# Potential Vfd Motor For Craftsman Lathe?



## Wisrianni (Jan 26, 2016)

i was looking into doing a vfd conversion and searching for potential motors and this one seems like a good price. what do you guys think.

http://www.ebay.com/itm/Reliance-1-...630792?hash=item43e8634d48:g:4B4AAOSwJkJWjZgF


----------



## Country_Bubba (Jan 26, 2016)

Hi,
That should do the job, but remember the original motor is a 56 frame and that one is a 143 and for starters, the shaft size is 1" vs 5/8" on the original.
Do a search for NEMA motor sizes as I am not sure it will fit in place without some modifications.
Yes, there are 56 frame 1HP 3PH motors available as I found one on ebay that is going in my Craftsman 12x36.

Hope this helps.


----------



## mksj (Jan 26, 2016)

This might be worth looking at as far as an inverter rated 1Hp 3Ph motor in a 56 frame size and same price.  I read this motor  is a TENV, not sure how sure how these motors stay cool with no fins, but you are looking at pretty light loads.
http://www.ebay.com/itm/361463107005?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT


----------



## kd4gij (Jan 26, 2016)

If you need to buy a VFD also then checkout this site.
http://dealerselectric.com/variable_frequency_drive.asp


----------



## Wisrianni (Jan 26, 2016)

Country_Bubba said:


> Hi,
> That should do the job, but remember the original motor is a 56 frame and that one is a 143 and for starters, the shaft size is 1" vs 5/8" on the original.
> Do a search for NEMA motor sizes as I am not sure it will fit in place without some modifications.
> Yes, there are 56 frame 1HP 3PH motors available as I found one on ebay that is going in my Craftsman 12x36.
> ...



that helped a lot thanks! im gonna do more research and find one that hopefully is a direct fit or one that fits with little modification. what HP size am i looking for. the one on there now is a 1/2 hp


----------



## Wisrianni (Jan 26, 2016)

kd4gij said:


> If you need to buy a VFD also then checkout this site.
> http://dealerselectric.com/variable_frequency_drive.asp



wow those are some great prices imo for complete vfd and motor packages!


----------



## Wisrianni (Jan 26, 2016)

http://dealerselectric.com/item.asp?cID=50&scID=181&PID=24790

i was thinking of this one. it spins 3600 rpms. not that id ever need it but i figured better more than not enough?


----------



## Country_Bubba (Jan 26, 2016)

Wisrianni said:


> that helped a lot thanks! im gonna do more research and find one that hopefully is a direct fit or one that fits with little modification. what HP size am i looking for. the one on there now is a 1/2 hp


I think if you check the nameplate of the motor you have now, you will find it is a 56 frame.
I went with the 1 HP motor because of the needed torque at low speeds.  Mine has the original 1/2 HP motor also, but I intend to use the original pulleys and therefore wanted to try and regain the torque that would normally be gained by pulley reduction. 
I don't think there is a larger motor in a 56 frame so that is what I went with.


----------



## Country_Bubba (Jan 26, 2016)

Wisrianni said:


> i was thinking of this one. it spins 3600 rpms. not that id ever need it but i figured better more than not enough?



Remember, that twice the speed at the same HP is half the torque!  Using a VFD, you can overspeed the motor, but that is at constant HP. So that means the torque goes down as the speed goes up!  Besides that, how fast do you really want to turn this lathe???


----------



## Wisrianni (Jan 26, 2016)

Country_Bubba said:


> Remember, that twice the speed at the same HP is half the torque!  Using a VFD, you can overspeed the motor, but that is at constant HP. So that means the torque goes down as the speed goes up!  Besides that, how fast do you really want to turn this lathe???




not that fast lol. probably not more than 1800 however i read the smaller the work the faster the speed has to be due to the reduced diameter


----------



## wa5cab (Jan 27, 2016)

The rated or recommended horsepower for the Atlas 10" and early (3/8" bed) 12" was 1/2 HP.  For the later 1/2" bed 12" it was 3/4 HP.  The only thing that running a larger single speed motor will buy you is additional grief if you ever did have a crash.  The machine will not work any better and your electric bill will be higher.  There is some justification in going to 1 HP on the Commercials if running a VFD.  But I wouldn't go any larger.

Avoid the 3600 RPM motors.  For one thing, they don't last as long.  Although some of the information is a little dated (as far as specific alloys are concerned). the Atlas MOLO contains a fair amount of information on speeds, feeds depth of cut (DOC) and surface speeds for machining metals and some plastics.  All of the 10" and 12" Atlas metal lathes have a rated speed range of 28 to 2072 RPM.  I suspect that this chart is based on a motor RPM of 1740 (the old standard) but 1800 or 1725 differ by only about 1%, not enough to worry about.  You cannot get that speed range with satisfactory operation out of a variable speed motor without keeping the back gears and at least a 2-step motor pulley.  The motor will overheat at the slowest speed you would have to run it at.  Also, motors over 1 HP usually have a larger frame size than the 56 which fits the Atlas lathes and a larger than 5/8" shaft diameter.  So before you rush out and buy your dream VFD system, be sure to check the fine print.

Optimum cutting speeds vary with the material being worked and are usually specified as surface feet per minute (SFM).  Spindle RPM required to achieve the desired surface speed varies inversely with the diameter of the work piece (or of the milling cutter or drill).  There is a chart in the MOLO showing the nearest standard Atlas RPM versus diameter for various surface speeds.  It covers 30 to 500 SFM.  The smallest diameter at which the standard Atlas lathe can hit 500 SFM is 3/4".  For reference or feel, most steels are machined at speeds between 50 and 150 SFM, and aluminum at 300 to 500.  If you use carbide cutters, you may be able to run higher SFM (the figures in the MOLO are based on high speed steel (HSS) cutters) but you do not have to.  The machine will last longer if you don't.  And is more comfortable to operate (you don't have to think so fast ).


----------

