[dwalsh62]

The truth about spindle motors and power and the things you don't want to know/hear.

Interestingly enough, many people buy these spindles under the assumption they are getting what they pay for and all I can say is they are getting something but far less than they think.

Let's examine some details about some of these motors, lets start by looking at the water-coolder ER20 3.0KW spindles.

First and foremost, they are not 100% efficient, testing has revealed them to be only about 71% to 72% efficient (I'll calculate based on the higher efficiency).

Second, 220V-3PH, 8A is not 3.0KW it's 1.76KW (do the math) and since the efficiency is 72% this equates so 1.2672KW, a far cry from 3.0KW.

Third, the stators are basket-wound which is easier and quicker to produce over the more efficient lap-wound stators and is how most china manufacturers wind for maximum profit.


The square body spindle motor being sold on ebay is another prime example of false advertising.

I have had many of these sent to me for warranty/repair under the assumption it is the one I produce and I can't stress enough that there is no way my parts will fit in the china spindle body.

These are using almost the same stator/rotor as the water-cooled ER20 China spindle motors most users buy except length is longer by 5mm giving a little more mass and effeciency is around 73%.

They specify input current as 8A, some do specify 10A and those burn up much faster.

My square body spindle is larger because I use a larger and longer stator/rotor that is lap-wound which has an efficiency of 92% to 94% (I'll calculate based on the lower efficiency), I rate them at 12A knowing it will out-perform the china brand by 200%.

The main reason for running under a reduced input current (and I can get away with it) is to increase life and reduce heat and running at 2.43KW (220 x 12 = 2640 x 0.92 = 2428.8) is effectively double that of the china spindles but they will operate at 14.8A without burning up providing 3.0KW of power (220 x 14.8 = 3256 x 0.92 = 2995.52).


We've all seen real spindle motors on large VMC's and milling machines.

These are not normal induction motors with encoders attached, these are true asynchronous servo spindle motors.

Low power ones (2.2KW) are about 94% efficient and the size is 140mm x 140mm x 500mm and weigh approximately 60lbs, larger ones like the 5.5KW are 208mm x 208mm x 680mm and weigh more than 100lbs.

The 2.2KW motor starts around $1,300.00USD plus shipping from china, better quality ones start at $2,100.00USD plus shipping still produced in china and for a US manufactured product starting at $6,000.00.


Like many, finding a proper powering soultion is not easy and I understand why everyone settles for the cheapest solution they can obtain and unfortunately these solutions are by no means acceptable.



I decided that a real solution is what I want and that it had to deliver what I need and not by false information.

I wanted a larger stator/rotor that what is used in the cheaper spindles and I want to belt drive a cartridge with 2HP minimum and the size has to be small enough that I can use it without fear of being under-powered wihtout adding a lot of weight and it had to be capable of 8,000RPM without using gears or pulleys to alter the upper RPM and the motor must be capable of positioning and indexing for for things like rigid taping.

It is my belief that this motor should have a retail price of less than $500.00USD however I couldn't find a factory making and selling such a motor so I decided to make my own.

Attached is a picture of my prototype 1.5KW 12,000RPM asyncrhonous servo spindle motor with 2500PPR encoder.

The specifications, 220V-3PH, 8.25A, 22mm output shaft, 86% efficient giving 1.56KW of power weighing in at only 14lbs.

Stator/Rotor details:
Size: Frame 56 (80mm or 83mm OD Stator)
Slot/Bar: 24 / 18

Winding details:
QZY-2/220 0.74mm bifilar wound / 18 turns / 4-poles / 3-phase
Phase current: 8.27A (2.18A no load)
Current Density 10.2A
R/Min: 12,000 (14,900 no load)

I had the stator and rotor plates laser cut from some 35W270 laminate material, there are companies that will make the rotors and stators for you of you can buy the plates and assemble it yourself for more savings.

I will tell you that it took me about 6 hours to wind 3 stators so if your planning on doing it make sure you have enough time as it's not something you want to start and stop and start again.

I made a mould to hold the rotor lamenents so I could pour meltated aluminum to make the rotor and this process was pretty easy and I used scrap T6 aluminum from a job we were running for a customer (I used a table saw to make sand sized chips) and I basically metled the aluminum in the steel mould.

The front hearing is hard mounted to prevent excesive end-play from damaging the encoder and the rear bearing is wave-spring loaded to maintain constant preload.

The body was made from 3.5i x 3.5in aluminu stock, machined externally for shape and bored 83mm ID.

The rear bearing holder is aluminum, the front hearing holder is steel.

The encoder cap is aluminum (it could have been plastic) and the fan holder was sheet metal cut like a plus bent and tig'd with an ID of 94mm x 94mm

The cooling fan is 220V single-phase 43CFM 92mm x 92mm fan (called a 90mm fan) with a washable filter.

This is the perfect upgrade motor for a bench mill/ATC conversion and outperforms the DC motor that comes on most bench mills like the SEIG X3.

The prototypes were made entirely by hand and not currently in production by any company which is a shame as it is my belief that a motor like this is needed.

I did produce a prototype running at 24,000RPM (I have a couple of spare rotors/stators already wound) however, the encoder seems to drop off when RPM exceeds 18,000RPM and an encoder capable of higher RPM costs about $300.00 making it uneconomical.

I've provided all of the technical information and pictures that should allow you to make your own.


If you need help making one you can contact me directly as it is unlikely I will respond to PM as I don't frequent here much any more but thought that sharing this information was beneficial to the hobby community.

-- Dale