Take a look at this thread. I just am starting on my PM 1130V. https://www.hobby-machinist.com/threads/electronic-lead-screw.79812/
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Electronic Lead Screw
- Thread starter ttabbal
- Start date
I ran into that on my lathe. I updated the code and sent it to him. It's been added to the main code. It adds a new setting for threading.
@ttabbal - I've begun the process of converting my similar machine to ELS equipped. The thread is here: https://www.hobby-machinist.com/threads/els-conversion-on-weiss-1127.103745/
I used a 4 Nm closed loop stepper motor from StepperOnline - https://www.omc-stepperonline.com/t...t-nema-24-motor-driver-w-2m-cable-1-cl57t-s40
It appears that you used a 2 Nm closed loop stepper similar to this: https://www.automationtechnologiesi...brid-servo-system/hybrid-servo-drive-kl-5080h
My stepper motor seems very weak, i can easily stop the carriage by putting my hand on the handwheel and offering a bit of resistance. The torque curves on my stepper motor seem to exceed yours at every RPM that is listed so i would think that it would work fine. In fact i have seen many folks use a 2Nm stepper motor without issues with the clough42 solution.
On my lathe the lead screw is 8TPI. The gearbox on my lathe is A - Direct, B - 1:2 or C - 2:1. The stepper does not like moving the carriage in setting B at all as it's overdrive, and will do it under low load for A. C is where i've been testing with it as the stepper doesn't labor as much. This means the stepper spins faster which should be less torque according to the documentation. It looks like you're gearing it down 2 or 3 to 1 by what i see in the pics whereas i'm running 1:1.
I'm trying to figure out if this is something specific to my lathe or something with the stepper motor/driver portion of the system. When i had the gear train setup on the banjo it seemed to feed just fine and the carriage travels back and forth fairly easily. It's not like it freewheels if i spin it fast and let go but i wouldn't call it hard to move.
Thank you in advance for any advice or thoughts you might have.
I used a 4 Nm closed loop stepper motor from StepperOnline - https://www.omc-stepperonline.com/t...t-nema-24-motor-driver-w-2m-cable-1-cl57t-s40
It appears that you used a 2 Nm closed loop stepper similar to this: https://www.automationtechnologiesi...brid-servo-system/hybrid-servo-drive-kl-5080h
My stepper motor seems very weak, i can easily stop the carriage by putting my hand on the handwheel and offering a bit of resistance. The torque curves on my stepper motor seem to exceed yours at every RPM that is listed so i would think that it would work fine. In fact i have seen many folks use a 2Nm stepper motor without issues with the clough42 solution.
On my lathe the lead screw is 8TPI. The gearbox on my lathe is A - Direct, B - 1:2 or C - 2:1. The stepper does not like moving the carriage in setting B at all as it's overdrive, and will do it under low load for A. C is where i've been testing with it as the stepper doesn't labor as much. This means the stepper spins faster which should be less torque according to the documentation. It looks like you're gearing it down 2 or 3 to 1 by what i see in the pics whereas i'm running 1:1.
I'm trying to figure out if this is something specific to my lathe or something with the stepper motor/driver portion of the system. When i had the gear train setup on the banjo it seemed to feed just fine and the carriage travels back and forth fairly easily. It's not like it freewheels if i spin it fast and let go but i wouldn't call it hard to move.
Thank you in advance for any advice or thoughts you might have.
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- Dec 18, 2019
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- 7,318
You have PM.
What voltage power supply are you using for your stepper motor driver? How many volts, how many amps? An 18V power supply will be anemic. So will 24V. To deliver the required torque you need around 48V for this 4Nm motor.
If the supply is indeed 48V and at least 5A, the motor should deliver the torque. If it does not, while disconnected from your lathe, then something is wrong with the motor, driver, wiring or power supply. If it does deliver the torque disconnected, then something is going on with your mechanical configuration. We need to be systematic about decomposing the problem, or we will be chasing phantoms forever.
I think @WobblyHand has the right idea. We need to track down where the problem is.
I run mine with a higher speed for lower torque requirements. The belt drive is 3:1 and the lathe gearbox gives another 2:1. Even then, I would like to replace the motor with a stronger version. It's pretty tough to stall the lathe, but I can do it easier than I'd like. In addition, I have to power down every thing to reset the stepper driver if it trips. I haven't had a chance to research a replacement yet though.
I run mine with a higher speed for lower torque requirements. The belt drive is 3:1 and the lathe gearbox gives another 2:1. Even then, I would like to replace the motor with a stronger version. It's pretty tough to stall the lathe, but I can do it easier than I'd like. In addition, I have to power down every thing to reset the stepper driver if it trips. I haven't had a chance to research a replacement yet though.
We're private messaging each other - haven't found the issue but we're walking through it step by step to troubleshoot. I can stall mine and cause everything to need a reset by engaging the power feed at .0025"/rev and put just over light but not quite moderate resistance on the hand wheel.
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- Dec 18, 2019
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Yes we are PMing. Doesn't seem sensible that light pressure would do that, but on the other hand, I have not tried that particular test. Maybe I should try that tonight. My setup will cut 4 TPI threads in steel, using the identical motor, controller and power supply, so its not that anemic. But I can still stall it with some effort.
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- 121
Looks great. I have seen that controller on Chinese lathes and tried, but failed to get a manual. I am very interested in your completed task.
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@ivel03 as a follow up, I just did the same test on my lathe, and it stalls. With a 0.0025"/rev feed. But if I let go it jumps to where it should have been. If I hold it too long, the stepper motor driver stalls and has to be reset. I'm going to say this, and it may not sound right to you, but it doesn't matter that it stalls for that test. What matters is it cuts the proper threads under normal use. By holding the hand wheel you are exceeding the stall rating of the stepper motor. You will see why later, in the third paragraph. Normal threading and feeding does not require that amount of torque unless you are trying to take huge cuts.
So what I would do is to get a chunk of 1" steel. Find a 1" nut with a coarse thread and make the 1" steel rod match the threads. I suspect it will work fine. Lacking a nut, just cut something like 8 TPI, it should work ok too. I cut a 4 TPI thread, but I can't recommend it because it is near the limit of the system. I don't think your lathe originally came with gears to cut 4 TPI, mine didn't. If you have some large diameter stock, try cutting a coarser thread.
If you want to actually test the motor torque, I believe @RJSakowski describes a Prony brake he made to measure motor torque. I think maybe even Clough42 has a video on the same thing. Basically (from memory, so forgive me if I get this wrong) it is a pulley with a rope slip clutch. One end of the rope goes to a bucket with weight in it. The rope is wrapped around the pulley a few turns. I think if you pull the loose end and snug it, the rope tightens and the rotating stepper will pull up the weight. By knowing the pulley radius and the weight, you can calculate the torque. By increasing the weight in the bucket, you can find when the motor stalls. At the point of stall, we can calculate the stall torque. Torque is given by the product of the radius and the weight. You have to remember, 4Nm is 566 oz-in, which is only 2.94 ft-lbs. It's not that much, which is why you can stall the hand wheel, but 4Nm is more than adequate to cut threads in steel, on your size lathe. Probably 2Nm is adequate...
If you want tens of ft-lbs, you need a LOT larger stepper. And it won't cut threads any better, at least not on your lathe. I found a 30Nm stepper - it is NEMA-42. That's only 22 ft-lbs. The motor alone costs $200 and you need to buy the driver and power supply. Your current motor is a NEMA-24, which measures 2.4 x 2.4 inches, the NEMA-42 measures 4.2 x 4.2" x 9", its very big. I think such a large motor is totally unwarranted for this application, especially on your class lathe. The top speed would be lower as well, and it would end up costing a lot and not working significantly better, since your lathe would become the limiting factor.
I'm not sure my answer is satisfying at first glance, but cut some steel threads and see how it works. If it works, its good. If it isn't working and the motor tests to 4Nm, then you will need to up size that motor. I will continue to support your efforts to get you up and running. I think you will find, that a 4Nm motor cuts all the threads that your lathe is rated for, and possibly a bit more.
So what I would do is to get a chunk of 1" steel. Find a 1" nut with a coarse thread and make the 1" steel rod match the threads. I suspect it will work fine. Lacking a nut, just cut something like 8 TPI, it should work ok too. I cut a 4 TPI thread, but I can't recommend it because it is near the limit of the system. I don't think your lathe originally came with gears to cut 4 TPI, mine didn't. If you have some large diameter stock, try cutting a coarser thread.
If you want to actually test the motor torque, I believe @RJSakowski describes a Prony brake he made to measure motor torque. I think maybe even Clough42 has a video on the same thing. Basically (from memory, so forgive me if I get this wrong) it is a pulley with a rope slip clutch. One end of the rope goes to a bucket with weight in it. The rope is wrapped around the pulley a few turns. I think if you pull the loose end and snug it, the rope tightens and the rotating stepper will pull up the weight. By knowing the pulley radius and the weight, you can calculate the torque. By increasing the weight in the bucket, you can find when the motor stalls. At the point of stall, we can calculate the stall torque. Torque is given by the product of the radius and the weight. You have to remember, 4Nm is 566 oz-in, which is only 2.94 ft-lbs. It's not that much, which is why you can stall the hand wheel, but 4Nm is more than adequate to cut threads in steel, on your size lathe. Probably 2Nm is adequate...
If you want tens of ft-lbs, you need a LOT larger stepper. And it won't cut threads any better, at least not on your lathe. I found a 30Nm stepper - it is NEMA-42. That's only 22 ft-lbs. The motor alone costs $200 and you need to buy the driver and power supply. Your current motor is a NEMA-24, which measures 2.4 x 2.4 inches, the NEMA-42 measures 4.2 x 4.2" x 9", its very big. I think such a large motor is totally unwarranted for this application, especially on your class lathe. The top speed would be lower as well, and it would end up costing a lot and not working significantly better, since your lathe would become the limiting factor.
I'm not sure my answer is satisfying at first glance, but cut some steel threads and see how it works. If it works, its good. If it isn't working and the motor tests to 4Nm, then you will need to up size that motor. I will continue to support your efforts to get you up and running. I think you will find, that a 4Nm motor cuts all the threads that your lathe is rated for, and possibly a bit more.
You're probably correct. I only cut in aluminum but that seemed to cut without issues. @ttabbal - i am not trying to hijack your thread but the reason i posted in your thread is because you have nearly the same lathe. I think that there is a fair bit of resistance added to the system with the second shaft and power feed system. Both of my gearboxes have 85w90 in them and it's 24* out currently so if it's 35* in the shed i'd be lucky. I think the single shaft lathes that use the lead screw for power feeding offer less resistance to the stepper motor.
I think you pretty much confirmed my suspicions with this:
"I run mine with a higher speed for lower torque requirements. The belt drive is 3:1 and the lathe gearbox gives another 2:1. Even then, I would like to replace the motor with a stronger version. It's pretty tough to stall the lathe, but I can do it easier than I'd like. In addition, I have to power down every thing to reset the stepper driver if it trips. I haven't had a chance to research a replacement yet though."
I think you pretty much confirmed my suspicions with this:
"I run mine with a higher speed for lower torque requirements. The belt drive is 3:1 and the lathe gearbox gives another 2:1. Even then, I would like to replace the motor with a stronger version. It's pretty tough to stall the lathe, but I can do it easier than I'd like. In addition, I have to power down every thing to reset the stepper driver if it trips. I haven't had a chance to research a replacement yet though."