Mill Work Holders - 2: The Mill Vise and Alignment
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WARNING: Machine tools present a safety hazard. Improper operation can result in severe injury. These topics are for non-laboratory study only and are not to be used in conjunction with the operation of any tool or machine described herein. Never use a machine tool without the supervision of a qualified instructor.
The vise is by far the most widely used work holder in a machine shop. The vise is typically attached to the milling table through the table's T-slot. This video shows how to insure that the back jaw of the mill vise is set parallel to the longitudinal slide of the milling machine.
  • Using an indicator attached to the milling machine indicator holder, turn the cross feed handle to position the indicator to contact the back jaw.
  • Set the indicator to zero and move the longitudinal-feed handle until the indicator has reached the other edge of the jaw. Note how much the indicator moves and in what direction. In this case the reading on the indicator is four thousands of an inch minus (meaning the vise jaw is further away from the operator on the right side)
  • Loosen the bolt holding the vise to the table and gently tap the vise with a rubber hammer to set the indicator about half way back to zero.
  • Retighten the bolt and repeat the table movement to check your work.
Help with alignment

1. As the vise is loose on the table, pull it towards you, and then push it away to get an idea where the center of the t-slot is. Push the vice to the center of the T-slot. This ensures you will not run out of room in the slot when adjusting the vice.

2. The order in which the vise holding bolts are loosened or tightened is important. Keep the bolt on the indicator side of the vice snug, loosen the opposite bolt, set the indicator to zero, then run the indicator to opposite side, and tap the vise to bring the indicator to zero. The vice will swing around the pivot of the snug bolt. Then repeat the process for the other side. Soon you will be tapping the vice to zero while you are moving the indicator to the other side. This may be method easier and faster than taking half of the difference of the reading, since if both bolts are more or less equally tight, the pivot point is uncertain.

NOTE: make sure the washers holding the vice are flat and not worn or bent concave, because if they are concave they will cause the vise to move as it is tightened. Hardened washers are best.

3. While you have the indicator in the vice, check to see that the fixed jaw is truly vertical: This should be done under load. Tighten a piece of stock in the vise on parallels, leaving enough space on one side for the indicator to run up and down the fixed jaw, using the knee (not the quill) motion. Make sure the reading on the indicator is not more than a few tenths. This is important, because nothing can be machined square if the jaw is not perpendicular to the table. Some jaws of cheaper vices flex under load. Sometimes someone has put a shim between the fixed jaw and vise casting, and then the jaw flexes under load, driving the machinist crazy when he/she can't figure out why the parts aren't square. Tony Trammer

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label: Milling machine, work holding, clamps, regidity, precision, vise, alignment, edge finder, DRO, interchangable vise jaws, sanp jawa, collet, chuck, jogs, modular fixturing, table clamps