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5-Axis Swarf Looks Correct - Code is Wrong


Reko
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Hi,

 

I have a 5 axis swarf of a groove that backplots and verify's perfect.

 

The geometry looks great too, but I wrecked the part because the code sent the cutter through the side of the groove.

 

I change from a custom post/machine def, to the HAAS generic one that comes with Mastercam, and it correctly machined one of the trouble spots, but went through the side of the other bad spot.

 

I feel like this is a machine def/post problem, but I was hoping to get some suggestions.

 

Thanks.

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I never thought of that.

 

I guess I could try to cut it into sections beginning and ending where the violations happen.

 

I hope someone can point me in the right direction though... it seems like it should work if it backplots and verify's correctly.

 

I also just sent this file into support... I will post a solution if they find one.

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Is it a singularity problem?

 

Bingo!

 

Your machine doesn't know what to do when it sees this.

 

We use CAMplete for our Matsuura and even that needs some fanagleing.

I had to do a dovetail groove on a profile with only one entry point in 5 axis the other day and it would have shot through the part if I didn't catch it.

 

For a Haas I would split the part.

 

Also, I found that a 5 axis Curve toolpath sometimes works better depending on geometry constraints.

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Okay... so, I've been reading about singularity and it sure sounds like this is my issue.

 

It is strange that just by switching posts one of the trouble area's was corrected.

 

Now the next question... where do I split this part up? I guess I can step the program through to the point where it breaks out of the groove... then, split the tool path there... but how would I know that point going into a part like this to stop it from happening in the future?

 

I will give the 5-axis curve a try too.

 

Another thing I ran across on this forum, was advice to "resist the temptation" to program with everything set up symmetrically... to tip the part on an angle to begin with and that will virtually eliminate any points of singularity.

 

I will try that too.

 

My brain hurts now... so, thanks Ron, thanks Oscar... I will post my final solution and also what my reseller comes up with too.

 

:oldforumcheers:

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Reko,

 

You can try using the Generic Haas VF-TR post, and setting 'brk_mv_head' to '0', and 'brk_max_ang' to '-1'. This will disable the "reposition" moves that are being output. It may or may not address your problem, but it's worth a try. You should check the Gcode carefully to make sure the A/B values don't suddenly have a large rotation.

 

One other trick I use often is to apply the rotary "Limits" in the 5X Toolpath, to remove any vector that is within a quarter degree of vertical. This helps to eliminate those pesky singularities.

 

Please also send this issue to your Reseller and ask them to forward it to the Post Department at CNC. We've been making some improvements to the logic in the binned portion of the 5X posts and we could always use more test cases. (We do need the request to come from a Reseller though.)

 

Thanks,

 

Colin

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the geometry looks fairly flat. If it is positioned near A zero where the Haas platter is horizontal you can get these big reversals of the B axis. changing the angle increment can help (.03 degrees has worked for me).

best solution for the setup would be to fixture the part at an angle where all the work will be done in a quadrant without risk of sign reversals on both rotaries.

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In order to combat the possibilities of singularity occurring, fight the general urge to have everything symmetrical. You don't have to shift or rotate it much, just enough so the rollover doesn't run into a situation where their Re an infinite number of solutions.

 

HTH

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invest in vericut or camplete or the like. This is the only way to be confident in the 5 axis paths coming out of mastercam !

 

Well, IMHO, not only for Mastercam but any CAM tool. 5 axis depends a lot on UV lines of surfaces, the math in the PP, the skills and knowledge of the whole chain, you name it... There's a lot under to hood and a CAV tool is the only thing that can process the code like the machine would.

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What people need to understand regarding singularity is that it is not necessarily the CAM system's fault. CAM systems are dumb for the most part. They require user input to do anything and on top of that, they have no kinematic awareness, meaning they don't know how all the axes integrate with each other. That's where solutions like CAMplete, ICAM, and to a certain extent Vericut come into play. CAMplete and ICAM are integrated Simulation, Collision Detection, Verification, and Post Processors, whereas Vericut is strictly Simulation, Collision Detection, and Verification. You'll see the rollover in those packages whereas your CAM system will NEVER be able to show you that.

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invest in vericut or camplete or the like. This is the only way to be confident in the 5 axis paths coming out of mastercam !

 

So true Fishy :). If I hadn't used Vericut, our spindle and table would have some bad marks in already :)

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Okay... nothing has worked so far... I haven't heard back form my reseller yet, so if anyone has any other idea's... please, let me know.

 

The problem is on the left arrow (picture at top of page) the toolpath actually tries to BACKUP and loops out of the groove breaking through the wall.

 

 

Here is what I have tried:

 

- Curve 5-axis using the same curve and the lines saved from the swarf geo

- 5XSwarf and 5XCurve only the corner that is deviating from the backplotted path

- Changed the post settings 'brk_mv_head' to '0', and 'brk_max_ang' to '-1' (this was a really bad deviation from the path)

- Applied rotary "limits" in the 5X toolpath (I set this to .25 as I assume it would break anything more than a quarter degree)

- Changed the "angle increment" to .030"

 

Nothing works.

 

I believe I can see what is happening though... the groove comes flat in that area to A0 and the B axis is making huge move, just like everyone is talking about.

 

The only suggestion I haven't tried is to remount the part at an angle to remove the possibility of the part coming to A0 in the program.

 

Any other suggestions would be appreciated here... I have learned a ton on this part... thank you to everyone!!!

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Can anyone point me to a good explanation of singularity? I have to be honest, I've never heard of it until now..

 

It's basically a situation that gives the machine an infinite number of solutions to go from one angular position to the next. It's quite common in head/head machines but it also happens if the conditions a right in table/table machines. It usually happens when trying to go from a completely vertical position to an angular position. Adding side tilt can help in some instances or using lead/lag, basically you want the axises to have an initial tilt so the solution for the next position will have one or possibly two solutions.

 

If you're interested in the physics of singularity there is a paper that was written and can be purchased from Science Direct.

 

http://www.sciencedirect.com/science/article/pii/S0890695503002876

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It's also very common in robotics. the more flexible a machine is, the more points of redundancy there are. Because no direction is technically 'better' to the machine, and it doesn't actually know that your part is 'there' (it's just looking at lines of code) it decides to move in one direction vs. another which is why the cutter went through the part.

 

look at it as a challenge in that if you can solve it mathematically once and for all you will be a rich person

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It's basically a situation that gives the machine an infinite number of solutions to go from one angular position to the next. It's quite common in head/head machines but it also happens if the conditions a right in table/table machines. It usually happens when trying to go from a completely vertical position to an angular position. Adding side tilt can help in some instances or using lead/lag, basically you want the axises to have an initial tilt so the solution for the next position will have one or possibly two solutions.

 

If you're interested in the physics of singularity there is a paper that was written and can be purchased from Science Direct.

 

http://www.sciencedi...890695503002876

 

Thanks for the info. I'm in the midst of ironing out some post processor issues with our 5 axis. We're looking at cutting our first die on this machine, and I want to get it right :)

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For the purposes of post-processing 5-axis,

it could be stated that a singularity exists when the tool axis vector contains a vector component value of 1.0

and that vector component is the center-line of the PRIMARY rotational axis.

 

Example.

Tool Axis Vector is Vertical.

Vector components I,J,K = 0,0,1 in a C/A Nutating Head Machine.

C rotates about Z and is the primary rotational axis both mechanically and mathematically.

(Table/Table machines have the primary mechanical axis as secondary mathematically and the secondary mechanical axis as primary mathematically).

The K component value of the Tool Axis Vector equals 1.0.

This means that there are an infinite number of solutions for a C-Axis angle for a vector of 0,0,1 .

 

The typical and most common solution in a post is to round the other vector component values of zero to the lowest non-zero double-precision value.

This prevents division by zero errors in the angle calculations and will provide the most common solution of C0.

Because this is being done in the post, you need to track the previous, current and next value to ensure a continuous transition.

 

Without a toolpath calculation algorithm that is based on the kinematics of the specific machine,

the post-processor will always have to contain the 'intellgence' to process the tool axis vectors accordingly.

 

The thing to do now is look at the actual CL data from the NCI to see what is being generated by each attempted toolpath strategy.

By looking at the CL data you should be able to determine where the problem is and the best approach for a solution in the post.

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Can you share the file?

 

I put it on the ftp under "unspecified_uploads" and named it "5X_SWARF_GROOVE_SINGULARITY_PROBLEM.MCX-7"

 

I labeled everything in the ops manager.

 

The "bad" corner is the one that I can not resolve.

 

The "good" corner is the one that was breaking out using our custom post, but then I changed over to the generic Haas 5x post, this corner was corrected.

 

As I stated earlier, the toolpaths all backplot and verify correctly, but the code/toolpath deviates from the proper path when it is running in the machine.

 

Thanks in advance for any help!

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