Question concerning Tormach 1100 Spindle Motor HP

I currently am using a Prolight 1000 mill which has a Baldor Motor which has the following specs

HP: 1 TE
5.3 Amp
180 Volts DC
Type: PM
Duty: 1HR

I am limited on the amount of heavy cutting with this machine as the spindle will bog down on heavier cuts, so I am considering upgrading to a Tormach PCNC 1100 Series3

But I noticed they use a 1 HP motor also, so I'm concerned that I won't be gaining anything.

Maybe I shouldn't only be looking at the HP to make my decision?

Any feedback would be greatly appreciated...

Kent

Rigidigy will also help taking heaveri cuts, but it's not magic.

The Series 3 1100 has the following spindle specification:

Quote:

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Spindle Power: 1.5 hp Brushless AC 3-phase Induction Motor,
Vacuum Pressure Impregnated (VPI) Windings

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Tormach says it's a horse and a half. My 1100 will remove around 6 cu in/min of aluminum using a Superfly. I'm pretty sure it'll do more; I chickened out at that point. GWiz said I had around a quarter horse left. Nameplate on my 1.5 hp 1100 motor says 230VAC, 60hz, 4.5A, 1715 rpm, 1.1Kw. 1.1Kw = right close to 1.5 hp.

And I betcha a nickel I just figured out why it's an "1100".

DC PM and AC induction motors have vastly different operating characteristics. For DC PM motors torque is a linear function of RPM with the RPM dropping as the torque load increases until maximum torque and stall are reached. At the maximum HP operating point doubling the torque cases the motor to reach the stall (zero RPM) point. This results in very poor open loop speed regulation (see first reference).

Three phase AC induction motors have a totally different behavior where a doubling increase in torque load only causes a relatively small change in RPM (see the second reference). This is because a relatively small change in slip angle causes a large change in output torque.

Note that I have avoided providing a mathematical treatment or links to the mathematical explanations since I presume that most here would have difficulty following the sometimes quite complicated mathematics involved. The PM DC motor math is easy but 3 phase AC motor mathematics are far more complicated. Check out Wikipedia if you want to see the mathematics.

References:
D.C. Motor Torque/Speed Curve Tutorial:::Understanding Motor Characteristics
INDUCTION MOTORS:INDUCTION MOTOR TORQUE-SPEED CHARACTERISTICS | electric equipment

there isn't much difference between a dc 1 hp motor and a 1hp induction motor regardless if its single or three phase. both will have similar rpm drop under load of 1800 to ~1750 rpm.

Regarding the Prolight, how much does it weigh and what kind of ways are used?

the Tormach 1100 weighs about 1100 pounds and uses dovetail ways with some kind of equivalent to Turcite.

Quote:

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Originally Posted by Eldon_Joh

there isn't much difference between a dc 1 hp motor and a 1hp induction motor regardless if its single or three phase. both will have similar rpm drop under load of 1800 to ~1750 rpm.

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Your claim is partially irrelevant since the Tormach mill in question actually has a 1.5HP 3 phase induction motor (not 1HP) and it is marvelously incorrect about the open loop speed regulations of these two types of electric motors.

As can be easily seen from the speed vs torque curves that I displayed above, a torque load change on the PMDC motor causes a proportional drop in RPM following that straight line (also commonly known as the load line). In contrast the same load change on an induction motor causes the rotor slip factor to change and the available torque can actually increase by a large amount, easily self regulating the speed to within a few percent. The AC induction motor performance plot shown assumes a constant frequency and constant AC voltage on the motor stator (of course neither of those are true due to the Tormach 3 phase inverter) . Note that the pullout torque limit is over 4x the continuous run load torque and the RPM drop there approaches 20%.

Compare the higher slope magnitude of the vertical torque vs RPM curve on the AC induction motor to the much lower slope magnitude of the PMDC motor curve. For the AC induction motor to exhibit the same open loop speed regulation as the PMDC motor the AC induction motor RPM vs torque curve would need to be a straight line between the starting torque point (zero RPM) and the full load torque point.

A PMDC motor having similar speed regulation characteristics to the same power 3 phase induction motor at full load torque would need to be very large and also be operating at a quite small fraction of its stall torque in order to have a speed regulation curve similar to the high slope portion of the AC induction motor. Note that a "perfect motor" would have a speed regulation curve that was completely vertical for the PMDC motor and completely vertical for the AC induction motor, with both starting at their no load speeds. Both of those curves would indicate that the motor RPM was completely independent of the load torque. An AC induction motor exhibits a much higher slope than an equivalent power PMDC motor.

Please provide evidence that the PMDC motor in question has similar self speed regulation as a 3 phase induction run motor of the same power. I looked up the Prolight 1000 mill since I am totally unfamiliar with it and all of my Prolight information comes from the Prolight 1000 User's Guide (see below link). There appears to be a paucity of information about this specific machine on the web.

I see that the mill spindle RPM ranges are essentially the same (200 to 5,000 RPM vs 200 to 5,140 RPM, for the Prolight and Tormach, respectively). Both mills utilize stepper motors for the XYZ axis movements, although the Prolight has much slower rapids than the Tormach 1100 (50 inch/minute XYZ vs 110 for XY and 90 for Z, respectively). It is also quite obvious that the Prolight is a *much* lighter machine than the Tormach 1100 since runs off of only 120VAC and 12 amps (240VAC and 120VAC for the PCNC 1100), uses thin guide rods for the XYZ axes instead of dovetail ways like the Tormach, and both the table size and the XYZ travels are *much* smaller than the Tormach 1100 as well. The guide rod bearings are actually split bushings that get compressed to size using multiple setscrews. They need adjustment for wear and such adjustments must be done at the ends of travel top prevent binding (most guide rod wear generally occurs near the center of travel). There is no built-in lubrication system; the bellows must be disconnected and the ball screws hand greased after every 200 to 250 hours of use. I was unable to find any ball screw accuracy specs for the Prolight.

I attempted to look up the specifications of the Baldor motor. Having the Baldor motor model number is *very* desirable, so please post that if you know it. Baldor is now ABB and the closest PMDC motor that matched what was shown above has these specs: 1,750 RPM, 180VDC max on the armature (note that this is a brushed motor), 5 Amps, and 3 Pound-Feet (this appears to have a 1 hour time limit instead of being continuous). It uses ceramic instead of NIB magnets in the field (possibly due to motor temperature limits). Unfortunately they do not list the no-load current and RPM, armature winding + commutator + brush resistance or else the stall current. Having those parameters I could easily plot the RPM vs torque load performance curves since I had created programs and even spreadsheets to do just that for PMDC and stepper motors given only a few easily measured or manufacture supplied parameters.

Size wise, the PCNC 700 is a much closer fit to matching the Prolight 1000, but I would personally recommend the PCNC 1100 over the PCNC 700 due to the larger travels, higher HP motor, and increased rigidity. The only downside for the 1100 vs the 700 is the spindle RPM on the latter goes to 10,000 RPM, which is no problem for me personally since I own a pristine air turbine grinder with an R-8 taper that goes far above 10K RPM (purchased used on eBay years ago). Tormach has a "speeder" for higher RPM on the PCNC 1100 but I cannot provide any feedback on how well that works.

Prolight User's Guide link:
http://www.google.com/url?sa=t&rct=j...PbLT3MegHBrcBu

Baldor motors link:
https://www.baldor.com/mvc/DownloadCenter/Files/BR600

Thanks for the info.... Yes, I was mistaken on the HP being only 1 HP

Quote:

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Originally Posted by Zetopan

As can be easily seen from the speed vs torque curves that I displayed above, a torque load change on the PMDC motor causes a proportional drop in RPM following that straight line (also commonly known as the load line). In contrast the same load change on an induction motor causes the rotor slip factor to change and the available torque can actually increase by a large amount, easily self regulating the speed to within a few percent. The AC induction motor performance plot shown assumes a constant frequency and constant AC voltage on the motor stator (of course neither of those are true due to the Tormach 3 phase inverter) . Note that the pullout torque limit is over 4x the continuous run load torque and the RPM drop there approaches 20%.

Compare the higher slope magnitude of the vertical torque vs RPM curve on the AC induction motor to the much lower slope magnitude of the PMDC motor curve.

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the slope is very similar for similar motors of similar efficiency.

no load speed of an induction motor is the synchronous speed, say its 1800 rpm. at full load it will be 1720 to 1760, depending on the efficiency. typically its 1750 rpm.

a 1-2hp dc motor of similar efficiency will have a similar drop in rpm. (proportionally, since the rpm is whatever you want it to be)

anyhow, if you're bogging down a 1 hp dc motor, then you either have a not very efficient motor (which is a possibility), or you need to find a 2-3 hp replacement. a dc amp meter on your spindle motor will help you out here, if the motor is bogging down but not drawing more than 5 amps, then you can just replace the motor with a better one. if you are pulling 7 or more amps then the 1.5hp motor of a tormach will still be pushed to the limit.


note also your motor has a 1 hr rating. what this means is its actually probably a 1/2-3/4th hp motor. an 1800 rpm 1 hp motor will weigh about 32 pounds.

Quote:

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Originally Posted by Eldon_Joh

the slope is very similar for similar motors of similar efficiency.

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And I fully agree, but there's the rub. The efficiency of a multiphase induction motor generally runs from 85% to 97% at full load (see link #1). To get high efficiency with a PMDC motor it must be *very* lightly loaded and no where near its maximum power output point. As a result a high efficiency PMDC motor must be seriously oversized to achieve the high efficiency point in actual operation. For a given motor physical size the polyphase AC induction motor will always be more powerful and higher efficiency than a same sized PMDC motor. I personally doubt that the Prolight spindle motor is a high efficiency unit, but that is merely an opinion since I currently don't have sufficient data to indicate the efficiency and load line, etc.

I have attached an example PMDC motor plot to illustrate my point. This is data for a real PMDC motor but much lower voltage and power than what Prolight uses, I am only including this motor because I happen to have the data and it is a high efficiency PMDC motor. If I could get sufficient data about the Prolight motor I could trivially plot that for real.

The important things to note in this plot are that the peak efficiency point (blue curve, use the right hand side vertical scale divided by 10 to read the efficiency) is far away from the maximum output power point (green curve with the right hand vertical scale showing the shaft output power in Watts). This particular PMDC motor reaches about 92% efficiency but only at a torque load that is about 4%(!) of the (non-stall) torque at the maximum rated power. A lower efficiency PMDC motor has those two points *much* closer together. In contrast a polyphase AC induction motor in the smaller sizes (around 1.5HP) will exhibit maximum efficiency from around 50% to 100% of its rated load. Higher HP induction motors have even flatter efficiency curves. See the attached plot.

Quote:

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no load speed of an induction motor is the synchronous speed, say its 1800 rpm. at full load it will be 1720 to 1760, depending on the efficiency. typically its 1750 rpm.

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Your numbers are correct for a 4 pole 60Hz AC induction motor.

Links:
#1 https://en.wikipedia.org/wiki/Induct...tor#Efficiency

google 3 hp tormach and watch my video. I changed my motor pulley and vfd!! I haven’t bogged down ever again I run 90% stainless steel on the mill with larger diameter cutters 0.500 to 0.750 endmills usually.

so it looks like dayton and baldor don't publish motor curves for their dc motors. this is slightly a bummer because i have about a dozen of their motors, mostly 1/2 hp but a few .75hp motors and a 1.5 hp motor. also several treadmill motors of dubious "2.3 hp" ratings.


I was able to find this: 42A Series Permanent Magnet DC Motor Model N4432 Specifications

Category NEMA 42CZ Face Mount
Speed (rpm) 2500
Rated Torque (oz-in) 180
Amps 3.4
Motor HP 1/2
KT (oz-in/A) 57
KE (V/krpm) 42
Winding Resistance (ohms) 2.7
Winding Inductance (mH) N/A
Rotor Inertia (oz-in-sec²) 0.12
Radial Load (lbs) 90
Length XH (inch) 7.87
Weight (lbs) 14.5
Product Type 42A7FEPM
Rated Voltage 130V


3.4 amps times 2.7 ohms is 9.18 volts, which is 7% of 130vdc.

the volts/rpm constant of 42*2.5 is 105, which implies 105v/130v or a 19% rpm drop under load.
3.4 times 130 volts is 19% more than 1/2 electrical hp, implying the motor is 84% efficient.

anyhow a lot of the scr drive controls incorporate IR feedback. --so without an amp meter on OP's spindle we won't know if he is overloading the motor or if its just a lightweight motor.

5.3*180v is 954 watts, so 746/954 is 78% efficient. so, its quite possible that OP's motor has worse rpm drop under load than the above 1/2 hp motor from bodine.

All of my Bodine motors are small fractional HP; generally under 0.2 HP. Unfortunately I cannot plot the performance of your motor without making a number of assumptions since the provided data is incomplete. The data is not only incomplete but it also appears to be self contradictory. With a Kv of 42 and a 130 VDC supply a "perfect" PMDC motor (no losses of any kind anywhere) would run near 3,100 RPM with no load. At a stated 2,500 RPM operation that implies an obvious 593 RPM drop, which also means a back EMF reduction of about 25 VDC. That DC drop over a 2.7 Ohm resistance results in an armature current of over 9 Amps while the stated operating current drain is only 3.4 Amps. Hence there must be much more than 2.7 Ohms of total resistance if the stated Kv and rated supply voltages are correct. With a total wiring resistance of about 7.3 Ohms the operating current matches the stated value and the output power is close to matching its rating. In short, the specifications are incomplete and unspecific enough to make much sense of them without fudging something.

If you have the motors in hand a few measurements would allow for plotting the performances though. Simply determine the Kv (Volts per 1K RPM) by measuring the unloaded back EMF while spinning the armature shaft at a known (or measured) RPM if you don't already have that data. Also measure the total resistance; armature windings plus brushes plus any other wiring (includes power supply). And measure the RPM at at least two different supply voltages (e.g. at full supply and half supply) with the motor being unloaded and also record the current drain at the full supply voltage. Those latter measurements allow for estimating the friction and viscous losses.


"its quite possible that OP's motor has worse rpm drop under load than the above 1/2 hp motor from bodine."

Based on the general lightness of the Prolight 1000 construction it is my personal suspicion that the 1HP rating is actually a peak HP number and not a continuous HP rating.

Quote:

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Originally Posted by Zetopan

All of my Bodine motors are small fractional HP; generally under 0.2 HP. Unfortunately I cannot plot the performance of your motor without making a number of assumptions since the provided data is incomplete. The data is not only incomplete but it also appears to be self contradictory. [...] Based on the general lightness of the Prolight 1000 construction it is my personal suspicion that the 1HP rating is actually a peak HP number and not a continuous HP rating

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i agree with both statements.

its not clear to me if the rpm stamped on the nameplates of bodine, baldor, dayton, and others is the no load rpm or the full load rpm.

here is another example of a 0.3hp motor
https://www.groschopp.com/data/other...ance/04404.pdf
the back emf at 1650 rpm works out to 85 vdc, not 90vdc.

there is one solution for this: the torque needed to turn the motor at no load is not negligible. it could easily cost you 5% just to turn the motor due to bearing and commutator drag. but this doesn't account for the 19% discrepancy in the published data in my previous post.


I can relatively easily chuck the motors I have in my lathe and short circuit the motor through an amp meter and measure the torque and rpm needed to generate nameplate amps through the leads. but at the short circuited, full load torque, at an rpm of say, <200, it does not fully account for the armature reaction and higher frequency losses of the rotor core and the copper armature coils. so there would still be a discrepancy but it would be minor.

as you probably know the larger the motor the more efficient it is. but i do agree (though i disagreed with it initially) with your initial statement that induction motors have stiffer rpm regulation. They also have lower efficiency than dc motors and consume much higher no load losses.
An average 1/3rd hp induction motor in my experience has a minimum of 200 watts no load loss and about 50-60% full load efficiency.

A lot of interesting things have been posted about the torque curves of induction vs. brushed DC motors, but most of them really don't apply here.
Is your current mill variable speed (as in a knob to adjust the speed, not changing belts or gears?) If it is, and you aren't running at full speed, you aren't getting full power. Generally, brushed motors have constant max torque limited by current/heating. So if you halve your RPM's, you halve your power.
The Tormach uses an induction motor with VFD. Below it's 'rated' speed it behaves the same as the brushed motor, constant max torque. But it can be oversped, I think the Tormach has max power between about 2000 RPM and 4000 RPM in high gear (from memory, might be 2500ish on the low end.) Below that the power drops linearly, above that it drops off a bit to it's top speed around 5000 RPM. Then it's got a low speed pulley that is somewhere around 1/3 that ratio if you're using a face mill or whatever.
So most likely the Tormach will have a lot more torque at the RPM's you need it at. Looks like it's a bit heavier machine than what you've got as well, so it should perform better all around.

The PCNC 1100 spindle motor HP reaches its maximum at 1,715 RPM where it is rated at 4.5A, 230V and 1,100KW. Below that RPM it is operating in constant torque mode and above that RPM it is operating in (essentially) constant HP mode. I said essentially because there are some increased viscous and eddy current losses at higher RPMs. Induction motors rated for VFD use (note that *many are not* rated for VFD usage) will have minimal eddy current losses at higher RPMs while motors not so rated will have much larger losses at higher RPM. By the way, as the Tormach PCNC 1100 spindle approaches 8,000 RPM the head heats up very quickly and could reach temperatures that negatively impact the spindle bearing lifetime due to the bearing preload and viscous losses heating.

Since the original poster was complaining about the maximum metal removal rate of his Prolight mill I suspect that it would be fairly safe to say that he was not purposely operating his spindle motor at a low power setting.

If you examine the PMDC vs AC induction motor performance curves that I previously supplied you will clearly see that at light loading (relative to the motor's output power rating) PMDC motors can be more efficient than induction motors, since for efficient PMDC motors their peak efficiency is generally well below their maximum output power point. Inefficient PMDC motors will have the maximum efficiency operating point quite close to their maximum power point and will approach 50% or even much less efficiency. In contrast, at maximum load industrial 3 phase induction motors can easily outperform the efficiency of PMDC motors. Note that the vast majority of my motion control designs have used PMDC motors, so it isn't like I am biased against PMDC motors. The lowest efficiency 3 phase induction motor that I have ever seen was a speed controlled fan in a portable instrument, and that had trouble reaching better than 30% efficiency. Industrial 3 phase induction motors are *far* better than that exceptionally wimpy cooling fan.


"If ... you aren't running at full speed, you aren't getting full power."

To address that statement I only need to point out that at a motor speed of perhaps 1,600 RPM upwards the Tormach PCNC 1100 spindle motor is producing very near its maximum output power. Note that since the Tormach VFD uses a sensorless vector drive the VFD cannot fully compensate for the slight RPM drop at increased torque loads (beyond what induction motors already inherently exhibit due to the changing slip factors), but that specific drive does utilize an internal model of the motor with the appropriate motor parameters in the DSP controller, so it actually partially compensates for increased torque loads over and above the inherent induction motor characteristics. My assumption would be that the Prolight surely has some type of motor RPM feedback for regulating its output speed.

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"If ... you aren't running at full speed, you aren't getting full power."

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I'd like to be a little stronger on this statement than you were: This is true for internal combustion engines, but is not at all true for electric motors.

There are three things limiting the top speed of an electric motor:

1) Controller electronics switching speeds -- as the switching speed goes up, more power gets lost switching the voltages around to drive the motor; the actual power lost isn't so bad but the additional heat generated in the controller MOSFETs is what really limits you. The faster you go, the more you lose in switching losses, and the hotter things get.

2) Bearing and output losses -- there is some amount of friction between the rotor and the output shaft/spline, and additional friction in your real load. The faster you go, the more output losses there are, and those also heat things up (hence, why high-RPM bearings are expensive.)

3) Back EMF in the motor. This is the big one. A motor can also work as a generator/alternator, because there is movement of electrical conductors (windings) in a magnetic field (either the AC inductive field, or the permanent magnets in PMDC or BLDC or IPM motors.) As the motor spins faster, this "generator" current fights against the current that wants to make the motor run; this is known as "back EMF." Once the back EMF is as high as the maximum current you can provide to the motor within your heat and voltage parameters, you can't make the motor spin any faster. At the theoretical max RPM point, the back EMF is as big as the propelling force, basically leaving zero power left for you to actually use. So, at the maximum possible RPM, you have MINIMUM possible power in an electric motor!

Zetopan is absolutely correct in summarizing that electric motors generally work in constant torque mode, where power goes up linearly with RPM, until some cross-over point, where power starts falling until you hit the theoretical max RPM of the motor based on back EMF. Given that you don't get any useful work out of the motor if you operate at that point, you'll want to be below that, and given that output losses and switching losses are highest with high RPMs, you never see motors actually operated up to the theoretical max RPM.

Most importantly, though: The power/speed relation for electric motors is TOTALLY DIFFERENT than for internal combustion engines.

Ok, perhaps, in its original context of referring to his current mill (with a brushed spindle motor,) I should have said if you don't have the dial cranked all the way clockwise, you aren't getting full power.

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if you don't have the dial cranked all the way clockwise, you aren't getting full power

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Even that is not necessarily true, assuming he's using a brushed motor controller. The same back EMF happens in brushed motors and counteracts power as the RPM goes up.
We have no way of knowing whether "rightmost cranking" only goes to the max-power point, or whether it goes past that point to achieve higher RPMs and some loss of power (which is not an uncommon design AFAICT.)

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Originally Posted by jwatte

We have no way of knowing whether "rightmost cranking" only goes to the max-power point, or whether it goes past that point to achieve higher RPMs and some loss of power (which is not an uncommon design AFAICT.)

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not possible for a pmdc motor unless you can rotate the brushes relative to the magnets, or if you can weaken the magnets.

"[Induction motors] also have lower efficiency than dc motors …"

Not exactly. At light loading relative to its nameplate rating a PMDC motor can have higher efficiency, but at max power load it is far easier to achieve higher efficiency with 3 phase induction motors. Large industrial 3 phase induction motors can easily reach at least 95% efficiency, well outside the full load range of PMDC motors. (I have stood right next to a fully loaded 2MW (about 2,700 HP) 3 phase motor that was 4KVAC line powered running at full power and it was not producing anywhere near 100KW of heat (5% loss on 2MW) and it was only air cooled by a fan clear across the room. Don't assume that inexpensive Sears or Granger single phase induction motors represent well designed induction motors, they generally have design cost targets that precludes much of anything related to having high efficiency. Also note that the induction motor graph that I previously supplied shows that small induction motors (including fractional HP) are significantly less efficient than larger (higher HP) versions since much more care goes into the design of the larger sizes.


"… [Induction motors] consume much higher no load losses."

That is usually true, but the Prolight mill owner was presumably not operating under those conditions since he was trying for a maximum metal removal rate.


I did examine the PMDC motor ratings at your link (https://www.groschopp.com/data/other...ance/04404.pdf). I cannot get the printed motor performance data to be exactly consistent with the displayed plots. The printed Ke and Kt do match each other, the printed efficiency and loaded RPMs do match the plots. To their credit they also show the motor’s performance variations with temperature (not all manufactures provide that data) and their plots clearly show field weakening at higher currents and temperatures, and the wiring resistance increasing with higher temperatures, but their Hot and Cold temperatures are undefined values.

The printed peak efficiency current is given as 3.11A and with a printed Kt of 4.37 lb-in/A which comes to 13.6 lb-in (187 oz-in) of torque. Since the printed output torque is 11.7 lb-in that clearly indicates that there is 1.9 lb-in (30 oz-in) of torque lost due to friction and viscous losses at 1,660 RPM. An examination of the stall torque and current allows for computing the wiring resistance (3.468 Ohms) and those former values indicate a Kt (Torque Constant) value of 4.03 Lb-in/A, which is a reduction of 8% (the field weakening amount), even at their “cold” temperature. The stall current and torque values are clearly at their “cold” temperature.

If I use their stated non-stall Ke I get 76.3% efficiency vs their 78.4% at 1,517 RPM vs their 1,660 RPM with a total frictional and viscous loss of 1.9 lb-in. I have to make assumptions about the frictional vs viscous losses that total to that 1.9 lb-in torque loss at 1,660 RPM. I also get 12.8 lb-in (205 in-oz) of output torque vs their stated 11.7 lb-in. I get 230 Watts of output power vs their stated 229 Watts. At maximum power the efficiency of this motor is 47.8% although they do not state a maximum power efficiency. There is also a minor discrepancy in their data since they state 1,660 RPM in one location of their data sheet and 1,650 RPM in another location.

My plots (see attached) for this PMDC motor also assume that there is no field weakening occurring and that all of their numeric data corresponds to their "cold" temperature operation. Field weakening would increase their output RPM by the same ratio (8% weaker field means about 8% higher RPM).