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Manual Operation After Cnc Conversion
- Thread starter grepper
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- Jan 8, 2016
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- 171
Thanks once again, Jim. I really appreciate your replies. I don't want to make any expensive mistakes deciding what to get (been there, done that!). I've done so many hours of research trying to get up to speed it's actually somewhat exhausting. Lot to learn! I want to do it right the first time.
Grepper:
The thing you have to get your head around (if you go with the Nema23 steppers that you have referenced in your other thread) - is the fact that the dual shaft versions only have 1/4" or 6mm shafts coming out the back end... Not much to hang a hand-wheel on.
Another thing to remember is that the handwheels should be removed when you are operating in NC - they add significant inertia to the system.
The thing you have to get your head around (if you go with the Nema23 steppers that you have referenced in your other thread) - is the fact that the dual shaft versions only have 1/4" or 6mm shafts coming out the back end... Not much to hang a hand-wheel on.
Another thing to remember is that the handwheels should be removed when you are operating in NC - they add significant inertia to the system.
- Joined
- Jan 8, 2016
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Thanks, Jim H.
Have you done this? Is that an actual problem or just something to be aware of?
I can machine my own handles. I'm surprised that would add significant inertia! Hadn't thought of that. Really? The motors are moving the whole table, etc. Why would an aluminum handle add so much inertia?
I haven't thought the whole thing through, but I was thinking I could put a keyway in the shaft and use a set screw. That would be quick and easy to remove.
I really like the idea of not giving up on manual operation. It makes me wonder why I never see it done.
Have you done this? Is that an actual problem or just something to be aware of?
I can machine my own handles. I'm surprised that would add significant inertia! Hadn't thought of that. Really? The motors are moving the whole table, etc. Why would an aluminum handle add so much inertia?
I haven't thought the whole thing through, but I was thinking I could put a keyway in the shaft and use a set screw. That would be quick and easy to remove.
I really like the idea of not giving up on manual operation. It makes me wonder why I never see it done.
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- Feb 8, 2014
- Messages
- 11,144
Think flywheel attached directly to the motor shaft vs. the table with a screw thread moving it.
It is done, my machine can convert between manual and 2 0r 3 axis CNC in seconds. But you are correct, it is not that common. I don't have to take off my handles, but the cranks fold up. I also have big DC servos, so the inertia of the handles is not really a factor.
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- Jan 8, 2016
- Messages
- 171
Fold up handles. Good idea.
Jim, your mill would crush mine. But I can only wish...
I'm doing a LMS HiTorque 3990. Been looking at 425 oz Nema 23 motors. Is that enough holding? What about a Nema 24 400 oz? I'm a little surprised that the torque of these motors is so close to requirement that that the added inertia of the handles would effect it so much! This is great information! Thanks. Stuff I would not have thought of.
I'm going to use the CNCFusion kit #5 conversion. Would Nema 24 motors fit their motor mounts?
Do I need to rate the power supply by the combination of all three motors. Say each motor is 3.5A, would a 10A supply be enough? I'm guessing that full torque on all three motors at the same time is not likely.
Sorry, so many questions! The more I learn, the more questions I have. It seems endless. It's frustrating!
Jim, your mill would crush mine. But I can only wish...
I'm doing a LMS HiTorque 3990. Been looking at 425 oz Nema 23 motors. Is that enough holding? What about a Nema 24 400 oz? I'm a little surprised that the torque of these motors is so close to requirement that that the added inertia of the handles would effect it so much! This is great information! Thanks. Stuff I would not have thought of.
I'm going to use the CNCFusion kit #5 conversion. Would Nema 24 motors fit their motor mounts?
Do I need to rate the power supply by the combination of all three motors. Say each motor is 3.5A, would a 10A supply be enough? I'm guessing that full torque on all three motors at the same time is not likely.
Sorry, so many questions! The more I learn, the more questions I have. It seems endless. It's frustrating!
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I'm just a professional engineer (mechanical) with 30+ years of design/manufacturing/commissioning experience with industrial machinery that used hydraulic and AC servos for some applications.
And I've been crunching the numbers for my own conversion.
So I plugged some numbers into my model.
Suffice to say, a 6mm thick x 100mm OD aluminum disc at motor speed has as almost 8X the inertia as a 100kg mass load driven with a 5mm pitch screw.
And a little over 3 times the inertia of the Nema23 motor I have in my spreadsheet.
It effectively doubles the inertia of the whole Nema23 system as I have it modeled.
The reality is, while machining, it will likely never be an issue. But it will definitely become a limiting factor when you try to go faster with a stepper system, and you don't know when you've lost a step or two.
It's easy enough to remove the handles, and basically enable double the acceleration potential.
BTW, Mr. Dawson with his DC servos and direct reading closed loop feed-back has a real industrial control system on his machine, not the hobby grade toy stuff we are playing with here. To replace his stuff with new industrial gear, you are likely talking north of 10k per axis, and that's without the CNC software.
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- Feb 8, 2014
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- 11,144
I looked at the drawings for NEMA 24 and NEMA 23 motors. The mounting holes look the same 47.14mm spacing, and the centering flange is the same size, 38.1mm, the outside dimensions of the frame is slightly larger. The shaft size might be different so you will have to confirm that. So yes, it looks like they will interchange.
425 oz motors should be big enough for your mill, but bigger is always better. You can always cut them back, but it pretty hard to get more power if you need it.
That power supply should be good. You are correct, the motors don't all run at anywhere near full torque at the same time. I'm running two NEMA 23 steppers (coolant pump and 4th axis), one NEMA 34 stepper(Z-axis), and two DC servos (X & Y axis) on my 70V, 5 amp supply. No problems so far.
I took a look at the pictures on the CNCFusion site, I can't tell what motors most people are using. It almost looked like people were using NEMA 34 motors and mounting them diagonally on the mount. I'm surprised there is no motor size recommendation on the site. You might read through the CNCFusion forums, there might be some information there on motor sizing.
425 oz motors should be big enough for your mill, but bigger is always better. You can always cut them back, but it pretty hard to get more power if you need it.
That power supply should be good. You are correct, the motors don't all run at anywhere near full torque at the same time. I'm running two NEMA 23 steppers (coolant pump and 4th axis), one NEMA 34 stepper(Z-axis), and two DC servos (X & Y axis) on my 70V, 5 amp supply. No problems so far.
I took a look at the pictures on the CNCFusion site, I can't tell what motors most people are using. It almost looked like people were using NEMA 34 motors and mounting them diagonally on the mount. I'm surprised there is no motor size recommendation on the site. You might read through the CNCFusion forums, there might be some information there on motor sizing.
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Grepper:
You posted while I was typing the above.
The "holding torque" number the vendors all publish for the stepper motors do not mean squat - What really matters is the torque curve (or "lack of torque" curve, more correctly)
These are the most believable NEMA23 stepper curves that I've found - just go to the link and download the PDF, and scroll down.
See how the torque drops off at speed? That's what I'm talking about.
Reality is, just copy what others have done on similar machines, and you should get similar performance!
Doing the math, those 425 oz-inch motors should be adequate to power the knee on my Clausing, if I gear them for 100 ipm at 1000 rpm. At 40% of the published torque value, it should result in about 400lbf being available to lift the table and accelerate it, ignoring friction.
You posted while I was typing the above.
The "holding torque" number the vendors all publish for the stepper motors do not mean squat - What really matters is the torque curve (or "lack of torque" curve, more correctly)
These are the most believable NEMA23 stepper curves that I've found - just go to the link and download the PDF, and scroll down.
See how the torque drops off at speed? That's what I'm talking about.
Reality is, just copy what others have done on similar machines, and you should get similar performance!
Doing the math, those 425 oz-inch motors should be adequate to power the knee on my Clausing, if I gear them for 100 ipm at 1000 rpm. At 40% of the published torque value, it should result in about 400lbf being available to lift the table and accelerate it, ignoring friction.
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