless of grain orientation you will be cutting against the grain on part of the arch.

PS: I no longer attempt climb cutting with a spiral carbide flush trim, very scary! It really digs in quick!

[glenn bradley]

You've got good advice here; largest bit possible, slower bit rotation speed, read your grain. I had a blowout in red oak once that I couldn't believe. Nearly cut the rail in two. The post-mortem revealed a seriously bad grain read (or lack of attention on my part . . or both).