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A pillar drill makes holes along a vertical axis in a metal part clamped to a fixed table, and also countersinks, reams and taps threads. For other motor pages arranged by industry, see the list of electric motors for industries. This page deals with the spindle motor of belt-drive and geared-head pillar drills and the radial drill; multi-spindle boring machines for wood are the subject of another page.
Belt-drive, geared-head and radial drills
On a belt-drive pillar drill the motor is mounted vertically at the back of the head; a V-belt runs between the stepped pulley on the motor shaft and the matching pulley on the drill spindle. The operator opens the head cover and moves the belt to another step to change speed. On some models an intermediate pulley with two belts gives a wider speed range.
On a geared-head drill the motor sits on top of the head with a flange and feeds its power straight into a gearbox; speed is selected with levers on the side of the head. On a radial drill, the motor is at the top of the head assembly that travels along the arm swinging around the column. Radial machines also have separate small motors that raise and lower the arm and clamp the column.
Hole diameter, feed and motor torque
On a drill, the torque the motor has to supply depends largely on hole diameter and feed. As the diameter grows, the cutting lips of the drill bit get longer and the cutting force rises; at the same time a large bit must be run at low speed. So when drilling a large hole the motor gives its highest torque at the lowest spindle speed, and the gear or pulley ratio multiplies that torque.
Small holes need high speed and the motor is lightly loaded meanwhile. With a very small bit the motor runs almost idle; what matters here is a high enough speed. A blunt bit, chips jamming in the flutes or lack of coolant raise the load suddenly during drilling; increasing motor power does not solve these problems.
How feed is applied while drilling
With hand feed the operator pulls the lever; the load varies with the operator's feel. On geared-head drills with automatic feed, the feed is provided by a gear train proportional to spindle speed and needs no separate motor. In this case the motor load is more even but continuous during long drilling runs.
Reversing when tapping
Tapping is one of the hardest jobs for a drill motor. The tap enters the hole, the spindle stops at the set depth and reverses to back the tap out. On drills with a tapping function this reversal is automatic through a pedal or depth switch, and the motor is reversed by contactors.
In a workshop producing threaded holes in series, the motor may stop and restart in reverse dozens of times an hour. Every start adds heat to the winding; if the motor frame gets noticeably hot after such frequent starts, a PTC or PT100 sensor can be requested in the winding. If quick spindle stopping matters to avoid breaking taps, the machine has a brake arrangement; if a brake motor is needed, state it in your order.
Example motors by drill type
| Drill type | Typical work | What to check | Example HEM model |
|---|---|---|---|
| Small bench drill | Thin sheet and small holes | Pulley steps, supply | 71M2-4 aluminium — 0.37 kW, 1,340 rpm |
| Belt-drive pillar drill | General workshop drilling | Motor plate, belt line | 80M2-4 aluminium — 0.75 kW, 1,420 rpm |
| Geared-head pillar drill | Large diameters, tapping | Flange size, reversing frequency | 90L-4 aluminium — 1.5 kW, 1,445 rpm |
| Radial drill spindle | Large holes in heavy parts | Mounting on the head, cable route | 100L2-4 aluminium — 3 kW, 1,450 rpm |
These models were chosen as a guide; the final decision is made according to the drill's actual load, the required speed, how the motor is attached to the head and the working environment. The existing motor's nameplate is the first place to look.
Vertical mounting, belts and oil mist
A drill motor almost always stands vertically with the shaft pointing up or down. On belt-drive models the motor is usually fixed to a slide plate with the shaft up; on geared-head models the shaft points down and enters the head through a flange. Depending on size, HEM frames are prepared in vertical V1, V3, V5, V6 and V15 arrangements, as well as foot-mounted B3, flange B5 and B14 and foot-and-flange B34/B35; flange and shaft dimensions are matched with the old motor during ordering.
On a motor running shaft-up, the head cover should be kept closed so that water or oil does not run under the pulley. Cutting oil used for tapping can spread inside the head as mist; over time this mist forms a sticky layer on the fan grille. Belt tension and pulley alignment should be checked once a year, and a cracked belt should be replaced.
For those who want stepless speed
Workshops that do not want to bother moving belts can add a frequency converter to the drill. Our series are suitable for this use; still, drilling large holes at very low speed for long periods weakens the motor's own fan and an independent cooling fan may be needed. If the cable between drive and motor is long, a dv/dt or sine filter should be considered. These operating conditions should be reported in the order.
Information to share for a drill motor
For a quotation, write the machine information (belt-drive, geared-head, radial), the motor power (kW), speed (rpm), supply voltage, mounting (slide plate, flange, shaft up or down), whether tapping is done and how many units are needed. In a workshop without a three-phase line, the single-phase electric motor series (between 0.18 kW and 5.5 kW) may suit a small bench drill.
Sending a photo of the nameplate is the shortest route; details are in the article on finding an equivalent motor from the nameplate. For flange connections see the flange-mounted electric motors page, view current prices in our electric motor shop, and use the contact page for WhatsApp or phone.
Frequently Asked Questions
My drill stalls on large holes — is the motor too weak?
First check that the belt is on the right step: large holes should be drilled at the lowest speed step. Then review bit sharpness and feed rate; if the motor still exceeds the nameplate current, the power may be insufficient.
On a belt-drive drill, does the motor shaft point up or down?
On most belt-drive drills the motor shaft points up and the pulley sits under the head cover. The new motor must be prepared for this vertical position; the mounting should be stated in the order.
Why does the motor get hot when tapping?
Each reversal restarts the motor and produces extra heat in the winding. In series tapping this heat builds up. Adding a winding sensor or using a tapping unit protects the motor.
Can I also replace the motor that raises the arm on a radial drill?
Arm-lifting and column-clamping motors are low-power and usually attached with a machine-specific flange. If you send the nameplate data and flange dimensions, we can assess together whether a suitable standard motor exists.
