Asymmetry in Parts due to Direction of Cut

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Asymmetry in Parts due to Direction of Cut

Postby CaduCues » Thu Dec 13, 2018 1:08 am

Hello all,

Does anyone know if there is a way to ensure that part symmetry can be addressed in V Carve toolpath calculations?

I am attempting to cut a cavity into a rounded work piece using the wrapped job setup / pocket toolpath features in V carve.

In the simulator, the cavity looks exactly like the part. The part is .062" wide until it tapers into itself at the top and comes to a point, the center of the piece is hollow.

So the part is about 5 inches long, tapers from a point to around .55" wide. It looks like an upside down V if you are having trouble visualizing.

The problem I am running into is that when I cut the cavity into a rounded work piece, one side of the cavity has a much larger chunk taken out of it than the other. This of course makes the inlay loose on one side and the cavity is officially unsuited to my work. I have addressed the hardware issues that may be causing this. My rotary axis is calibrated, my cut is being initiated from top dead center, and my svg is perfectly symmetrical, as is the inlay part that was cut with V carve with the exact same bit.

When trying to solve the problem, I have discovered that the cutter makes a pass going the opposite direction of the pass made on the other side of the part. When I look at the calculated tool path in V-Carve, I can see the exact pathway that is causing me problems, but I cannot find anyway to calculate the toolpath without it appearing in the final cut path.

Does anyone know if there is a way to ensure that part symmetry can be addressed in V Carve to alter the pocket toolpath calculation?
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Re: Asymmetry in Parts due to Direction of Cut

Postby 4DThinker » Thu Dec 13, 2018 1:37 am

Without seeing a picture of what you describe, it sounds like your rotary axis isn't aligned perfectly with the X (or Y) travel of your CNC. You can save the rendered image of your job and post it here, and that would explain better what you are trying to cut. If you've got a photo of what actually cut that you can post it would also help the brilliant folks here zero in on what may be happening and how to fix it.

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Re: Asymmetry in Parts due to Direction of Cut

Postby tomgardiner » Thu Dec 13, 2018 1:11 pm

It sounds like the final pass is against the grain and pulling into the workpiece. I don't have any rotary experience but I would be looking for any backlash as I am sure you have.
Another option is to manually remove the lines of code for the final pass. You can open the post processed file in your computer's text editor and delete the offending lines. Remember to leave the footer that turns off the spindle etc.
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Re: Asymmetry in Parts due to Direction of Cut

Postby CaduCues » Fri Dec 14, 2018 8:43 pm

4DThinker wrote:Without seeing a picture of what you describe, it sounds like your rotary axis isn't aligned perfectly with the X (or Y) travel of your CNC. You can save the rendered image of your job and post it here, and that would explain better what you are trying to cut. If you've got a photo of what actually cut that you can post it would also help the brilliant folks here zero in on what may be happening and how to fix it.

4D


I have taken your alignment hypothesis and done a couple of cuts with it at variable changes in angle, but the problem persists. I do not have a surefire way to align it on a geometric plane, so I do believe that it could still be this problem. If you have any way to show how to align a 4th axis rotary table on a 6090 USB CNC machine from china, I'd greatly appreciate that.

Anyways,

Here is a picture of the render: https://photos.app.goo.gl/qYLdZFrpJHvjMk9Q6

Here is picture of the actual cut: https://photos.app.goo.gl/xMV95DBviHd8p75r9

Here is a copy of the G-Code: https://drive.google.com/file/d/0B4xEqS ... sp=sharing


Thank you for looking at this problem!
Jake
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Re: Asymmetry in Parts due to Direction of Cut

Postby CaduCues » Fri Dec 14, 2018 9:29 pm

Here is a picture of the vector cut path at the internal point: https://drive.google.com/file/d/1iBGql- ... sp=sharing
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Re: Asymmetry in Parts due to Direction of Cut

Postby garylmast » Fri Dec 14, 2018 11:24 pm

I"m not sure if this is the same problem you're having, but once I did a modeled car on the rotary, where the "Seat Area" came out slanted/didn't cut down straight. What I did in that area was I created another file and machined it sitting flat, as if it was just a flat board, using the rotary only to hold it in place.

Gary
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Re: Asymmetry in Parts due to Direction of Cut

Postby sharkcutup » Sat Dec 15, 2018 2:00 pm

Nice looking Car - good job!!! Garylmast


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Re: Asymmetry in Parts due to Direction of Cut

Postby tomgardiner » Sat Dec 15, 2018 2:54 pm

You could check the alignment of the 4th axis with a v bit in the spindle. Align the tip with the center of the headstock manually (I assume that you have a drive with a center pin). Then manually jog the spindle to the live center on the tailstock and adjust if there is runout. You will be looking for runout in the z and x or y axes.
Are you turning the cue blanks on the cnc? If not then mounting the blank might be a source of error.
You can have more control over the direction of cut if you were to toolpath this as a profile cut not a pocket. You could split it into two open vectors and have the cuts travel from top to bottom on both sides.
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Re: Asymmetry in Parts due to Direction of Cut

Postby CaduCues » Mon Dec 17, 2018 8:28 pm

Thank you very much for your suggestions, I am going to give them a try and report back if and when success appears.
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