BUMAX screws hold world’s largest telescope together


World-leading specialist manufacturer of premium stainless steel fasteners BUMAX has been chosen to supply thousands of high-strength and corrosion resistant fasteners for the ELT, the Extremely Large Telescope, presently under construction.

BUMAX of Sweden has received an order for 11,000+ fasteners model BUMAX 109 for the construction of the European Southern Observatory Extremely Large Telescope (ESO ELT). The EUR 1bn ELT will be the world’s largest telescope by far when it goes operational in the dry Atacama desert in northern Chile in 2024.

The ELT is a reflector telescope, collecting universal light using a massive curved mirror that is 39 meters across, three times the area as the world’s second largest telescope. Such a giant mirror is much too large to be made from a single piece of glass, so it will consist of 798 individual hexagonal segments, each measuring 1.4 meters across and driven by electrical motors for fine tuning. The segments will work together as a single huge mirror to collect 100 million times more light than the human eye.

BUMAX fasteners are used to fix the nearly 800 telescope mirrors to all the segment supports. 12 pieces of 10mm long BUMAX 109 M6 bolts per segment are used for more than 900 segments in total (the 798 support segments plus an additional 133 segments for a continuous swapping process to allow the mirrors to be cleaned and coated while the ELT stays operational).

Customized bolts required special tools

The ELT is presently under construction by the Dutch company VDL ETG Projects in the Netherlands:

“Standard stainless steel bolts lack the strength required for the ELT,” said Michael Evers, Project Manager at VDL ETG. “We required a 10.9 strength bolt, and with the corrosion resistance of stainless steel. BUMAX offered us the perfect solution.”

“The high strength BUMAX 109 fasteners prevent damage to the mirror segments, which is very costly. Their corrosion resistance is also essential as the fasteners are sometimes open to the elements and will reduce future maintenance requirements.”

The bolts are a customized product that required special tools to manufacture. At the customer’s request, the bolts have been coated with a special surface treatment commonly used for fasteners used in telescopes.

“This order is yet another testament to BUMAX being able to provide the very best fasteners for the most demanding applications,” said Patrik Lundström Törnquist, Managing Director at BUMAX. “We have also been trusted with supplying fasteners for the CERN accelerator in Switzerland, satellites, submarines etc. When it really matters, use BUMAX.”

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