Sunday, February 5. 2006
Ever since I started my mill for the very first time, I knew the spindle motor was gutless. 1/8 HP is gutless. Just to give you an idea of how mindbogglingly gutless it is, consider that the motor was too weak to spin the spindle with no load at the highest pulley ratio until the bearings warmed up. If I needed 10K RPM (for PCB work, for example), I had to run it at the second highest pulley ratio for 10 minutes before switching to 10K RPM. In fact, taig knows that those motors were waaay too weak, and now they ship their mills with, I believe, 1/4HP motor. This is not super-powerful by any stretch of imagination, but that's twice the power that I had when I bought my mill.
Having such a weak spindle is painful. I've stalled it more times than I want to admit.
No more of that! Ladies, and gentlemen, let me introduce a brand new surplus DC motor! 2.5 HP intermittent duty at 130 volts, 1.5 HP continuous duty at 95 volts. The controller that I bought along with the motor does not quite output as much current as the motor might want, so it is not running at the rated 1.5 HP, but it sure beats 1/8 HP! Also, no more pulley changes - now I have a true variable speed spindle. And I've added a Hall Effect sensor to measure RPM.
Plan of action. I ordered the motor and the controller online at the surplus center. The motor weight is very similar to the 1/8HP stock motor that came with the mill, eliminating the need to do any magic with springs / gas struts / counterweights, or whatever else people sometimes need to do to keep the weight on the z axis reasonable. The size was also similar, so it actually fit in my enclosure (a tight fit, but a fit nevertheless). And I could use the same mounting plate and belt that I used with the original motor. Of course, it wasn't quite a drop-in replacement. First, I needed to adapt the mounting plate a little because I could not drill the holes in the motor in the right places to match the plate. Also I needed to add a spacer between the motor and the plate. In addition to that, the motor had a fairly large shaft (.675", I believe). I did not want to bore out the pulley that came with the 1/8 HP motor, because I was not entirely sure that my conversion idea was not fundamentally flawed, and would not fail for one reason or another. So, I needed to make a custom pulley. On the one hand, that's a lot of extra work; on the other, making something from scratch gives you a lot more freedom. I wanted to make the pulley that is just large enough to run the spindle at 10500 RPM when the motor is spinning as fast as it can go.
DC motor testing. But first I wanted to see if the surplus treadmill motor spins at all, and whether it would work with the controller I bought. It turns out that yes, it does spin, but no, it does not spin like I'd expect it to. After powering up it revs up quickly and then coasts back down, followed by a jolt of energy to rev up again, and coast back down, rev up, slow down... Very peculiar. If I started the motor from zero and slowly increased the speed, it would keep running smoothly, but I only needed to touch the shaft to disturb the delicate balance and it started misbehaving again. Obviously, the compensation that is built into the controller to keep the motor running at a constant speed was working too well. It might have worked perfectly if the motor was loaded, but when the motor is not loaded, that "IR compensation" feature overcompensates all the time. I ended up having to turn it off before the motor started running like I'd expect it to. Oh, well... no huge loss, as far as I am concerned. If somehow the RPM sags too much on heavy cuts, I can always adjust it by hand.
Tachometer circuit. With the motor running, I was happy to start designing the new pulley. But how large should it be? Good question! In order to calculate that I needed to know the maximum RPM of the motor. The maximum RPM was printed on the side, but that's either for a 130V or 95V. I was not sure which one, and I had a 90 volt supply anyway, so I needed to perform a small experiment. I do not have a
tachometer, but I was planning to eventually add a spindle RPM sensor and use mach2 software to measure RPM anyway. So this was a good place to start. I bought an OH360U Hall Effect Sensor from Digikey and a small .2" diameter, .061" thick 10K+ gauss neodymium magnet from Radioshack (the packaging says 1/8" magnet, but neither the diameter, nor the width are anywhere close to 1/8", so I am not sure what they are talking about). An old audio connector and some hot glue were used to make a rigid mounting tab that holds the sensor in place. I used a regular phone wire to connect all that back to the controller box. I needed only 3 wires, so you can see that the 4th, green, is dangling unused in the pictures. The 5V from the power supply inside my controller box is a few hundredths ov a volt higher than the 5V I measured on the parallel port. I did not want to exceed the voltage of the parallel port, so I used a couple of resistors to make sure that the voltage stays within the acceptable range.
Actual Motor RPM measurement. Now that the sensor was ready, I had to measure the true RPM of the motor. In order to do that I made a small wooden plate with two holes - one in the center, a little bit smaller than the motor shaft diameter, and the other - close to the edge, just large enough to press-fit a small magnet. After pressing the magnet into the plate and mounting the plate on the motor, I placed the assembly into my relatively bullet-proof mill enclosure. I ran the motor at maximum RPM for a few seconds, accelerating and decelerating several times to make sure the magnet does not fly away. I did not want to find out if loose items flying off of a 6K RPM motor hurt. I think they do. Everything seemed sturdy. I set the motor at low RPM and brought the hall effect sensor close to the spinning magnet. Hooray! I could see mach2 counting RPM, and the value was pretty close to what I had guessed visually. I increased the RPM to the maximum and recorded what mach2 showed. I repeated that several times. All measurements were within 100 RPM of each other. Nice! Now we know the true maximum speed of the motor! I can't remember the exact number anymore, but it was around 6K RPM.
Custom pulley. Knowing the maximum RPM allowed me to calculate the pulley ratio needed to drive the mill at 10.5K RPM. I wanted to use the longest groove possible on the spindle pulley. And yet I also wanted to be able to use the original original motor mounting plate and belt. If I chose a groove that was too large, my pulley would have needed to be large as well, and the two pulleys might not even fit inside the tiny v-belt. On the other hand, if I chose a groove that was too short, there would not have been as much surface contact between the pulley groove and the belt as I wanted, reducing maximum power transfer. It looked like I could use the third 'fastest' groove, but after doing the math I found out that the pulley would need to be larger than what I could turn on my taig lathe. Oh, well... I guess, we'll have to settle for the second groove and a smaller pulley.
Turning the pulley was straight-forward. I used a compound slide set at 30 degree angle,
After making the groove I drilled and bored the center hole without removing the pulley
The other (spindle) pulley also needed a little modification. I drilled a shallow blind 0.200" hole in it for the magnet. When mounting the spindle pulley back on the spindle I heated the pulley with a gas torch, and I think I might have overheated it a little. The magnet appears to be a lot weaker than it was during my earlier tests. I guess, neodymium magnets are very sensitive to heat. Oh, well... lesson learned. But it still works well enough.
Connecting it all together. The last thing left was to make a small bracket that will
Testing. First I checked the RPM range with no load. My new range is between 200 RPM and 10700 RPM (I must've made a small error when calculating pulley ratios, so I did not get exactly 10500 RPM). To test my new setup I took a 0.1" deep cut in 7075 Al with a 1/4" 2 flute endmill at 4300 RPM and 8.6 IPM. The indicated RPM almost did not drop at all. Nice! I could not do that before. How about 0.2" deep? That worked well too. I am not sure that my setup was rigid enough to take that deep a cut, so I had some excessive vibration, but the spindle showed no signs of slowing down. How about increasing RPM to 10K RPM and running it at 20 IPM? A little loud, a bit more vibration than I would have wanted, but it did cut with confidence. Nice! Now I am probably more limited by how rigid my mill is than by the power of my spindle. I like that.
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Nice write-up! I use that same motor on my Taig lathe. The only thing I miss about the (GE induction) motor is how quite it was. Did you have to do anything to the spindle on your motor? (My motor had a worm on the end to drive a tach. that I had to cut off.)
No, I did not have to change anything. It has, I think, between 1 and 2 inches of .675" diameter shaft followed by some left-handed thread. I mounted the pulley on the round shaft section, and just left the left-handed thread unused - it does not obstruct anything, so it does not bother me at all.
I have recently bought a lathe [chinese] 11"swing by 30" 1.1kw dc motor varaible speed. brush
This is the first time I am dealing with a dc motor,I have always used ac motors.
I can stall this motor by putting both hands on the chuck at,50 rpm,200,rpm,and 500 rpm.
The motor will want to "speed up" and the dial shows that too but ,keep applying presure and it stalls.
Am I expecting to much? I cannot "fathom" dc.
I run it on the "low" setting most of the time but I can still stall it and blow my 10amp fuse.
What am I doing wrong? I am NOT electrical .
If you are blowing a 10A fuse, you are obviously pulling more than 10A, at least for a short time. This can be due to a number of reasons. Is your controller capable of driving your DC motor? Is it PWM? What's the feedback mechanism? Does the fuse blow when you stop the motor by hand? The current is the highest when the motor is loaded, and is at really slow (or zero) RPM. By stalling the motor you could be pushing the motor beyond what it's designed for.
On a different, but related note, if you were to think of your motor and power supply as a simple DC circuit, there's more than just current that you'd have to take into account. If you have a 1.1kw motor, and a 10A fuse, you'd have to have at least 110V to drive the motor at full power before the fuse blows. Is the power supply capable of supplying that much? It's no small feat.
I recently purchased two of the Argord motors to use on my Taig micro-mill and my Lathemaster 8x14 lathe. However, I can't seem to find any wiring diagrams for the motors, and have very little experience in this area. I will be using a Danfoss Cycletrol 15O controller, and am not sure how to connect the motor's 4 wires despite hours of web research. All of the articles and diagrams I've found deal with motors with two wires.
Can you provide some guidance, or direction to a site that can?
I finally took the motor apart yesterday, and the solution became obvious, especially given the "thermal switch" verbiage on the motor label. The two blue wires are for a thermistor that provides protection against overheating.
Once I figured that out, I simply connected the blue thermistor wires in series to one of the wires for the power circuit (using the connectors that were already on the wires). In hindsight, I shouldn't have had to take the motor apart to deduce the solution as I've been through the thermistor issue with home appliances.
However, one of the controllers I purchased has separate terminals for "field" wires, which together with my lack of experience with dc motors introduced just enough confusion to complicate my reasoning process. While I know these Argord motors are permanent magnet rather than wound, and my online research indicated field connections should therefore not be required, I didn't want to end up destroying a motor or controller.
I just put one of the Argord motors onto my Taig lathe and am about to get another one for the mill. I'm using one of the Surplus Center controllers (#11-2449) that has no field outputs-- just Blue and Red (switching those through a DPDT switch allows reversing) and it works fine. Thanks for the info on the blue wires; I just left them loose.
FWIW, to cut the custom pulley, I bored a piece of 1.5" AL bar to the spindle diamater and then just drove a 60-degree threading V-bit from a 'brazed carbide" lathe tool set straight in. Not the prettiest thing, but it's working great after a little cleanup.
i want to purchase a taig machine on ebay. what was the motor size and model that you bought from surplus center. i like the machine but that spindle is gonna be a problem. the item is listed on ebay http://cgi.ebay.com/Taig-cnc-mill-4-axis-milling-router-engraver-machine_W0QQitemZ260083457936QQihZ016QQcategoryZ12584QQrdZ1QQcmdZViewItem . let me know what your thought are and any more ideas you might have. keep in mind that i know only a little about motors and wireing.
thanks for your time
Surplus center has 2.5 HP motors for both 110 and 220 volts. I don't have the exact part number, but those are treadmill motors, run for under $40 and are quite lightweight.
I wanted to say thanks for the inspiration to use one of these motors and a Dc controller. I bought mine from the surplus Center. I have limited the voltage to 95 volts and just run a test sample. I was amazed.. normally with the 1/3hp motor the Taig mill came with I was restricted to 1mm deep cuts in aluminium and 150mm min. I ran the spindle at 4300 rpm at 95v and did 2 test samples, milling with 1/4" cutter to a depth of 15mm at 200mm min. The first part was a simple goround a square in 2mm increments which it managed fine. The second test was a pocketed circle 15mm deep and that was in 3mm cuts. Again it managed it with no fuss. The motor might need a cooling fan on large jobs though.
what input did you use and how did you configure Mach 2. I am using Mach 2 and would like to reference spindle speed
Input for the tachometer? I can't remember off the top of my head which one I used -- there are several inputs available on the parallel port. Some are dedicated input pins; others tan be used for input or output. I picked a dedicated input one. This is well documented in multiple places on the internet.
The input is either pulled toward V+ or ground depending on whether the sensor is next to a magnet or not. Mach2 can read such signal. You can configure that in the "Ports and Pins" menu.
My answer is pretty general, but I am not entirely sure what exactly you are asking. If you rephrase your question to be more specific, I may be able to give you more info.
I have read your post several times.
And was wondering what you used for the PWm controller?
you never mention that end of it. as well as if you have it tied into
Mach for speed control
Also When using the Dc motor. how did you overcome the "Soft start" ie if your using some treadmill controller they are not happy to start at any speeds other than low.
Also, great job!
Ah, right, the PWM controller. The motor came with one. All I had to do was add the trivial circuit mentioned above to get the feedback back to the computer.
The controller is operated manually; I only read the actual RPM from mach3.
The original plan was to start/stop and control the RPM through the computer as well, but in the end it did not work too well. The RPM is never constant as the computer and the controller are in a constant struggle -- the computer sees that RPM is too low, cranks it up a notch, the controller obeys, but does a bit too good of a job, so RPM goes up above the desired limit, the computer senses it, tells the controller to slow down, the controller slows down too much, the computer recognizes that, tells it to speed back up, and so on. Eventually things settle down. But once you actually start cutting, especially if the bit is making heavy non-continuous cuts, the load on the motor changes, and the system becomes unbalanced again. Annoying, poor surface finish and more stress on all the parts. I am sure I could do something to "dampen" that effect a bit, but I never had the motivation to. I do not mind setting the speed by hand since I do not have to change it very often at all. Much simpler, and very reliable.
There is no "Soft Start" with the controller I have. It did not come with all that "soft start" logic. The controller speed is controlled by resistance between two connectors on the board. Real treadmills probably have some fancy logic that starts with high resistance, and changes it slowly to do the "soft start". Since I replaced all of that extraneous circuitry with just a single potentiometer, there was never a problem. If I turn the motor ON when the controller is set to full RPM, the whole milling machine cabinet jumps a bit.
Thanks for the reply.
I found a treadmill setup thr motor label says 180v DC with Amp draw of 17amps and a max speed of 9700.
When i test it with the controller it cam with it maxes out at just over 100V with a draw of perhaps 1.5 amps and the rpm well I didnt get that far to to make a quick setup to read in Mach. I have one I just need to make a portable one. It seems to me the motors rpm is quite low at full throttle. (at least for what the controller can supply.) I would hate to spend much time retro fitting it then find its not got enough UMPH! if you now what i mean. I looked at controllers seems if I wanted to get the max potential of this motor I would need to goto 220V
then I could ramp up the supply voltage. I also was quite skeptical about Mach3's ability to control the speed as the controller it came with is quite touchy. I was able to bypass the "Soft start" thats inherent to my controller. So on your setup
what is the Max motor rating in relation to your controller and what does it max out at?
I no longer remember the numbers. The motor is rated at 1.5HP, and I tested it to about 1 HP. Both the motor and the controller get a bit warm, but are able to cope with the heat well.
This is a 110V motor. 1.5 HP translates to a bit over 1 KW, I think, so that would come out to roughly 10A with no losses. Don't know what the losses are, but presumably somewhere between 0-50%. The circuit breaker is 20A, and has not tripped, even though the motor "dims the lights" a bit when starting. Not very numerical, I know, but that should give you an idea. The controller is able to pump quite a bit of juice to the motor.
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