# VFD for my Lathe



## GasMan (Oct 6, 2014)

First, Thank You for passing on your knowledge.

I have a import 12\36 gear head lathe.  It seems to me when turning motor on, it hits pretty hard(like popping the clutch in your car).  Would installing a VFD soften the hit on the gears?

Motor is wired for 240, single phase,2 HP, 15 AMPS. Could not find RLA on data plate.

VFD could be wired using apron control for FWD and REV?

Thank You, have enjoyed this site, learning each visit...


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## JimDawson (Oct 6, 2014)

GasMan said:


> First, Thank You for passing on your knowledge.
> 
> I have a import 12\36 gear head lathe.  It seems to me when turning motor on, it hits pretty hard(like popping the clutch in your car).  Would installing a VFD soften the hit on the gears?
> 
> ...




A VFD will not run a single phase motor.  Having said that, yes, a VFD could be wired to operate from the apron control, and it would soften the hit on the gears.  If you replace your existing motor with a 3 phase motor then you can install a VFD.


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## GasMan (Oct 7, 2014)

Mr JimDawson, Thank You for your reply, Maybe I can think of something else..


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## JimDawson (Oct 7, 2014)

Look for a single phase soft starter.  I did a quick web search and found a few for smaller motors, but not a 2HP.


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## pdentrem (Oct 7, 2014)

Can always go visit the local motor shop. Likely they have a couple used 3 ph motors for cheap, then your major cost would be the VFD unit. Yes, an inverter rated motor would be better, but for the casual user a standard motor plus a fan can work just fine. Or limit the lowest setting to 30 hz to not over heat the motor.
I purchased a Techtop inverter rated motor for $230 new, just last week. I need a few minutes or hours with interruptions to complete the wiring of the lathe to the VFD.
Pierre


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## GasMan (Oct 8, 2014)

Thank You for the suggestions, last night I checked Graingers for soft start controller.  I think a new 3 phase motor and VFD would be very close in cost.  Maybe could use VFD for both my lathe and mill, not looking for speed control, just softer start.  Thanks again...


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## JimDawson (Oct 8, 2014)

That sounds like a good plan.  Yes, you could run both the mill and the lathe off of a single VFD.  Size the VFD for the larger of the 2 motors, and have a socket coming off of the VFD that you can plug one or the other into.  Also put a disconnect ahead of the VFD so you can turn it off before swapping the machine plugs.   Don't disconnect the VFD from the motor with it turned on.


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## mksj (Oct 9, 2014)

Given that lathes in this size do not come with soft starts and survive for many years without issue, it is probably not a significant issue. Belts also help soften the initial shock. A 2HP soft starter (like the Square D ATS01N112FT) will run about $100-150 and is a quick easy drop in type of replacement. http://www.gordonelectricsupply.com...ocess~search?gclid=CPXGytXjn8ECFQiIaQodH7sAnw . Granger tends to be a very expensive industrial parts warehouse, usually 1.5-2X the price of others. 

Three phase motors tend to run much smoother (less cogging), so surface finish on a lathe is usually improved and the soft start/electronic braking is a real plus. A VFD with a new or used inverter motor is an option, this would easily be 2-3x the cost of a soft starter, and would require time/knowledge to install them correctly.  Care most be given to use properly shielded wires for the VFD controls and wiring from the VFD directly to the motor.  Having done this recently on my lathe, getting a replacement 3 phase motor properly sized (space, metric footprint and shaft dimensions) is also a consideration. Marathon Metric series are very reasonably priced inverter rated motors, that often fit Chinese lathes. A decent VFD and inverter rated motor affords you a wider operating speed with constant torque below the motor base frequency and constant horsepower above the motor base frequency. There is a wide range of VFDs and functions, so some care must be given to the application and needs of the project.  Technically you can run the VFD off the lathe apron controls, but direct connection to the VFD may bypass the lathe safety interlocks. It is possible to use the existing motor contacters (or replace them with relays), one would need to disconnect the contacters 230V and could use them to operate the low voltage VFD signals. When using the original contactors, the contacts may need to be cleaned, otherwise the resistance from prior arcing may be too high for the VFD low voltage signals. A good understanding of VFD function and programming is needed to get the most out of the VFD capabilities.

At the cost of 2-5HP VFD's these days, it is probably more ideal to have a dedicated unit for each machine, as the VFD programing and controls are usually machine specific.


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## GasMan (Oct 9, 2014)

Thank You for the suggestions, I like the soft start controller idea, and price from Gordon Electric...


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## Earl (Oct 17, 2014)

I purchased a 3 phase motor from an on line surplus dealer for less than a hundred bucks. I bought a Chineese VFD off of ebay for 125 bucks. I have other chineese vfd's (huanYang) so I was comfortable with that. I did have to bush the pulley and cut a special key for the motor but everything bolted up fine to my 12 x 36 grizzly g4003g. I disconnected the fwd/rev switch from the control box and wired it directly to the vfd. I did have to remove one wire from the control box but the only thing that doesn't work with the original controls is the "inch" switch. I never use that anyway. I also added a mach-tach ($65 or so) so I can read the spindle speed directly and it also gives the surface feet per minute. I just added a chineese digital readout that I can't remember the name of right now. It was less than $400 - very good quality with glass scales. I have a 6 jaw Buck adjust tru on my southbend heavy 10 so I stold the spare buck 3 jaw adjust tru from the SB spares and put it on the Grizzly. I am very pleased with the additions to the lathe, the vfd allows me to forget about changing gears. I can go from about 100 rpm to almost 1400 with the turn of a dial. It also is set up for about a 6 second start up and the same for stopping. If I change gears, I can go all the way down to about 15 rpm with full torque. (probably never use that). The only thing left to do with the lathe is to fabricate a lever to replace the carriage lock bolt. The 3 phase motor dramaticaly improved the surface finish. ( I knew it would as I have a 3 phase on my southbend 10L and the finish on that is amazing) The only other advise that I can give is to run the belts loose on your 12x36. That made a big difference in surface finish even before I got the 3 phase motor.

Good luck,
Earl

I forgot about the shipping on the motor.  That was about 25 bucks as well


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## Earl (Oct 17, 2014)

My SB has 2 motors,  One for the main drive and another one for the "fine feed option"   The banjo can be moved so that the second motor drives the lead screw.   I run both the motors off the vfd at the same time.  Before the vfd,  the lathe ran from a rotary phase converter.   I merely unplugged the phase converter and hooked the VFD to the lathe.  There are two fwd/rev swithes on the lathe.  One for the underdrive motor and the other for the fine feed option.   I run them both at the same time and have no issues.   The vfd is very forgiving.  It understands over current and shuts down.  It understands overspeed and shuts down.  I have a lot of faith in the guys that design them.  I am a EE but spent most of my career in the computer industry not in industrial controls.


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