There have been a couple of threads here recently about fly cutters, and as one has been on my todo list for a while, I thought it was time. Quin at Blondihacks made a video where she attempted to make a "balanced" version, and that seemed like it wouldn't hurt. I realize it's probably unnecessary, as unbalanced fly cutters have been in use for ages, but it was a fun project. I made a model in FreeCAD, and used the FCinfo macro to help find the center of mass, and just made tweaks to get it near (within 0.1mm) the XY origin when the toolbit is centered in the flycutter. The body is a simple cylinder, only the slot for the bit is angled. The top is bored and threaded 1_1/2-18 to match the R8 arbor that came with the boring head I got with the mill.
I made a second flycutter to hold a CC*T tool that uses the obtuse angle on the insert. While the Tormach SuprFly I've seen mentioned here is tempting, I'm trying to avoid spending loads of money on different inserts, so getting more use out of the obtuse angle on these inserts seemed worth trying.
They both work great and produce the great surface finish flycutters are known for.
-Pete
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