Custom Honeycomb Structures

Special Vibration Control Systems is an area in which Newport has made substantial investments in terms of application lab facilities, equipment and engineering capability. Extensive development work in this area has benefited the users of standard and custom table systems, and an ever-widening range of capabilities and designs are available. As might be expected, most special tables involve modifications or variations in design of standard systems. Special sizes, shapes, materials, and hole patterns are common, as are tables with holes, apertures or cut-out sections. With an installed base of over 30,000 vibration control systems, Newport possesses the expertise and largest accumulation of data in the industry —bar none.

Newport offers assistance and advice on the construction or use of special table systems as a service to our customers. Newport can also provide detailed system design, computer modeling and analysis of proposed table system designs. The construction and testing of scale models have been found to be a useful and cost effective means of estimating dynamic performance of complex or unusual table structures. In general, it pays to consult Newport early in the design phase to take advantage of our technical expertise, application experience and manufacturing capabilities available with our specialized production equipment and tooling. In addition, our application lab regularly accepts equipment for customer testing. Just call us with your requirements.

Custom tables in OEM quantities with guaranteed, rapid delivery times are a Newport specialty. Newport also offers JIT —Just in Time delivery and KanBan stocking and testing services. Call us for more information.

Special lengths and widths are probably the most common variation for a custom table. Rectangular sizes are usually charged at the standard price for the next larger size. Newport has the equipment available to fabricate, machine, and handle panels up to very large sizes. For example, 1 in. spaced mounting holes can be installed in panels up to 14 ft (4.25 m) wide. As a general rule, the limiting factor with regard to size is most frequently the availability and the characteristics of the raw skin material, which in turn will determine the construction approach.

Special mounting hole patterns (in English or metric sizes) can be drilled and tapped in the working surface per customer print. Note that the cost increases rapidly with tighter tolerances, so do not over specify the tolerance on either the hole diameter or its position. For sizes larger than about 1/4-20 (M6), a solid plug is usually welded to the backside of the skin to reinforce the hole. The plug is typically 1–2 in. (25–50 mm) in diameter and 3/4–1 in. (18–25 mm) long. In some cases, the plugs extend completely through the table and are welded to both the top and bottom skins. The latter are used for reinforcing areas with very large local stresses, such as with lifting hooks attached to the table or for securing heavy equipment. Such inserts will typically affect flatness for a radius of 1.50 in. (38 mm) around the insert.

Access holes going completely through the table can be of any size or shape. The holes are usually metal sleeved with the sidewalls bonded or welded to the top and bottom skins. Small holes are usually less expensive if they are round, however above 10–12 in. (25–30 cm) it is generally less expensive to install square or rectangular holes.

Special metal side panels greatly reinforce the overall stiffness of the panel and are recommended wherever one anticipates large stresses at the edges. Side panels are also strongly recommended whenever tension forces on the skins are anticipated (forces which tend to pull the skins away from the core of the table). The side panels may be constructed from the same material used for the skins, or even thicker material if heavy items will be mounted there. The metal sidewalls are tightly bonded to the honeycomb core to avoid any "drumhead" effects, and are most commonly attached to the top and bottom skins by welds.

Panel thickness can be adjusted arbitrarily. However, Newport stocks raw honeycomb core material primarily in those specific sizes used for standard products. Other thicknesses may involve delays and set-up charges. Call us for information on current availability.

Special shapes for the surface of the panel constitute no particular difficulty except that the edges typically must be machined to shape, a procedure which substantially raises the cost. Also, curved table edges are more difficult to finish than straight ones. Non-uniform panel thickness should be avoided, since transferring the skin stresses across discontinuities presents additional problems.

Multi-Level panels are usually constructed by building one panel on top of another so that the top surface of the lower panel constitutes the bottom surface of the panel above it. Thus, a two-level panel has three skins. Newport has a wealth of experience avoiding thermal problems that can plague structures of this type.

Vertical tables provide a particularly efficient way to conserve floor space. Also, this configuration neatly avoids the cantilevered optical mounts that result when vertically oriented components are mounted on a horizontal table. Components can be mounted with extraordinary dynamic rigidity at a relatively low cost when they are oriented parallel to the plane of the table and close to its mounting surface. Sealed hole grid arrays can be provided on both sides of the vertical structure.

Newport has designed and built vertical table systems with vibration isolation mounting and rigid attachment to the floor or other support structure. A major consideration has been given in these designs to avoid any resonance between the cantilevered table structure and the driving frequencies in the environment. Many of the systems also have included provisions for high accuracy aiming and alignment of the entire integrated table system.

Other metal skin material options include: 300 Series stainless steel (nonmagnetic); aluminum (nonmagnetic, low weight, high machinability, availability in large sizes); titanium (nonmagnetic, low thermal expansion, low weight, high strength-to-weight ratio); carbon steel (low cost, excellent availability in large sizes with a wide choice of thicknesses, easy to weld); magnesium (nonmagnetic, lowest weight); and Super Invar (low thermal expansion coefficient).

Other metal honeycomb core materials are available, such as non-magnetic stainless steel, aluminum or special materials.

Internal stiffeners are appropriate wherever the panels are subjected to unusual loads or stress, such as the junction of two panels. Note that such stiffeners inevitably lower the stiffness-to-weight ratio of the overall structure.

Isolator pockets are frequently installed as a custom option on 36 in. (914 mm) thick tables when they are vibration isolated. The recesses are cut into the sides of the table to contain the air mounts within the volume of the table and allow the panel to sit lower to the ground. This provides a more convenient working height and a lower center of mass for better stability.

Outriggers for mounting the isolators along side the table rather than underneath are another common modification to tables. They provide better overall performance than cut-outs, although they tend to somewhat block access to parts of the table surface.

Vacuum compatible table tops are now almost a commonplace requirement. We have developed a broad selection of materials and construction techniques that are consistent with good vacuum practice down to less than 10^-7 torr. Our results, from these investigations, include measured data on outgassing rates for actual completed structures. Custom versions of Newport tables and breadboards have been certified for airborne and space applications.

Both nonferromagnetic and nonconductive materials can be substituted in the construction of Newport tables and breadboards. Aside from the more usual nonferromagnetic metals, other potential alternatives include graphite epoxy, fiberglass, ceramics, and some of the exotic new composite materials.

Cleanroom machinery applications sometimes require that laminar airflow or a vacuum be pulled through an optical table, breadboard or honeycomb equipment pedestal. Newport offers a perforated honeycomb core design to allow air to move through and between individual honeycomb cells. Used with a non-sealed grid hole top, full laminar airflow can be achieved through the honeycomb structure. Pipe couplings can be installed into the top, side or bottom of the structure to allow connection of negative pressure air handling systems.

Connecting together smaller panels is usually the best way to produce large, irregularly shaped structures. Tables can be joined together in a variety of configurations including: "T"-shapes; "L"-shapes; angles, and multiple levels. The connections can be either permanent or detachable. Detachable sections make for easier transportability and permit on-site reassembly past doorways or other obstructions.

Doubler interfaces are described in the section on modular tables. They are the preferred attachment between table sections because the resultant table exhibits virtually no compromises in performance as compared to a monolithic structure. Doubler interfaces are effective in transferring stresses across regions where there are discontinuities in skin planes and they are, therefore, the recommended attachment for panels with differing thicknesses.

Flanged interfaces are generally used where two panels are joined with their planes at right angles, i.e. with the end or side of one attached to the surface of the other.

This type of joint requires the greatest amount of internal reinforcement, particularly for the table which has the flange attached to its surface.

Beam connectors are appropriate where two separated table sections must be held together as a single rigid entity with a minimum of intervening hardware between them. Examples are optical diagnostics setups that straddle some wind tunnels and gas dynamic lasers. Note, however, that beam connectors as a class provide less rigidity than continuous honeycomb constructions.

Welded connections are usually substantially cheaper than detachable assemblies. However, the differences are frequently overridden by increased transportation costs. Large welded assemblies also provide fewer opportunities for stress relieving the welds after completion, often placing stringent, and expensive restrictions on weld procedures.