Dimensional tolerance effect on large mirror polished spheres

On any surface, a mirror polish shows every blemish. Fortunately our sphere fabrication technique is free of localised imperfections such as joint misalignment or rippling around the weld area, but we have found that if a mirror polished, stainless steel sphere is rotating about the equatorial axis, particularly under lights, any ovality will tend to show.

◄Polar mounted forming spigot

POLAR (USUAL) AXIS OF ROTATION
(Any variation between the polar and equatorial diameters is hard to detect)

If the viewing angle of the sphere is static however, few if anyone could detect up to 7% variation in the diameters, and if the display is out-doors, in natural lighting, reflecting mostly natural objects such as in a garden, probably much more out-of-roundness could be tolerated.

We do manufacture within 0.75% up to 1000mm, but depending on the size, the costs can be 70% more than when the tolerance is 7% For sizes over 1000mm the tolerance exceeds our own 7% acceptability limit if manufactured by the simpler process, so all larger spheres are proportionally more expensive.

Note that ours is a custom manufacturing process, every sphere is made to order out of minimum 2.0mm (0.079") material. They are consequently very robust. If you're looking for decorative type spheres up to 24 inches diameter, where dimensional accuracy is not really necessary and surface rippling is acceptable, the lighter gauge type, supplied by others should cost a lot less.

Some industrial applications, such as large, scraped surface mixing bowls or plastic molds may require less than 5% out-of-roundness, and there may be some scientific applications where even our guaranteed closer tolerances are not adequate. If yours is such an application, please email us with your needs. We have serviced many industries who have found our manufacturing technique very cost effective, including cinematography and the space industry.

All other common applications can accept the lower cost, 7% maximum dimensional tolerance. Revolving Globe

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