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CROSSED ROLLER BEARINGS AND SLIDE ASSEMBLIES
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CROSSED ROLLER BEARINGS AND SLIDE ASSEMBLIES
WHAT ARE TYPICAL APPLICATIONS FOR CROSSED ROLLER LINEAR PRODUCTS?
- Typically Crossed Rollers are used in high accuracy, short travel (< 12" stroke) applications where noise, vibration and accessibility are key considerations. These include, but are not limited to Vision Inspection, Wafer Testing and Handling, Optic Alignment, Disk Certification, Precision Dispensing, Precision Gauging, Automated Production Equipment, ect.
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WHAT ARE THE PERFORMANCE CHARACTERISTICS OF CROSSED ROLLER PRODUCTS?
- The standard published linear tolerance for travel accuracy (flatness and straightness) is .0001" per inch of stroke (2.5 um / 25mm). In reality the ways and slides perform to a higher degree of accuracy. Several Factors influence travel accuracy. If your application requires a tighter degree of control, please discuss our "select" grade with an Applications Engineer. Please remember when specifying higher accuracy that specialized inspection equipment is required for verification.
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HOW IS THE STROKE RANGE SPECIFIED?
-With an "in-Line" bearing, stroke is specified as off center. Thus ½ the specified travel to each side of center. I.e.: a 2" stroke model will travel 1" in each direction off center.
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HOW DOES DYNAMIC LOADING RELATE TO DEFLECTION?
- The deflection is related to several variable determined by the slide unit and the application. It is impossible to publish a standard deflection specification due to vast combinations of these variables. ALM engineering can accurately determine deflection only by conducting a test with the actual slide and the load oriented per the application specifications. Presented load data is given in relation to the life expectancy only.
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WHAT MATERIALS ARE AVAILABLE?
- Crossed Roller linear ways and rollers are available in standard hardened steel or stainless steel. Slide assemblies are constructed from standard aluminum or cast iron. Stainless steel, brass and other material construction is available upon request.
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ALUMINUM OR CAST IRON?
- Slide construction is offered in anodized aluminum or finish ground cast iron. The heavier, ground iron can be made to perform more accurately and is less susceptible to vibration. In Gauging applications, cast iron material is common, both for thermal stability and accuracy. Cast iron has a coefficient of thermal expansion that is very similar to the steel bearings. The aluminum slide has twice the expansion rate of the steel. Typically most application can utilize aluminum construction and avoid the ~ 25 - 30% cost premium and corrosion issues associated with cast iron.
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WHAT CORROSION RESISTANT OPTIONS ARE AVAILABLE?
- Crossed Roller linear ways are available in standard steel with chrome plating or stainless steel. Rollers are supplied in stainless steel for both options. Slide assemblies constructed from cast iron are available with electroless Nickel plate.
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WHAT ARE THE MAINTENANCE AND LUBRICATION REQUIREMENTS?
- In most applications maintenance and lubrication are not required. Due to its rolling nature, and low coefficient of friction, heat and wear are minimized. Certain extreme applications may require maintenance consideration. Under no circumstances should dry film lubrication be applied.
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WHAT CONTAMINATION RESISTANCE OPTIONS ARE AVAILABLE?
- Certain Slide assemblies are available with bellows, way wipers, seals and air purge options. Bellow option also serves as a "pinch point" restriction. In addition custom enclosures can be designed and fabricated.
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WHERE ARE THE STANDARD MOUNTING HOLES?
- To maintain maximum flexibility for our customers, "blank" (no mounting holes) assemblies are available. This permits application specific pattern, sizes and features to be added prior to final assembly. This also permits rapid "alternative source" capability. Standard ALM bolt holes patterns are available in English or Metric sizes. All CAD drawings include the standard pattern and dimensional reference charts are available by model type. It is highly suggested that mounting holes be added prior to assembly at the factory to avoid damage and warranty issues.
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ASSEMBLY MOUNTING CONSIDERATIONS?
- Assemblies must be mounted to flat stable base structure using the available mounting holes. Crossed roller product may be used in any attitude without degradation of performance. Orientation of product (i.e.: vertical, ceiling mount, wall mount, ect.) may affect load rating.
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WHAT ARE THE LIMITATIONS / RESTRICTIONS OF CROSSED ROLLER PRODUCTS?
- Utilizing an "in line" bearing structure requires a longer length operating envelope than a recirculating type product. Crossed Roller Linear bearings should not be used in application with shock loading or continuous chatter. Special precautions must be taken in harsh environments.
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IS CUSTOMIZATION AVAILABLE?
- Standard assemblies are available with several options from size to material to finish. ALM is the industry leader in quick response, product customization. These include simple modifications to standard product or complete design and build "specials".
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IS ALM A MANUFACTURER OR DISTRIBUTOR?
- The parent companies of ALM have fabricated crossed roller linear bearings and assemblies, as the sole US based source since 1970. ALM fabricates most components in house. Our modern factory employs most fabrication capability and highly skilled machinist. ALM only offers sales of the products we make. ALM does not offer private label products for resale. Service, repair and retrofit are available on any crossed roller mechanical linear motion device.
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WHY DO SOME CROSSED ROLLER SLIDES HAVE DRILL ROD WAYS?
- Typically the rods have a flat milled on one side and the balls are replaced with cylindrical rollers. These imitation crossed roller slides are generally less expensive to fabricate while utilizing roller that are crossed at 90 degrees. However the performance characteristic and price of these products should never be compared to a hardened tool steel way product. ALM does not offer this product.
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WHAT OTHER TYPES OF LINEAR BEARINGS ARE AVAILABLE?
- The Linear Bearing umbrella encompasses several types of products. From simple bushings on shafts or wheels on flats to high-end crossed roller products. Linear bearings are offered as "in-line", "sliding", "telescoping", "recirculating", ect. Although many products appear identical in form and fit, performance and price vary dramatically.
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HOW DO CROSSED ROLLER PRODUCTS COMPARE IN PRICE AND PERFORMANCE TO THESE OTHER TYPES?
- The old adage "You get what you pay for" applies here. High end crossed roller products are the finest mechanical bearing available. Subsequently, it generally is the most expensive per inch when purchased. However the phenomenal life expectancy, without maintenance or adjustment often make these products the preferred choice of machine designers. Build it and forget about it.
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ARE CAD DRAWING FILES AVAILABLE?
- ALM standard product drawing files are available in both 2D and 3D format. Several formats are available. Our website includes 2D .dwg and 3D .dwg AND .stp files for immediate download. Other formats may be requested from ALM Engineering. PDF files are available to review dimensions, and mounting hole callouts.
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MOTOR READY STAGES
WHAT DOES "APPLICATION SPECIFIC" MEAN?
- Not all stages are created equal. Although they may provide the same travel range, there are several additional application considerations, which affect the component level of a stage. The proper specification of these components will affect the performance and life expectancy of the stage. These include, but are not limited to attitude of use, speed required, duty cycle, load, environment, ect. Please refer to our "Engineering Considerations and Terminology" page for further detail.
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IS CUSTOMIZATION AVAILABLE?
- Although several options are available for each stage, sometimes the application will require further "customization". ALM is the industry leader in quick response, product customization. These include simple modifications to standard stage or complete design and build "specials".
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DOES ALM OFFER OTHER THAN CROSSED ROLLER STAGES?
- In response to customer demand ALM launched its SR series in 1997. This series of stages offer cost effective longer strokes utilizing recirculating ball or roller type linear bearings. These stages employ a similar "application specific" approach as the crossed roller stages. SR series stages are presently used in a wider spectrum of applications due their "Industrial Grade" construction and features. Machine tool grade steel slides with recirculating roller ways are available. Standard configurations and literature creation is in process
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DOES ALM OFFER MULTI AXIS CONFIGURATIONS ?
- X-Y, X-Z, X-Y-Z, gantry type and others are available.
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DO ALM STAGES OFFER "PLUG AND PLAY" CAPABILITY ?
- Upon request Motors, Switches, Encoders, ect. are offered in cable management carriers with standard DB connectors. Due to the wide variety of component options it is necessary to specify these options through ALM Engineering.
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DOES ALM OFFER MOTORS AND CONTROLS ?
- ALM is primarily and mechanical bearing, slide and stage manufacturer. This focus permits ALM to supply the right product for the application at a fair price. Support issues and defective product returns rarely occur. Upon request ALM can make motion control product recommendations. These products can be bundled with ALM stages and be supplied as a system. In most cases, complex technical requirements are often best left to local integrators and distributors of these products. This permits local support at the customer site. Integration of ALM stages with a variety of motion control hardware should be considered very basic.
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LR 08/01/2003
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