Soft foot is the common term used for the improper contact between a machine casing, and the base plate used to support it. It may be either an angular or parallel soft foot, but often it is a combination of the two. This condition is identified when there is an unequal gap at all four corners of a foot. A soft foot can occur when one leg of the driver is too short, when the foot mounting pad is not in the same plane as the other(s),
or
The foot has an inadequate amount of shim under it. If the alignment process has been started, and an accurate or consistent alignment cannot be obtained, it is likely that there is a soft foot condition present.
When the anchor bolts of a machine with a soft foot are tightened, the machine body gets twisted causing it to stress. Over tightening will cause the foot to bend. This stress will not allow the machine to align. The gap under the short foot must be shimmed before starting the alignment process. If loosening a bolt changes the alignment readings, soft foot is present. To check for the soft foot, set up the dial indicator on a foot and loosen mounting bolt. If the foot moves more than 0.05mm, or the soft foot standard defined by the user, the foot is considered soft and needs to be corrected. This should be done for all feet.
To calculate the amount of shim to add to compensate for the short foot, the sum of the smaller gap values are subtracted from the sum of the larger gap values.
This amount is divided by two. Use 80% of the quotient as the amount of shim that should be added under each foot to remove the parallel air gap. If two foot, foot@2 and foot@3 have soft foot gap are 0.5mm and 0.4mm respectively as well as foot@2 and foot@3 have soft foot gap are 0.05mm and 0.0025 mm respectively . The equation can be shown as:
Shim to add under Foot @2 and Foot @3 = {(Gap2 + Gap3) + (Gap1 + Gap4)/2} x 0.8
The foot has an inadequate amount of shim under it. If the alignment process has been started, and an accurate or consistent alignment cannot be obtained, it is likely that there is a soft foot condition present.
When the anchor bolts of a machine with a soft foot are tightened, the machine body gets twisted causing it to stress. Over tightening will cause the foot to bend. This stress will not allow the machine to align. The gap under the short foot must be shimmed before starting the alignment process. If loosening a bolt changes the alignment readings, soft foot is present. To check for the soft foot, set up the dial indicator on a foot and loosen mounting bolt. If the foot moves more than 0.05mm, or the soft foot standard defined by the user, the foot is considered soft and needs to be corrected. This should be done for all feet.
To calculate the amount of shim to add to compensate for the short foot, the sum of the smaller gap values are subtracted from the sum of the larger gap values.
This amount is divided by two. Use 80% of the quotient as the amount of shim that should be added under each foot to remove the parallel air gap. If two foot, foot@2 and foot@3 have soft foot gap are 0.5mm and 0.4mm respectively as well as foot@2 and foot@3 have soft foot gap are 0.05mm and 0.0025 mm respectively . The equation can be shown as:
Shim to add under Foot @2 and Foot @3 = {(Gap2 + Gap3) + (Gap1 + Gap4)/2} x 0.8