TMC How to Select a TMC Optical Top

Optical Tops,
Breadboards & Supports

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How to Select a TMC Optical Top

The major factors to consider when selecting a TMC optical top are:

Level of structural damping
Skin thickness
Top thickness
Environment
Tapped-hole convention
(imperial vs. metric)

1. Damping
TMC offers three levels of structural damping, though not all levels are available in each construction. Because the damping mechanisms are expensive to manufacture, it is prudent to specify only the level of damping required.

All TMC damping levels incorporate broadband dry damping. For a complete description of broadband vs. tuned damping, see the TMC Technical Background.

Maximum Dry Damping. TMC’s maximum dry damping provides a level of performance unsurpassed in the industry. It is recommended for the most demanding applications including holography, interferometry, ultra-fast optics, and spectroscopy. In addition, it is recommended in particularly noisy vibration and acoustic environments. For pulsed lasers and other noise generation equipment, it is especially helpful.

Standard Dry Damping. An economical alternative for less sensitive applications incorporates our standard dry damping level. This broadband damping level provides a top with performance characteristics that exceed the majority of other manufacturers’ highest performance levels. Peak compliance levels for standard damping exceed peak compliance levels of our maximum damping by a factor of four.

Radius Corners

TMC tops now include a user-friendly 1 in. radius corner as a standard feature at no extra charge. These “hip-savers” are especially appreciated in darkened rooms. This feature does not impact overall dimensions or the hole pattern.

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Radius Corners

Nominal Dry Damping. This damping level is not recommended if sensitive work is being conducted on the table. The nominal damping level is appropriate for general lab work when the main consideration is a rigid, flat mounting surface. Please Refer to the Dry Damping Performance Summary for more information.

2. Skin Thickness
The vast majority of TMC optical tops are available in a choice of two thicknesses: 3/16 in. (5 mm) and 1/8 in. (3 mm). For structural performance reasons, the 3/16 in. thick version is generally recommended. In addition, since the top skin includes an array of drilled and tapped holes, the 3/16 in. version gives nearly four full threads for more secure mounting.

When cost is an overriding concern, 1/8 in. skins are an attractive alternative. The

stainless steel top skin is a major cost element in the top and eliminating 33% of the stainless steel reduces the manufacturing cost significantly.

A third skin thickness is available as an option for 2 in. (50 mm) thick breadboards. Patented techniques allow TMC to form a top skin 0.075 in. (2 mm) thick, while maintaining a full three threads tapped directly into the skin. Advantages include low cost and light weight.

3. Overall Top Thickness
A top length-to-thickness ratio of 10:1 is a safe rule of thumb for most applications, although for very sensitive work in severe environments, a ratio of 7:1 may be justified. It should also be kept in mind that while top thickness is proportional to top static rigidity and dynamic natural frequency, it does not directly affect compliance, which is primarily controlled by structural damping.

Small, 2 in. (50 mm) thick tops should be supported on uniform flat surfaces, not post mounts. Our 4 in. (100 mm) thick tops may be supported on post mounts, but they do not incorporate the same proprietary damping techniques used on our thicker tops.

We recommend that all sensitive work be done on tops at least 8 in. (200 mm) thick.

4. Environment
For most applications, our CleanTop^® II optical top is the best choice.

ClassOne™ CleanTop^® II:
The ClassOne™ version takes CleanTop II one step further. Designed for maximum cleanroom compatibility, the ClassOne CleanTop II has not only a stainless steel top skin but stainless steel sides and a stainless steel bottom skin as well. Nylon 6 CleanTop cups are standard and 304 alloy stainless steel cups are available as an option.

Wiped down with lint-free cloth, the ClassOne™ is wrapped in plastic prior to shipping and may be brought directly into a cleanroom.

Non-Magnetic CleanTop^® II.
For work in a highly magnetic environment, we now offer our new non-magnetic construction. This table is made from 304 alloy stainless steel rather than the conventional ferromagnetic 430 alloy. Though the skins, sides, dampers, and core are a 304 alloy, no stainless steel top can be said to be “100%” non-ferromagnetic. In some cases, 316L alloy is preferable and custom construction from this material is available on special order.

5. Tapped Holes
TMC offers both imperial 1/4 - 20 tapped holes on 1 in. centers and metric M6 tapped holes on 25 mm centers. Though there is no price difference between tops, imperial tops have imperial overall dimensions while metric tops have metric overall dimensions.

In addition, we now offer both imperial 1/4 - 20 tapped holes on 1 in. staggered centers and metric M6 on 25 mm staggered centers, doubling the number of tapped holes on conventional 1 in. or 25 mm grids. The DoubleDensity™ construction is available with any version of our CleanTop^® II at a nominal additional fee. For more information, see DoubleDensity™ tops.