Electric Motor Replacement on a Pillar Drill: Pulley, Power and Mounting

When replacing the motor on a pillar drill, the easiest route is to choose a motor with the same power, the same number of poles and the same shaft diameter as the old one and to move the stepped pulley onto the new shaft. On these machines spindle speed comes from the motor speed and the pulley steps; the motor body is usually attached to the back of the drill head with the shaft pointing upwards. That is why three issues are checked together during replacement: pulley, power and mounting.

The drive arrangement of a pillar drill

On the most common type of pillar drill in workshops, the motor sits on a bracket at the back of the drill head. At the end of the motor shaft there is a pulley with several steps (stepped pulley); above the spindle there is a matching pulley arranged in reverse. The speed is selected by placing the belt on opposite steps of the two pulleys. Some models have an intermediate pulley with two belts, some a variable-diameter variator pulley, and larger machines a geared head.

Whatever the arrangement, the motor is at the very top of the machine with the shaft pointing up. This brings out a few details that differ from horizontal machines: the weight of the pulley and the belt pull act on the motor shaft from above, and the motor is often attached through a mounting plate or a flange rather than feet.

The pulley: the part that sets the speed

Spindle speed comes from the motor's rated speed and the ratio of the motor pulley and spindle pulley diameters: spindle speed = motor speed × motor pulley diameter ÷ spindle pulley diameter. The speed plate on the machine gives this calculation ready-made for each belt position and is usually laid out for a 4-pole motor.

A hypothetical example

The values are only meant to show the method. Let the motor be 4-pole with a rated speed of 1,420 rpm. If the belt is placed on a 120 mm step on the motor side and a 60 mm step on the spindle side, the spindle speed is 1,420 × 120 ÷ 60 ≈ 2,840 rpm. If the belt is moved to a 60 mm step on the motor side and a 120 mm step on the spindle side, the speed drops to about 710 rpm. If a 2-pole motor were fitted to the same machine, every step would double, and at the highest step the spindle bearings and chuck would run far above their design speed.

Moving the pulley to the new motor

• Shaft diameter and key: The bore of the stepped pulley hub is machined for the old motor shaft. If the new motor's shaft diameter and keyway are not the same, the pulley will not fit. The same IEC frame code is the easiest way to get the same shaft end.
• Pulley height: The motor pulley and spindle pulley must be in the same horizontal plane. If the new motor's shaft length differs, the height at which the pulley sits on the shaft changes; the belt runs at an angle and wears on its sides.
• Pulley fixing: The pulley is usually held by a set screw and key. On a motor with the shaft pointing up, a loose pulley slides down; always check that it is tight after fitting.
• Imbalance: Fitting an old, cracked or bent pulley to a new motor causes vibration. If the pulley is damaged, it is better to replace it together with the motor.

Power: what does the old motor's nameplate say?

On a pillar drill, motor power is set by the manufacturer according to the largest hole diameter to be drilled, the material and the structure of the machine. On workshop machines this power is usually around 1 kW or below; on large geared machines it is higher. For the exact value, check the nameplate of the machine or of the old motor.

Moving up to the next power is often unnecessary. If the machine struggles with large holes, first check whether the speed step is correctly selected: a large drill bit needs a low speed, and at a low step the pulley ratio already increases the motor's torque. Belt slip, a blunt bit or excessive feed can also look like an undersized motor. If the machine still struggles after these are fixed, the next power is considered; since the frame may grow as well, bracket and pulley compatibility are checked again.

If the workshop has only a single-phase supply, a three-phase motor cannot be connected directly. HEM Motor's single-phase series cover 0.18–5.5 kW; ask us about the single-phase option together with the nameplate details.

Mounting: vertical operation with the shaft up

On a pillar drill the motor usually runs vertically with the shaft pointing upwards. The connection, however, depends on the machine:

• Motor on a mounting plate (foot-mounted): The motor is bolted by its feet to a vertical plate, and the plate is hinged to the head. Belt tension is adjusted with this hinge.
• Flange-mounted motor: The motor sits directly on a bracket with the flange on its front end shield. In this arrangement the bolt circle and spigot diameter of the flange must match exactly.

At HEM Motor, B3, B5, B14, B34, B35 and vertical V1/V3/V5/V6/V15 arrangements are offered according to the frame; the flange size is confirmed with the order. Always state in the order that the motor will run vertically with the shaft up. The fact that the old motor is simply called "B14" does not mean it fits your bracket; measure the hole spacing. For a dimensional comparison see the 2D technical drawings, and for mounting options the question on mounting arrangements.

You can browse suitable HEM Motor models and current prices in the buy electric motors section.

Direction of rotation, tapping and electrical connection

Drill bits cut in the right-hand direction. After connecting the new motor, check the spindle direction without a bit fitted; if it is wrong, swap two phases at the motor terminal box.

On machines with a tapping function, the motor reverses at the bottom of the hole. In this arrangement the motor makes forward and reverse starts at short intervals. A standard motor can handle this duty, but the control circuit that provides reversal and the thermal protection setting must be compatible with the old machine. Set the thermal relay to the current on the motor nameplate.

On low-power motors the nameplate is usually 230/400 V (Δ/Y). On a 400 V three-phase supply this motor is connected in star (Y). Noting the position of the terminal links on the old motor and making the same connection on the new one reduces the risk of a wrong connection.

Example models for pillar drills

The 4-pole models below are examples of the powers found on workshop pillar drills. All are 230/400 V (Δ/Y), 50 Hz, IP55 with class F insulation:

• 80M1-4 aluminium frame: 0.55 kW, 4 poles, rated 1,400 rpm, IEC 80M, 1.31 A (400 V).
• 80M2-4 aluminium frame: 0.75 kW, 4 poles, rated 1,420 rpm, IEC 80M, 1.75 A (400 V).
• 90S-4 cast iron frame: 1.1 kW, 4 poles, rated 1,445 rpm, IEC 90S, 2.48 A (400 V).

80M1-4 and 80M2-4 share the same 80M frame; the power difference can be chosen with the same shaft end and connection dimensions. When moving to the 90S frame, the shaft end and flange size may change; in that case pulley and bracket compatibility are checked again. On heavily used, vibrating machines a cast iron frame may be preferred. The current price is on the product pages. For general industrial machines, you can also see the general-purpose industrial motors page.

Conclusion: what is needed for a motor replacement

The essence of a pillar drill motor replacement is to keep the old motor's speed and shaft end and to seat the new motor on the same bracket arrangement with the shaft up. That way the stepped pulley, speed plate and belt are used as they are. For a quotation, send us:

• A photo of the old motor's nameplate (power, speed, voltage, frame code)
• How the motor is mounted (foot-mounted plate or flange) and, if possible, a photo of the bracket
• The bore diameter and key size of the pulley hub
• Supply type (three-phase 400 V or single-phase) and whether there is a tapping function

You can see suitable models and current prices in our online sales section. Send the nameplate photo, speed and mounting details of your current motor through the nameplate submission page and request a quotation for the right model.

Frequently Asked Questions

My drill struggles with large holes; should I upsize the motor?

First check the speed step, the sharpness of the bit and the belt tension. When a large bit is run on a low step, the pulley ratio increases torque; the problem is often not the motor power.

Will the old stepped pulley fit the new motor?

It will if the new motor's shaft diameter and keyway are the same as the old one's. The same IEC frame code is the easiest way to ensure this; otherwise the pulley is re-machined or replaced.

What should I state in the order for a motor running with the shaft up?

State that the motor will run vertically with the shaft up, whether the connection is a foot-mounted plate or a flange, and the flange dimensions if flanged. The flange size is confirmed with the order.

My workshop has only single-phase power; what should I do?

A three-phase motor cannot be connected directly to a single-phase supply. For the single-phase motor option, contact us with the old motor's nameplate.