Universal Metal Milling Machine Electric Motors

On a universal metal milling machine the electric motor does three separate jobs: it turns the main spindle carrying the cutter, it feeds the table and knee, and it pumps coolant to the cutting zone. The spindle motor runs at 1.5–2.25 kW on small turret and drill-mill machines, 3.2–7.5 kW on knee-type universal machines and up to 11 kW on large types. The feed motor sits between 0.55 and 1.5 kW. All of these values fall within our aluminium housing electric motors.

DRG Motor is a manufacturer, supplier and seller of electric motors. The mill itself, its heads, gearbox, cutters, inverters, CNC drives, servo motors and motor spindles are things we do not sell; what we deliver is the standard three-phase motor for the spindle and the feed of a manual mill.

How many motors does a universal mill have, and what does each do?

Spindle: horizontal and vertical head

A universal mill has a horizontal main spindle in its column and a swivelling vertical head on the front. On some machines a single motor turns both spindles through a gearbox; on others each head has its own motor. The horizontal spindle motor inside the column usually mounts as foot-type B3 or as B35 carrying both feet and flange. The vertical head motor sits on top of the head on a B5 flange with its shaft pointing down.

Table feed and rapid traverse

On a knee-type machine, X, Y and Z movements come from one motor through a separate feed box. Clutches inside the box take both the slow cutting feed and the fast approach to the workpiece from the same motor. The feed motor starts often, reverses and runs in short bursts.

Coolant pump

The coolant pump is very small, given around 90 W in product sheets, and mostly comes in one piece with its pump. That pump motor is not in our range; on failure the whole pump is replaced.

Turret mill and drill-mill

On a turret mill the motor stands vertically on the head at the end of the ram and tilts with it. Power is small, values like 2.25 kW appear. Geared-head drill-mills often use a two-speed motor.

Milling motor ratings in catalogues

A) Values taken from conventional mill and drill-mill sheets:

As head and table grow, so does the spindle motor; the feed motor stays at roughly one fifth to one tenth of it. The figures come from sample models; on your machine the plate and the machine maker’s documents govern.

B) Overlap with the DRG range: for spindles rated 1.1–7.5 kW look at frames 90 to 132 of our aluminium list, for 11 kW at the 160M; feed drives of 0.55–1.5 kW land in frames 80 and 90. Coolant pump motors such as 90 W fall below the range. Mills that need more than 11 kW at the spindle leave the aluminium range; cast iron motors for them are listed under General Purpose Electric Motors.

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Milling motors outside our range

Two-speed motors

On drill-mills and some knee machines the main motor is two-speed: it switches poles to run at two speeds and doubles the number of steps in the head. Our product list has no pole-changing motor. If a single-speed motor goes in instead, part of the steps are lost; before that decision the machine maker’s motor data and mounting dimensions are checked.

CNC servo and motor spindle

On a CNC mill the axes are driven by servo motors and the spindle by a spindle motor matched to its drive, or by a motor spindle. These are machine-specific parts and not DRG products. Even large universal machines now often come with servo direct drives on the axes; on these, only auxiliaries with standard motors can be covered by us.

Brake and single-phase motors

Some machines use a brake motor to stop the spindle quickly; brake motors are not in our range. Small bench mills may come with a single-phase motor; those are not offered either, so fitting one of our motors there means bringing a three-phase 400 V supply or adding a drive that converts single phase.

The real benefit of an aluminium frame on a mill

Vertical and turret heads tilt and swivel, and the motor rides on top of them. A light motor makes it easier to tilt the head by hand, set the angle and clamp it again, and puts less load on the slides. When a head motor is changed, one person can hold it and seat it on the flange more safely. For the horizontal spindle motor in the column, the gain lies mostly in fitting and handling. Cast iron comes to the fore on heavy machines above 11 kW and in constantly interrupted rough milling.

Checklist for a motor change

Dimensions

Plate power, speed and voltage are kept. On a head motor, measure flange outer diameter, bolt circle and spigot; on a column motor, foot holes and shaft height; on both, shaft diameter, length and key. The motor must be ordered for vertical mounting and the axial load must be confirmed by the machine maker (V1, shaft down). For flange dimension details, see our article on milling machine motor selection.

Belt, coupling and gearbox

The spindle motor is mostly coupled or geared straight to the head; a turret mill uses a belt and step pulleys. A direct connection needs shaft and flange to match to the millimetre; on a belt layout the pulley ratio is checked together with motor speed.

Starting, reversing and environment

The feed motor starts and reverses hundreds of times per shift; this heats the winding and makes the overload setting important. The spindle motor does not start under load, but with a big cutter its inertia is high. Coolant and chips run down from the head: IP55 protects against dust and low-pressure water jets, not against high-pressure washing or steam cleaning. Point the cable gland of the terminal box downwards or to the side, and clear swarf off the fan cowl regularly.

Example: panel current of spindle and feed motors

Assumption: a knee mill uses a 5.5 kW DRG-132S-4 for the spindle and a 1.1 kW DRG-90S-4 for the feed. Values are for 400 V; starting current comes from the Is/In ratio in the product record:

Started direct-on-line, the spindle motor draws 84.5 A for a short moment; star-delta brings this down to about 28.2 A. The 5.5 kW model is wound 400/690 V, so it runs in delta on 400 V mains and suits star-delta. The feed motor starts often while the spindle runs; at those moments the line sees about 27.6 A. Fuses and overloads are chosen from this table.

How it differs from a wood spindle moulder

On a wood spindle moulder the motor drives, by belt and at high speed, a vertical spindle rising through the table, and the operator pushes the workpiece; on a metal mill the cutter turns slowly, the gearbox multiplies torque and the table feeds the part. That is why 2-pole motors also appear on the wood side while 4 poles are common on metal mills. Woodworking machines have their own page: Wood Spindle Moulder Motors.

Information requested for a quote

• Which motor: horizontal spindle, vertical head, feed or turret head
• Plate photo; two-speed or with brake?
• Flange dimensions or foot hole spacing, shaft diameter and length
• Does it stand vertically or horizontally on the head?
• Supply: 400 V three-phase or single-phase?
• Daily running time

Aluminium DRG models for milling machines and prices

4-pole aluminium models matching the feed and spindle points:

Live price table

Prices are pulled fresh from the shop on every visit:

DRG MOTOR motors are guaranteed against material and manufacturing defects for 2 years from the delivery date (warranty certificate).

Motors in this power range

• DRG-90S-4 – 1.1 kW – 1445 rpm – 90S aluminium frame
• DRG-100L1-4 – 2.2 kW – 1450 rpm – 100L aluminium frame
• DRG-132S-4 – 5.5 kW – 1460 rpm – 132S aluminium frame

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Browse the products, ask for a quote: all models are on the Buy Electric Motors Online page. Send photos of the head and motor plate via WhatsApp; we will check flange, shaft and speed fit together.

Frequently asked questions

Can the horizontal spindle motor and the vertical head motor be the same?

Their power may differ and their mounting almost always does: one is foot-mounted in the column, the other flange-mounted on the head. They are not treated as spares for each other.

The turret head motor burned out; is it replaced with the head?

No, the motor comes off the head. But many turret heads come with a two-speed or inverter-fed special motor; it is not swapped for a standard motor before plate and flange are examined.

The feed motor runs hot; should I upsize it?

First check slide lubrication, the clutches in the feed box and the overload setting. If current is below the plate value, frequent starting is the cause; the fix is usually in adjustment or mechanical maintenance.

For questions: +90 (542) 666 11 11 · info@drgmotor.com · contact.