jacampb2
03-23-2009, 03:00 AM
Last year when I initially brought my CNC B'port S2 back from the dead, it was suggested by John Stevenson and others that I spend the money and replace my factory steppers. The reasoning being that the old steppers were likely never adequate for the job, and being about 30 years old only made the matter worse as the permanent magnets degrade with time.
Anyhow, they have served me well for over a year. I have recently been doing a lot of high(er) speed machining of plastic, and am starting to see problems with my Y axis. I had the motors originally tuned with a acceleration of 8 in/sec/sec(I think this is how Mach lists the units?) and a top speed of 120 IPM. It did fine with normal machining, and rapids were fine, no real issues. Over the last year, it began to very rarely cog the steppers, most of the time while manually jogging it into position. I Slowed the rapid speed to 100IPM, and it never had another hicup. When I started doing a lot of this acrylic engraving, I started to have problems again. The machine would make it though a ~9x4 piece, about 30 minutes of machine time with no issues. The problems showed up when I started running multiple parts on a single sheet of acrylic. After running for 45 minutes or so, it will occasionally loose steps in the Y axis. Normally when it is traversing at rapid speeds in an X/Y direction simultaneously. It makes it to the X destination, but not the the Y. This of course screws up the whole sheet.
So, I slowed the acceleration in the Y axis down to 6 or 7, I can't remember now off the top of my head, but since I slowed the Accel down, it hasn't given me any trouble in the last five or six runs of engravings. I still feel the need to babysit it though, to make sure I am there to stop the program is it looses steps.
Since it seems to be more related to how long the mill has run, and presumably how warm the motors are getting, my question is, is it time to replace the steppers with new units? The engravings have a lot of small moves, so a lot of the time the mill never hits the target feedrates because the acceleration is set so low. It is typically within 10% or so of the target feed rates, but I would love to be able to get it machining even faster. Will new 1200oz or so steppers help at all with that? My feed rates in the acrylic are typically around 50 Ipm. My budget would currently allow me to replace the X and Y steppers, I could swing the Z too, but it has not had any problems. I am just wondering if I might be pissing money away on them. Should I save longer and go servos?
TIA,
Jason
Anyhow, they have served me well for over a year. I have recently been doing a lot of high(er) speed machining of plastic, and am starting to see problems with my Y axis. I had the motors originally tuned with a acceleration of 8 in/sec/sec(I think this is how Mach lists the units?) and a top speed of 120 IPM. It did fine with normal machining, and rapids were fine, no real issues. Over the last year, it began to very rarely cog the steppers, most of the time while manually jogging it into position. I Slowed the rapid speed to 100IPM, and it never had another hicup. When I started doing a lot of this acrylic engraving, I started to have problems again. The machine would make it though a ~9x4 piece, about 30 minutes of machine time with no issues. The problems showed up when I started running multiple parts on a single sheet of acrylic. After running for 45 minutes or so, it will occasionally loose steps in the Y axis. Normally when it is traversing at rapid speeds in an X/Y direction simultaneously. It makes it to the X destination, but not the the Y. This of course screws up the whole sheet.
So, I slowed the acceleration in the Y axis down to 6 or 7, I can't remember now off the top of my head, but since I slowed the Accel down, it hasn't given me any trouble in the last five or six runs of engravings. I still feel the need to babysit it though, to make sure I am there to stop the program is it looses steps.
Since it seems to be more related to how long the mill has run, and presumably how warm the motors are getting, my question is, is it time to replace the steppers with new units? The engravings have a lot of small moves, so a lot of the time the mill never hits the target feedrates because the acceleration is set so low. It is typically within 10% or so of the target feed rates, but I would love to be able to get it machining even faster. Will new 1200oz or so steppers help at all with that? My feed rates in the acrylic are typically around 50 Ipm. My budget would currently allow me to replace the X and Y steppers, I could swing the Z too, but it has not had any problems. I am just wondering if I might be pissing money away on them. Should I save longer and go servos?
TIA,
Jason