Selecting a VFD for South Bend 13" lathe.

MikeInOr

MikeInOr

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I recently purchased a 70's vintage South Bend 13" lathe with a 2hp 3ph motor.

SouthBendMotor.jpg

30 years ago I built a 10hp balanced rotary phase converter to power my 7 1/2hp radial arm saw. Since then I have been mostly using VFD's to power my machines (mostly woodworking machines). All of my 3ph machines have been very simple as far as controls... start, stop... with a speed control that I actually use on a wood shaper.

When I purchased my SB lathe I got to see it under power and was very impressed with the instant reverse and could see how this would be useful for operations like threading! I know VFD's do not like having the load suddenly cut from the VFD and I am sure they would like having the load cut, two legs swapped and re-energized much less. My thinking is if I want speed control and instant reversing I am going to have to get more intimate with VFD's.

I THINK I have decided on a Hitachi WJ200-022SF rated for 3 HP, 11 Amp, 2.2 kW, Constant Torque Sensorless Vector AC Drive, Input: 200 - 240VAC 1ph.

https://www.driveswarehouse.com/WJ200-022SF-P21546.aspx

What attracted me to the Hitachi WJ200 is it has some basic programming capability. I believe I can program it to brake the motor from full speed to a stop then spin the motor back up to speed in the opposite direction. I believe with a braking resistor I can make this reversing operation happen pretty quickly. I chose the WJ200-022SF because it is rated at 3hp giving me a bit of head room in muscling the 2hp motor direction quickly.

Does this make sense? Does anyone else quick reverse a lathe? For threading? Is quick reversing even acceptable practice for a lathe?

My other option is to pull out an old 7.5 RPC and just run the SB lathe on that without having to re-engineer the controls. My 10hp RPC is in the woodworking side of my shop and running a line to it from the SB would be a lot more hassle than I want to deal with.

Any thoughts? Any advice from other lathe owners controlled by a VFD?
 
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Install a DPDT switch, perhaps a braking resistor for a quicker stop, and get the VFD programmed to your liking. That should work fine.
 
The lathe already has a reversing switch (with a center off position)... which I assume is just a DPDT center off switch. Everything I have read regarding VFD's is they don't like having the motor they are controlling cut... and re-engaged.

All the VFD's I own incorporate a soft start feature. Besides being easier on the machine the soft start also greatly reduces the starting current on the motor. Instead of going from 0 rpm to full blast and sucking up a huge starting current to do so the VFD ramps up the motor speed which greatly reduces the starting current. Just switching two legs with a DPDT switch would be even worse than an instant on starting current in that the VFD would have to instantly stop and then reverse the motor drawing even more current. I don't think a VFD could handle a motor instantly switching direction?
 
Most newer VFDs have braking ability, so with a braking resistor you can achieve rapid stops. On a lathe you have momentum in the system, so there are some limitations as the speed increases and the weight of the chuck. Most threading is done at low speed so should not be a problem. If you are threading then you are not reversing the direction just disengaging the half-nut in the relief groove. Alternatively with quick braking you can stop the machine in the relief grove, withdraw the cutter and then reverse the lathe direction (assumes you are leaving the half-nut engaged). If you have a VFD going in one direction and then send a reverse command, it will ramp down to a stop and then accelerate in the opposite direction per the programmed parameters. You connect the VFD directly to the motor, it does not go through a switch to reverse the motor lead directions. Normally I recommend that a VFD be programmed for two different braking rates (per one of the inputs), on normal use it is 3 seconds, and for fast braking 1 second. The WJ200 has two programmable acceleration and deceleration rates. You may also have some limitations as to the belting and if it can handle rapid stops vs. slipping.

The WJ200 works well and are robust for the most part. I have not had any issues with them with dozens of installs. You do not need to up size the VFD to a 3Hp model for a 2Hp motor, unless you think you will be running a bigger motor at some later point. Normally one controls the VFD direction via the programmed inputs and these can be wired to your drum switch. The danger is that the VFD will go into a run mode if you accidently knock the switch on. There are a number of alternatives, simple relay system with use of momentary run buttons, one can also program the WJ200 to not start on power-up.
 
I used the WJ200-022SF for my 2hp Clausing and wired it with reversing switch, different brake ramps, etc.
On heavy braking with an 8" chuck there is a lot of mass and it can "kick out" the control, so there is a limit to how quick it can brake.
Mine has 50 ohm 400 watt brake resistor, maybe a lower value would be better... I think you can go down to 35 ohms.
You just need to back off on the braking constant until it is stable.
I have used the reverse switch for power tapping (using tap in tailstock, unlocked) and it works good for that.
I think if single point threading you will have an issue with the slop when it reverses, unless you can pull the cross feed back quickly.
 
All of my VFD machines have a 2 step startup. Engage the power cut off switch to the VFD. Press the start button on the VFD. I have never used the start at power on feature on my VFD's.

I agree with you on having more than one stopping rate for the lathe. The normal power down coast to a stop and a near instant braking function. It is good to know that the WJ200 supports multiple ramp down rates.

WJ200-015SF (2hp) = $275. WJ200-022SF (3hp) = $326.
All my other VFD's are sized to their motors... for $50 I think I might opt for the extra head room of the oversized VFD.
I have a Hitachi SJ on one of my RAS's and it has always done a good job for me... I like the Hitachi's.

I am not sure if I will use the reversing switch on the lathe as a control switch for the VFD or not??? I will see when I get there. I have probably a hundred different odd switches, buttons and pots laying around that I can use to cobble together a control panel for the VFD... I might integrate a tachometer into the control panel if I decide to go that direction.

Thanks for the comments mksj, Bob & Pete!
 
You can use the lathe reversing switch to control the VFD. Not the motor wiring (with a VFD), instead the VFD auxiliary inputs. The VFD has to be the sole direct control of the motor.
 
Quick brake
That's great unless you have a threaded chuck..be careful or you may have a spinning chuck come your way.
I have seen it in person, but fortunitly was not the operator
 
There's a number of cheap 2hp VFD's out there in the $100 range. Has anyone had experience with them? I need at least three of them (SB 14 1/2" lathe, Bridgeport, 3 phase grinder, etc) and have considered making my on. There's several companies offering VFD controller chips (pretty much do it all except for the power devices) so it would be handy to add a touch screen display and tach while I'm at it.
 
I have a cheap ebay 3hp VFD on a wood shaper. It runs fine. Feels cheaper than my Hitachi, Leeson and Allen Bradley VFD's but the cheapy has been running fine for 2+ years now. I ordered the Hitachi WJ200 for my lathe yesterday because I wanted more control on my lathe. The cheapy VFD has capabilities for configuration and controls but the documentation is so awful that trying to do anything more than basic 1ph to 3ph and speed control is very frustrating.

I am all for diy projects... especially electronic projects... but I don't see how you would come out ahead by making your own VFD. Yeah, a VFD is just a rectifier, Power transistors (IGBT's) and a control board but by the time you put although together even with quality surplus parts I can't see the advantage. I assume the control chip would need some sort of low-level operation code... I don't know if the code comes on the bare chips.

If you do decide to go the roll your own route I would be very interested in watching your project!!!!
 
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