Need Help With Decision on New Lathe and VFD

Lucky Liverider, you made a wise purchase decision. . I’ll definitely be posting pictures as I go through the process.
Mark is very popular on these boards and it’s obvious why. He’s been very, very helpful to say the least.
Just a quick question - Do you have 3 phase available? Residential areas and many farms only have single phase. Industrial areas have 3 phase in Alberta.
I just have single phase available as far as I know....I’m assuming single phase
 
If you are running at 20 Hz you should be be in gear box low in the first place so torque should not be an issue. If you are tapping or making threads you surely don't need maximum torque. I can't prove it but I would think it best not to exceed the maximum spindle rpm intended for the lathe? So if the pulley diameters in the VFD setup are close to the original then no reason to run over ~60 Hz?

If you are buying a 3 phase motor for your lathe, why would anyone go with a TEFC "explosion proof" motor unless you were working the machine shop in a gas plant? I have heard some talk about rigidity due to the cast iron frame. Why? That is simply not needed. A rolled metal frame is beyond sufficient. I think open frame drip proof will get the job done and operate sufficiently cool.

What I want to know (and this is off topic of course) is it better to go with a lower or higher resistance on the break resistor (given the same power rating)?
 
If you look at factory installed VFDs, they generally reduce the gearing/pulley ratio to 2 or 3 speeds, the rest of the speed range is handled by the motor. The motor is generally oversized by 1.5-2X so that the performance (Hp/Torque) is similar to the non-VFD multi-speed version. The goal is not to have a faster spindle speed, but to adjust the ratios for optimal performance over the desired spindle speed range, so you have a mechanical advantage when over speeding the motor and changing the drive ratios to give the same spindle speed as a 60 Hz. motor. So if you have a 2 Hp motor 60Hz with a 1:1 final drive ratio vs. a 2 Hp motor at 120 Hz with a 2:1 final drive ratio, you have a mechanical advantage of 2X with the latter with the same Hp. You need to change the drive ratio when using a VFD. When you go below the motors base speed the torque is flat and Hp drops in a linear fashion, but you loose the mechanical advantage if you are running the VFD at say 20 Hz instead of 60 Hz. In practice most VFDs can provide up to around 180% torque for up to 1 minute, beyond that you will get an over current fault if you exceed 100% of the output amperage.

TEFC, TENV and TEBC are pretty much the industry standard for motors on lathes and mills in the 2-5 Hp range, and larger. TENV and TEBC are primarily used in VFD driven motors. The cooling will be better at speed extremes due to the mass/design, and there is no risk of chips/swarf entering the motor with a totally enclosed case.

Regarding a brake resistor, there is usually a range of resistance specified by the manufacture based on the size and voltage of the VFD, and it is also dependent on the type of machinery being operated (momentum and frequency of braking) and if the braking is static or dynamic. I have attached the recommendations for the Hitachi WJ200. Bigger/lower resistance is not necessarily better, the lower the resistance the more voltage/current can be dissipated over a shorter period of time. This is at the expense of a decreased duty cycle, or frequency of stops over a given time period. Since in mills and lathes, there are not a lot of stop start cycles and there is no static brake hold, usually being at the lower end of the recommend resistance is preferable. So something like the 2 Hp 200V WJ200 I usually recommend something in the 50-75 Ohm range for a braking resistor. Since common resistor sizes are 47 Ohm and 68 Ohms, I recommend using the 68 Ohm. On the 3 Hp 200V WJ200 either 35 or 47 Ohm resistors are commonly available sizes. With high braking duty cycles the resistors can get very hot, and there is usually a thermal oveload contact built into the braking module provided by the VFD manufactures, in mills and lathes this is not needed because of the low duty cycle time.

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I’ve reviewed Mark’s (mksj) documents re: VFD conversion components and wiring and I have done up a diagram showing as much detail as I could fit in. My goal was to make sure that I understood the components and and how they are wired together. Details such as how the contactors are wired to each other and exactly how wires are connected to switches have been left out. Otherwise everything is in the attached PDF file. There were a few places where I wasn’t sure, so I just took my best guess. As they say, a picture is worth a thousand words, so I’m hoping that I can get some feedback re: where I might have misunderstood Mark’s information.
 

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  • VISIO-1440E Wiring (Basic) v2.pdf
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I’ve reviewed Mark’s (mksj) documents re: VFD conversion components and wiring and I have done up a diagram showing as much detail as I could fit in. My goal was to make sure that I understood the components and and how they are wired together. Details such as how the contactors are wired to each other and exactly how wires are connected to switches have been left out. Otherwise everything is in the attached PDF file. There were a few places where I wasn’t sure, so I just took my best guess. As they say, a picture is worth a thousand words, so I’m hoping that I can get some feedback re: where I might have misunderstood Mark’s information.

I think you can eliminate a lot of complexity by taking advantage of the USP and ESD features built into the WJ200. This is how I rigged up my VFD. Not shown is a breaking resistor I recently added. I do not use a coolant pump.

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Thanks Bretthl. You are so far ahead of me, it’s going to take time for me to catch up. I’m committed to learning this stuff though. Installing a Roush supercharger in my 2013 Mustang was difficult, but it was more mechanical focused than electrical...more up my alley.
 
One issue with the USP is that if the lathe is powered up with the E-Stop or cover switch open, if the spindle switch is in a run position the lathe will restart when either of those are reset. A latching relay always needs to go through the spindle stop position to reset. I use USP, but only in conjunction with another interlock system. Redundancy of systems, I have also had spindle switches break and switches can fail either NO or NC.
 
One issue with the USP is that if the lathe is powered up with the E-Stop or cover switch open, if the spindle switch is in a run position the lathe will restart when either of those are reset. A latching relay always needs to go through the spindle stop position to reset. I use USP, but only in conjunction with another interlock system. Redundancy of systems, I have also had spindle switches break and switches can fail either NO or NC.

If power is applied to the VFD with the motor control switch in the FWD/REV position, the USP function will prevent the lathe from starting until the motor control switch is returned to neutral.

If the lathe is shut down using the ESD (E-Stop) the lathe will not start until the ESD and the VFD are reset. If the motor control switch is in FWD/REV at that point then lathe will start. You can't engineer out all of the idiots.

I have not tested the scenario where the ESD is tripped before power is applied to the VFD with the motor control switch in FWD/REV. I suspect that if the operator resets the ESD (with the motor control switch in FWD/REV) the lathe would not start until the motor control switch is cycled back to neutral. I will test that in a few weeks when I return home.

I like your new lathe. Awesome. How did you get QMT to order that machine for you?
 
Lucky Liverider, you made a wise purchase decision. . I’ll definitely be posting pictures as I go through the process.
Mark is very popular on these boards and it’s obvious why. He’s been very, very helpful to say the least.

I just have single phase available as far as I know....I’m assuming single phase
I only have 1ph; going with a Teco E510 VFD
 
late to the thread... sorry. I've converted my mill and surface grinder using the Teco 510 VFD. Happy to help if you need additional info. Not too far away, either.
 
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