Fly cutter questions

Since @mikey summoned me....

My HSS flycutter grind is really just a LH square tool with 15 degree angles. I did about 1/32" nose radius, just a little to help smooth the cut. It chews up aluminum, but has to go pretty slow in steel. If you have a power feed it's not so bad. Just let it do its thing. It does leave a really nice surface finish though. If I do a lot of steel, I would like to get a decent carbide tool just for the higher RPM for faster stock removal.

Here's a steel block I used the flycutter on.

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pontiac428 said:
Are there any formulae for depth of cut and feeds/speeds? I am not sure that my books cover that.
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Totally forgot to address this. There are no formulas for depth of cut, feeds or speeds that I am aware of. Each flycutter has different capabilities and this is especially true of those that use HSS cutters. When I used HSS many years ago, I would try not to exceed 0.010" depths of cut because I wasn't really all that aware of tool geometry back then. So, it took a long time to square the work piece up.

I have since switched over to carbide and usually use the common formula for speed (CS X 3.82 / D) and feed so the tool takes a continuous chip (it is faster than you think). I try to listen to and feel the machine. If I think the machine can handle it, I up my speed to the max it can handle without vibrating. This is to lower cutting forces. If I feel the mill is loading up too much, I back off the speed. Sorry, I know this doesn't help much but that's how I do it - listen to and feel the machine.

My Sherline flycutter is a single insert tool that easily handles up to 0.020" to 0.050" roughing depths of cut in mild steel. My Tormach Superfly can handle the same in steel and up to 0.070" in aluminum. For taking fine cuts, I limit my cuts to 1/2 the nose radius or deeper; I do not go shallower than that to limit deflection. When I do fine cuts, cutting forces tend to be higher because of tool deflection so, again, I increase my speed to reduce those forces and tend to feed a little slower; this produces a very fine finish even with carbide tooling and the cut is very accurate.

I always use cutting oil with a flycutter. I prefer A-9 for aluminum. For steels, any cutting oil I have handy seems to work okay.

Much depends on the geometry of the cutter, the rigidity and power of the mill and experience. The more you screw up, the faster you learn!
 
Having that cutting edge on centre is everything when it comes to an efficient cut. Being above or below changes the cutting forces and your tool geometry goes out the window with the radius of the hole.
One thing you do need to have in your grind for flycutting is the appropriate relief on your trailing edge. Much more so than a lathe tool.
I keep my stickout to one inch or less to avoid the deflection Mikey is talking about. I See people sticking out there tool ridiculous amounts. I am sure Mikey does it right!
I like hss with cobalt unless I need the speed from the carbide.
 
somewhere I lost a reply I made. My plan involves cutting a pocket for carbide inserts on the bar. I stumbled on the answer to my question about being on center line. Truth is, the tip of the cutter will always be on center line as it rotates, what changes is the angle of the cutter in relation to the work as it moves across the surface.
 
Gotta' say, Joe sure has a way of proving a point!
 
mikey said:
I found a 5/8" straight shank adapter with an MT1 female taper at the end. I cut the adapter to length, inserted the Sherline tool into the end and drilled it for a roll pin. After pinning it, it is very secure. I hold the straight shank in an R8 collet and it works quite well. I actually prefer to use this tool whenever I can, and not just for flycutting. It is essentially a single insert face mill that is capable of pretty deep cuts so I often use it that way.
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Just a follow up. I started to look at my options, and contacted Sherline to see if it was possible to get an unfinished flycutter that could be finished with a different taper or straight shank. It isn't as step one is forming the shank, but they have just added a version of their insert flycutter with a 1/2" straight shank instead of the MT1. It wasn't even up on their website yet, but is now. I have one on its way to me.

Sherline Insert Fly Cutter / Straight shank
 
That might be useful. Let us know how it works out for you.
 
mikey said:
That might be useful. Let us know how it works out for you.
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It seemed like it would be easier to either use directly with an MT2 collet, or if I run into slippage buy an extra 1/2"-MT2 collet and fasten the two together vs playing around with trying to make an MT2 to MT1 adapter. I can't share the flycutter between the two machines, but it will still provide the benefit of using the same inserts.
 
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