SKF shims for machine alignment: usage and selection guide

SKF shims are metal sheets of exact thickness used to level and align rotating machines. They are placed under the machine feet to correct unevenness and eliminate so-called soft foot. A soft foot occurs when one of the supports does not sit properly on the base, generating vibrations, misalignment, and premature bearing failures.

In Argentine industry, these shims are used in pumps, electric motors, compressors, gearboxes, and any equipment that must be perfectly aligned with its coupling. Precise alignment is key to extending bearing life and avoiding unplanned downtime. Calibrated shims allow fine leveling adjustments that are difficult to achieve with other methods.

SKF offers these shims within its mounting and maintenance tools line, specifically in the TMAS series. They are kits that include sheets of different thicknesses, designed to cover typical field alignment needs. Being calibrated, each sheet has a defined thickness, allowing them to be stacked to achieve the required height.

Soft foot is detected during alignment with dial indicators or laser systems. If loosening an anchor bolt causes the machine foot to lift or move, there is an unevenness that must be corrected. It can also be checked with a feeler gauge: if a thin sheet enters between the foot and the base, there is a gap to fill.

SKF shims are the standard solution to correct this unevenness. They are placed under the affected foot until all four supports are in the same plane. It is important not to use improvised shims, such as sheet metal cutouts or washers, because their thickness is not uniform and they can deform under load, misaligning the equipment again.

An uncorrected soft foot causes uneven loads on the housing, bearing distortion, and increased temperature. Therefore, correctly aligning with calibrated shims is a preventive maintenance task that avoids major failures. At MR we supply SKF TMAS kits so you can solve this problem with genuine parts.

The shim size must be larger than the support surface of the machine foot. If the shim is smaller than the foot, the load concentrates on a smaller area and it can become marked or deformed. Ideally, the shim should protrude a few millimeters around the foot, but without interfering with other components.

The diameter of the anchor bolt must also be considered. Shims usually have a U-slot or a hole for the bolt, and that space must match the bolt diameter. If the slot is too tight, it makes assembly difficult; if it is too loose, the shim can move.

To choose the correct kit, measure the length and width of the machine foot and the bolt diameter. With that data, you can select the shim size that covers the entire support surface. At MR we advise you to choose the appropriate TMAS kit, whether it is TMAS 340, TMAS 360, TMAS 380, TMAS 510, TMAS 720, or TMAS 2-050.

SKF shim kits include sheets of different thicknesses. By combining them, the necessary height can be achieved with precision. The key is to use as few sheets as possible to minimize the risk of slipping or deformation.

A good practice is to start with the thickest sheet that is close to the required measurement and then add thin sheets for fine adjustment. This way you achieve the exact height with few sheets and the pack remains firmer.

Avoid stacking too many thin sheets, because it reduces the rigidity of the assembly and increases the possibility of shifting. If the pack starts to grow, it is advisable to check if there is a more efficient combination or if the unevenness is so large that it requires machining the base. SKF shims are designed to stack stably, but it is always better to minimize the quantity.

One of the most frequent mistakes is using shims of insufficient size that do not cover the entire foot. This generates high-pressure points and can deform the shim or the machine foot. Always verify that the shim is larger than the support surface, as explained above.

Another mistake is not cleaning the base and foot well before placing the shims. Any dirt, rust, or burr can distort the measurement and cause poor alignment. Use fine sandpaper or a dressing stone to leave the surfaces smooth and free of particles.

It is also a mistake to tighten the anchor bolts without verifying that all four feet are supported. After placing the shims, perform a check with feeler gauges or the alignment system to confirm that no soft foot remains. Only then tighten the bolts in a cross pattern and with the recommended torque.

Shims are precision tools and must be stored in a dry, clean place to prevent corrosion. If they rust, their thickness can vary and they lose calibration. Store them organized by thickness to quickly find the one you need at the workplace.

Before using a shim, check that it has no burrs, dents, or deformations. A bent sheet or one with raised edges will not seat properly and will distort the leveling. If you find a damaged one, replace it with a new one of the same thickness.

Do not use shims as wedges or for prying, because they deform. They are precision elements and must be handled with care. At MR we distribute SKF TMAS kits so you always have shims in good condition.

To request a quote for your SKF shims, send us the code of the kit you need, for example TMAS 360 or TMAS 720. If you do not know the code, send us the measurements of the machine foot and the bolt diameter, and we will indicate the appropriate kit.

You can also send us a photo of the shim you are using, with a ruler next to it for size reference. This way we can identify the thickness and format, and offer you the exact replacement. We also carry other SKF mounting and maintenance tools.

Write to us via WhatsApp or email and we will quote you promptly. We are from Buenos Aires, Argentina, and we market genuine SKF products for industrial maintenance. Tell us what machine you are aligning and we will help you choose the correct shims.