3/8" vs 1/2" diameter flush cut router bit

[John Appleseed]

Guys what is the difference between a 3/8" vs 1/2" diameter flush cut router bit.....What will determine which one I need for flush cutting....or maybe it doesn't matter........I made a pattern out of 1/4" hardboard and will be cutting 3/4" plywood....

[Kent Fitzgerald]

If you're routing inside curves (concave), the smaller bit will follow a tighter radius. For outside curves (convex), it doesn't matter.

[Kristian Wild]

John it kind of depends on how tight any inside corners are on the template you're routing. 1/2" is pretty "standard" but if there's something tighter than a 1/4" radius then you need to go to a smaller bit.

Oops, Kent beat me to it!

[Mack Cameron]

Hi John; the difference is obvious.......1/8". It makes no difference which one you use. My preference would be the 1/2" one.

[John Appleseed]

Many thanks guys, I'm doing just outside, so I will go with the 1/2".........

[pat warner]

Diameter plays a role in cutter life & finish.
Skinny cutters (where the cutting diameter is = or < than the shank diameter) bend & deflect. They slam against the work and produce chatter which wears the bit out prematurely.
If the radius is not important (because there are no tight turns) use a bigger cutter. Once a cutting diameter is > the shank, (usually starts at about 5/8" for 1/2" shanked tools), the cutter deflects a lot less and benefits accrue.
More on cutters. (http://patwarner.com/routerbits.html)

[Brian Gumpper]

I second what Pat said. I actually sell as many 1-1/8" diameter flush trim pattern bits as I do the smaller diameters.