So, he told me to come get the darn thing out of his garage... Big Ole Arn!

[TDKPE]

Is wiring a 6 pole motor easy enough? Would I still be able to use it with a VFD?

A 6- (magnetic) pole motor connects no differently than a 4-pole or 2-pole (1725 and 3450 rpm typically).  It just runs slower, with proportionately more torque (hp = torque x speed, so a slower speed motor delivers more torque for the same hp rating).  The FLA may be a little bit higher (or not), so just make sure the VFD has a FLA rating at least as high as the motor's nameplate FLA.

[TDKPE]

Here's a NOS Baldor, TEFC, 2 hp, 6-pole, 208-230/460V.  For $84.95 + $42.66 shipping.  Looks like a real bargain.

http://www.ebay.com/itm/Baldor-Prod-ID-3...SwnTJXAazW

And a used 3 hp Baldor.

http://www.ebay.com/itm/BALDOR-M3704-3HP...SwrhBZDMoA

They're out there.

[Gregory of Sherwood Forest]

The motors that came with it use an 143T frame mount. Can't locate one of those used on Ebay, unless there are alternatives?

Correction, 143T mount. I can find adjustable mounts, though...

[TDKPE]

The "14" part of the frame size, for 3-digit frame sizes, is the distance from the mounting foot surface to the shaft centerline, in quarters of an inch.  So the 143T is 14/4", or 3-1/2".  All the motors that start with "14" will have the same distance.  The other numbers will differ in shaft length and/or bolt spacing, but they should all have a 7/8" dia. shaft.  Unless it has a "Z" on the end of the frame size, which means 'special' - what's special isn't part of the spec (could just be a threaded hole in the end), but it's something to look out for.


The 3 hp is a larger frame, which isn't unexpected.  It's probably too big for your machine, especially the shaft dia.  Frame size is dictated in large part by torque, and a torquey motor like a 3 hp, 1200 rpm motor is like a 9 hp at 3600 rpm, if there was such a thing.  So it'll be big.  You should probably stick with the 2 hp.  There are a couple of them.  Or the 1.5 hp, of which there are many more still.  

The fan on the last 2 hp I found is on the shaft end, which shouldn't cause a problem.  It's listed as a TEAO, but it has a fan, so it's TEFC.  I would ask for a clean pic of the nameplate.  That motor is listed on another site (found it by searching on the product ID).

I'm guessing the 2 hp and smaller, in rolled steel frames at least, would fit, maybe with a couple of holes drilled in the mount.  Shaft size is probably key for that Reeves drive, though - that's not a sheave that's easy to replace, and you want the slow mechanical reduction first and foremost, before slowing the motor to get to a crawl at the work.

[Gregory of Sherwood Forest]

Great info! Thanks. I know little about the motor side, so this is giving me an education as well as helping me work out how to get where I want.

So, I'm thinking that if I get a 6 pole 1180 RPM 3 phase 3HP motor, and put it on a VFD, then I should be able to get as low as I want, but I wouldn't be able to get over 1180 RPM then, would I?

So, maybe going the route of a 3450 RPM, 3 phase 2 or 4HP (in either 6 pole or 4 pole) motor and a VFD is still the best option for complete speed range from around 50 RPM to 3k??

I sure don't mind dropping $300 for the VFD. If I can get good torque and a full range of speed for around $500 or so, I'm thrilled. I don't have anything into this so far.

[TDKPE]

So, I'm thinking that if I get a 6 pole 1180 RPM 3 phase 3HP motor, and put it on a VFD, then I should be able to get as low as I want, but I wouldn't be able to get over 1180 RPM then, would I?

You can run that motor higher than it's rated speed.  I run mine down to 16 Hz and up to 125 Hz.  That's 16/60 x 1725 rpm = 460 motor rpm, or 0.27 x 'normal' spindle speed, at any mechanical 'gear' (4-step pulley set on mine).  Published lowest speed on mine is 915 rpm using a 1725 rpm motor, so .27 times that is 244 rpm.

If it was an 1140 rpm motor (6-pole), it would be 2/3 of that yet again, or 162 rpm.  Maybe too fast your your needs, but the lowest speed your lathe can do via a 4-pole (1725 rpm) motor and the Reeves drive might be lower than mine to start with.  And you can always set the minimum frequency to something lower than 16 Hz - I just did that because it's slow enough for my needs on my small (12") lathe.

If you run the motor on 10 Hz power, the motor speed and lowest spindle speed will be 1/6th that of 'normal' speed using a 'normal' 4-pole, 1725 rpm motor.  Using a 6-pole, 1140 rpm motor, it's 67% of that figure.  With a vector drive, you can go pretty slow, though I don't know how slow.  Cranes with vector drives (but with sensors) can stop and hold the load still with just the motor, or creep it up or down (the brake sets when you get off the stick, of course).  The really old overhead cranes with DC motors could do that, too.

I think I confused you with the number of poles in a motor.  The synchronous speed of a motor (the speed it would run at if the rotor could keep up with the magnetic field rotation) can be calculated from speed (rpm) = 120 x line frequency (Hz) / number of poles.

2-pole: 120 x 60Hz / 2 = 3600 rpm
4-pole: 120 x 60Hz / 4 = 1800 rpm
6-pole: 120 x 60Hz / 6 = 1200 rpm
8-pole: 120 x 60Hz / 8 = 900 rpm

and so on.  The rotor can never quite catch up to the magnetic fields, which is how they induce a current and therefore magnetic field within the rotor, and is why they're called induction motors.  So full-load speed is always a little less than synchronous speed, like about 96-97% of synchronous speed (1725 rpm full-load spped on 1800 rpm synchronous speed).

For 50Hz power, they work out to 3000, 1500, 1000, and 750 rpm, respectively.  And there are generators (like in hydro dams) with way more poles, so they can turn quite slowly and still generate 60 or 50Hz power.  Old diesel generators, going back to the 30's and up, used to be 1200 rpm, so they had 6-pole generators.  Really big diesel generators are still available new with 1200 rpm operating speed, but anything normal size, like 1000 kVA and down, spins at 1800 rpm these days.  The little portables (without inverters) run at 3600 rpm, so they have 2-pole generators.

If you look in motor manufacturers catalogs, the speeds are normally given in terms of number of poles and line frequency, at least for filtering your selections.  

But the important thing to you is that an 1140 rpm motor will have 3 times the torque as a 3450 rpm motor, and 1.5 times the torque as a 1725 rpm motor of the same rated HP.  That's the whole reason for going to a slower speed motor - it's like a built-in reduction gear.

[Gregory of Sherwood Forest]

Gotcha. Yeah, I was missing something in the translation. That last post helped, thanks.

Boil this down for me, as it appears that I am finding that there is more to consider than I previously thought.

I'd like to get speed ranges from ~50-2000 rpm. 2 HP minimum. Good torque, as I want to do very large platters without having to visit someone else's lathe again.

How can I get there, at a reasonable cost ($500 +/-), and without having to go for yet another Masters Degree?

Is there a VFD and motor combo recommendation you have?

Thanks, and sorry for all the requests...

[wmesquite]

Sir Gregory, the tool gods have truly smiled upon you. Did you perchance make a blood sacrifice of some sort to appease them first? Just wow.

A sensorless vector VFD and 3-phase motor is a nice setup, will get you what you want in speed range. But the 3 hp (Versus 2 hp) may not give any extra power in use because of belt slippage- I've had slippage  on my 1 hp drill press with a vee-belt  at 6 hz. A separate fan should be used when you  run the motor below 30 hz (1/2 speed) for extended periods. Consider room to install this- 3" on back side of motor would be nice, though on far side of belt okish. A computer/muffin fan works, you may also need a 12V transformer; with a relay you could have it on only when the VFD is in a run state.

As far as motor replacement- frame and shaft size are key. You need 7/8" shaft to use your drive pulley, and a 143T/145T frame will be direct bolt in replacement. A 184 (NOT 184T) also has a a 7/8" shaft and can be used with a plywood adapter plate if you have 1.5" additional vertical travel on your motor mount.  You also need an additional inch clearance in front and back of the motor. Glad to help on the adapter plate if  asked. Larger motors than listed below have larger frames/shafts.

A 3 hp 1150 rpm motor won't fit in your lathe base, plus you'd need a new Reeves pulley for it- likely have a 1 3/8" shaft. Watch the C dimension- aka motor length from shaft tip to end of motor housing- bigger hp motors in same frame size get longer.  Bigger C dimension might fit but could interfere with extra fan space, My first 2 recs below,  M3161 and M3607 have C= 14.3" BTW.

Having a 20 year old Baldor catalog helps, they have discontinued so much.  Their only 3 hp motor with a 145T frame is a M3161T. Open frame- but they run cooler and could be a benefit here. None on ebay now, some have sold recently.  Leeson still makes one equivalent.

My motor of choice for your setup would be a Baldor M3607T, a 184 frame 1.5 hp in 1150 RPM. Always better to have native speed slower if you're gonna run it slower (better cooling as well as torque), and you can set VFD max speed to 90hz for top speed.  Seller wants $200, may take $150-worth a try. http://www.ebay.com/itm/172445397659?

A 2hp 1750 rpm 145T frame is easiest to find/cheapest. Make sure USA made, not "globally sourced." This one is a Baldor M3558T and is ok at $150 shipped to door. Seller is very good, but no pic so I'd ask if clean, paint mostly ok and especially if shaft looks real good-rust ok, mangled not ok . Also can ask on OWWM for spare.  http://www.ebay.com/itm/391784281787

The 2hp 1150 rpm TDKPE linked is problematic, with a 184TZ frame. Ostensibly would have a 1 1/8" shaft since a 184T. But the Z suffix means there is shaft funkiness involved. Could be longer, shorter, stepped, bigger, different keyway, or smaller. I think TEAO on the box means additional fan needed even with one on the motor.

Wade, followed this from general forum, back to occasional lurk mode

[wmesquite]

BTW, reference links for most of my previous commentary, all from the Cowern Papers

Main (note this discusses the Z suffix on a motor frame):
http://www.motorsanddrives.com/cowern/motorterms2.html

Frame size dimensions reference
http://www.motorsanddrives.com/cowern/mo...chart.html

Motor hp versus frame size
http://www.motorsanddrives.com/cowern/mo...bl1&2.html


And the reason I focused on Baldor is mostly because they seem to have made about twice as many motors as all others put together.
Later,
Wade

[Gregory of Sherwood Forest]

Great read. I just ran through the basics of the Cowern Papers for the last hour and learned quite a bit. Thanks.

Now, I have to choose a VFD. I suppose just fitting it to the proper HP and phase is an oversimplification???