CNC PCB milling
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Yesterday I was doing copper removal with a 2mm end-mill, and several times when plunging it brought the motor to a complete stop. The motor recovered and continued in the x-y dimension at the new z.
So, obviously, the z-feedrate was too high. Is there a feedrate specific to the z-axis, or is it just the same as the general feedrate used by the x-y? I know there are velocity and acceleration parameters that can be different for x,y, and z. Do I control it using that instead of the seemingly general purpose "feedrate"?
Also, not sure why I experienced the problem this time and not previous times, as I was running the same g-code as before. Perhaps the end-mill acquired too much plastic gunk clinging to it? What's the best way to clean that stuff off?
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Yesterday I was doing copper removal with a 2mm end-mill, and several times when plunging it brought the motor to a complete stop. The motor recovered and continued in the x-y dimension at the new z.
So, obviously, the z-feedrate was too high. Is there a feedrate specific to the z-axis, or is it just the same as the general feedrate used by the x-y? I know there are velocity and acceleration parameters that can be different for x,y, and z. Do I control it using that instead of the seemingly general purpose "feedrate"?
Also, not sure why I experienced the problem this time and not previous times, as I was running the same g-code as before. Perhaps the end-mill acquired too much plastic gunk clinging to it? What's the best way to clean that stuff off?
@neverdie said in CNC PCB milling:
Is there a feedrate specific to the z-axis, or is it just the same as the general feedrate used by the x-y?
I ran some tests and proved that the general feedrate does apply to the z-axis. However, at the moment, the rest of the answer remains unknown to me.
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So, anyhow, maybe another way to check for job completion would be to monitor the DATA+ line from the USB cable feeding the WoodPecker controller. I'm guessing that if it shows no activity, then the job is done.
@neverdie said in CNC PCB milling:
So, anyhow, maybe another way to check for job completion would be to monitor the DATA+ line from the USB cable feeding the WoodPecker controller. I'm guessing that if it shows no activity, then the job is done.
I tested this, and it won't work. It seems that USB is constantly sending data frames (or something) regardless of whether actual serial data is being transmitted.
So, to take the idea any further, I'd have to tap into and monitor the Serial Rx pin on the Woodpecker atmega328p chip itself.
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@neverdie said in CNC PCB milling:
So, anyhow, maybe another way to check for job completion would be to monitor the DATA+ line from the USB cable feeding the WoodPecker controller. I'm guessing that if it shows no activity, then the job is done.
I tested this, and it won't work. It seems that USB is constantly sending data frames (or something) regardless of whether actual serial data is being transmitted.
So, to take the idea any further, I'd have to tap into and monitor the Serial Rx pin on the Woodpecker atmega328p chip itself.
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I tried measuring the current with an INA219, and wow, the current measures much higher than what my bench power supply had been telling me. Doing just auto-leveling consumes about 0.5a at 24v. Turning on the spindle and just carving air consumes over 1a at 24v. So, I'm guessing that actually routing PCB material (not just air) might well exceed the 2a limit of the INA219, at least in worst case scenarios where the bit may bind (or the feedrate too high) enough to slow the motor down.
So, I'll simply slam a couple more shunt resistors in parallel with it, and then it should be good for measuring up to 6 amps.
All this assumes that the Woodpecker contains a proper snubber diode, so that I don't get voltage spikes when turning the spindle off. Indeed, it looks as though the woodpecker does have an SS54 schottky diode installed just below the spindle power plug, and I'm guessing it is intended to serve that purpose.
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Virtually every screw on this CNC has come lose, so I'll be applying Loctite on all of them to hopefully avoid a repeat in the future.
I think there will just inevitably be some amount of vibration during the milling process (which obviously gets worse if there are lose screws). So, beyond Loctiting everything, I wonder if it makes sense to also rest the whole thing on some vibration dampers such as:
https://www.amazon.com/Anti-walk-Silent-Feet-Anti-Vibration-Machines/dp/B00536VQE0/ref=sr_1_8?ie=UTF8&qid=1518798934&sr=8-8&keywords=vibration+laundryI mounted our clothes dryer on these particular feet, and they work fantastic, at least for that purpose. Maybe not the right choice for this CNC though.
In the case of 3D printers, I notice that the Prusa I3 Mk3 sits on rubber feet, presumably for a similar reason.Anyone found good vibration damping feet for their CNC?
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Virtually every screw on this CNC has come lose, so I'll be applying Loctite on all of them to hopefully avoid a repeat in the future.
I think there will just inevitably be some amount of vibration during the milling process (which obviously gets worse if there are lose screws). So, beyond Loctiting everything, I wonder if it makes sense to also rest the whole thing on some vibration dampers such as:
https://www.amazon.com/Anti-walk-Silent-Feet-Anti-Vibration-Machines/dp/B00536VQE0/ref=sr_1_8?ie=UTF8&qid=1518798934&sr=8-8&keywords=vibration+laundryI mounted our clothes dryer on these particular feet, and they work fantastic, at least for that purpose. Maybe not the right choice for this CNC though.
In the case of 3D printers, I notice that the Prusa I3 Mk3 sits on rubber feet, presumably for a similar reason.Anyone found good vibration damping feet for their CNC?
@neverdie Crazy though it may sound, have you considered cheap engine/gearbox mounts (for vehicles) for the base frame onto some baseplate or U-mounts?
All excess energy in a machine has to be dissipated to maintain base accuracy, the more rigid the structure is, the more that undamped energy is transferred to somewhere to dissipate, the base is probably the easiest to resolve... -
@neverdie Crazy though it may sound, have you considered cheap engine/gearbox mounts (for vehicles) for the base frame onto some baseplate or U-mounts?
All excess energy in a machine has to be dissipated to maintain base accuracy, the more rigid the structure is, the more that undamped energy is transferred to somewhere to dissipate, the base is probably the easiest to resolve...@zboblamont
Not sure how that would be setup exactly.I'll try this:
https://www.amazon.com/dp/B00B84FNBS/ref=cm_sw_r_cp_ep_dp_H.1HAbVV7GBAFThat way the aluminum frame will be supported all the way around.
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@neverdie Out of curiosity, I thought most CNC machines used ball screws. That to me looks like a lead screw.
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@neverdie Out of curiosity, I thought most CNC machines used ball screws. That to me looks like a lead screw.
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@neverdie Good, then I don't feel so bad using plain 5/16 threaded rods in my build. I would assume that there is some sort of anti backlash where it connects to the carriage though, correct? There is not a lot of play in mine to begin with, but I am using two threaded rod coupler nuts with a spring in between on mine to take up any little bit of backlash it might have.
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@neverdie Good, then I don't feel so bad using plain 5/16 threaded rods in my build. I would assume that there is some sort of anti backlash where it connects to the carriage though, correct? There is not a lot of play in mine to begin with, but I am using two threaded rod coupler nuts with a spring in between on mine to take up any little bit of backlash it might have.
@dbemowsk said in CNC PCB milling:
I am using two threaded rod coupler nuts with a spring in between on mine to take up any little bit of backlash it might have.
Yes, mine has a similar spring, and I assume for the same reason.
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For now, I've settled on this hardware for monitoring the CNC when I'm not in the garage:
The bottom unit monitors the current that the CNC consumes to determine whether or not the CNC is active. When the CNC transitions from active to inactive, it sends a wireless signal to the battery powered node (above it in the photo), which rings a buzzer to let me know that the CNC has finished.Since my 3D printer that's on order is also 24 volts, I think there's a good chance this hardware may work with it as well. :)
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The sorbathane helped a little, maybe, but there's still a lot of vibration. Found this video on how to dampen a 3D printer. It has some Interesting ideas on how to dampen vibrations:
https://www.youtube.com/watch?v=OnfYA5QLA84The video is aimed at Mk3 i2 owners, but I imagine similar tricks might work for a small CNC such as that discussed on this thread.
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Based on a file test, it appears that the smooth rod is not hardened. Not sure how much improvement I might see if I upgraded to hardened.
Unfortunately, this thread seems to have fizzled out....
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Looks as though upgrading to hardened and chromed rods is fairly inexpensive:
So, less sagging in the middle, and maybe less vibration also.
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Looks as though upgrading to hardened and chromed rods is fairly inexpensive:
So, less sagging in the middle, and maybe less vibration also.
@neverdie As part of my CNC build, I have gotten 8mm rods that I pulled out of old scanners and old ink jet printers, I guess I never checked to see if they were hardened or not. How much of a difference would it make?
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@neverdie As part of my CNC build, I have gotten 8mm rods that I pulled out of old scanners and old ink jet printers, I guess I never checked to see if they were hardened or not. How much of a difference would it make?
@dbemowsk Well, let's put it this way: the set screws on my rods had come lose, so I noticed considerable sagging when the spindle got to the middle of the rods. When I tightened up the set screws, a lot of that sagging went away. So, I think that means the spindle is now, in part, being supported by tension.
Hardened rods should flex less. I'm sure there are formulas that could tell you by how much. Also, there are different degrees of hardness.
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On the other hand, according to this thread:
http://forums.reprap.org/read.php?1,113177
deflection isn't affected by hardness. I had thought hardened would be stiffer.
