I have seen and used big flycutters that were a rectangular bar welded to a shaft. Usually holding 2 cutter bits at opposite ends of rectangular bar. On mills using a R8 collet large flycutters beat up the key / keyway holding the R8 collet. Also the pounding of the flycutter can shake and loosen bolts (also can loosen a part in a vise).
With CNC sometimes a small Carbide Insert mill like (or a Face Mill with APKT Inserts) at a high rpm and high feed but light depth of cut can work very well. When feeds are over 20 inches per minute chips are flying, many times faster that a flycutter at a lower feed.
Only real advantage of flycutters is tooling is cheap and cost to resharpen is cheaper if labor cost is low. |