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General Mach Discussion / Cut parts are wrong size, CNC knee mill problem
« on: July 25, 2012, 10:34:34 AM »
Hi Guys,
I'm having a similar problem to the user in this thread: http://www.machsupport.com/forum/index.php/topic,21962.10.html
My setup:
Acer 5hp knee mill
Brushed servos
Granite Devices Servo Drives and interface card
This is my second cnc conversion but my first servo setup. I have brand new ballscrews in the machine, Hiwin ground screws with preloaded nuts.
I've set my travels with a mitutoyo digital dial indicator with accuracy of 0.001mm. My travels are accurate to within 0.002mm and it doesn't matter if it's 1mm or 100mm of travel. I have around 0.028-0.032mm of backlash on both axis that is 100% consistent.
The problem that I have is that my parts after being programmed in Solidcam were cutting outside diameters perfectly, but inside diameters were always 0.2mm too small. It didn't matter if it was a hollow circle, square, rectagle etc.. always 0.2mm. I adjusted feeds to super fast and super slow and always the same result. I rechecked the travels with the set steps function and it was always the same as mentioned above. I also tried cutting parts that were 2 inches thick, in 5mm step downs to see if the machine was missing steps as there woudl be ridge marks but it always cut perfectly. It doesn't make a difference if I cut 5mm deep, 12mm deep, 20mm deep, at 100mm a minute or 700mm a minute, the results are always the same. The bit has always been a new 3 flute, 0.5" diameter (12.7mm) carbide that just eats aluminum like butter.
Last night my dad suggested that I use the onboard wizards to cut a circle as I've used them on my smaller mill and it always generates code that cuts to size. The same problem occured, when I cut a circle or a circular pocket the diameter is always 0.2mm to small. So this has eliminated the cad/postprocessor and it has something to do with Mach3 but for the life of me I have no idea what could be wrong. There is no play in the table, no play in the angular bearings that support the ballscrews, the ballscrews are mint and 100% repeatable with 0.03mm of backlash, the servo drives are set to stop the machine if there is more than 30 encoder errors from target to destination (4000 encoder inputs per revolution, that's around 0.75% error) and based on my observation it never exceeds 15 errors.
Any ideas? I'm thinking of going back to the same version of Mach3 that my benchtop mill has but I don't know if I will be able to find it as it was installed 7 years ago.
Cheers,
Sebastian
I'm having a similar problem to the user in this thread: http://www.machsupport.com/forum/index.php/topic,21962.10.html
My setup:
Acer 5hp knee mill
Brushed servos
Granite Devices Servo Drives and interface card
This is my second cnc conversion but my first servo setup. I have brand new ballscrews in the machine, Hiwin ground screws with preloaded nuts.
I've set my travels with a mitutoyo digital dial indicator with accuracy of 0.001mm. My travels are accurate to within 0.002mm and it doesn't matter if it's 1mm or 100mm of travel. I have around 0.028-0.032mm of backlash on both axis that is 100% consistent.
The problem that I have is that my parts after being programmed in Solidcam were cutting outside diameters perfectly, but inside diameters were always 0.2mm too small. It didn't matter if it was a hollow circle, square, rectagle etc.. always 0.2mm. I adjusted feeds to super fast and super slow and always the same result. I rechecked the travels with the set steps function and it was always the same as mentioned above. I also tried cutting parts that were 2 inches thick, in 5mm step downs to see if the machine was missing steps as there woudl be ridge marks but it always cut perfectly. It doesn't make a difference if I cut 5mm deep, 12mm deep, 20mm deep, at 100mm a minute or 700mm a minute, the results are always the same. The bit has always been a new 3 flute, 0.5" diameter (12.7mm) carbide that just eats aluminum like butter.
Last night my dad suggested that I use the onboard wizards to cut a circle as I've used them on my smaller mill and it always generates code that cuts to size. The same problem occured, when I cut a circle or a circular pocket the diameter is always 0.2mm to small. So this has eliminated the cad/postprocessor and it has something to do with Mach3 but for the life of me I have no idea what could be wrong. There is no play in the table, no play in the angular bearings that support the ballscrews, the ballscrews are mint and 100% repeatable with 0.03mm of backlash, the servo drives are set to stop the machine if there is more than 30 encoder errors from target to destination (4000 encoder inputs per revolution, that's around 0.75% error) and based on my observation it never exceeds 15 errors.
Any ideas? I'm thinking of going back to the same version of Mach3 that my benchtop mill has but I don't know if I will be able to find it as it was installed 7 years ago.
Cheers,
Sebastian