Variable Frequency Drive (VFD) for Manual Lathe?

Mirage_Man · Jul 28, 2008

So here's the deal. I'm soon to be the owner of a new 13x40 manual lathe. However it's got a three phase motor and as most of us here I only have single phase power. So I need a way to get three phase power to it.

Until now I've been mainly focused on getting a RPC to power it and possibly any other machines I might end up with in the future. Today someone asked why I wasn't considering a VFD. Honestly I don't know. However after doing a tiny bit of research here on the forum I still don't know if it would be the right thing or not.

I understand that VFD's can be used as a single to three phase converter. I also understand the ability to have variable speed. However I have some questions that make me think a VFD would be way more hassle to use than an RPC.

#1) When being used on a machine like a lathe that normally requires changing of gears to achieve speed changes where would you have the gears to work properly with the VFD?

#2) Don't you loose torque with a VFD at slower speeds?

#3) Wouldn't your Forward/Neutral/Reverse lever become useless?

#4) Would the foot-brake be taken out of the equation all together?

#5) Where would one mount the control box so that it wouldn't be in danger from coolant and chips?

#6) If the control box is mounted out of danger how do you control the speed?

#7) Is it possible for an amateur to wire one safely? I have some experience with electrical but I'm certainly not an EE.

BTW this is the lathe I'm getting.

Finegrain · Jul 29, 2008

Mirage_Man said:
#1) When being used on a machine like a lathe that normally requires changing of gears to achieve speed changes where would you have the gears to work properly with the VFD?

Whatever you want. 4:1 for normal use, 10:1 for threading, or whatever. There isn't necessarily a "properly" setting. just don't routinely drive the motor at way more than 60 Hz, or less than 10 Hz for extended periods. I like to run the VFD at 30-40 Hz, it's quieter but still plenty of airflow over the motor, and plenty of torque.

#2) Don't you loose torque with a VFD at slower speeds?

Yes. But, how much torque do you need when threading at 40 RPM? In my experience, I need max torque when taking a deep cut on 3-5" stock, which with carbide is like 400 RPM, which if you set the gears for a 4:1 reduction, you'd be running at 60 Hz and getting max torque. I can single-point 1" 4140 HT to 8 TPI at 5 Hz (with 4:1 mechanical reduction). Any bigger than that, and I have to bump up to 7 or 8 Hz. Since you'll still have your lathe gearing, you can use it to get torque multiplication when needed, and run the VFD at 20 or 30 Hz.

#3) Wouldn't your Forward/Neutral/Reverse lever become useless?

Not at all. You wire the existing F/N/R switch to the VFD control inputs, and use it to control the VFD.

#4) Would the foot-brake be taken out of the equation all together?

Not at all. Same as #3. If there's a shutoff on the foot brake, it goes to the VFD and shuts down the VFD.

#5) Where would one mount the control box so that it wouldn't be in danger from coolant and chips?

I have the VFD itself inside the cabinet. You can hang it on the wall if you want, out of reach of swarf and fluids. I haven't touched the VFD itself since I got all the control wiring hooked up.

#6) If the control box is mounted out of danger how do you control the speed?

I have an external speed control (potentiometer) on a pedestal that travels with the carriage. You can put it wherever you want. Mine weighs a couple ounces and sits in a 20 cubic inch enclosure.

#7) Is it possible for an amateur to wire one safely? I have some experience with electrical but I'm certainly not an EE.

Yes. I managed it, as have many others on PM. The manuals are sometimes cryptic, but if you take your time and write down exactly what you need to do, it's simple. All the control wiring is low-amperage 10V. The only high amp hookups are the 220 V 1-phase to the VFD and then 3-phase to the motor, just like an RPC would need.

YMMV, but I'm very pleased with the VFD (Teco 7300) running my lathe.

Regards.

Finegrain

JunkyardJ · Jul 29, 2008

Answers.

First, changing gears is a GOOD thing, it increases the mechanical advantage of the motor. You can't just slap a VFD on a 3 phase motor that drives the spindle at a fixed ratio, and have adequate torque, and high speed capability. In fact, the BEST combination is a VFD on a machine with a selection of fixed ratios. You only need about 3 or 4 speeds, but the more the better. You'll still want to select the appropiate gear for the work, but you can cheat the speed 50% without penalty of torque output using the VFD, and avoid changing gears as much.

Second, VFDs can actually make MORE low RPM torque if they're vector type. Those are becomming more common, but the really cheap ones are still straight v/hz which provides a constant torque over most of the RPM band. You can get away with a cheap v/hz type VFD on that lathe because of the range of speeds it has. You really don't need to boost the low RPM torque, but it COULD be nice. If it were me, I'd get a vector type drive.

Third, NO, you can wire the fwd/neutral/reverse switch to the VFD to do the same functions. In fact, where the power and e-stop are is where I'd put your speed control knob. Looks like there's a couple spots for controls blocked off. So, you wouldn't need a control box! You can also wire the e-stop to the VFD, which is the way I'd do it.

Fourth, the foot brake needs to be wired to the VFD the same way you would the e-stop. You'll also need to set the VFD to free run stop so it doesn't try to fight the foot brake, but that's easy.

Fifth, the control box isn't necessary, as stated above, all the lathes controls can be wired to the VFD to make it do what the controls originally did.

Sixth, see above! All you need for a speed control is a potentiometer. Put the pot where the unused holes are by the e-stop. Should be safe there if you use one of the high quality sealed pots for about $10.

Seventh, MORONS have wired VFDs up to machines, so you'll be OK. Harder than the wiring is programming the VFD to use the external controls. Even that's not too difficult.

:cheers:

DaveKamp · Jul 29, 2008

3rd the motion...

I'll third the motion, with the following notes:

Many people worry about under- or over-speeding the motor. As noted above, you can select appropriate gearing to drive your spindle... if you need MORE power, you can overspeed the motor (run it above it's base speed) by running the VFD at a frequency ABOVE 60hz, and between that, and gearing, you can put substantially MORE power on-tap at the chuck, than you would with the stock system.

Next... the only concern you SHOULD have... is that if you're 'creeping' the motor, it's internal fan will not be moving much air. In this case, remove the motor fan, and mount a separate fan ON the motor... say... a Muffin-type fan or similar.

Next... when you E-stop the spindle of a VFD-controlled machine, you can program in a 'dynamic braking' function... which is when the E-stop circuit is broken, the inverter will shunt motor EMF through some big resistors, and cause the motor to rapidly slow to a very slow velocity... even without the mechanical brake.

I've already got an RPC... and have already converted several machines to VFD. Given your situation, I'd go VFD.

Pierce Butler · Jul 29, 2008

Integrating a VFD to a metal lathe is a task that can be a challenge but it is worth the effort. I recently added a VFD my 12x36 import lathe and it turned out very nice. All the stock controls work including jog. I did combine some functions for the operators panel. In my case there are 4 holes. The stock configuration consisted of Estop, power on, jog, and a pilot lamp. Now it consists of an illuminated Estop, power on, jog and a speed pot.

In looking at the pictures of your lathe, I would mount the VFD inside the base cabinet with the rest of the electrics. I also see some empty switch holes which is quite nice. It is as if the designers made the front panel for more options.

With 3 extra holes one can put in a speed pot, jog control, and a pilot light.

A copy of the lathe's wiring diagram will make the integration quicker and easier.

In my case there was a panel that had a few contactors, relays, fuses, etc. I took the old panel out and made a new one since I decided to not use any of the original contactors.

Very nice looking lathe BTW. Not sure I have seen too many lathes with a square lead screw shaft. I can understand why they chose that design. What is the lathe and where did you see it? Interesting toolholder too.

http://s39.photobucket.com/albums/e...athe/?action=view&current=DMTGPictures021.jpg

Mirage_Man · Jul 29, 2008

Pierce Butler said:
Very nice looking lathe BTW. Not sure I have seen too many lathes with a square lead screw shaft. I can understand why they chose that design. What is the lathe and where did you see it? Interesting toolholder too.

http://s39.photobucket.com/albums/e...athe/?action=view&current=DMTGPictures021.jpg

The lead screw is in fact round. It's 1+1/8" diameter 4TPI. What you're seeing is the cover or guard that protects it. Pretty nice feature if you ask me

.

The tool holder is actually not the one I'll be using. The actual machine I get will have a t-slotted compound for use with a standard Aloris type post.

Mirage_Man · Jul 29, 2008

How do you tell the speed at which the spindle is turning? Is there a remote display you can mount somewhere?

Pierce Butler · Jul 29, 2008

Mirage_Man said:
How do you tell the speed at which the spindle is turning? Is there a remote display you can mount somewhere?

In my case I have a 9 speed gearbox. I look at what I have the gearbox set to and guess from there. Full clockwise on the pot is the published speed.

Having variable speed while threading is handy. Especially when threading metric since you cannot disengage the split nut without reindexing.

Certain models of VFD will allow you to remote mount a display. You will need to buy a cable. For example the TECO FM50 does not have that ability. The Teco 7300CV however does.

Finegrain · Jul 29, 2008

Mirage_Man said:
How do you tell the speed at which the spindle is turning? Is there a remote display you can mount somewhere?

The position of the pot rotary knob gives me a ballpark, and the sound of the cut, lifetime of the edge, and color of the swarf dials it in :cheers:

.

Actually that brings to mind one really great benefit of a VFD with remote pot. Let's say you're putting a 1/2" wide 3" OD shoulder on a 1" shaft. With the VFD + pot, you can dial up the speed as you work your way in, to maintain optimum SFPM, without having to shut down and switch gears or belts. Also think about taking a finishing facing cut on a 6" disk -- without a VFD, you gotta pick some speed and make the whole cut. With a VFD, you can start out slow at the edge, then speed up as you get smaller. Major timesaver

.

Regards.

Finegrain

slugger · Aug 4, 2008

I'm in the same boat as MM and I find the VFDs very confusing. The RPCs are pretty simple to peruse, but how does one know what VFD they need or will find adequate? What about sizing? Can a 3 hp VFD be used on a 3 HP lathe or do they have to be oversized as well? Are all brands pretty similar or is there a big difference in them?

Mirage_Man · Aug 4, 2008

slugger said:
I'm in the same boat as MM and I find the VFDs very confusing. The RPCs are pretty simple to peruse, but how does one know what VFD they need or will find adequate? What about sizing? Can a 3 hp VFD be used on a 3 HP lathe or do they have to be oversized as well? Are all brands pretty similar or is there a big difference in them?

I spoke with a tech from American Rotary who sell Hitachi VFDs in addition to their RPCs. He said the sj200 3HP VFD would work fine with a 3HP lathe. At this point I'm still undecided as to which route I'm gonna go.

Pierce Butler · Aug 4, 2008

Mirage_Man said:
I spoke with a tech from American Rotary who sell VFDs in addition to RPCs. He said a 3HP VFD would work fine with a 3HP lathe. At this point I'm still undecided as to which route I'm gonna go.

If it were me I would get a 3hp FM50. Very basic and rugged unit plus it has a 2 year warranty. $185.00 + shipping.

http://www.factorymation.com/s.nl/it.A/id.198/.f?category=32

If you ever do any threading you will be so glad you have the VFD. Cutting metric threads is a joy with a VFD equipped lathe.

Even Grizzy offers a lathe with a VFD on it for variable speed.

VFDs are more complicated than a RPC because they do so much more than a RPC. Once the VFD is set and wired up, there is nothing to do. You turn on your lathe and go to work.

Finegrain · Aug 4, 2008

slugger said:
I'm in the same boat as MM and I find the VFDs very confusing. The RPCs are pretty simple to peruse, but how does one know what VFD they need or will find adequate? What about sizing? Can a 3 hp VFD be used on a 3 HP lathe or do they have to be oversized as well? Are all brands pretty similar or is there a big difference in them?

It's really not that complicated. Match the VFD to the motor. Nothing to it. As for sensorless vector, it's pretty dang nice. I peeled 15# of 4140 HT this weekend -- .080" DOC x .008" feed, 25 Hz on the VFD -- no slowing, surging, or cutting out.

I have 2 Teco 7300's. I can heartily recommend this unit. If you get this one, there's several of us on this site that run them, and we can step you through any rough spots. Admittedly, the manual can be tricky to decipher.

Regards.

Finegrain

J Lauffer · Aug 4, 2008

It's really not that complicated. Match the VFD to the motor. Nothing to it.

True as long as the VFD is fully rated for single-phase input. Otherwise you will need a unit that is approx twice the size of the motor to account for the derating.

John

Pierce Butler · Aug 4, 2008

Finegrain said:
It's really not that complicated. Match the VFD to the motor. Nothing to it.

Finegrain

Might be better to say "Match the VFD to the motor and to the power source." Teco has VFDs already rated for single phase input.

The 7300 is a very nice unit if you need 100% torque at 5hz (85 rpm) or so. The manual leaves a little something to be desired. The nice part about the 7300 is the PLC programmability of the unit. Most will never need or want to program the VFD in that manner.

willbird · Aug 4, 2008

I'm firmly in the "go with a vfd" crowd.

If you buy a RPC your buying yet ANOTHER 3 phase motor to go with the one on the lathe already :-).

I have an AC tech VFD on my Bridgeport, at first wiring it up SEEMED daunting, but the manual will explain how to wire it up, and did so for me, and I just know the normal electronic stuff most guys pick up working in a shop.

You can often download the manual for a VFD you are thinking of buying BEFORE you buy the vfd....and read over it and make sure the unit is what you want. There are a jillion out there for 3hp that are rated for single phase in with no derating. They can do all kinds of neat stuff like skip frequencies that cause a vibration as just one example.

Bill

slugger · Aug 4, 2008

So- which is the better unit, the Hitachi or the Teco? Where is the best place to buy them?

Also- kinda OT on this, but what is the best way to trouble shoot when this stuff stops? I have a jib borer that use to surge and buck when I started it up with my static PC. If finally gave one last chug and quit. I don't know if it's the motor, the converter or some relay?

Mirage_Man · Aug 5, 2008

Alright I'm starting to see the light concerning using a VFD. However I hope I have not discovered an issue that may throw a wrench into the works. While reading through the literature for both the Hitachi LS200-022NFU and the Teco 7300 I noticed the rated amp outputs are 11A and 10A respectively. I was told that the 3HP motor on the lathe I'm getting pulls 13A. Now I don't know if that's FLA or not.

Does this mean I would have to step up to a larger VFD? If so I have not seen any that take single phase input that are for anything larger than 3HP. If I understand correctly one can use one that takes 3Ph in but you have to half the rating. That would likely mean a 7.5HP or even 10HP VFD in which case the cost savings over an RPC nearly becomes moot.

JunkyardJ · Aug 5, 2008

13 amps might be the draw of the whole machine.

I dont think a 3hp motor will draw 13 amps unless it's a total inefficient pos. I'd be willing to bet that's the current draw of the whole machine. Most 3 phase 3hp motors draw between 7.5 and 9 amps. The big old pig of a 3hp motor on my friend's big old pig of a lathe only draws 8 amps. 11 amps is usually PLENTY of overhead. I bet they looked at the back of the lathe, and took the amperage rating off of that. It includes all the controls, and lights, possibly a coolant pump. I dunno what else is there, but I bet the motor draws about 8 amps. :cheers:

Mirage_Man · Aug 5, 2008

Oh I almost forgot. What about the coolant pump? This will be my first lathe that comes with one. The specs list it as 220V single phase. I assume it's somehow wired in with the rest of the lathe. How would it get its power?

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