How much air can a fly cutter cut?

Hi Dave, don't mean to butt in . I'm no pro machinist but I've studied and done some flycutter work on my mill. I saw once some professional machinist demonstrate flycutting and he said that the best scenario is having the cutter diameter greater than the work width. It seems to work for me. A project I did a while back involved milling 5 honda gx200 cylinder heads for the local go-karters.One who happens to run the local automotive machine shop and has a state of the art milling machine for automotive type heads was tickled pink when I did his cylinder head as well.
I accomplished this using a 4 jaw chuck adapted to my omni head with (2) 5/8" brazed (untouched) carbide lathe bits facing appropriately, tediously set and per my automotive machinists suggestion, trammed so just a sliver of light was visible between 1 bit and whatever surface I used to set the team .The total width was around 5-1/2". The heads came out true and awesomely smooth.
This morning I used a flycutter with a "parallel ground and angled 18.5*" bit to slot the end of a boring bar for a threading project iv been working on. Beats the snot out of an 1/8" end mill I tried last time. My new plan is to make a "flat" flycutter just for that purpose.
 
Dave, you have grasped the salient point of my comment. Moving the cutter your illustrated position "B" takes the impact point and shifts it back away from the most fragile part of the tool. This principle applies to multi-inserted face mills the same way.

I think you could possibly improve your surface finish and tool life by changing the lead angle to a more gentle approach. In your cutter view, you note that you have "slight angle back from point". That should rarely if ever be the case. If you need to clean up all the way to a shoulder, then a neutral angle can be used. Also, the bottom edge you show as horizontal to the work, and there should be a bit of clearance there. It's not unusual for a bit to be ground with a complex geometry that has a fairly sharp leading point with a rounded bottom to work as a "wiper" and allow a faster feedrate while leaving a nice finish. A truly horizontal tool bottom would likely trap chips and mar the finish, so you wouldn't want to risk that.

Sorry it took so long to get back to this. Haven't felt well the last couple of days.
 
Interesting stuff. I fed a small muffin pan ingot casting under the fly cutter this afternoon twice, just to see if I've learned anything here. Once, right down the middle and once offset as far as I could stand. FWIW, the offset surface seemed a little bit smoother, but I was as nervous as a cat listening to the table float... every pass ticked the table back and forth through the back lash play just a little bit. The conventional or side load style cut is good enough of a surface for me for most applications, especially aluminum where you're likely using a gasket of some sort anyhow!
 
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