VFD and G4003G in 2023

D

Damn Yankee

H-M Supporter - Diamond Member
H-M Lifetime Diamond Member
Joined
Nov 30, 2022
Messages
105
Hi All,

I looked but found no 'recent' posts relevant to my question and certainly nothing definitive.

Has anyone in the last year or so converted a G4003/G4003G to 3 HP using a VFD? I found some posts that skimmed this subject which left more questions than answers. For instance:
  1. What is the general consensus as to the 2 HP motor in terms of power? Too little, just right, too much (see next question).
  2. I've read many say that the lathe is a 1.5 HP max machine and are surprised it has a 2 HP motor. I look at the gearbox and though I am not a Mechanical Engineer, the gears and casting do not look all that beefy but I haven't seen any gripes about broken gear train or casting and the lathes have been around for some time.
  3. Going the other way (assuming the gearhead is up to it, there must be conversion (efficiency) loss with the VFD and I wonder if 3 HP may be appropriate? Current (thus torque) can always be controlled through the VFD (I presume it has current limits in the run mode) - so derating to 2 1/2 HP?
  4. If going the 3 HP route, I don't mind changing the mount but really do not want to remove or cut sheet metal.
  5. Previous posts reference motors/VFDs that are now obsolete. Any sources or substitutes?
So, has anyone gone 3 HP on these lathes and can share? Do others have thoughts or comments?

Thanks,
John
 
Replace the motor with the same size frame, or similar size in a US frame size, so most likely a 145 frame, go with a TENV as they are much shorter/compact for the same Hp and are not affected by low speed cooling. On that size lathe I would stay with a 2Hp inverter/vector style motor, power wise should be more than sufficient. You will need a different motor pulley as most likely the shaft will be different. You also benefit by using a smaller pulley and running the motor to higher Hz say 100 or 120 if a vector type motor like a Marathon BlackMax/BlueMax, Baldor IDNM or similar. These maintain full torque down to ~0 RPM, but you loose Hp below the 60 Hz base speed. Drive train should not be an issue.
 
When converting a geared lathe, the thing to keep in mind is that a VFD driven and rated motor doesn't produce full HP over the full operating range. RPMs up to 100Hz or so generally are pretty good, but power drops off as you go down in RPM (below 60Hz). Rule of thumb is it goes down linearly, but you have to look at the motor curves to get exact info.

People sometimes oversize the motor on a VFD so that they get a wider range of power. (This is particularly relevant when replacing a variable speed DC motor with VFD and induction motor, where you don't have a lot of gear combinations/options. ) For example, using a 3 HP motor means you still get 2HP at 40Hz. So if you run a 3HP motor you get at least 2HP all the way from 40Hz to 120Hz. (Roughly) . That gives a 3:1 speed range before you have to shift gears. But you do risk overpowering the machine in the middle range. Sometimes you can work the VFD parameters to mitigate this but unless you speak VFD this isn't always obvious how to do it.

The alternative is to keep the typical operating range more narrow (say 2:1, 50Hz to 100Hz), and just shift gears more often. Then a smaller motor and VFD is cheaper and you avoid the overpower risk.

A realistic approach is to use the lower power motor, set it to a wide range, but be aware that you are loosing power especially at the lower end of the range, so when you need a lot of effective power/torque, you are better shifting the gears and keeping the VFD in the 60-90Hz range. Often in hobby use we don't need that full power frequently. Hopefully this helps you understand the tradeoffs and issues. Numbers aren't exact here, but should work pretty well.

re: #3
For hobby use, the practical answer is no, the VFD doesn't incur any efficiency loss. A VFD will use slightly more electrical power at 60Hz than the same motor driven directly by line power. So there is an inefficiency in terms of electric cost. But the motor will still produce the same amount of power.
 
Last edited:
Thanks for the replies.

I don't mind changing gears to regain torque. I want the speed control between gear changes and I would like to have the lowest speed below 70 RPM - approaching 50 if possible. It would be nice to extend the upper limit of spindle speed or at least not fall below the 1,400 RPM as I'm fine with HSS, but it would be nice...

I am really out to cut tough steel or even iron with least difficulty and have a great finish on anything - thus the low-speed/high torque desire. Having never used a VFD before, I am definitely a Newbie at this and would like to get it right the first time.

While cost is of course a concern, the additional money for the 3 HP and heavier inverter, should it fill the gaps is worth it to me. And unless I crash it (which I'll probably have major problems anyway), I don't need to push it so hard to use all of the 3 HP.

Does any of this make sense?

Thanks,
John
 
I do not feel you need a 3Hp motor for this small a lathe, if you look at the PM-1236T and 1340GT there are numerous motor/VFD conversions with a 2 Hp motor and nobody has complained about cutting power. I did a conversion on my 1340GT using a Baldor IDNM 2Hp and you could not alter the motor RPM by more than +/-1RPM at any speed. You are also limited by the rigidity of the lathe and size of the tooling, I cut all types of steels w/o any issues with 0.1" DOC and aluminum 0.2" DOC. Only would recommend say a 3Hp motor if turning large diameter work say over 4-5" at 50-60 RPM. This is based on having done numerous VFD installs. Over sizing the motor is only needed if you plan to run the motor over an extended RPM range like 20-200Hz with a 2 speed gearbox. Then I oversize the motor to the next size up. As mentioned if needed you can run a smaller motor pulley to run the motor at 60Hz at 60-80 spindle RPM and then overspeed it to 100 or 120Hz to get the desired top end speed. I would recommend 1800-2000 RPM maximum spindle speed.

Motor size and orientation of the electrical box are the major limitations in motors mounted to the headstock, as most motors the electrical box is right angles to the base and will not fit unless you mount the motor horizontal with a new base. A 3 Hp motor is unlikely to fit as it is usually a 182/184 frame size.

I would go with the Hitachi WJ200 VFD as there is extensive information in this forum on this model for this application.

Some motors to look at, download the motor specs. for size.
www.ebay.com

NEW MARATHON 2 HP 3 PHASE MOTOR / E2007A 230/460 VOLT 1760 RPM | eBay

Find many great new & used options and get the best deals for NEW MARATHON 2 HP 3 PHASE MOTOR / E2007A 230/460 VOLT 1760 RPM at the best online prices at eBay! Free shipping for many products!
www.ebay.com
www.ebay.com

Marathon R319A Electric Motor 2 HP 1800 Rpm 3PH 230/460 Volt 90L Globetrotter | eBay

Find many great new & used options and get the best deals for Marathon R319A Electric Motor 2 HP 1800 Rpm 3PH 230/460 Volt 90L Globetrotter at the best online prices at eBay! Free shipping for many products!
www.ebay.com

These will require a horizontal motor mount
www.ebay.com

CVM 145TTTN6027 BA P MARATHON MOTORS MARATHON 2HP 3P 1725RPM 230/460,E354,TE | eBay

<p>New old stock w/o box!!</p><p>3 months warranty!!!</p><p>Full refund!!!</p><p>(TE00-00-00)</p>
www.ebay.com
www.ebay.com

Marathon Blue Max SVE145THTN8029ABP 2HP NEW | eBay

Find many great new & used options and get the best deals for Marathon Blue Max SVE145THTN8029ABP 2HP NEW at the best online prices at eBay! Free shipping for many products!
www.ebay.com

3Hp probably too big to fit motor space.
www.ebay.com

MARATHON XVF182THTY7726AAM Black Max | eBay

Find many great new & used options and get the best deals for MARATHON XVF182THTY7726AAM Black Max at the best online prices at eBay! Free shipping for many products!
www.ebay.com
 
I agree with Mark. Your money is better spent on a quality VFD inverter motor at 2HP (like he linked to above) and a decent VFD, than getting something rated higher HP but not as suitable for VFD use. There are significant differences in the quality of inverter duty motors and VFDs. Overkill on HP isn't worth it, good inverter duty is. (VFDs are sometimes called inverters) One big win on 2HP w/ VFD is also that you can typically run 2HP VFD on 20a 220V circuit. 3HP gets marginal and may call for a 30a circuit. You need to check the VFD specs to be sure.

I run a 3HP VFD in a 3500 lb 14x30. My control panel includes a load meter from the VFD. I rarely use more than 50% load (1.5 HP) on a substantially stouter lathe, mostly using carbide inserts on steel and steel alloys (pretty much worse case for load). That lathe had a factory option for a 5HP motor, I don't regret not upsizing, although admittedly I have a much larger lathe (10HP) if needed, although that one doesn't use a VFD.

Basically a bigger motor allows you to make fast, heavy, rough cuts up to the machines limits. If you're doing a lot of work where time is money, than that is more iimportant. For hobby use, I don't think dealing with huge hot chips is worth the few minutes saved.
 
Last edited:
Our old SB 14.5 has, if I recall, a 2 HP 1940's 3 phase motor with a 3 hp Allen Bradley VFD. The manual states this is the correct size combination for single phase input.

The AB VFD does not have the fancy controls of newer units, just basic stuff.

The motor is 1946 or so.

The lathe has 4 belted speeds plus back gear.

We run it in the second from fastest belted speed and use the VFD to go from slower to faster. Just go by what works.

If we need real slow, we can use back gear and VFD.

Have yet to stall it.

We can go from RPM to MPR.

We can get fairly slow without back gear but no torque, which is expected.

Ours is the original motor, so I'm not worried about overpower.

In your case, if the original motor is 3 phase, keep it. If not, locate 3 phase of same rating.

For VFD, download the manual before you buy.

You can confirm which one you need and determine if it will work.

Also, if there is no manual available or can not understand it, it signals the level of support for that unit.

Sent from my SM-G781V using Tapatalk
 
I would say I have some convincing arguments to stay at 2 HP, which makes my chore considerably easier.

I truly appreciate the photos/links/opinions as to options regarding motors/drives for that is where I am really behind the curve here.

Great Group!

John
 
You must log in or register to reply here.
Back
Top