Motors AC DC

[ozzie34231]

Not sure if this is the right place to post, but can't find better.
Here goes:

My lathe has a 2HP 220v ac Taiwan motor, works well but single speed.
I'd like variable but don't have the money for a VFD setup.
I have a few DC "treadmill type" motors that claim 2 + HP, but unlike the old versions of these, some actually have wattage specs that work out to nearly 3HP.

There is a big spindle speed difference and a big weight difference. To try one I'd need to do some fancy pulley reduction.

So before I go to the trouble of trying one I'd like to hear what you all think about the actual power produced.

Thanks,
Ozzie

[LeeWay]

Just like many other motors, the actual HP may vary depending on setup. I used a 2.5 HP treadmill motor and initially installed it in my mill using an underpowered motor drive that ran on 110. I was not pleased at all with the torque or the speed. I upgraded the driver to the proper size and run it on 220. There is a world of difference. I thought I came close to stalling the motor in the mill, but actually the little V belt was slipping.
I think with the right drive, you can have a very decent motor using a treadmill motor. The motor and driver together was about $150.
If you can, use a drive with adjustable pots on it. This will allow you to tune it the way you need.

[ozzie34231]

Thanks Lee,
I have a few of the motors and suitable controllers.
It's a 14" lathe and I'm just a bit concerned about the power in these physically small motors.
How big is your mill?

Anyone else have an opinion on the comparison?

Thanks,
Ozzie

[LeeWay]

I'm not sure these would work for that size lathe.
The lathes I had in mind were 7 and 8" and possibly a 9", but that may be a bit much. Apparently, lathes need more torque than mills. If you are going to run these motors on 110, I doubt you will like the results on a 14" lathe. Especially if you like having some torque at speed.
If it is just a matter of making do or getting by, then maybe these will work on a limited basis. No way the size would be optimal though.

The mill I made is on par size wise with an X3 I think. I used an X2 spindle head, but it's on steroids with that treadmill motor.

[ozzie34231]

I looked at what I have yesterday.
One motor says 130 v 18.5 a.
That's over 3 HP, full efficiency. Even if the efficiency is only 66% I should have 2 HP. I have both 110 and 220 controllers that will deliver the needed watts.

The lathe is a gear head so I can reduce the running ratio by 15 t0 1 .
The present top RPM is 1500.
If I pulley the DC motor for a top RPM of 2500, (for small collet work), I can still get down to about 170 RPM without any electrical reduction.
The idea of 9 gear ratios coupled with electrical speed control is very appealing. I guess one question is will the bearings and gears on the machine take 2500 RPM.
I have DC controlled motors on my Shoptask, (1HP) and often find myself changing RPM a little in mid cut.
I'd also be able to use CSS (constant surface speed) with the proper interface.
I'm talking myself into this thing while I'm typing.

I'm hoping some engineer will chime in and tell me what is wrong with my reasoning. !!!

Ozzie

[Al_The_Man]

DC motors with the right controller make for a nice setup.
A couple of things concerning quality to keep in mind on motors and controllers, whether AC or DC.
The term 'Treadmill Motor' is a bit of a generic term, and covers many types and qualities of motors.
Treadmill manufacturers are in a highly competitive market, so they are often looking for a motor manuf that will make something to fit their competitive needs, so the end result can vary quite a bit.
I have seen anything from AC/DC universal, low end PM DC to some labeled 'Servo Motor' (Baldor), one that although not bad quality, I would not have though qualified for the label servo motor.
Having said that, there are some fairly decent DC motors that will fit the bill for spindle duty.
Look for good construction and state current as well as voltage, not just HP.
With controllers, their are deals to be had on ebay, such as DC regenerative 4 quadrant drives, these offer braking and reversing, and have options such as tach input, this will control the rpm to ~1%.
Whether DC and SCR control or AC and VFD control, you really get what you pay for. This is why it sometimes pays to shop ebay and obtain higher end motor/controller that meets your budget that way, instead of buying lower end at the full price.
Regarding the spindle RPM, I put a tach on a quality import lathe from Lathmaster, and found that that actual rpm of the spindle was 20~25% higher than the manual spec.
I don't think that 2500 will affect the spindle, some have observed that the bearings get fairly hot at the higher rpm, and they have ended up putting in quality bearing, just for peace of mind.
For constant surface speed you will need an encoder or feed back on the actual spindle.
Al.

[ozzie34231]

Yes to all Al,
Today I bought a DC motor, TEFC, 1 1/2 HP but wattage about 2HP, 180 V, continuous duty, 2500 RPM. This is a much heavier motor that I have more confidence in.
The controller I have has all the goodies and I do have an interface from Honnan to be able to allow Mach 3 to control the speed and accomplish CSS.
I'll definitely mount this one.
You're right about the stock speeds being a bit conservative, so mounting this motor with the same belt ratios will give me about 2500 spindle: I might even push that just a bit.
I'll be very surprised if this doesn't satisfy my needs.

I rarely make heavy cuts, I was just a bit worried about large diameters.

Anyone need a 2HP ac with low voltage control box and switches, relays, reversing!

Ozzie