Quality Innovations: Combine Roughness and Roundness Checking

Instrument inspects as a surface finish measuring system, a roundness measuring system or both at once.

An Automatic Follow feature allows centering and measuring of eccentric parts and features. Source: Taylor Hobson Inc.

Too often, manufacturers of cylindrical parts invest a great deal of money in special fixtures to minimize alignment problems that cause errors with traditional surface finish checking devices. Hard fixtures must be scrapped when components change size or shape; flexible fixtures are prone to setup errors and tend to lack stability. A new roundness-measuring instrument, the Talyrond 365 from Taylor Hobson Inc. (Leicester, England), combines roughness and roundness checking into one inspection station.

Programmed routines give the instrument the changeover flexibility of a machine tool, while eliminating the need for dedicated operators. "Fully automatic alignment and positioning reduce human errors and improve consistency," says Tom Brem, product manager at Taylor Hobson. "Inspecting the part complete in one setup saves time and shrinks the uncertainty budget by eliminating multiple fixtures and multiple opportunities for errors."

Surface finish must be measured along the axis of a cylinder with the stylus at the "top dead center" position. This ensures that data is collected at the tip of the stylus rather than along the flank of it. "Another major source of setup error is when the stylus crosses over the component axis," Brem says. "That's a common problem when the component axis is not parallel to the measuring instrument traversing axis."

The instrument automatically centers and levels the component for near-

flawless alignment without any special fixturing. That solves setup problems and saves money too-both in the purchase of fixtures and also the calibration and maintenance of them.

Other system advantages include:

- Less capital expense-one instrument instead of two.

- Reduced overall inspection time.

- Better consistency, improved gage repeatability and reproducibility.

- Handle, clean and stabilize parts just once.

- Faster first-article inspection minimizes machine tool downtime.

- Unattended, automatic inspection cycles free the operator for other tasks.

- Programmed measurement runs mean less operator influence and fewer operator errors.

- Perfect alignment of the component for "top dead center" surface finish checks.

Automatic analysis routines for many common measurements such as camshaft lobe lift and phase are provided with the instrument. Source: Taylor Hobson Inc.

One Instrument, One Operator

Inspectors of both roundness and surface finish on cylindrical components benefit. Instead of two instruments, two operators and two sets of measurement results, inspection can be done on one instrument by one operator with significant savings of time and money plus improved measurement consistency.

This system is particularly helpful to manufacturers of crankshafts and camshafts. These products can be very difficult and time consuming to measure using conventional surface finish instruments. A crankshaft, for example, can take several hours to inspect the mains, pins, journals, thrust walls and flange. Then the part has to be passed to another instrument to have roundness and geometry checked on all the same features.

For small components such as fuel injectors, both roundness and roughness tolerances are so tight that even slight deviations in one characteristic will cause deviations in the other. "With traditional instruments it's a ‘chicken and egg' dilemma trying to figure out if roughness or roundness is the culprit," Brem says. "This system checks both at once to greatly speed the inspection process and to much more accurately pinpoint the source of the problem."

Three-dimensional cylindrical mapping of wear scars aids research and development; 3-D analysis of machining defects helps refine the manufacturing process. Source: Taylor Hobson Inc.

An automatic follow feature ties movement of the gage head to movement of the horizontal positioning arm. As the gage approaches an over-range condition, the arm will move to return the gage to its null position. The process is seamless and will repeat itself as often as necessary to effectively increase the gage range from ±1 to 200 millimeters, which is the length of travel of the horizontal arm. This feature is ideal for checking form on such things as camshaft lobes. It also simplifies fixturing of a workpiece, because automatic centering and leveling can be carried out no matter how eccentric the part may be to the rotating spindle.

Other key technology factors include:

- 200,000 data points-0.25 micrometer spacing-in the vertical and horizontal measuring axes.

- 0.15 micrometer/100 millimeter straightness uncertainty in the vertical and horizontal axes.

- 0.25 millimeter and 0.5 millimeter measuring speeds to comply with international standards.

- Low instrument noise-less than

30 nanometers.

The above specifications are comparable to most dedicated roughness checking instruments. The following features are not available at all on traditional surface finish instruments, but are available on the Talyrond 365:

- 72,000 data points-0.005 degree spacing-in the rotary axis for circumferential roughness.

- Dual-purpose gage head with

1-millimeter range (max) and 0.0012-micrometer resolution (min).

- Totally seamless integration of roughness and roundness

analysis software.

- Automatic centering and leveling alignment of the component.

- Fully programmable automatic measuring runs.

The ergonomic floor-standing system can be configured with a 300-millimeter, 500-millimeter or 900-millimeter vertical measuring column. Source: Taylor Hobson Inc.

Installation and Training

Installation for the Talyrond is handled by a Taylor Hobson service engineer. "It takes about a half a day and includes certification that the instrument has been calibrated with traceable artifacts and is performing to specification," Brem says. "The engineer also runs through maintenance and handling procedures so that the operator can keep the station running at optimum levels on his own."

Training is methodical and thorough, as it needs to be for an instrument with this level of sophistication and capability. Every aspect of operation from powering up to program creation is covered in step-by-step fashion using a DVD running on a separate PC. An instructor guides the operators through the initial training to ensure that all points of operation are covered. The DVD stays with the end-user for refresher training or for getting new operators up to speed.

Routine operation of the station requires no training at all. After a measurement program has been written, it is a simple matter of loading the workpiece and pushing the start button. "A lot of people look at automation as only a way to save time," Brem says. "We look at automation as a way to get error-free, consistent, accurate results regardless of operator skill or training."

Roughness and roundness should always be inspected together. "It's no surprise that surface finish and roundness specifications are nearly always indicated on the same engineering drawing; they are inseparable in the manufacturing and eventual functioning of the component," Brem says. "With awareness that errors of roundness and surface finish occur simultaneously at the manufacturing stage, it seems logical that an inspection instrument would measure roughness and roundness at the same time."

QUALITY SPECS

- Programmed routines give the instrument the changeover flexibility of a machine tool and eliminate the need for dedicated operators.

- For small components such as fuel injectors, both roundness and roughness tolerances are so tight that even slight deviations in one characteristic will cause deviations in the other.

- The station automatically centers and levels the component for near-

flawless alignment without any special fixturing.