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Sieg SC4 (LMS 3540) doesn't stop quickly enough

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Four Corners

Swarf
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#1
I have a Sieg SC4 from Little Machine Shop. I've contacted them for help, and I'm sure they will, but I always like several opinions. In the link below you will see that my lathe takes a long time to respond to the stop and direction buttons. At full speed it take around seven seconds before the lathe stops or changes direction. This is dangerous for so many reasons. Is mine the only machine that does this

https://photos.app.goo.gl/gdKQGp9XXseL9GTa2

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darkzero

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#2
Looks normal to me. Don't know if that's safe to do but I wouldn't feel comfortable forcing spindle direction like that. Being electronic I assume precautions are built in but still.

Many non-electronic drive, belt & gearhead lathes take much longer than that to slow down/come to a complete stop. Bigger the chuck the longer it will take also. Sounds like a VFD with braking or a mechanical foot brake is what you want but even then it's not recommended to stop the spindle instantly all the time.
 

DAT510

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#3
I don't have a Sieg Lathe, but I do have a Sieg SX3 Mill. I've noticed during startup/ramp-up the "stop" button has no effect until it reaches operating speed. The "emergency stop" button works regardless. Once up to speed, the stop button is immediate. My thought was, the controller has a very simple processor and the way the controller is programmed is only one operation can occur at a time. Meaning the next operation can't start until the first is finished. In my case Ramp-Up, then the stop command. It startled me the first couple of times it happened.

Hope this helps.
 

4ssss

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#4
Throw an anchor out.
 

higgite

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#5
Four Corners,
It’s hard to tell exactly what’s going on in your video, but I think what you are experiencing is the stop button doesn’t work while the spindle is automatically accelerating back to its previous speed when you restart after using the stop button or when you reverse direction with it running. However, the E-stop button will immediately shut it down quickly at any time, even when the stop button won’t. At least, that’s how my LMS 3540 (Sieg SC4) works. Sounds the same as Dat510's SX3. I haven't tried it on my LMS 5500 (SX2.7) mill, but I'm guessing it works the same.

Darkzero,
I hear what you're saying about reversing polarity at speed, but the controller on these machines doesn't reverse the contactor until the spindle has slowed to zero.

Tom
 
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T Bredehoft

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#6
My little Atlas Clausing MK2 doesn't have any electronic braking, I use my hand on the chuck. Works a treat.
 

darkzero

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#7
Darkzero,
I hear what you're saying about reversing polarity at speed, but the controller on these machines doesn't reverse the contactor until the spindle has slowed to zero.

Tom
I assumed that the controller would do something like that as I mentioned. Perhaps I'm missing what the OP is asking. Whether if the buttons don't seem to respond as fast as he would like of if he thinks the spindle is not stopping/slowing down fast enough when pressing stop. If the latter, doesn't look abnormal to me.
 

mksj

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#8
Your are limited in braking speed in particular with lathes due to the momentum in the system. The SC4 uses a smallish DC motor and it is probably limited as to braking capacity depending on the design of the controller. Some DC controllers (like KB Electronics) you can set these parameters with pots, some have forms of dynamic braking vs. regenerative, but I would assume the SC4 uses a rudimentary design. If pushed to harder braking (assuming it is adjustable) it might damage other components not rated for the higher dissipation. There are two pots on the control board, but no information as to what they do.

Faster stops are desirable in an emergency situations, but short of a manual foot brake or electronic braking with a braking resistor, lathes take many seconds to stop. As far as switching directions, as others mentioned (and what I am familiar with VFDs) is that the controller needs to cycle down to 0 RPM per its programmed rate and then change direction. The control systems/VFD programming for systems I build, an E-Stop or limit stop reverts to fast braking, but this is using a large braking resistor and even with this it can be tripped into a free run stopping from maximum speed.

You might watch this video which shows start/stops and speed adjustment of the SC4 and compare with yours. It does seem to stop in 3-4 seconds from speed.
 

Four Corners

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#9
Firstly, I would like to thank you all for taking the time to respond. However, it seems that I didn't properly describe the problem that I'm having. I understand that because of the momentum of the chuck spinning it takes a small amount of time for the lathe to stop. But that's not what I'm talking about here. My problem is that the lathe doesn't respond to the stop command until after the target speed is reached. In the video you can see that I press the start button and then immediately press the stop button but the lathe continues to accelerate for about 7 seconds. If this is the way the machine is supposed to work then I don't understand why it was designed this way. It's quite dangerous, I would say. Any more thoughts on this would be greatly appreciated.

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higgite

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#10
Firstly, I would like to thank you all for taking the time to respond. However, it seems that I didn't properly describe the problem that I'm having. I understand that because of the momentum of the chuck spinning it takes a small amount of time for the lathe to stop. But that's not what I'm talking about here. My problem is that the lathe doesn't respond to the stop command until after the target speed is reached. In the video you can see that I press the start button and then immediately press the stop button but the lathe continues to accelerate for about 7 seconds. If this is the way the machine is supposed to work then I don't understand why it was designed this way. It's quite dangerous, I would say. Any more thoughts on this would be greatly appreciated.

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As I said in my previous post, the spindle comes to a stop very quickly if you press the red E-stop button, whether the machine is accelerating, reversing, steady state or whatever. I don't have a problem with that, but some might.

Tom
 

Four Corners

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#11
So, just to summarize, my machine is not faulty; the SC4 is supposed to work like this. Is that correct?

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higgite

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#12
So, just to summarize, my machine is not faulty; the SC4 is supposed to work like this. Is that correct?

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The green "stop" button on mine works exactly as you described in post #9, including the ~7 second acceleration time from zero to 2000 rpm. But, as said before, there is no delay with the red Emergency stop button, even during acceleration.

Tom
 

Four Corners

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#13
Thank you Tom. Much appreciated.

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higgite

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#14
No problem. Glad I could help.

Tom
 
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