Unexpected pocket toolpath behavior in Aspire 10.507

[StephenRDashiell]

I constructed a simple test case of a recess that tapered from 0.05 inches wide at one end to 0.2 inches wide at the other end. Using a pocket tool path with a 1/8 inch diameter endmill gives the expected result, which is that only the region of the recess wider than the endmill is machined. If a second tool is added, a 1/16 inch tapered ball nose bit, and the tool path is recalculated, the result is odd. A dialog box opens which states: "The following tools produced empty toolpaths ( the 1/8 inch endmill). They may not be able to fit anywhere the previous tool could not with their current parameters." Previewing the Pocket 1 [Clear 1] tool path shows that it is indeed empty. Previewing the one associated with the the tapered ball nose shows that it is machining the entire pocket, but at the narrow end the depth of cut is 0.05 inches, not the 0.10 inch depth specified. If the 1/8 inch endmill is deleted and the toolpath is recalculated, the depth of cut is correct everywhere the ball nose bit can reach.

So, I have a couple of questions:

1.) Why does the addition of a smaller bit eliminate the clearing function that should be handled by the larger bit?
2.) If the toolpath associated with the 1/8 inch endmill is truly empty, why does it cause an error in the depth of cut with the 1/16 inch ball nose that is eliminated by removing the endmill?

Steve

[Adrian]

I haven't drawn it out to check but my initial reaction would be that it's not cutting to the full depth at the 0.05 end as if it did so that would be using the full diameter of the ball end which wouldn't fit into the available width so it's cutting as deep as the available width will allow.

[StephenRDashiell]

Adrian,

I thought that the way a pocket tool path worked was that it would machine to the specified depth everywhere that the current tool could reach, that previous larger tools had not already machined to the specified depth. In my limited experience, this is what I've seen.

The other issue that your theory does not explain is why if the 1/8 inch endmill is removed so only the 1/16 inch ball nose is used, the discontinuity in machining depth is not there. The discontinuity is abrupt, stepping from a 0.1 inch depth to a 0.05 inch depth. I'd expect it to be a gradual change if it had to do with the taper of the ball nose bit.

Steve

[Rcnewcomb]

The geometry of the tapered ballnose along with the stepover settings means the smaller tool will re-machine any areas the larger tool would have covered.

If you switch the 1/16" tapered ballnose for an 1/16" end mill you will get the expected results.

[StephenRDashiell]

I tried a test with a 1/16" endmill, and it did not result in an empty toolpath for the 1/8" endmill, but it did remachine much of the area the 1/8" endmill had already machined. In the online help for the pocket toolpath, all it says about this issue is: "When multiple tools are chosen then the first tool removes as much material as it can, all subsequent tools in the list will remove as much material as it can from any previously unmachined areas." This is not what is happening either with the 1/16" endmill or the 1/16" tapered ball nose. It also makes no mention of bit geometry interactions. Is there somewhere I could get more information about this behavior?

Steve

[Adrian]

You would need to contact Vectric if you're not happy with the explanations offered by other users. This is primarily a user to user forum so for any detailed technical explanations of how the software works you need to go to the "horses mouth" so to speak.

[StephenRDashiell]

Adrian,

It is not that I'm unhappy with the explanations, it is that when an explanation is made based on information I don't have, I'm interested in understanding what the responder knows that I do not.

Steve

[StephenRDashiell]

I found another weird behavior. Using the same tapered closed vector region, machine first with a 1/8" tapered ball nose. The result is that the machining happens only in the region of the closed vector where the bit fits. Add a 1/16" tapered ball nose to the tool path, and recalculate the pocket tool path. Now previewing the path associated with the 1/8" bit shows that it is going well into the narrow end of the tapered region where it does not fit. If someone can explain why adding the smaller bit would modify the region the larger bit clears out, I'm interested in hearing it.

Steve

[RalphPitz]

Try changing the order of the tools. The 1/8" bit will then cut what it can and you won't get an error message when recalculating

[gkas]

Also on the top center of the screen is the toggle 'Toggle 2D Toolpath Visibility'. Turn this on and select your toolpath, and it will display EXACTLY what your toolpath will cut. Especially nice for visualizing pocket allowance, etc.

Toggle Toolpath 2D Drawing Visibility

[StephenRDashiell]

Thanks to RalphPitz and gkas for their suggestions. I've been using Aspire for less than three months, and I appreciate feedback from those community members with more experience.

Reversing the tool order in the pocket toolpath did eliminate the error message, but the end result is that the tapered ball nose bit completely re-machines the area the endmill cleared. This can't be the intended behavior, since it makes the clearance tool useless. It just adds time to the machining process. Either I'm missing something fairly fundamental here, or there's a bug. Any thoughts?

I'm also interested in feedback on the other issue I raised about using the 1/8 and 1/16 inch tapered ball nose bits. It seems to me that any combination of bits that results in cutting outside the boundary of the closed vector is an error, since it will ruin the workpiece. If it isn't an error, I could use an explanation of why this is reasonable and expected behavior, and how to avoid it.

Getting a good understanding of pocket tool paths is proving more challenging than I expected it would be.

Steve