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- Feb 20, 2019
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The VFD converts single phase to 3 phase.
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Which 3 Jaw Chuck and collet chuck for incoming PM1340GT
- Thread starter Serpico1985
- Start date
- Joined
- Jun 12, 2014
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- 4,817
In single phase motors one can see pulsations in the work surface where in 3 phase the the pulsations are reduce in amplitude and phase because there are 3 phase operating on the motor at any one time each staggered by 120 degrees. Some machines like lathes and surface grinders these can show up as surface finish striations with an even repetitive pattern. It seems to be quite variable for even the same model, some individuals seem to have more issues than others, and some have none or very little. Three phase motors can have their speed varied and do not need start or run capacitors, so are not limited as to the number and frequency of start cycles per hour. With a single phase motor that uses a start capacitor, it can fail with too frequent start/stop cycles and also the motor starter switch will eventually fail.
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Three phase can be generated from a single phase power source and the two most common methods that provide full power to the motor is a rotary phase converter (RPC) and a variable frequency drive (VFD). An RPC generates the 3rd leg through the use of another 3 phase motor to generate the 3rd leg and capacitors to balance the voltage between legs, they are considered plug and play in that you do not need any modifications to the machine it is running and can run multiple machines. It produces a fixed frequency output, 60Hz in the US. RPC's are heavy (big), consumer power when running and also can be a bit noisy. A VFD electronically generates a 3 phase output by taking the single phase power converting it to DC power and then chopping the DC into many smaller segments (PWM) to simulate smooth sinusoidal wave. This works acceptably with motors because the coils act as inductors and smooth the PWM, but this does not work well with other electronics. So the VFD output needs to be directly connected to the motor, no contactors or switches. VFD's also have what is called sensorless vector control which is a form of feedback from the motor to the VFD, so that the VFD can very accurately control the motor speed and performance parameters. It can control not only speed, but also acceleration and rapid braking. VFD's are very compact and minimal weight. A VFD has low voltage inputs that control most of its functions, typically these operate at 24VDC and a few milliamps. VFD's for the most part are machine/motor specific, and need to be programmed for each application.
VFD's allow adjusting the motor speed on the fly, and typically have fairly flat torque curves but the Hp drops off in a linear fashion below the motor base speed of 60Hz. It is not a direct substitute for a gearbox, but the stock 1340GT motor works very well in the 20-90Hz speed range. If taking very deep or heavy cuts then one would want to gear down the spindle speed and do the fine adjust with the VFD. Many turning, drilling and boring functions can be very speed sensitive, so like my larger MT drills I use in the tailstock will have a sweet spot for drilling in a material and too fast will result in chatter.
The downside of the VFD is that you need to directly wire its output to the motor and cannot use the stock motor run controls, it requires wiring in the low voltage inputs and maintaining the same safety interlocks that the machine originally had, and adding other controls say for speed control, braking rate, jogging direction, etc. Installing a VFD requires some basic understanding of electricity and control systems, and there are numerous different ways to install them. One "relatively basic/simple" method is outlined in this thread and I believe Precision Mathews also has a similar document that they can provide:
www.hobby-machinist.com
I would do some reading up on RPC's and VFD's and see if they fits into your plan or not. As mentioned the 1340GT is a great lathe, many people do go 3 phase route because it affords them more control and surface finish.
1340gt surface finish problem
O.K. guys, and gals, I've tried every speed/feed combo, every carbide insert I have, every HSS tool I have, I've even put vibration isolation pads between the stand and the floor...nothing seems to work. Here's what I get... Please excuse my photography skills. You can not only SEE the...
www.hobby-machinist.com
Three phase can be generated from a single phase power source and the two most common methods that provide full power to the motor is a rotary phase converter (RPC) and a variable frequency drive (VFD). An RPC generates the 3rd leg through the use of another 3 phase motor to generate the 3rd leg and capacitors to balance the voltage between legs, they are considered plug and play in that you do not need any modifications to the machine it is running and can run multiple machines. It produces a fixed frequency output, 60Hz in the US. RPC's are heavy (big), consumer power when running and also can be a bit noisy. A VFD electronically generates a 3 phase output by taking the single phase power converting it to DC power and then chopping the DC into many smaller segments (PWM) to simulate smooth sinusoidal wave. This works acceptably with motors because the coils act as inductors and smooth the PWM, but this does not work well with other electronics. So the VFD output needs to be directly connected to the motor, no contactors or switches. VFD's also have what is called sensorless vector control which is a form of feedback from the motor to the VFD, so that the VFD can very accurately control the motor speed and performance parameters. It can control not only speed, but also acceleration and rapid braking. VFD's are very compact and minimal weight. A VFD has low voltage inputs that control most of its functions, typically these operate at 24VDC and a few milliamps. VFD's for the most part are machine/motor specific, and need to be programmed for each application.
VFD's allow adjusting the motor speed on the fly, and typically have fairly flat torque curves but the Hp drops off in a linear fashion below the motor base speed of 60Hz. It is not a direct substitute for a gearbox, but the stock 1340GT motor works very well in the 20-90Hz speed range. If taking very deep or heavy cuts then one would want to gear down the spindle speed and do the fine adjust with the VFD. Many turning, drilling and boring functions can be very speed sensitive, so like my larger MT drills I use in the tailstock will have a sweet spot for drilling in a material and too fast will result in chatter.
The downside of the VFD is that you need to directly wire its output to the motor and cannot use the stock motor run controls, it requires wiring in the low voltage inputs and maintaining the same safety interlocks that the machine originally had, and adding other controls say for speed control, braking rate, jogging direction, etc. Installing a VFD requires some basic understanding of electricity and control systems, and there are numerous different ways to install them. One "relatively basic/simple" method is outlined in this thread and I believe Precision Mathews also has a similar document that they can provide:
Pm1340gt Lathe Basic Vfd Control Conversion Using The Stock Control Board And Switches
Many individuals buy the PM1340GT lathe as a 3 phase machine with the intent to convert it over to a VFD system, the usual VFD that is used is the Hitachi WJ200-015SF. Unfortunately the conversion often requires a somewhat complex and costly conversion process to optimize many of the VFD...
www.hobby-machinist.com
I would do some reading up on RPC's and VFD's and see if they fits into your plan or not. As mentioned the 1340GT is a great lathe, many people do go 3 phase route because it affords them more control and surface finish.
- Joined
- Dec 26, 2015
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An 8" 3J Bison is a huge chuck for the 1340GT. I am very happy with my 6" 3J. I did however go with 8" 4J. I'd be interested to hear what the PM pricing on the Bison. Mark makes noteworthy comments in his post about 3-phase benefits.
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- Mar 25, 2018
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- 131
That's the route I'd take.
- Joined
- Mar 22, 2020
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- 175
I’ve been extremely satisfied with my 6” TMX 6 jaw chuck. With a little bit of fiddling, all my work has easily dialed into to .0005 TIR.
I use the PM 8” 4 jaw (rarely) for larger work on my 1236T.
I use the PM 8” 4 jaw (rarely) for larger work on my 1236T.
- Joined
- Dec 12, 2020
- Messages
- 33
mksj,
I appreciate your thorough response! I have read that other thread about surface finish issues. I get what your saying about getting a 3ph machine and adding a VFD. I did not realize that I could use single phase with the VFD/3ph lathe though. It certainly sounds like it is the best option. The problem I'm running into is that I know even less about electricity than I do lathes! Haha. I'm apprehensive about doing it, assuming I could switch out my order for a 3ph machine with PM, because I would be at the mercy of my electrician as to what he would charge to do this. And I'd have to buy a VFD from someone as you mention.
Can you advise the cost of buying a "VFD kit" so to speak? Or whatever extra parts I would need to re-wire the stock parts? I will contact my electrician and discuss this with him and see what he says.
Thank you again.
I appreciate your thorough response! I have read that other thread about surface finish issues. I get what your saying about getting a 3ph machine and adding a VFD. I did not realize that I could use single phase with the VFD/3ph lathe though. It certainly sounds like it is the best option. The problem I'm running into is that I know even less about electricity than I do lathes! Haha. I'm apprehensive about doing it, assuming I could switch out my order for a 3ph machine with PM, because I would be at the mercy of my electrician as to what he would charge to do this. And I'd have to buy a VFD from someone as you mention.
Can you advise the cost of buying a "VFD kit" so to speak? Or whatever extra parts I would need to re-wire the stock parts? I will contact my electrician and discuss this with him and see what he says.
Thank you again.
- Joined
- Dec 12, 2020
- Messages
- 33
I can go with a 6" chuck if it makes more sense. I guess I just assumed 8" since that was the size of the 4 jaw from PM.
- Joined
- Dec 12, 2020
- Messages
- 33
Also,
I wanted to clarify about one of my posts in this thread that was deleted. I was contacted by a moderator who explained that they received complaints about the meme I posted of a guy in a business suit saying "explain it to me like I'm 8 years old". I didn't mean to offend anyone by that. I was trying to make fun of myself for my lack of knowledge in the arena. The meme is from a show called "The Office". The guy in the picture is a loveable moron. We share some commonality. No harm intended. Thank y'all for your assistance!
I wanted to clarify about one of my posts in this thread that was deleted. I was contacted by a moderator who explained that they received complaints about the meme I posted of a guy in a business suit saying "explain it to me like I'm 8 years old". I didn't mean to offend anyone by that. I was trying to make fun of myself for my lack of knowledge in the arena. The meme is from a show called "The Office". The guy in the picture is a loveable moron. We share some commonality. No harm intended. Thank y'all for your assistance!
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- Oct 4, 2016
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- 7,023
All I know about electricity is don't let the smoke out, and if your the ground, it's not a comfortable feeling. I have an electrician friend who did wiring for my garage on standby for the VFD at friend pricing. Mark has a list for everything needed, some assembly required, and I got the VFD from PM for my 1340, EBay might be cheaper.
- Joined
- Mar 25, 2018
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- 131
Just to make sure there's non confusion, my remarks endorsing the 6" jaw, not the six inch chuck. It's that six jaw security that impresses me most for gun smithing.