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Converting to electronic variable Speed?

bowlman

bowlman

Joined
Apr 27, 2004
Messages
117
Likes
4
Location
Indianapolis, IN
Website
www.dickgerard.com
I have a 25 year old General 260 w/ custom machined riser blocks. I have been considering going to state of the art electronic variable speed. Can my old reliable General be converted? How much does it cost (ballpark figure ... I am retired and living on a very tight budget) and who do I contact? I would be especially interested if there is someone in Indiana close by who could do it.

All help greatly appreciated!
 
i don't know anything about ac VFD conversion but I have converted several power tools to dc varriable speed and what is required is pretty simple a controller and motor both of which I bought on ebay originally for $300. With my first setup I started having some problems with the high speeds on the motor but I think that was something I did running the motor at low speeds with a fairly high torque and then replaced the motor which cost me another $250 but I put the old reeves drive back on the unit and can run the motor wide open and use the reeves drive to set the base speed and the control for fine tuning of the speed. I also use the same controller on my mc motor mounted mini lathe and 2 different belt sanders by way of using quick connects.

the one thing I will say about my homemade systems is it don't seem have the same power that my variable speed ac drive of my oneway 1224. but I can say the cost difference certainly makes dc something to look into. because separately bought a 1.5hp tfec dc motor and controller ready to hook up to the motor won't be more than $450 and VS ac will be condiderably more especially if you have to have someone else do it. All except my first DC setup which had a treadmill motor all mounted directly in place of their old motors.
 
Last edited:
bowlman said:
I have a 25 year old General 260 w/ custom machined riser blocks. I have been considering going to state of the art electronic variable speed. Can my old reliable General be converted? How much does it cost (ballpark figure ... I am retired and living on a very tight budget) and who do I contact? I would be especially interested if there is someone in Indiana close by who could do it.

All help greatly appreciated!
Click to expand...
Hi,
I'm new to the forum. I've lurked for awhile and participate on another forum.
FWIW there is a thread at SawmillCreek DOT org that was started by a man who has worked with Variable speed drives for a long time. The thread is titled "Applying electronic variable speed drives to lathes" and is located in the turner's forum about the third page at this point. You can do a search and find it as well. The author's name is Don Baer and if I'm not mistaken he has helped some people aquire a drive for a reasonble cost. I didn't make a direct link as I'm not sure it is allowed. Good luck.
John
 
Dick,

I am in the process of doing the same to my Powermatic 90. I found a 2hp 3phase 220v motor with a 220v 1phase variable frequency drive at Dealerselectric.com at a fairly good price. I have everything installed and running but I am tweaking the system now.
 
Dick,

The cost is probably more than you would like to pay. "State-of-the-Art" is just a buzzword and does not necessarily mean that it is better -- just newer and more expensive.

The decision to modify your lathe should depend on what you hope to gain. It might be that buying a new (or used) lathe or even keeping the same lathe and not making any changes to it would be way better to go.

Here is a short list of typical hoped for benefits when changing a lathe drive system to EVS (Electronic Variable Speed):

  1. More power or torque needed at certain speeds.
  2. Continuously adjustable speed without the mechanical problems of a Reeves drive and the inconvenience of changing belt positions on stepped sheaves.
  3. Wider speed range is desired.
  4. Hope that "old blue" (or, "old green" in your case) can get a new lease on life and not spend the money that a new machine would cost.
Behind every silver lining is a dark cloud, so here are a few things to consider before converting a lathe drive to EVS:

  1. First of all, you will not be able to use the motor that is on your lathe so there will be the expense of a new or used motor. If you are thinking about a DC drive, the type of DC motor that you need will be somewhat more expensive than an AC motor. The type of DC motor that you would need is not the same as what you would find on most shop hand tools like routers and circle saws (which are DC motors that can also run on AC). The cost of an EVS drive for a DC motor will be less than an EVS drive for an AC motor (known as a VFD -- Variable Frequency Drive). If you want a drive system with an AC motor, then it will need to be a three-phase induction motor rated for inverter duty and able to operate over the speed range that you are interested in. The motor's cost depends a lot on its capabilities. Basically, AC motors will be less expensive than DC motors, but if you are interested in a very wide speed range capability, the cost can soar like an eagle (the same can also be said for high performance DC motors). Most importantly, it can be a complicated task to convert a lathe drive to an EVS system and meet the design goal of improving power or torque in deficient areas while not degrading it in others. There a lot of design tradeoffs that should be carefully evaluated.
  2. The continuously variable speed control that an EVS drive system provides comes with a penalty in performance and one or two other "gotchas". On a system with either stepped sheaves or a Reeves drive, the spindle horsepower remains constant. This also means that the spindle torque is increased when its speed is slower than the motor speed. However, with an EVS drive, power decreases as the speed is decreased and the torque usually remains constant when the motor is operated below base speed. Two options are generally used to improve the performance of an EVS drive system: Increase the HP of the motor and used a two or three step sheave arrangement to have different operating speed ranges. Therefore, one of the "gotchas" is that you are not entirely away from changing belt drive ratios, but it will be less frequent, hopefully.
  3. Getting a wider speed range is one of the more difficult parts of designing an EVS system and that is another one of the reasons that stepped pulley speed control is still necessary. A good three-phase motor designed for VFD may have a speed range between 25% of base speed at the low end and 125% of base speed at the top end. That would mean that a motor with a base speed of 1750 RPM would be able to operate from about 440 RPM up to about 2185 RPM. The biggest problem with running a motor slow is that it does not get as much cooling as it does at normal speed if it is a TEFC motor and, therefore, the motor must be designed to deal with heat dissipation more efficiently and also rated to operate at a higher temperature. At the high speed end, the main problems are iron losses, viscous drag, and bearing limits. Three-phase induction motors can be had that will operate all the way from zero speed up to a maximum of 6000 RPM at a cost of about $2200.00, not to mention that a suitable VFD drive will cost around $2400 (OK, so I did mention it).
  4. Upgrading an old machine is not necessarily a bad thing if it has all of the features and capabilities that you otherwise want. If you are a shrewd shopper, you can sometimes find used industrial motors and controllers for a fraction of their original price. EBay is one of the places to look, but you must be wary because there are a lot of people selling junked out equipment and you must sort the wheat from the chaff. The other hurdle is finding a knowledgeable person to design the upgraded system. You might luck-out by just hanging a new motor and controller on the machine and have everything work OK, but most likely it will not quite live up to your expectations. If it makes any difference to you, the resale value of the lathe will not go up much, if any, as a result of your modifications. Another way to look at this is to figure out what you could get by selling your lathe and how much would an EVS upgrade cost -- if you add those numbers together, find out what kind of new lathe would you be able to buy. If you thrown in the cost of headaches, aggravation, and lost time, now what kind of new lathe could you buy?
Although it sounds like I am trying to discourage you from the idea, my intention is to just point out some stuff that you may not have already considered. Sometimes ... we do things "just because" and cost or any other rational factor is not part of the equation. That is the case with me and my lathe -- I found a great deal on a used industrial motor and controller and have been working for months on redesigning my Delta 1440 lathe which currently has a Reeves variable speed drive. I guess that it just because I am an engineer and spent most of my career designing closed-loop control systems and so this project is right up my alley and that is reason enough to do it.

Bill
 
Dick not famillir with your particular Lathe but I assume it has a 1 Ph Motor?

You will require a 3 Ph Motor and an Inverter plus one or two small items.

Both can be obtained on E-Bay at reasonable cost.

The Inverter requires a 1 Ph Power Supply and the Inverter will convert this to a 3 Ph supply for the Motor.

I carried out such an upgrade a couple of years back and posted the details, including Wiring Diagrams etc. in the Hints and Tips Section of my Web Site.

http://www.laymar-crafts.co.uk

Richard
 
Hi Dick, This is my first post here but I actually sell Motor Speed Control Packages on eBay for purposes like this. As per all the other comments, you will need to use a three phase motor that is operated by a single phase input drive. This is because single phase AC motors can not operate with variable speed while maintaining torque.

The drives I use with my packages are made by AC Tech, I've uploaded a pdf of the manual here, if you wish to read up on it. These drives will operate a motor from 0 to 240 Hz. For example, if you had a 1800 RPM 60 Hz motor, you could run from speeds of 0 to 7200 RPM. However, constant torque will only be maintained when running the motor above a ratio of 30:1 of the rated motor speed. At lower end speeds the motor can also get extremely hot, so if you plan on maintaining a slow speed for more then 5 minutes, other cooling may be necessary. You even program acceleration and deceleration times into the drive, as well as up to 3 preset speeds. Everything is controlled by the buttons on the face plate but the drive has terminals where you can attach a forward/reverse, start/stop, and speed up/down switches. Also available is a remote keypad that has buttons for all of these as well as a digital readout.

If you have any questions or concerns, please feel free to reply to this thread or email me and I'll be more then happy to help. I can even put together a motor package specifically for your lathe if you can provide me with spec information about your lathe motor and the kind of power/voltages you have available in your location.

-Koko Ratanaphasouk
Friesen Electric
eBay Store
 
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