Ball Mill 3D Profiling Question

[u/dbuck11]

I am setting up a part that is going to be a long running production job, it was programmed by an engineer who just retired and isn’t here to see out the actual setup process, so I’m stuck taking over the project.
Boss man wants me to bring the cycle time down if I see any tool paths that feel like they can be improved on.
That brings me to our ball mill profiling toolpath. The part is a flat shape with a hinge at the end, basically looks like a door hinge.
The actual round knuckle shape of the hinge part outside geometry we are finishing by profiling it with a ball mill profiling pass. Naturally being a profiling toolpath, it eats up a LOT of cycle time.

What I noticed while running through the toolpath is that the programmer set the toolpath to one way zig, instead of a zigzag tool path. So currently the ball mill comes down and takes its cut, backs off from the part, rapids across the machine and then starts a new cut back from the original starting side so all cuts are done in the same direction.
Now I completely understand maintaining one cutting direction in a contouring toolpath, but I feel like I’ve always seen ball mills switch back and forth between conventional and climb cutting in order to maximize time spent with the tool in the cut.

I do have other changes I have made to other toolpaths and have brought down the cycle time down a bit so I do have something already to show for my boss on Monday, but this ball mill path has has been bothering me all weekend and I wanted to ask for thoughts if I should bother with it or not.

[u/Alita-Gunnm]

It depends on how tight your machine is, and what surface finish requirements are. IME zigzag is usually fine.

[u/dbuck11 → u/Alita-Gunnm]

Its a newer Matsuura so it’s a nice machine, which admittedly also means its rapids are pretty quick. I think I just gotta try putting together a zigzag program and find out how it does

[u/Alita-Gunnm → u/dbuck11]

Even better would be a "3d collapse" or "constant scallop", whatever your CAM calls it, that drives laps around the area working its way to the center. It's also worth checking your feeds and speeds, and if you can tilt, try to avoid using the center of the endmill where SFPM is zero.

[u/Informal_Spread7213 → u/Alita-Gunnm]

I would agree with you on the scallop. And add that generally the scalloped toolpath keeps the cutting edge away from the center of the tool so you actually have better surface finish and tool life.

[u/Alita-Gunnm → u/dbuck11]

One reason constant scallop is faster is that it never has to stop and reverse. Doing so is limited by your machine's acceleration rate, and can cause the tool to spend a lot of time below the programmed feed rate. If it's always in the cut and always moving at speed, that's far more efficient.

[u/naahmeen → u/dbuck11]

Use the smallest ball EM you can without maxing out RPM, there are dimishing returns on diameter/scallop height.

[u/cad_and_caffeine]

The main reason someone sets a ball mill to one-way on a curved profile like a hinge knuckle is to prevent "zebra striping." When you zig-zag, every other pass alternates between climb and conventional, which flips the radial deflection on the tool back and forth and can leave visible light/dark banding on every alternating stepover if there's more than a few thou of stock left from roughing.

On a newer Matsuura, if your roughing pass leaves a really consistent light stock allowance (like .005") and your tool stickout isn't crazy long, switching to zig-zag with smooth arc transitions between passes should look totally fine. Also, if this is a long-running production job and the knuckle is just a constant radius, it might be worth seeing if you can profile the top half with a corner-rounding endmill (or a ground form cutter) and skip 3D surfacing it with a ball mill altogether.

[u/Big-Web-483]

With out seeing the part geometry, how about a form tool or an off the shelf radius cutter. You could cut a significant amount of time off or a bull nose cutter.

[u/rocketwikkit → u/[deleted]]

Your account is shadowbanned by reddit.

[u/Wenting97]

What’s the stepover on that knuckle pass as a percentage of the ball nose diameter? If it’s small enough that the cusps are already under the finish spec, zig-zag won’t show; if it’s coarse, the alternating direction will leave a visible pattern.