Straightness

 Measurement & Machine Technology

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Straightness & Flatness
Adjustments and Measurements

 One of the basic alignment steps required to optimize your machine tool.

Machine Tool precision leveling should be the first step of machine tool straightness
Straightness of travel does not mean the machine is level. A straight line can be at a 45 degree angle, without being at least somewhat level the machine may have hidden stresses causing abnormal wear, unnoticed until it is too late.
Precision leveling is one benchmark you can use in the future.
If a part is cut out of tolerance you can verify the machine is still level, if found not level you start the corrective process one step ahead of the game. Without this benchmark you have no way of checking the machine without a laser.  A precision level costs only hundreds of dollars compared to many thousands of dollars for a laser alignment system.

Machine leveling is not as simple as it looks. Axes that are on the floor should be loosely tied down and leveling points adjusted evenly to start out. Machine guards and covers need to be removed or put out of the way so that the slideway top surface is exposed where leveling is to be checked. Machine level should not be checked on the table top, unless geometry between table top and way top surface is known. Normal wear to the table top and the possibility of worn sliding surfaces, introduces the uncertainty that the table top may not be parallel to the way top causing a false level reading. The only way to know for sure is to remove this uncertainty. Therefore, only the way surfaces should be used for leveling unless the condition of the table top to way top surface can be verified.

Starting out the moving machine component is traversed to one end and the ways are evenly adjusted level, then moved to the opposite end and adjusted evenly from the middle to the end. This takes place several times until the anchors and levelers are all tightened evenly and the ways are level.

If there is a saddle the saddle ways need to be leveled first in both directions (in-line and cross) then the table ways are leveled in both directions. (in-line and cross) Cross leveling done on a separate precision parallel removes the “ROLL” of an axis. After the axes are adjusted the previous axis should be rechecked to verify that no movement occurred. Anchor points must be tightened evenly during the leveling process to maintain the straightness (flatness) condition of the axis. Thus stabilizing the machine and increasing the longevity of the adjustments. After the main axis is leveled the secondary axis can be leveled much the same as the main axis. Minor differences between machines tool design dictate the exact process.

Now that the machine is anchored to the foundation and the adjustment points are evenly adjusted the table top can be checked for level and the geometry compared to the final way surface level. This gives the machinist knowledge for future set-up procedures, and possible difficulties if any.

Now the laser system is brought out and the final adjustments if needed are made to fine tune the straightness of travel and document the final results.

Leveling the top way surfaces using a precision level in line with the ways removes PITCH, using a precision parallel and a level across the ways to remove ROLL. Yaw is controlled by the straightness of the way positive edge, and the adjustment of the GIB assembly.

Roll is cross rail leveling. (Parallelism)
Pitch is top surface leveling. (Flatness)
These two must be adjusted correctly for precision machining.
Yaw is positive edge straightness. In most cases this is not adjustable. (Duck Walk)


 

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27729 Bohn
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Tim Pray

E-mail timpray@measurementandmachine.com

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