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I define a CNC machine tool's accuracy as how precisely its axes can follow intended paths to commanded end points while under load. I define its repeatability as how precisely it may duplicate commanded motions (again, under load) during multiple cycles throughout the day.

They are definitions for dynamic accuracy and repeatability. They likely vary from your machine builder's specifications. Builder specifications commonly indicate static accuracy and repeatability; that is, the device is not in cycle performing machining operations when related measurements are taken.

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In fairness to machine builders, dynamic accuracy and repeatability vary with the amount of stress exerted on machine components. The more the stress, the more difficult it's to keep up accuracy and repeatability. This makes it impossible for machine builders to supply, much less guarantee, dynamic accuracy and repeatability specifications. There are simply way too many variables.

Having said that, machine builders should have the ability to establish whether their machine can achieve accuracy/repeatability requirements for your particular application. They must be ready to guarantee just as much if you question them to do so just before purchasing a fresh machine tool.

Certain accuracy-related factors are beyond a CNC user's control once a device is installed. These generally include:

• The machine's construction. It must have the ability to perform the most powerful machining operations in your application without excessive deflection of its support components.

• The feedback system. Linear scales directly monitor the positioning of the moving component for an axis. Unlike rotary encoders, they're not highly based mostly on the integrity of axis system components (way systems, ballscrews and couplers).

Other accuracy-related factors are the responsibility of the device user. These generally include:

• Machine tool calibration. Machine builders initially calibrate pitch error and backlash compensations, but if accuracy will be maintained, end users must repeat these calibrations at regular intervals during a machine's life.

• Environment. Machine tools must certanly be put in a stable working environment that minimizes ambient temperature and humidity variations.

Ensuring that a machine installation provides adequate dynamic accuracy for your application—and keeping it properly maintained—is but half the problem of producing consistent, acceptable components. You should also make sure the device can accurately repeat from the initial workpiece to the last—hour after hour, day after day—whilst machine components loosen up after idle periods.

An important repeatability-related issue associated with machine design is thermal variation of moving components. Primary concerns are the machine's spindle and way systems because they've the largest impact on machined surfaces. As these components warm, they grow. Because they cool, they shrink. This makes it difficult—maybe impossible—to carry size on critical, tight-tolerance surfaces during the device warm-up period.

Machine builders head to great lengths to minimize thermal changes in machine components (cooling the spindle and/or way systems, for instance). Additionally, they incorporate design methods that minimize the repeatability impact of thermal variation. With CNC turning centers, for instance, the headstock may be perpendicular to the bed. As it warms, only the height of the cutting tool's edge changes. This minimizes the amount of machined diameter variation from part to part as the device warms up.

When purchasing any new CNC machine, you must know how the builder handles thermal variation. Moreover, you need to make sure machined-surface variations caused by thermal growth during warm-up won't exceed tolerances. Otherwise, you could maintain for a productivity-wasting surprise whenever you discover that the new machine must run for a warm-up period before it can be used in production.

Some of the very most severe repeatability issues have nothing to do with machine design. Instead, they're influenced by the machine's application. Variations of any kind—during a generation run or from one time a job is run to the next—can impact repeatability. Issues that differ from cycle to cycle can cause the need for a time-consuming adjustment. If the variation is excellent enough, it may lead to scrap.

What are samples of variations? Types of variations during a generation run include:

• Tool wear. As cutting edges wear, machined surfaces will vary. External surfaces grow while internal surfaces shrink

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• Dull tool replacement. When dull cutting tools are replaced, extreme care is required to ensure cutting edge(s) don't vary from their predetermined position(s).

From one time a job is run to another include:

• Workholding setup. Many factors affect workpiece stability (placement/alignment of the workholding device, clamp location and force applied, and program zero assignment, for instance).

• Cutting tool assembly, measurement and offset entry. Component and assembly variations lead to rigidity variations that could lead to machining issues.Hit on positioning accuracy and repeatability of cnc machine to explore more about our services and sites. Hope you ll like our more services.

• Machine condition. Variations caused by mishaps and the neglect of preventive maintenance may result in sizing issues with jobs that have run successfully in the past.