Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: lopata on August 30, 2016, 02:27:07 PM
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Hello fellas cnc enthusiasts.
I have build up a High speed machine in last few weeks, and I am having trouble with understanding Mach3 logic.
My machine setup.
Leadshine easy servo motors with drivers, 4Nm.
Max feedrate 10000 mm/min
Acc: 2000mm/s/s goes up to 4000 mm/s/s without problems, but that is insane acceleration.
Ball screw 2505 C3 precision.
All axis are below 0.01 true, with work table max 420x420x100 mm.
Machine does not stutter and shakes. Cutting in pure motion, without any hiccups.
Few problems which occurred.
1. Mach3 does not cut the same paths on the feed rate on 100% (around 30 mm/s) and on 50 %. How can this be, and why is that?
2. Making a part on CV=180 is not the same as CV=1, or ever CV=0.1 -- Can anyone explain a bit on this.
Questions:
1. Is this common issue with Mach3, and should I consider moving to EMc2 or Mach4?
2. What is the lowest CV tolerance that can be set? Mine is set to 0.1 mm, but I will be going to 0.01 or even less.
I have been making JIGs for my parts, and to tolerances from that CV is affecting my parts significantly. I should be running tolerances around 0.005 mm on 100 mm range, but there are tolerances greater than 0.1 mm.
The parts that has been cut on CV=180 cant fit my JIGS at all, while parts made on CV=1 can fit but with some convincing.
I have read up all the common issues with CV and Mach3, but I just need an answer why does Mach3 cuts differently on different speeds.
Thank you
Marko
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The CV Tolerance setting in Mach3 is not a part size tolerance.
You're best bet may be to turn off all CV settings, except "Stop CV on Angles <", and set that to whatever works best for you.
Mach3's trajectory in CV mode is influenced by a lot of factors. IN addition to the CV options, lookahead and acceleration also have an effect on the trajectory.
High speeds tend to show Mach3's limitations in it's trajectory planner. High acceleration is the best way to avoid these issues.
This might help explain some of the details:
http://www.machsupport.com/wp-content/uploads/2013/02/Mach3_CVSettings_v2.pdf
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Hey Gerry
My current setup on the acceleration is 2000mm/s2, which is pretty high. Actually, maybe acceleration is extremely high for the hard aluminium.
Regardless of acc, the sharp corners get rounded. When I reduce the CV, its better.
I dont have the problems with CV as much, as all of my parts are rounded, and there are no sharp corners.
My problem is that Mach3 is making shortcuts when applied with different speeds. For example: If I run it with 30 mm, and slow it down to 50 % of feedrate, the mach starts to be more precise. If I return it back to 100%, it will not be precise again, which is disturbing thought.
Also, I am milling a socket which is 6.2 in diameter, with 6 mm end mill, and that sockets are making troubles, not fitting in the JIG. Roughing and finishing passes, but also finish pass is also a bit high speed.
I could be missing something. What I will try, is to make smaller cutter, and make another jig with new setup of CV.
What about EMC2 or Mach4?
Image will show you.
First two are my products, and last two is machine while being built.
Will also upload the video of milling.
(http://i1258.photobucket.com/albums/ii528/lopataos/20160830_131322_zps9e0emunu.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160830_131322_zps9e0emunu.jpg.html)
(http://i1258.photobucket.com/albums/ii528/lopataos/20160829_210317_zpsihbzvati.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160829_210317_zpsihbzvati.jpg.html)
(http://i1258.photobucket.com/albums/ii528/lopataos/20160730_194145_zpscpyugfl2.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160730_194145_zpscpyugfl2.jpg.html)
(http://i1258.photobucket.com/albums/ii528/lopataos/20160801_2022121_zpslaitrncg.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160801_2022121_zpslaitrncg.jpg.html)
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I've never used EMC (now LinuxCNC), and afaik, Mach4 still has no CV control at all. Although I believe that some CV control was being tested.
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Regarding the issue I am having. Maybe the pictures will explain better.
First picture was made on 100% feedrate, on around 25 mm/s with CV=180, but unchecked.
(http://i1258.photobucket.com/albums/ii528/lopataos/20160815_105004_zpsbrvmg97p.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160815_105004_zpsbrvmg97p.jpg.html)
Second pic shows the same Gcode but on 50% feedrate, reduced in mach3. Also CV=180, and unchecked.
(http://i1258.photobucket.com/albums/ii528/lopataos/20160816_163329_zps9y6oycjd.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160816_163329_zps9y6oycjd.jpg.html)
How can this be and why is it happening?
Tomorrow I will do some test on CV settings =0.000001 units (mm) and will run the same Gcode on same speeds.
In backup, I will give it a go on EMC2 to see how it goes.
I know I am doubling my post on cnczone and machforum, but I really need answers.
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I have noticed odd things happen when increasing feed rate in Mach, done via code its ok but increasing via feed rate override does odd things sometimes.
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Hello Davek
Well, this is the problem. When I leave my feedrate on 100% (normal speed), it get rounded corners, and when I reduce it gets more squared.
25mm/s was initial settings for engraving end mill. I fuess its 2 fast for it.
Mach3 is just not as it should be. Ita very anoying to have that kind of setup which I cant rely on it.
Moving to emc2 in a few days.
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Just out of curiosity what values do you have set for Velocity and Acceleration for the X and Y axes in the Mach3 Motor Tuning ?
Are you using the Parallel Port or an external motion controller ?
Tweakie.
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Hey Tweakie
Velocity is 5000 mm/m
Acceleration is 2000 mm/s/s
For now its parallel port, but moving ASAP on some good motion controler.
By elimination, I will remove the weak points, and mach3 seems to be one.
Will do more testing today with different settings and report here.
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Yep it's not perfect but still damn good;) You just have to know the limitations between software and hardware i think.
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Well, I need it to be perfect.
Machine mechanicly has the precision of 0.0015 per step, as I designed it to make pressure mold for plastics on it.
Now the software are limitations.
Also, when making JIGs, it has to be perfect due the each side macining.
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I can fully understand your issues but maybe Mach3 was not the correct choice?
I don't know, i'm only guessing as i only use it on plasma cutting - not very precise, engraving - machine only has 0.01mm and seems ok and a Bridgeport so not mould-making.
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Now I am thinking it too. Well, 0.01 would be acceptable, if it was proper 0.01 and not like this. Cutting corners and low tolerance on makog jigs is very bad, as my parts dont fit anymore when I flip them.
This is just simple milling, nad mach3 by deafult fails in that direction.
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What is the following error when running code at 1500mm/min ?
Hood
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Lopata
To get that kind of accuracy none of the controller software you have mentioned will do it
Mach 3 or 4 are budget end and Linux CNC is a freeby
You will need to spend some big bucks to get that degree of accuracy you desire
Is your Machine rigid enough to take the g forces that your acceleration of the machine mass is subjecting it to?
What happens if you put a 0.0001 dti on the spindle to work piece and push on the gantry with o out 100 pounds force?
IMHO the controller software that you or using is not up to it
And remember no part is ever 'perfect' there will be some tolerance variation ,it's if that is within your expectation
Regards
Stuart
Sorry to down play Mach software but mach4 works for me and will hold the tolerances for my parts repeatedly over tens of runs.
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Have you tried running exact-stop instead of CV ??
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Hello Davek,
I havent tried exact stop, as that was not the problem, problem was rounding up on higher speeds.
I am on to something now, as I have been playing with setups today, and here are my current machine setup.
Velocity 6000 mm/s
Accleration 1000/s/s (was set to 300 mm/s/s)
In the video, I was engraving with 35 mm/s feedrate.
CV is set to 0.0001 (0.1) units, and Lookahead is 120 (Old value was 20).
The finish move is clearly slowing down and there is slight jerky feeling, but it was due the configuration of the spline.
In pictures you will see much higher precision, and all the corners are pretty correct.
(http://i1258.photobucket.com/albums/ii528/lopataos/20160901_1414421_zpsoiifygni.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160901_1414421_zpsoiifygni.jpg.html)
(http://i1258.photobucket.com/albums/ii528/lopataos/20160901_1412041_zpsvzjvswbw.jpg) (http://s1258.photobucket.com/user/lopataos/media/20160901_1412041_zpsvzjvswbw.jpg.html)
https://www.youtube.com/watch?v=XYTflFqMk0g&feature=youtu.be
Youtube Video on this address: https://youtu.be/XYTflFqMk0g
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That looks nice to me :)
What tool was that running?
I think my lookahead is on 1000 at the moment, velocity 5000 and acc is 500, these may need tweaking though.
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I am on to something now, as I have been playing with setups today, and here are my current machine setup.
Velocity 6000 mm/s
Accleration 1000/s/s (was set to 300 mm/s/s)
??? Throughout the thread you've said your accel was 2000mm/s/s.
If you actually have been using 300mm/s/s then that explains everything you've been seeing. 300mm/s/s is hopelessly low for CV to produce the accuracy you're trying to achieve.
When using CV mode, the accuracy of the actual path, i.e. how close it is to the programmed path, is directly proportional to acceleration. This I'm afraid is true of every machine and every controller on the planet - blame it on the laws of physics.
Acc: 2000mm/s/s goes up to 4000 mm/s/s without problems, but that is insane acceleration.
What's insane about it? 4000mm/s/s is not particularly high for a truly rigid machine. if your machine is capable of 4000mm/s/s then that is what you should be using. The ONLY reason you would turn DOWN accel. is when the jerk your drive system is capable of creating exceeds the rigitity of your machine.
A word about Mach3's CV settings like dist. tolerance etc.
ALL CV settings are there to try to help when a machine's acceleration is not good enough for the job expected of it. i.e. they ALL stop CV from working to its fullest extent one way or another i.e. they all take CV closer and closer towards exact stop. On a machine with accel. good enough for the job expected of it - they should ALL be completely OFF.
Finally a note for Dave. A Lookahead of 1000 is at best nearly always pointless and at worst counter productive. I don't really care about the hair-pin at john o'groats before I've left the car park at land's end. Well unless I'm travelling at the speed of light and my brakes are really crap - then I might. ;D
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Thanks Stirling, it was a value offered as "normal" somewhere, i will wind it back to 200 or so :)
BTW on a servo machine like my Bridgeport conversion, how is it best to arrive at an acceleration figure?
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BTW on a servo machine like my Bridgeport conversion, how is it best to arrive at an acceleration figure?
Like we once discussed for your plasma - ideally, you can never have too much accel. In the real world though, the limits are defined by the power of the motion system and the rigidity/strength of the machine. So, as high as you can get it before stalling/faulting or machine destruction rear their ugly heads.
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Ouch, ok will tweak it up a tad :) I think a drive over-current or lead-error would occur first.
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Seem to remember that Hood runs his Chiron around 0.5G - he'll be the best man to advise on real world values.
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Somehow the settings were dafuqed, and I was left miserable.
I had no chance to play with it today, but I will set it up as high as I can, and give an update here.
Making my move to make a heavy duty table to sit on, and flood it with epoxy, for vibration reduction.
Also, will post a render of the whole machine.
Thank you for such a detailed explanation, and I will try to give it a few tests with off settings.
I am on to something now, as I have been playing with setups today, and here are my current machine setup.
Velocity 6000 mm/s
Accleration 1000/s/s (was set to 300 mm/s/s)
??? Throughout the thread you've said your accel was 2000mm/s/s.
If you actually have been using 300mm/s/s then that explains everything you've been seeing. 300mm/s/s is hopelessly low for CV to produce the accuracy you're trying to achieve.
When using CV mode, the accuracy of the actual path, i.e. how close it is to the programmed path, is directly proportional to acceleration. This I'm afraid is true of every machine and every controller on the planet - blame it on the laws of physics.
Acc: 2000mm/s/s goes up to 4000 mm/s/s without problems, but that is insane acceleration.
What's insane about it? 4000mm/s/s is not particularly high for a truly rigid machine. if your machine is capable of 4000mm/s/s then that is what you should be using. The ONLY reason you would turn DOWN accel. is when the jerk your drive system is capable of creating exceeds the rigitity of your machine.
A word about Mach3's CV settings like dist. tolerance etc.
ALL CV settings are there to try to help when a machine's acceleration is not good enough for the job expected of it. i.e. they ALL stop CV from working to its fullest extent one way or another i.e. they all take CV closer and closer towards exact stop. On a machine with accel. good enough for the job expected of it - they should ALL be completely OFF.
Finally a note for Dave. A Lookahead of 1000 is at best nearly always pointless and at worst counter productive. I don't really care about the hair-pin at john o'groats before I've left the car park at land's end. Well unless I'm travelling at the speed of light and my brakes are really crap - then I might. ;D