Squaring a Block on the Mill - 4: Transferring Precision
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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 machinist often uses trust when machining a part. They trust that once the milling machine spindle is set perfectly perpendicular to the table that it will stay that way. The machinist does not make one cutting pass, stop to check the setup, readjust the machine, and then make another machining pass. Once the machine is set up the machinist is reasonably sure that it will stay in alignment... that the machine is square. This is true when squaring a part as well. The machinist "trusts" that the ways and the spindle of the milling machine are square. If the fixturing has been squared to the machine then the precision of the machine can be transferred to the part being machined.

For example from the animation below you know that the center line of the milling machine spindle is perpendicular to the to mill table.

The vertical surface of the rear jaw of the vise is known to be perpendicular to the base of the vice. Therefore that jaw face is also perpendicular to the table (and by default - but not shown in the animation - the rear jaw face is also*parallel* to the spindle)

The surface inside the vise is known to be perpendicular to the jaw (not shown) and parallel to the base of the vice. Therefore that surface is parallel to the machine table.

The use of the word "trust" has had some repercussions. It was never the author's intent to imply that all a machinist had to do was trust his machine and all of the machining would take care of itself. Indeed, the machinist should be very wary of the machine he is using until which time he is satisfied with its alignment and reproducibility. So perhaps it would be a good idea to substitute the word "validate" for "trust". Maybe that makes more sense. But in any event, never trust anyone over thirty.... Peace! R.S.
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label: milling machine, square, parallel, transfer precision, clamping, bolster, perpendicular, machinist's square