Baseplate Installation
Baseplates or soleplates are used to facilitate the setting of equipment. The baseplate serves as a flat, level platform on which to mount and fasten equipment. A good baseplate design can be better achieved if the designer has an adequate knowledge of how the baseplate will be installed. The proper design and installation of the baseplate are of paramount importance if the equipment is to be properly aligned.
Usually the baseplate will be installed at an elevation that is slightly lower than the desired elevation of the foot of the piece of equipment that is to be set. The reason for this is to allow for some minor adjustment using shims. The difference between the set elevation and the desired elevation is usually about 1/16”. If the piece of equipment is very large, like a paper machine calender, the baseplate may be set exactly at the elevation desired for the foot of the calender. This is because it is impossible to shim a large, heavy piece of equipment. Keep in mind that there are always construction tolerances, and terms like “exact” need to take the tolerance into account.
A baseplate is held in place by anchor bolts (ABs) that are secured in the concrete floor. For new construction, a template is usually made out of plywood, and the anchor bolts are locked in place with nuts. The template is secured in its proper place during the concrete pour, ensuring that the anchor bolts are located properly. Often a sleeve will be located around the anchor bolt. The purpose of the sleeve is to allow the anchor bolt to be “wiggled” as needed to permit the baseplate to be slid over the AB holes. On a large baseplate, it might be too much to expect that all of the ABs will be perfectly plumb. A little wiggle room is all that is needed. In order to prevent the concrete from entering the annulus between AB and the ID of the sleeve, the annulus is often filled with a ring of polystyrene. The polystyrene is dissolved after the pour with acetone, or it can be burned away with a torch.
When setting a baseplate on an existing concrete floor, the ABs may be cemented into the floor with chemical anchors. Often the floor is roughened by bushhammering to get a good bond between the old concrete and the new grout that will be placed under the baseplate. There is a wide variety of concrete bonding products available now though, and some recommend against roughening the surface because it can introduce microcracks into the existing floor.
The baseplate is then placed over the ABs. With nuts placed over the ABs, the elevation of the top of the baseplate is set. The elevation of the top of the baseplate is set in one of two ways. It may be shimmed, or it may be held up with jacking screws. If shims are used, it is best to remove them after the grout is placed. Otherwise, a square corner of a shim might produce a stress concentration in the grout. Usually, if shims are used, they are wedges that are greased to keep the grout from sticking to them. A better method is to use jacking screws. These are also greased to prevent the grout from adhering to them.
Tension is placed on the ABs by torquing the nuts. The level and elevation of the baseplate is checked, and the grout is placed. After the grout is completely set, the jack screws are removed from the baseplate.
There are many types of grout available. Some are very fluid and can be poured, and some are very dry and must be packed into place. It is important that the grout establish intimate contact with the underside of the baseplate, since it is the grout which distributes the weight of the equipment to the floor below. On large baseplates, there may be large pour holes in the center to permit better distribution of the grout.
When the grout begins to dry, it is often struck to produce a finished appearance. The easiest way to do this is to use the top of the baseplate as a guide or screed, and have the grout chamfered to the top of the baseplate (See Figure 1).
Figure 1
However, this is also the worst way to strike the surface, and will surely result in cracked grout. The reason for this is that changes in temperature of the baseplate will cause expansion and vibration of the baseplate will cause slight movement. This will cause the grout to crack.
Instead, the grout should only rise to the bottom of the baseplate, and be struck from there (see Figure 2).
Figure 2
Sometimes a grout pocket will be built up around the baseplate as in Figure 3. In that case, the grout is contained by a wall of concrete. In that case, it is acceptable to have the grout extend above the bottom of the baseplate, since there is little chance that it will crack.
Figure 3
Especially in wet environments, there is one additional step that is sometimes taken once the grout has cured and the jack screws or shims have been removed. In order to prevent water from standing in the counterbored holes where the AB nuts are, this space is sometimes filled with molten lead. This practice is probably falling by the wayside due to health problems related to lead. Certainly another material, even grout, could be substituted.
Before setting the equipment, the baseplate should be cleaned. The equipment is set. Bolts are passed through the feet of the equipment, and threaded into the baseplate. After alignment, the equipment may be doweled into place by reaming tapered holes through the equipment’s feet and into the baseplate. This ensures that there will be no movement between the machine and the baseplate. It also provides easier alignment if, in the future, the piece of equipment must be removed and re-installed.
Some millwrights will place blocks against the equipment feet and weld these to the baseplate, instead of doweling. This is adequate for imprecise installations, but must be considered crude, since the heat of welding will warp the baseplate. And if you have paid to have the baseplate machined flat, and carefully installed, a warped baseplate is no better than a piece of hot rolled steel.