Advanced Knife Machining WIP, Pointy Fighter

Nathan,
I'm guessing that the bevelling operation is not a linear tool path, based on my observation of the extra milled area near the tip. It looks like the bit is going 2-3mm in the -Y direction, as well as going -Z also. Maybe?

Regarding the curve of the tool path when bevelling with the end mill, near the tip of the blade, on the true edge... what is the technique used in software to create the change in cutting path for the +/-Y and / or -Z compound curve?

I'm _brand_ new to Fusion 360 and have not touched any software like this since 1992.
Cheers
Jordan
 
You're right, it is a non-linear 3 axis interpolation move. I have the allowable deviation segment length set to .00001 to reduce faceting which is a lot more noticeable then you'd think. It's important to keep those axis moving because if they stop for even an instant you get into a stick slip situation. So, although .0001" is enough to prevent visible faceting in most applications the machine dynamics at low feeds and small motions create artifacts otherwise.

The technique I use is to extent the bevel surface and intersect it with a smooth curve that creates smooth machine motion while still extending beyond the material that needs to be cut a little. The resulting intersection is a function of a conic (the bevel) and a NURBS (the intersecting curve) that I wouldn't begin to know how to program manually or even describe mathematically, but the CAM system figures out that "line" and I use it as a trajectory. My system can either use that line as a tool centerline (no good) or apply tool radius offset compensation. I use the later and cheat the diameter to give me both a roughing and a finishing path. You have to keep an eye on both radial depth of cut and chip load to keep things cutting and not rubbing because this approach can create distortion and work hardening otherwise. No spring passes, lol...


jztam said:
Nathan,
I'm guessing that the bevelling operation is not a linear tool path, based on my observation of the extra milled area near the tip. It looks like the bit is going 2-3mm in the -Y direction, as well as going -Z also. Maybe?

Regarding the curve of the tool path when bevelling with the end mill, near the tip of the blade, on the true edge... what is the technique used in software to create the change in cutting path for the +/-Y and / or -Z compound curve?

I'm _brand_ new to Fusion 360 and have not touched any software like this since 1992.
Cheers
Jordan
Click to expand...
 
Nathan,
Thank you for that concise tutorial {read as: Thank you for saving MY stock. ;) }.
Cool trick about mitigating the facetting effect with your nominal software tolerance. Unfortunately, the mill I get to use is a clapped out one from the 1970's, so I'm not sure that software tolerance of .00001 will translate into anything appreciable at the tool's edge, in real life, due to the accrued lash inherent in the mill.

I'll definitely try out the curve-blending and overshooting ... _that_ will surely help in my case.
Usually, running a little more agressive than the G-Wizard recommendations works out better in the end, in my experience. That said, I'm predicting slim to zero effects of work hardening, since I'm not working stainless - just 1084 for my next cuts.
Thanks for the geek speak... it is appreciated.
Jordan
 
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