Adaptive/Trochoidal Slotting and Acceleration Limitations


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Thread: Adaptive/Trochoidal Slotting and Acceleration Limitations

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    Default Adaptive/Trochoidal Slotting and Acceleration Limitations

    I'm currently trying to troubleshoot some issues related to the thread title. I'm cutting some slots that are 20% larger than the endmill diameter (.150 vs .125) and twice the diameter in depth (.250) using adaptive clearing in a single pass. 2 flute, 29k RPM (Kress spindle), 110ipm 15% engagement
    Theoretically this should be very fast, if not the fastest and best way for tool life, however, I believe I'm being limited severely by acceleration. What Fusion360 would like to be a 110ipm, 3 minute operation is turning into a 9 minute operation with feeds averaging much slower. The gcode feed is absolutely F110, but the display shows 10-30 during the operation. Here is an image of the toolpath produced by 2D adaptive:

    http://i.imgur.com/uNqEQfF.jpg

    Accel is the issue here, and there are obvious solutions. Ray might suggest upgrading to some manly servos , but I want to see what I can squeeze out of these Tormach steppers. I could jailbreak and increase accel tolerances since there's no weight on my table, but I'd like to avoid that too. I'm concerned that the fact that I can't seem to get Fusion360 to produce an adaptive path that uses actual arcs rather than short straight paths is limiting my acceleration more than it needs to be. I've been toying with super high tolerances in the smoothing setting with no joy. I want some damn smooth arcs, dammit! Anyone know how to achieve this in 360?

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    Default Re: Adaptive/Trochoidal Slotting and Acceleration Limitations

    Quote Originally Posted by GJeff View Post
    I'm currently trying to troubleshoot some issues related to the thread title. I'm cutting some slots that are 20% larger than the endmill diameter (.150 vs .125) and twice the diameter in depth (.250) using adaptive clearing in a single pass. 2 flute, 29k RPM (Kress spindle), 110ipm 15% engagement
    Theoretically this should be very fast, if not the fastest and best way for tool life, however, I believe I'm being limited severely by acceleration. What Fusion360 would like to be a 110ipm, 3 minute operation is turning into a 9 minute operation with feeds averaging much slower. The gcode feed is absolutely F110, but the display shows 10-30 during the operation. Here is an image of the toolpath produced by 2D adaptive:

    http://i.imgur.com/uNqEQfF.jpg

    Accel is the issue here, and there are obvious solutions. Ray might suggest upgrading to some manly servos , but I want to see what I can squeeze out of these Tormach steppers. I could jailbreak and increase accel tolerances since there's no weight on my table, but I'd like to avoid that too. I'm concerned that the fact that I can't seem to get Fusion360 to produce an adaptive path that uses actual arcs rather than short straight paths is limiting my acceleration more than it needs to be. I've been toying with super high tolerances in the smoothing setting with no joy. I want some damn smooth arcs, dammit! Anyone know how to achieve this in 360?

    Generally you get the best results with the "smoothing tolerance" set to 2-5x the "tolerance". I use 0.0002 for "tolerance" and 0.001 for "smoothing tolerance". If you go outside of the 2-5x rule you may get excessive or inefficient code. Are you not getting arcs at all or is it just not producing very many arcs? Any chance you could post your file here so someone can take a look?

    If the limitation really is the machine there isn't much Fusion can do about it. In this case you could try increasing the stepover and lowering the feed rate to reduce the required acceleration. Or it's possible you might even be better of with a different cutting strategy instead of adaptive. Adaptive is cool but it's not always the best answer.


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    Default Re: Adaptive/Trochoidal Slotting and Acceleration Limitations

    Here's the file. I can get arcs via smoothing, I just am not getting them in the crucial areas in the slots where it could allow the feedrate to stay higher without accel issues.

    I'll need to increase the stepover (tool engagement %) like you mentioned. I was just really hoping to get the low engagement HSM style machining to work... on my Low Speed Machine

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    Default Re: Adaptive/Trochoidal Slotting and Acceleration Limitations

    Quote Originally Posted by GJeff View Post
    Here's the file. I can get arcs via smoothing, I just am not getting them in the crucial areas in the slots where it could allow the feedrate to stay higher without accel issues.

    I'll need to increase the stepover (tool engagement %) like you mentioned. I was just really hoping to get the low engagement HSM style machining to work... on my Low Speed Machine

    When I turn on smoothing at 0.001" (with 0.0002" tolerance) I get pretty good looking code. Most of the passes in the slots have all arc moves except for the straight line linking move between passes. I don't really see how you could do much better. The only other thing you could try is to increase the lead in/out radius and see if that helps keep the axis speed up. I doubt it will matter though since the distance traveled will be greater, which may negate any speed gains.

    I tried posting with my Haas post and with the generic Tormach post and get pretty much the same code with both, so unless you have a non-standard post I don't think anything is wrong there.


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    Default Re: Adaptive/Trochoidal Slotting and Acceleration Limitations

    Thanks for that. The extra linking motion should negate the gains in reduced accel theoretically, but depending on how linuxCNC does the accel control, who knows. It would at least be nice to have my machining time estimates from Fusion360 be closer to reality. They're wayyyy off now.

    Is there a way to easily see in Fusion 360 if a path is an arc or not? When I zoom in on tool paths they look rather segmented even if they are arcs. In sprutcam (yech) I could match up lines of gcode with the toolpaths.



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    Default Re: Adaptive/Trochoidal Slotting and Acceleration Limitations

    Quote Originally Posted by GJeff View Post
    Thanks for that. The extra linking motion should negate the gains in reduced accel theoretically, but depending on how linuxCNC does the accel control, who knows. It would at least be nice to have my machining time estimates from Fusion360 be closer to reality. They're wayyyy off now.

    Is there a way to easily see in Fusion 360 if a path is an arc or not? When I zoom in on tool paths they look rather segmented even if they are arcs. In sprutcam (yech) I could match up lines of gcode with the toolpaths.

    Getting accurate machining times is tough because Fusion doesn't know about your machine's acceleration. In theory it could be done using machine simulation (which does exist in primitive form in HSMWorks) but that won't make it into Fusion for a long time.

    Seeing the exact paths in Fusion directly is not possible since the smoothing is applied at the post processor level. The best thing to do is to look at it with a back plotter, or just look at the code directly.


    Incidentally, I know all about working with really slow machines. I have a 2 axis Bridgeport that is pathetically slow. At feed rates over 20IPM it will come to a complete stop between EVERY move. This makes it pretty much useless for adaptive paths.


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    Default Re: Adaptive/Trochoidal Slotting and Acceleration Limitations

    I'll save my pennies for some servos perhaps.



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Adaptive/Trochoidal Slotting and Acceleration Limitations

Adaptive/Trochoidal Slotting and Acceleration Limitations