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    Member ubergeekseven's Avatar
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    Default Weird rotary movement with fusion wrapped toolpath

    I've been testing generating toolpaths for my rotary axis using fusion 360 cam. I've been successful with the parts and have indexing and rotary working. I designed a part that had several features that would require all kinds of toolpaths so that I may learn the operations needed.

    The problem is that I have what looks to be a simple toolpath to turn down the square stock on a location to a cylinder. I'm using an adaptive 2d toolpath. I wrapped the toolpath after creating a sketch to represent the area to be machined. Everything looks good but when I actually run it, all of the cutting works fine and the speeds are what I expect. The movement to position after a retract is extremely slow and is causing the job to take at least 5 times longer than what it should.

    The movement is jittery too. The a and x movements look like they move, pause, move until it finally makes it to the next location to cut. Then the cut happens at the expected rate. Retract, move, pause, move again.

    How can I get the movements to move as fast as the cuts do? I've been reading and I'm not sure what is the problem. Just guessing now, but the gcode posts the feedrate for both the a and x on the same line. But then again, the cuts are done in the same manner, so I can't figure out what the difference is.

    Here is a short video of what is happening, hopefully you can see what I mean.




    Anyone else familiar with this sort of issue?

    Sent from my SM-N950U using Tapatalk

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  2. #2
    Member ubergeekseven's Avatar
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    Default Re: Weird rotary movement with fusion wrapped toolpath

    So, after the time I posted this and attempted to talk to avid, fusion hsm post forum people and the folks at warp9 about what is happening, I finally figured it out.

    I tested the default mach3 post in fusion and it output inverse feed time correctly. However, I'm not exactly sure how to modify the post and comparing the Mach3 default to the cncrp past from a year and a half ago, they haven't updated their post since, I saw some seemingly major changes between the two.
    I spent a couple hours migrating the cncrp changes over to the Mach3 post. Tested and verified working and then produced an actual part with the settings. As of now my post works as I expect except that it doesn't add an m8 command that the cncrp one does and I cannot figure out which function is doing this just yet. I was more than happy to have a working post. The command turns on or off the relay for dust collection, but I use a switch because the dust collector is one I use in the shop as well. I would like to eventually understand how the m8 it's getting inserted, but that can wait.

    It looks as though cncrp modified the default mach3 setup and removed all of the inverse feed capability. Not sure why, but they did. I added it back and removed the g28 commands mach3 had built on theirs. I'm now working on adding now features to practice post modification while it's still fresh in my brain.

    I now have to figure out the maximum speeds I can use with my setup. I've run several of the same jobs and had a couple paths come out at different angles due to losing steps. Running at 100 ipm and taking cuts at .4 inch depths might be the issue. I attempted .2 inch depth and it didn't seem to lose steps. I was expecting 100:1 gear ratios to be more than enough for holding the position, but watching some cuts occur made me think twice about that. There is lots of force when moving into square stock at that rate on rotary. Makes me want a brake, but not sure if that's possible with my harmonic drive setup.

    I am thinking that I want to insert a reference all home command after each path finishes. I tested doing this after noticing the lost steps and it returns to the work offsets exactly how I need. You have to have a sensor on the a axis for referencing home though. It cost me less than $20 to do it. I printed a mount for the sensor to go on the rotary gear box and another print that holds an me bolt that rotates on the rotary chuck. Works very well and allows for easy referencing.

    If the roughing paths mess up the steps, then referencing between would allow the following paths to run in the right location again.

    Things learned, mach3 is messy and not intuitive. Fusion 360 is another ball of yarn and combining the two makes for a real hard to understand mixture. You only know it when you take the time to break down every line until you know it.

    Sent from my SM-N950U using Tapatalk



  3. #3

    Default Re: Weird rotary movement with fusion wrapped toolpath

    I had similar issues with Rhinocam and Mach4. Rhinocam found issues with how inverse time feed speed is calculated in their post for Mach4 but so far refused to provide a fix because I have 2018 version.




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    Default Re: Weird rotary movement with fusion wrapped toolpath

    I never got to try any property from rhinocam because I figured it out in fusion. I bet it's using the wrong code and should be creating inverse time calculations instead of calling every single line. Inverse time calculates how long it should take to go to the next position instead of calling every single position change by degree. It's degree per minute instead.
    I had to add another line to the fusion pp to make it work even after figuring that out. With the first change I made, fusion did it correct for the first section of code and then after that section would somehow revert to the previous output. Someone in one of the 10 forums I went through pointed out the fusion bug and how to get around it.


    Sent from my SM-N960U using Tapatalk



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    Default Re: Weird rotary movement with fusion wrapped toolpath

    I was able to produce this using fusion and my pp. Came out so much better than the vectric one. It's a little tedious doing the setup in fusion Cam because you have to constantly change the axis to get a good toolpath that goes into places deeper than what's possible with any wrapped path that only goes on x and z. I can't wait for better rotary support. True 4th with xy and z movements can produce amazing results compared to wrapping.
    The one on the left is vectric and right is fusion. I messed up the vectric one by somehow having reverse design checked and it mirrored everything. I even went through the Mach 3 settings attempting to change it to output inverse, but it took me days to figure out that vectric had the stupid box checked.
    Vectric is fine for flat stuff, maybe even simple wraps. But it can't do complex 4th well at all. You can't even go below center if you wanted to because of the whole singularity problem. Fusion allows for all of you have the time to setup.

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Weird rotary movement with fusion wrapped toolpath

Weird rotary movement with fusion wrapped toolpath