On movable units outfitted with jackbolts, it is relatively easy to calculate how many thousandths of an inch of axial travel is effected in one 360 turn of any size jackbolt.

Example: The jackbolt being used is 1/2" with 13 threads per inch (TPI).

Then:

Further, the axial travel per flat can be determined by dividing .077" (in this case) by either 4 or 6, depending on which type bolt head applies.

Avoid using jackbolts that are longer than necessary. Make sure that both internal and external threads are both clean and lubricated enough to be functional. In this manner, you can know if heavy resistance is from being mechanically bound or from corroded jackbolt threads. Also, on large units and/or units that have been anchored down for a long period of time with accumulated rust and corrosion, don t over-stress the jackbolts and nuts by fighting all that rust that may have the unit practically welded in place. Jack the unit up enough to clean the existing shims, the unit feet, and the base. Initially, this takes time, but when done it saves time; especially if broken jackbolts were likely to be involved.

Unless otherwise specified, never leave jackbolts in a bind against the movable unit to assist in holding said unit in place. Until the hold down bolts alone are sufficient to hold the movable unit in alignment, it s not properly engineered possibly due to outside stress factors such as unsupported pipe. The jackbolts are there to minimize the...