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what is a rotary unwind on 5axis trunnion?


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My fellow programmer ran a part today that contained a swarf. The part looks like the bow of a boat upside down.  The tool runs around the part on a 180 degree path with about 10 degrees of axis tilt.  Nothing unusual.  But is made some crazy moves and scraped.  When it posted he said he got a notification of an "unwind".  Neither of use have seen this before.   We made a zip to go and sent to our reseller but I would like to  understand what is our problem.   This is a 3 month old post and I thought we had it sorted out. This machine is an Okuma 4000 5x.  Thanks,

Steve A

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He ignored the warning and he scrapped it what more do you need to sort out? He made motion that didn't work within the travel of the machine. The post alerted him and he ignored it. Your machine has a certain range of travel and you hit that limit with the operation. Without running a Verification program to catch crashes you either run it a safe distance away when these things come up or you risk it and pray you don't tear something up. For whatever reason you guys decided to risk it and hopefully all you did is scrap a part and not hurt the machine.

The programmer needs to know the limits of travel when programming or needs to use a verification program to catch possible crashes. I have programmed 5 Axis machines since 2001 and trust me I still make mistakes. I still run into issue. I still tell anyone until it is run don't trust the NC program. I have seen Verified program do weird things. Know what you know by doing everything possible to know it. Ignoring the post warning sorry to say he got what he asked for.

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Unwind is there mainly for Head -Head (both rotational axis in the head not the table) machines. They can only go so many revolutions (or fractions of) before they need unwind so they don't break internal connections.

This might also be a machine parameter issue. I set up a 4 axis horizontal to do multi axis parts several years back and we discovered 3 different parameter settings to define how the y axis rotation was broken. The manual (translated from Japanese) was as clear as mud so we just tried them all until we found the one that worked for us.

You got the warning during posting though and normally such an unwind should be accompanied by a retraction from the part to allow the unwind. So look at machine/control defs, post and machine parameters to make sure all are playing nicely together.

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10 minutes ago, nickbe10 said:

Unwind is there mainly for Head -Head (both rotational axis in the head not the table) machines. They can only go so many revolutions (or fractions of) before they need unwind so they don't break internal connections.

This might also be a machine parameter issue. I set up a 4 axis horizontal to do multi axis parts several years back and we discovered 3 different parameter settings to define how the y axis rotation was broken. The manual (translated from Japanese) was as clear as mud so we just tried them all until we found the one that worked for us.

You got the warning during posting though and normally such an unwind should be accompanied by a retraction from the part to allow the unwind. So look at machine/control defs, post and machine parameters to make sure all are playing nicely together.

Sir I have to disagree with that statement. A trunnion machine can run into the same issues also. Sometimes the motion is made in such a way the machine cannot swing the table to achieve the motion programmed. That is when an unwind is needed. Not as common as a Head-Head, but table-table and head table-machine can still experience the issue of needing an unwind. Where the programmer has to know the kinematics of the machine and take them into account when programming in Mastercam. 

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17 minutes ago, C^Millman said:

Where the programmer has to know the kinematics of the machine and take them into account when programming in Mastercam. 

+1000000000000

The post giving you a warning about unwind 99.9% of the time means there is a problem with the toolpath not being setup in a way that is kinematically achievable.  The solution to this could be as simple as changing the misc integers.  Or could be that you haven't selected the right options in the path, this though should have been caught during backplot or simulation in mcam.  My guess is that the swarf path has the machine doing a loop de loop at the peak due to syncing or a gap in geo.  I have seen some unpredictable results with the new swarf in some cases.  If you feel the settings are what they need to be, relax or tighten the tolerance and you will be surprised how much different the output will be.  I had a case where .025mm was exactly what I wanted but not quite as dense as I needed for smooth angular motion,  .25 was all f'ed up.  .005 is less than desireable, .001 isn't much worse than .005mm.   I attached a sample where everything is the same except for the tolerance....  Toolpaths outcomes are all different.  

Pushing it through the Mastercam simulator quickly should identify travel limit issues if you have them setup properly.

 

 

Sample.mcam

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27 minutes ago, C^Millman said:

Sir I have to disagree with that statement. A trunnion machine can run into the same issues also.

I'm thinking he is talking about the C axis on your your typical table-table being unlimited Vs head-head C-axis having a very finite travel.

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33 minutes ago, mkd said:

I'm thinking he is talking about the C axis on your your typical table-table being unlimited Vs head-head C-axis having a very finite travel.

Yes, but that is where the A Axis may be forced into a position it cannot get into going in one direction and then the post would call it an unwind and in all reality it is just a reposition to put it where the A and B axis can work together to machine the feature not an unwind, but the post may call it an unwind when it isn't. In that case yes it is not your typical unwind thinking like a head-head with limited C Axis travel, but every Trunnion I know still has Limited travel on one of the axis. Yes the table may be unlimited, but sometimes depending how you program the part you create a motion that is not within the limits of travel and any good Mastercam post should give you a warning and it should never be ignored is my point. It seems the warning was ignored from what I have read and if it was then someone did this to themselves. Send it to the reseller all you want and maybe the post is at fault here not ruling that out, but again from what I read a warning was ignored. That makes me question other things beside the post and I was trying to give a different prospective to think about. Sorry if my meaning comes across the wrong way. I just tell it like it is doing my best to be respectful and honest.

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not judging your correct take on the situation. Mathematically and in the post logic there is probably no distinction so you're right to disagree; overtravel is over travel.

I think (probably incorrectly) of an "unwind" move for a head-head and an "overtravel" for a trunnion. A need for unwind of a head-head is far more likely in general and specifically in near perpendicular features (where A is near zero) where a trunnion would never bat an eye. That is basically the point  I think nickbe was making. so you're both right.

this was and A-B conversation

i'm going to -C- my way out of it.

:sofa:

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13 hours ago, C^Millman said:

That makes me question other things beside the post and I was trying to give a different prospective to think about. Sorry if my meaning comes across the wrong way. I just tell it like it is doing my best to be respectful and honest.

I think the  origin of "unwind" was from head/head machines  as you are effectively unwinding all the internal wires and connections to avoid breakage. And I believe many more modern machines (Makino MAG 4s?) do not require unwind. So I was trying to answer the question of what it was derived from.

Having said that C^Millman's main point was that a clear warning was ignored. My main 2 cents was from experience with the parameter issue and as was stated above there are many things which can cause odd movement in any machine and trying to look at it from a total system point of view. Not just the post or just the kinematic set-up (in the virtual programming environment), everything has to work together. And that, I think,  would include the parameter set- up of the machine. I have found that it is all too easy to get focused on just one component of the system and miss the woods for the trees.

And no offense taken. This is a tough game we play, make no mistake about it. Unlike most jobs once the rubber meets the road there is no delete or redo key to press to get you out of trouble. And it only takes one mistake in the many hundreds, or even thousands, of choices you make which ends in the successful machining of a part. So I never take this sort of thing personally, there is too much at stake.....and you ignore any suggestion or information at your peril.

I think threads like this are what the forum is all about. 

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1 hour ago, nickbe10 said:

I think the  origin of "unwind" was from head/head machines  as you are effectively unwinding all the internal wires and connections to avoid breakage. And I believe many more modern machines (Makino MAG 4s?) do not require unwind. So I was trying to answer the question of what it was derived from.

Having said that C^Millman's main point was that a clear warning was ignored. My main 2 cents was from experience with the parameter issue and as was stated above there are many things which can cause odd movement in any machine and trying to look at it from a total system point of view. Not just the post or just the kinematic set-up (in the virtual programming environment), everything has to work together. And that, I think,  would include the parameter set- up of the machine. I have found that it is all too easy to get focused on just one component of the system and miss the woods for the trees.

And no offense taken. This is a tough game we play, make no mistake about it. Unlike most jobs once the rubber meets the road there is no delete or redo key to press to get you out of trouble. And it only takes one mistake in the many hundreds, or even thousands, of choices you make which ends in the successful machining of a part. So I never take this sort of thing personally, there is too much at stake.....and you ignore any suggestion or information at your peril.

I think threads like this are what the forum is all about. 

Great answer and we are on the same page. I have been working with a customer for months trying to sort out this very issue on 8 machines. We are very close and I have learned more about parameters and post working to sort it out than I really every wanted to, but yes real easy to not see the tree for the forest. :whistle::whistle: (Raising Hand)

Agree we are all different and have different backgrounds and if we all thought the same then there wouldn't be a need for this forum. I learn something everyday and I would love to know what the route cause was so I can learn a different thing.

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Well I did not ignore anything.  Was only told of the warning and scrap after it happened.  We are both somewhat new to 5axis programming.  This is a table table machine with c axis unwinding.  Our reseller sent us back a toolpath to try and it was even worse but moved in different ways.  Both had Caxis spinning in the cut.  What troubles me is we have been making parts for months with little trouble.   We tried the same path on our haas trunnion and it looked just fine.  I am not passing blame.  Just trying to understand something I obviously don't.

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12 hours ago, lowcountrycamo said:

Well I did not ignore anything.  Was only told of the warning and scrap after it happened.  We are both somewhat new to 5axis programming.  This is a table table machine with c axis unwinding.  Our reseller sent us back a toolpath to try and it was even worse but moved in different ways.  Both had Caxis spinning in the cut.  What troubles me is we have been making parts for months with little trouble.   We tried the same path on our haas trunnion and it looked just fine.  I am not passing blame.  Just trying to understand something I obviously don't.

Okay sorry I misunderstood the posting. Again where you really need to understand what you are seeing and how what Mastercam does will relate to motion on the machine. You can send me a sample file with something similar and I will be glad to see if I can see anything that looks out of place. You have a great reseller in your area.

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So did your reseller send you a posted toolpath or did they send a source toolpath you then posted. Either way did you/they get another alarm while posting?

If not that would seem to point to a parameter problem. The problem I had above involved the y axis starting the cut and when it reached B0 (horizontal 4 axis remember) it wanted to do a full rotation before starting the cut again (with no retract) so that might be the C axis "spinning" you saw. I however never got a warning when I posted toolpath, so that kind of says that's not the whole problem, or even the actual problem as you did get a warning (or more accurately your co programmer).

When you ran the new toolpath did the machine movements "match" the code ? Single block and check that out. If the next line of code defines a specific move but results in an anomalous movement or the motion breaks and restarts that might tell you something.

This is going to take a methodical approach. I would recommend checking all the underlying components first, machine /control defs and look in the manual to see if there are actually different parameter settings for the axis rotations, there might not be for your machine. Then move onto toolpaths. If you simply make a toolpath work at the moment  you might find the problem rearing its ugly head again unexpectedly because the underlying problem hasn't been fixed. Don't forget you were happily machining away for some time before some specific combination of parameters caused a problem.

In the mean time you will need to be extra cautious on first runs, we call it full on step 2 here.....

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23 hours ago, lowcountrycamo said:

Well I did not ignore anything.  Was only told of the warning and scrap after it happened.  We are both somewhat new to 5axis programming.  This is a table table machine with c axis unwinding.  Our reseller sent us back a toolpath to try and it was even worse but moved in different ways.  Both had Caxis spinning in the cut.  What troubles me is we have been making parts for months with little trouble.   We tried the same path on our haas trunnion and it looked just fine.  I am not passing blame.  Just trying to understand something I obviously don't.

One thing to look at, is that while it is the C axis unwinding, it may be due to an A (or B?) axis limit, wherein the post is unwinding C to move to the other (always 2 combinations for any given 5 axis move), more achievable axis combination. This is where knowing your machine's kinematics as Ron said above is key in understanding how axis combinations are arrived at.

This could be as simple as seeding an MI$ secondary axis position. Or not. Knowing your kinematics is the answer.

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