The Art of Shimming

Properly shimming your mobile shear blades is a critical step that a lot of companies tend to overlook.  Failing to do this will cause your shear to jam, break bolts, reduce overall blade life, and make your shear operate inefficiently.  Mobile shears are not cheap to operate, so educating your maintenance crew on proper shimming is critical.

Shimming different blades

Almost all shears have 2 types of blades on the lower jaw that need to be shimmed.

  1. Primary and secondary blades (blades in the jaw)
  2. Guide blades (blades in the lower jaw that the tip cuts against)

When doing a blade rotation, make sure your blade seats are clean, add your adjustment plate, and add your blades.  Once the blades are installed and bolts lightly tightened, fire up the shear and drop the upper jaw into the lower.  Next, take a feeler gauge (or even a shim if you don’t have one) and check the gaps thicknesses between the blades on the upper and lower.  Most customers find it best to operate with a .010” – .015” gap between the Primary & Secondary blades and a .020” gap between the tip and guide blades.  Determine the appropriate thickness of shims that you will need to realize these tolerances, loosen the blades up, slide your shims in from the top, and torque the bolts to the appropriate level.  Drop the upper jaw back into the lower one more time to ensure that the blades are not rubbing and that your thicknesses have been achieved.

Shimming different applications

When cutting extremely thin material, tighter is better.  Some customers of ours choose to shim the primary & secondary blades with as little as a .005” gap with a .010” gap in the guide blades.  For larger material like I-beams customer often open up the gaps to .020” for the primary & secondary and as much as .030” on the guide blades to reduce the heat caused from piercing. 

Things to watch out for

From time to time we will hear from a customer that they were not able to shim the blades close enough on their 4th and final rotation of the blades without adding an excess number of shims.  9 times out of 10, it’s because too many hours were put on the first 3 edges of the blades and they’re too deformed to properly install.  In instances like these, it is best to flip the blades more frequently which will not only allow for the utilization of the 4th edge, it will also make it easier for your shear body and shear cylinder to cut material due to working with sharper blades – saving you money in the long run. 

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