Machinery Shims

What are machinery shims?

Machinery shims are thin, precisely made metal plates placed under the feet of machines, motors, pumps, gearboxes, and bearing housings to adjust their height and position. They are used to align shafts, level machines, and correct small gaps between a machine’s feet and its base, known as soft foot. Even very small alignment errors can cause vibration, heat, and early wear, so shims play an important role in keeping rotating machinery running smoothly and reliably.

Pre-cut machinery shims are made from stainless steel to an accurate thickness and usually have a slot cut into one side. The slot allows the shim to be slid in around the holding-down bolt without removing the bolt completely, making alignment work much faster. Each shim is usually marked with its thickness, so the right combination can be selected quickly.

Machinery shims are usually described by:

• Size - the overall dimensions of the shim, such as 50 × 50 mm, chosen to suit the size of the machine foot and bolt
• Slot width - the width of the slot, which must fit around the holding-down bolt
• Thickness - the exact thickness of the shim, such as 0.05 mm, 0.10 mm, 0.20 mm, or 0.25 mm
• Pack quantity - shims are often sold in packs, such as packs of 10

Key features:

• Precise thickness - accurately made to give exact height adjustments
• Pre-cut slot - fits around bolts without removing them completely, saving time
• Stainless steel - strong, flat, and resistant to corrosion
• Marked thickness - makes it easy to identify and combine shims
• Range of thicknesses - from very thin shims for fine adjustment to thicker shims for larger corrections
• Range of sizes - to suit small motors through to large machines and housings
• Reusable - can be removed and used again if undamaged

In simple terms, machinery shims are thin, precise plates used to raise, level, and align machines so their shafts line up correctly.

Why are machinery shims essential?

Machinery shims are essential because accurate alignment is one of the most important factors in machine reliability. When shafts are misaligned, bearings, seals, and couplings are put under extra load, leading to vibration, overheating, noise, and premature failure. Soft foot, where one or more machine feet do not sit flat on the base, can distort the machine frame when the bolts are tightened, causing similar problems. Using the right shims corrects these issues quickly and accurately.

Their main benefits are:

• Accurate shaft alignment - helps bring motor, pump, and gearbox shafts into line
• Corrects soft foot - fills gaps under machine feet so the frame is not distorted when bolted down
• Longer bearing life - reduces extra loads on bearings caused by misalignment
• Longer seal and coupling life - reduces wear on seals, couplings, and other components
• Reduced vibration and noise - well-aligned machines run more smoothly and quietly
• Lower energy use - aligned machines waste less energy through friction and vibration
• Faster alignment - pre-cut, slotted shims save time compared with cutting shim stock
• Reduced downtime - fewer breakdowns and repairs caused by misalignment

Machinery shims are used across a wide range of industries and applications, including:

• Motor and pump alignment - aligning motors with pumps, fans, and compressors
• Gearboxes and drives - aligning gearboxes with motors and driven equipment
• Bearing housings - setting the height and alignment of plummer blocks and bearing units
• Machine installation - levelling machines during installation and relocation
• Maintenance and repairs - realigning equipment after bearing, coupling, or motor replacement
• Manufacturing and processing - conveyors, mixers, rollers, and production machinery
• Power generation and utilities - pumps, fans, and rotating equipment
• Marine and offshore - aligning engines, pumps, and drive systems

The main types of machinery shims

Machinery shims are usually grouped by their design, material, and thickness.

By design:

• Pre-cut slotted shims - flat shims with a slot cut into one side, so they can be fitted around holding-down bolts. They are the most common type for machine alignment
• Shims with tabs - have a small tab or hole for easy handling, removal, and identification
• Shim stock - flat sheets or rolls of metal that can be cut to any shape, used for special sizes and applications
• Laminated shims - made from many thin layers bonded together that can be peeled off to adjust thickness

By material:

• Stainless steel shims - the most common material for machinery shims, offering strength, flatness, and corrosion resistance
• Carbon steel shims - economical shims for general use in dry environments
• Brass shims - softer, non-sparking, and corrosion resistant, used for special applications

By thickness:

• Very thin shims - such as 0.05 mm and 0.10 mm, used for fine adjustments
• Medium shims - such as 0.20 mm, 0.25 mm, 0.40 mm, and 0.50 mm, used for general adjustments
• Thick shims - such as 0.70 mm, 1.00 mm, and above, used for larger corrections

By size:

• Small shims - for small motors, pumps, and housings with smaller bolts
• Medium shims - for general industrial motors and pumps
• Large shims - for large machines, gearboxes, and heavy bearing housings with larger bolts

How to choose the right machinery shims?

Choosing the right machinery shims means matching them to the machine foot, the bolt size, and the amount of adjustment needed. Work through these points in order:

• Shim size - choose a shim large enough to cover the machine foot’s contact area, without extending too far beyond it
• Slot width - check that the slot fits around the holding-down bolt
• Thickness needed - measure the adjustment needed using a dial indicator, laser alignment tool, or feeler gauges, then select shims to match
• Combination of thicknesses - keep a range of thicknesses so you can build up the exact height required
• Number of shims - use as few shims as possible under each foot. Fewer, thicker shims give a firmer, more stable support than many thin ones
• Material - choose stainless steel for durability, flatness, and corrosion resistance
• Environment - stainless steel shims suit wet, outdoor, and corrosive environments
• Quantity - choose packs that give enough shims for all the machine feet you are aligning
• Quality and brand - choose shims from reputable suppliers for accurate thickness, flatness, and burr-free edges

How to use machinery shims

Using machinery shims correctly helps achieve accurate and lasting alignment:

• Clean the surfaces - remove dirt, rust, paint, and old shims from the base and machine feet
• Check for soft foot - loosen each holding-down bolt in turn and measure any gap or movement under the foot
• Correct soft foot first - add shims under any foot that is not sitting flat before carrying out the final alignment
• Measure alignment - use a dial indicator or laser alignment tool to find how much the machine needs to be raised or moved
• Fit the shims - slide the slotted shims around the bolts, making sure they sit fully under the foot
• Keep shim packs small - use the fewest shims possible under each foot for a solid, stable support
• Tighten evenly - tighten the holding-down bolts gradually and evenly to the recommended torque
• Recheck alignment - check the alignment again after tightening and make final adjustments if needed

FAQ - All you need to know about machinery shims

What are machinery shims used for?

Machinery shims are used to raise, level, and align machines such as motors, pumps, gearboxes, and bearing housings. They help bring shafts into line and correct gaps under machine feet.

What is soft foot?

Soft foot is when one or more machine feet do not sit flat on the base. When the bolts are tightened, the machine frame can twist, causing misalignment, vibration, and extra stress on bearings and seals.

Why are machinery shims slotted?

The slot allows the shim to be fitted around the holding-down bolt without removing the bolt completely, making alignment quicker and easier.

Why are machinery shims made from stainless steel?

Stainless steel is strong, stays flat, and resists rust and corrosion, so the shims keep their accurate thickness over time, even in damp or harsh environments.

How do I know what thickness of shim I need?

Measure the amount of adjustment needed using a dial indicator, laser alignment tool, or feeler gauges. Then combine shims of different thicknesses to match the measurement.

How many shims should I use under a machine foot?

Use as few shims as possible. Several thin shims stacked together can compress and act like a spring, so it is better to use fewer, thicker shims where possible.

Can I reuse machinery shims?

Yes, if they are clean, flat, and undamaged. Replace any shims that are bent, creased, rusty, or have burred edges, as they will not give an accurate result.

What thickness shims should I keep in stock?

A range of common thicknesses, such as 0.05 mm, 0.10 mm, 0.20 mm, 0.25 mm, 0.50 mm, and 1.00 mm, allows most adjustments to be made accurately.

Can I cut my own shims from shim stock?

Yes, but pre-cut shims are quicker to use, have accurate dimensions and clean edges, and are marked with their thickness, making alignment work faster and more reliable.

Why does my machine still vibrate after shimming?

Common causes include remaining misalignment, soft foot that has not been fully corrected, too many thin shims, loose bolts, or other issues such as imbalance or worn bearings. Recheck alignment and soft foot, and inspect the machine for other faults.