Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: PW8697 on January 03, 2016, 05:56:48 PM
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Hey all,
In the process of fine tuning and working out some issues with my Taig mill. Running a PC with a 3.16Ghz processor with 4Gig RAM, connected to a Leafboy77 (http://leafboy77.com/index.php/en/) USB motion board, connected to 3 each 2m542 stepper motor controllers, then connected to the 3 570oz/in stepper motors. Also installed is a 48VDC power supply.
I am curious as to the speed at which other owners have their Taig mills running. With backlash enabled, I am pretty much limited to 12in/min. Without backlash enabled I can jog at 25. I really would like to be able to machine close to that speed with backlash enabled. I only have backlash compensation enabled for Y at .003". Is backlash compensation a inhibiting factor?
Questions are, I have tried to follow the 50/50/50 rule talked about before with regard to backlash compensation. Took the middle of the two extremes of .050 and .005 for a setting of .0275 for the shuttle speed. Backlash speed set at 50%, and motor speed set at 15ipm. Again, the mill without backlash compensation enabled and speed set higher can traverse at about 23-25ipm. Again, I would like to be able to approach that with the backlash enabled. Assumed that with these motors, they would have the torque to do nearly anything I needed.
Also dealing with another abnormality. 20% of the time when jogging X and Y, X will sometimes slow and chatter, as if losing steps. I can let go of the Y arrow key and X will still chatter. I can also toggle off and on the Y arrow keys and stop and start Y at will all the while X is still chattering. Sometimes the roles are reversed, so it doesn't only affect X. I can run X and Y separately and never have a problem. Why does it happen when they are operated together sometimes? It can be a real pain especially when the part is zeroed and I am just moving the spindle out of the way or changing tools or moving to begin a tool touch. If I hear the steps being lost, I have to backtrack, waste time and reinstall the edge finder and rezero.
Would running CV help the issue? Also what effect does the kernel speed have on mill operation?
Ultimately, I would like to get rid of the stepping issue, and increase my machining speed.
Let me know what you all think.
Pete
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Sounds like your power supply isn't keeping up. Monitor the power supply voltage during a move with both axis. If it is a switcher it likely be the problem. A linear supply is actually better for driving steppers as they can handle brief overloads better and the large filter caps absorb the back emf better when motors decelerate.
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Gary,
Hooked the multimeter up to the power supply, am getting a solid 47.8V out of it while running the mill, so no problem as far as power.
Pete
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I'm sorry if you have seen this post before under a different topic, but I realized that this post is more relevant under this topic....
I have been struggling with getting my Taig MicroProto mill running reliably. It seems that every time I go to use the mill, new problems arise. The first time that I was able to get the unit running, it worked great for about a day. The next time that I went to use the mill, I noticed that the inline fuse in the controll box failed each time I turned on the machine. I thought this might suggest a short somewhere in the circuit, but after having someone with an electrical background look at it, we couldn’t see anything that was wrong. Does anyone know why this is happening every time I turn on the machine? Is this a voltage issue? I tried adjusting the potentiometer but nothing seems to make a difference. Could the motors be bad and causing a short?
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Hi,
I think Tweakie replied in another post and suggested inrush current. Try his recommendation of fitting slow-blow
fuses.
Switchmode power supplies are notorious for inrush current, Gary has suggested a linear (transformer/rectifier/capacitor)
supply. They tend to be more robust and forgiving.
Craig
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Hi,
correct me if I'm wrong but don't Taig mills have 1/4 or maybe 5/16 threaded leadscrews?
If I'm correct and recall that the screws are about 20 TPI then even to achieve 50 ipm will require you spin those
things at 1000 rpm. Your chances of doing that successfully are very poor.
Craig
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Hi,
I've found some advertising material on your mill and it suggests the leadscrews are 1/2 inch 20 TPI. The extra diameter will mean you could spin them
fast without them whipping but the pitch means you'll have to spin them very fast to get fast traverses.
Getting your machine to work well with its existing leadscrews will result in a very useful machine, well balanced with respect to speed/power and rigidity.
To make the alterations necessary to make it fast, say new leadscrews or ballscrews, would be quite extensive and the machine would lose its balance,
that is to say it would be fast but not powerful enough to go fast or rigid enough to control the extra cutting forces even if you did.
Craig
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If your 48vdc power supply is a switcher, they have very high inrush current on startup, so a slow blow fuse would be appropriate to fix that problem.
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Those motors are way too big for that machine and will have a hard time running above 12 ipm reliably. On mine I downsized the motors to something like
125 oz and then I could rapid at 50 ipm and machine at 25 ipm+ IIRC. Don't forget that with 20 TPI screws you will have a ton of torque even with a small motor.
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The only way a bigger motor would actually run slower is if it has a much higher inductance than the smaller motor. The bigger motor will have more torque at the higher speeds unless the the inductance causes it to fall off very fast. My 860 in/oz steppers turn 1500 rpm reliably without missing steps. They are low inductance and I have a 68 volt power supply.
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Hi Gary,
What drivers are you using? Cheap ones don't work as well as good ones.
Unless he is using high quality stepper drives with mid range antiresonance or whatever it is called it will be very hard to get his motors to run 1500rpm while moving a machine and all the accel and deccel that entails. My guess and it is only a guess is that the 48 volts is way too low for his motors. The only way to tell would be to know what his inductance is.
Questions that need to be asked are;
1. what version of Mach is he running? 066 is not recommended.
2. what resolution are the drives set to? Anything beyond 10 microsteps is overkill. 200 steps/rev x 10microsteps x 20 tpi = 40k steps/inch. way overkill on a Taig.
3. What is the motor inductance in mh? This way we can determine the proper voltage.
4. What is the acceleration set to. Too much accell is the easy way to loose steps.
5. If there is a setting for BC speed, what is it set to? since the problem is mostly with BC enabled, try cutting it in half of what it is set too.
More to come as I think of it.
Mike
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Hi,
I've recently posted about having issues with the inline fuse in the control box on my taig mill. After trying slow blow fuses in place of regular fuses, I have eliminated my problem of the fuse blowing in this place. ;D
Now, I am having issues with the main 2a fuse. I have discovered after trying different things that the main 2a fuse only blows when any of the stepper motors are plugged into the x-axis port on the machine. The x, y, and z stepper motors can be plugged into either the z or y axis and work properly, but once you plug a motor into the x axis the main fuse instantly blows. Does anyone have any suggestions on why this could be?
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Hi,
sounds like the X axis stepper driver is faulty. At a guess it sounds like the current sense PWM has gone faulty and the full voltage of the supply is being
applied to the stepper WITHOUT the moderation of controlled PWM. That'll pop a fuse for sure!
Craig