There are many manufacturers of alignment shims. Chances are you use whatever shims you started with, and haven’t considered looking for something different. Not all shims and kits are created equal. The below will help you understand if you should be shopping around for a better product.
1. You should have a full set including 13 thicknesses ranging from .001 to 0.125 “. A full set contains 20 of each size, although starter sets may be available with 10 of each size
2. Shims are available in a number of materials. Type 304 Stainless Steel is the standard, other materials are available for specialized applications
3. Shims should be marked with the nominal thickness on all shims (i.e. 0.015, 0.050)
4. Shims .050 and above should also be marked with the actual thickness. The allowable tolerance on shims goes up as they get thicker, a shim with a nominal value of 0.100 could be ± .004! Having the shims marked with the actual thickness improves the accuracy of your correction, and can save you an extra move or so when aligning
5. Markings on shims should be etched or stamped, so that they do not rub off
6. Shims should be easy to get in and out of their box! While this sounds insignificant, different suppliers use different means to secure and separate their shims. We have used shims at customer facilities that are very hard to remove from the box, and hard to replace when making a change. As a result, shims don’t get returned to their proper place, the shim kit ends up disorganized, and you run out of shims of one or more sizes
7. Your shim supplier should be able to provide replacement packs of individual shim sizes when you get low on one. Keep them organized, and you’ll know when its time to restock!
Shims come in several standard sizes, A (2 X 2”), B (3 X 3”) C (4 X 4”) and D (5 X 5”). The proper size is based on the bolt diameter. For large and specialized machines, custom shims can be manufactured to order.
A Word on Shim Packs:
When shimming a machine, you should do the correction with 4 or less shims. If there is an existing shim pack under a foot, remove it, add or subtract the correction to the existing thickness, and build a new shim pack. You will sometimes find a machine with feet supported by a “deck of cards” thanks to a history of small realignments (maybe a problem with the base?). Pull them out, and rebuild the pack. A stack of many shims can become “spongy” and makes a less than ideal foundation.
Other Best Practices:
Some mechanics go so far as to measure the thickness of their shim packs with a digital caliper. While this is not strictly necessary, it can make a difference in the number of moves required to complete an alignment. If you have a caliper available, it’s OK to use it!
Sometimes you will encounter a machine that needs excessive correction (say more than ¼”). It may make sense in these cases to fabricate “chocks” to put under all feet, and start the alignment from that point.
In extreme cases, the only solution to appropriately aligning a machine may be to have a new base machined and installed. This is especially true in the case of a flexible, non-rigid or otherwise poorly designed base.
In addition to our excellent Easy Laser Alignment Systems, I&E Central offers accu-sized shims in all sizes, and in full kits or replacement packs. Download our shim data sheet for details and pricing on all of our shim options, or contact us at 866-225-0182 with your questions!