July 16, 2015
Pry Bars, Sledge Hammers and Come Alongs – Oh MY!
By Stan Riddle
Precision alignment of rotating equipment is a task which requires precision. Those of us who perform this task are asked to position big, heavy machines to tolerances often less than the thickness of a human hair.
The measuring tools used to perform shaft alignment are quite capable of successfully showing us how to position these machines to perform this precise operation.
And then we attempt to move this equipment around with pry bars, sledge hammers, come alongs, fork lifts, bridge cranes, 4×4 lumber, hydraulic jacks, and whatever else we can grab!
In vertical positioning, these crude tools work well, simply because we are just using them to pick the machinery up. We then sit the machines back down on flat, clean bases, hopefully on precisely machined stainless steel shims. But all too often we then start “beating and banging” the moveable machine with the same crude tools, to attempt precise horizontal moves. In most cases, this causes much sweating, swearing, damage to the movable machine’s feet, and chasing the machine back and forth until we get lucky, and land it “close enough”!
Jacking bolts, or positioning screws are a much more accurate, precise, and controllable way to move machines horizontally. As an example, a ¾-10 bolt has 10 threads per inch. This means:
• One full rotation of the bolt moves the bolt linearly 0.100”. This means it can move the machine 0.100”.
• Rotating the hex head bolt one “flat” of the bolt head moves the machine 0.0125” (0.100”/8)
• Using a fine thread bolt (3/4-20) gives the user twice the accuracy.
It’s easy to see that jacking bolts can not only move the machine, but move it much more precisely than a 12 lb. sledge hammer!
Specify your equipment with jacking bolts already installed. If your machines don’t have jacking bolts:
- Buy them. Several companies sell jacking bolts and devices.
- If your company didn’t or won’t buy them, make them. In many cases, simply tack welding a nut to the baseplate, and using a standard bolt, works pretty well. Be sure to allow yourself room to position the machine.
- Can’t weld on site? Drill and tap a steel block, and bolt it onto the base.
- Can’t drill on the machine? Use a C-clamp. Clamp it onto the base, to see where a jack nut is needed. Then take it back to the shop, and weld a threaded nut onto the C-clamp. Make four. Since they are temporary, they can be used on similarly sized machines.
- Use a bar clamp. Rotate the moveable jaw 180 degrees. Slide the bar clamp under the motor. Rotate it so that the moveable jaw hooks onto the baseplate, and the threaded jaw can be used as a temporary jacking bolt.
That’s my take on jacking bolts. What have you “made up” to use as jacking bolts? Please share your ideas with us!