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chord size in small arcs too big
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Gentlemen,
I am trying to set up Mach2 to mill some VERY tiny parts. Some of the arcs have radii of .08 mm. In the tool path display, the displayed contour shows the arcs to be broken into very large chords, resulting in a small arc sometimes only having 3 chords in it. I need to have these arcs cut with chords placed around every 5 degrees of the arc. Is it possible to change the chord size Mach2 cuts in for these small arcs or is this beyond the capablility of the software? My motors turn at 8000 steps per rotation (2000 line encoders) and the ball screw pitch is 2 millimeters per rotation, so I have the mechanical resolution to do these cuts. I just need the cnc control to have the resolution. Tom Eldredge |
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Michael Milligan
Tom
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If you have Dolphin you can use the post processor to disable ARC output and replace them with a series of cut vectors, length of vectors can be controlled by setting an Arc Tolerance within Dolphin. Dolphin works to double precision so you Should be able to produce very small vectors. Regards Michael Dolphin Cad Cam Systems Ltd -----Original Message-----
From: davesmachines [mailto:techdave@...] Sent: 10 March 2004 16:52 To: mach1mach2cnc@... Subject: [mach1mach2cnc] chord size in small arcs too big Gentlemen, I am trying to set up Mach2 to mill some VERY tiny parts. Some of the arcs have radii of .08 mm. In the tool path display, the displayed contour shows the arcs to be broken into very large chords, resulting in a small arc sometimes only having 3 chords in it. I need to have these arcs cut with chords placed around every 5 degrees of the arc. Is it possible to change the chord size Mach2 cuts in for these small arcs or is this beyond the capablility of the software? My motors turn at 8000 steps per rotation (2000 line encoders) and the ball screw pitch is 2 millimeters per rotation, so I have the mechanical resolution to do these cuts. I just need the cnc control to have the resolution. Tom Eldredge Yahoo! Groups Sponsor ADVERTISEMENT < roupweb/S=1705063697:HM/EXP=1079023982/A=2019528/R=2/SIG=1410msq5d/*http :/ad.doubleclick.net/jump/N3349.yahoo1/B1282054.27;abr=!ie4;abr=!ie5;sz= 300x250;code=18634;dcopt=rcl;ord=1078937582052152?> Click Here <;abr=!ie4;abr=!ie5 ;sz=300x250;code=18634;dcopt=rcl;ord=1078937582052152?> Click Here < pweb/S=:HM/A=2019528/rand=171350416> _____ Yahoo! Groups Links * To visit your group on the web, go to: * To unsubscribe from this group, send an email to: mach1mach2cnc-unsubscribe@... <mailto:mach1mach2cnc-unsubscribe@...?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of <> Service. |
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Michael Milligan
Tom
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Send me a DXF off list and I will import and Post process it for you for mach2. michael -----Original Message-----
From: davesmachines [mailto:techdave@...] Sent: 10 March 2004 16:52 To: mach1mach2cnc@... Subject: [mach1mach2cnc] chord size in small arcs too big Gentlemen, I am trying to set up Mach2 to mill some VERY tiny parts. Some of the arcs have radii of .08 mm. In the tool path display, the displayed contour shows the arcs to be broken into very large chords, resulting in a small arc sometimes only having 3 chords in it. I need to have these arcs cut with chords placed around every 5 degrees of the arc. Is it possible to change the chord size Mach2 cuts in for these small arcs or is this beyond the capablility of the software? My motors turn at 8000 steps per rotation (2000 line encoders) and the ball screw pitch is 2 millimeters per rotation, so I have the mechanical resolution to do these cuts. I just need the cnc control to have the resolution. Tom Eldredge Yahoo! Groups Sponsor ADVERTISEMENT < roupweb/S=1705063697:HM/EXP=1079023982/A=2019528/R=2/SIG=1410msq5d/*http :/ad.doubleclick.net/jump/N3349.yahoo1/B1282054.27;abr=!ie4;abr=!ie5;sz= 300x250;code=18634;dcopt=rcl;ord=1078937582052152?> Click Here <;abr=!ie4;abr=!ie5 ;sz=300x250;code=18634;dcopt=rcl;ord=1078937582052152?> Click Here < pweb/S=:HM/A=2019528/rand=171350416> _____ Yahoo! Groups Links * To visit your group on the web, go to: * To unsubscribe from this group, send an email to: mach1mach2cnc-unsubscribe@... <mailto:mach1mach2cnc-unsubscribe@...?subject=Unsubscribe> * Your use of Yahoo! Groups is subject to the Yahoo! Terms of <> Service. |
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Robin Szemeti
On Wednesday 10 March 2004 16:51, davesmachines wrote:
Gentlemen,My understanding is that the display may show a chord, (because the display point is only sampled 10 times a second or so) but the actual machine will follow a true arc. One 'trick' you might like to try is to scale the part by 1000 and scale the motor tuning by 1000, effectivley your machine is now running in microns rather than mm, this can sometimes help with very small parts. You could also try slowing down some. Typically the trajectory planner plots a linear move for the next 1/1000th of a second or so, if your arc is only going to take 0.003 seconds to cut at your chosen feed speed, you'll get 3 short line segments. Slow it down and the situation improves. I'm not sure what Mach2 has set for the cycle time of the trajectory planner, so I cant really be sure if this is where your trouble lies. My advice is ignore the display, slow it down , and then examine the finished parts on a shadowgraph to see what is actually coming out. You might find that the stick/slip in your bearings is too great to allow you to acutally cut a 0.08mm radius. Having a motor/leadscrew arangement with 1 micron steps does not actually mean your router will move in 1 micron steps ... -- RapidCut CNC Technology CNC Plasma Cutter |
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Robin,
Thank you for taking time to respond to my question. I will study the movement more closely. I don't have the machine hooked up to the pc yet, but I do have the motors turning on the bench, and I should be able to tell whether the arcs are being produced by the x and y motors, running real slowly. I just assumed that the display tracked the actual tool path. Tom Eldredge display point is only sampled 10 times a second or so) but the actualmachine will follow a true arc.scale the motor tuning by 1000, effectivley your machine is now running inmicrons rather than mm, this can sometimes help with very small parts.planner plots a linear move for the next 1/1000th of a second or so, if your arcis only going to take 0.003 seconds to cut at your chosen feed speed,you'll get 3 short line segments. Slow it down and the situation improves. I'mnot sure what Mach2 has set for the cycle time of the trajectory planner, soI cant really be sure if this is where your trouble lies.the finished parts on a shadowgraph to see what is actually coming out. Youmight find that the stick/slip in your bearings is too great to allow you toacutally cut a 0.08mm radius. Having a motor/leadscrew arangement with 1micron steps does not actually mean your router will move in 1 micron steps ... |
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Robin,
Thank you for taking time to respond to my question. I will study the movement more closely. I don't have the machine hooked up to the pc yet, but I do have the motors turning on the bench, and I should be able to tell whether the arcs are being produced by the x and y motors, running real slowly. I just assumed that the display tracked the actual tool path. Tom Eldredge display point is only sampled 10 times a second or so) but the actualmachine will follow a true arc.scale the motor tuning by 1000, effectivley your machine is now running inmicrons rather than mm, this can sometimes help with very small parts.planner plots a linear move for the next 1/1000th of a second or so, if your arcis only going to take 0.003 seconds to cut at your chosen feed speed,you'll get 3 short line segments. Slow it down and the situation improves. I'mnot sure what Mach2 has set for the cycle time of the trajectory planner, soI cant really be sure if this is where your trouble lies.the finished parts on a shadowgraph to see what is actually coming out. Youmight find that the stick/slip in your bearings is too great to allow you toacutally cut a 0.08mm radius. Having a motor/leadscrew arangement with 1micron steps does not actually mean your router will move in 1 micron steps ... |
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Robin,
Thank you for taking time to respond to my question. I will study the movement more closely. I don't have the machine hooked up to the pc yet, but I do have the motors turning on the bench, and I should be able to tell whether the arcs are being produced by the x and y motors, running real slowly. I just assumed that the display tracked the actual tool path. Tom Eldredge display point is only sampled 10 times a second or so) but the actualmachine will follow a true arc.scale the motor tuning by 1000, effectivley your machine is now running inmicrons rather than mm, this can sometimes help with very small parts.planner plots a linear move for the next 1/1000th of a second or so, if your arcis only going to take 0.003 seconds to cut at your chosen feed speed,you'll get 3 short line segments. Slow it down and the situation improves. I'mnot sure what Mach2 has set for the cycle time of the trajectory planner, soI cant really be sure if this is where your trouble lies.the finished parts on a shadowgraph to see what is actually coming out. Youmight find that the stick/slip in your bearings is too great to allow you toacutally cut a 0.08mm radius. Having a motor/leadscrew arangement with 1micron steps does not actually mean your router will move in 1 micron steps ... |
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Tom, according to Art, this chord problem is only a toolpath drawing issue.
But i didn't verify yet. I uploaded some time ago a picture of the problem in the file section : mach2 exact stop problem.jpg Only visible with very small parts, and problem present since early versions of mach2. Best regards, Olivier. |
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