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Question:

How is the width and length of a shim determined for leveling machinery during alignment or installation? Are there general rule-of-thumb practices?

We have a recycle gas Ingersoll-Rand barrel compressor powered by an Electric-Machinery 1500 hp/2300 Volt motor with a 3420-S frame. The motor rests on two continuous 60" long x 6" wide sole plates. The two motor feet measure 59" x 5" each. What is the potential damage to alignment and/or the motor by using small (6" x 6") shims versus large (24" x 6") or continuous (60" x 6") shims?

Jerry Choate
Murphy Oil USA, Inc.
Superior, WI 54880

Luis F. Rizo, SABIC Innovative Plastics, offers this advice:

Hello Jerry,

The question you should focus on is... - How to create a monolith that will absorb all of the force to the base and foundation of the equipment? The unbalanced force of a reciprocating compressor is proportional to the reactive force. In a liquid slug scenario as you probably know, this force is not measurable, so it amounts to an "infinite" amount of force. So I would try to get a shim as large as practical to cover the width of the foot about the hold down bolt at each of the feet. Another option is to a liquid chock to level and hold your machine down, so that the complete structure becomes a monolith. I am attaching a few pictures of a similar compressor grouted many years back, that it is still operational today at the Exxon Baytown refinery/chemical plant complex.

Below are illustrations of an embedded optically set shim that has been embedded using epoxy chock.

1.4 Leveling techniques for horizontal baseplates

There are four (4) methods to provide vertical adjustments to a horizontal baseplate. A single wedge, parallel wedges, shim packs and jacking screws on metal plates. The preferred method of the author is the jacking screw on metal plates combined with metal shim plates. The following drawings illustrate the 4 methods.


Leveling screw application	Application of a wedge to assist in leveling

No.	Step Description	Date/initial
1.	Inspect all the shims to be sure that all are either 306 or 316 SS steel.
2.	Inspect the shims to be used to make sure that no single shim less than 0.005 in.(.13mm)is used by itself. Any smaller shims must be sandwiched between heavier shims (0.040in. (1mm) to 0.060 in. (1.5mm)).
3.	Verify that large stacks of shims have been replaced with equivalent thicker shims to avoid creating a spring condition under the base as a support.
4.	Verify that the initial stack of shims under the baseplate is sufficiently large to allow for multiple level adjustments. For example start with a shim pack under each foot made up of one 0.062 in.(1.6mm) and one 0.31in. (7.9mm), one 0.025in. (1mm) and two 0.015in. (.5mm), 0.010in. (.25mm) and .005in.(.127mm) (This combination has proven to allow great adjustment flexibility.)
5.	Check, with a torque wrench, that all anchor bolts have been properly tightened to the same torque value. Check to make sure that this procedure is followed after every shim change. See standard torque values for B-7 bolts for the diameter used.
6.	Using a machinist level (Starrett 98 or a master level) check the level of the pads with respect to each other. Maximum out of level is 0.002 in.(0.05mm)
7.	Inspect that all the machined surfaces on the baseplate are leveled within 0.0005 in. (0.013mm) / foot in two directions 90^o, after the anchor bolts have been snugged down. Use of a master level (0.0005 in./div.) is recommended. Do not exceed an overall level variation greater than 0.010 in. (0.25mm).
8.	Inspect that the shim packs or wedges used for leveling are located on both sides of the foundation bolt.
9.	Inspect that the baseplate height has been set to the correct elevation as call for in the drawing.
10.	Check that all the leveling devices are in full and solid contact with the concrete or the baseplate.
11.	After final anchor bolt tightening, recheck level. Do not exceed 0.010 in./ (0.25mm) maximum out of level over the entire length of the baseplate. Consult the responsible reliability team member before continuing.
12.	When all the above steps have been accepted, the baseplate leveling is complete and the baseplate is ready to be grouted.

Luis F. Rizo, PE
SABIC Innovative Plastics

IT Sourcing Services Manager

Julien Le Bleu also adds:

First question is generally try to size the shims to match the feet if possible. When I was with GE we often had large sole plates. Would make several non-shrink grout pads along the length of the plate and the same width as the plate. This was done after the plate was leveled with jacking screws and checked for not humping or sagging. The small pads were made with Styrofoam and liquid non shrink grout poured in and allowed to set up.

The plate was then pulled and the foam form was removed. The grout was cleaned and the plate set down again. If all is correct make another form around the entire plate and pour non-shrink grout into it and have it include the small pads poured previously.

If the plates need to be shimmed up to get to elevation do it with stainless steel shims on each of the small pads. When all is as you need it then do the step above and put it all in the final pour of non-shrink grout.

Julien Le Bleu