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Old 03-14-2007, 04:13 PM   #44
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Join Date: Aug 2005
Location: San Diego, CA
Posts: 3,005
My Ride: '99 323i
I'm now totally convinced the BMW Motorsports rotors made by SHW have drilled not cast perforations.

On their website - - you can find this photo of the actual machine they use to drill the holes. The caption of the photo translates as "Perforation machine for quantity production - qualitatively high-quality and economical"

The remainder of the text on the page is this - (bold mine)
Special solutions for brake disks: Individually to High ending in series-evenly the quantity production of raw and worked on quality brake disks SHW of automotives offers by know-how of many years also individual special solutions, in order to become fair the rising requirements at lightweight construction, security, optics and comfort. The associated development projection/lead benefits all our customers, since appropriate experiences will transfer to development and finishing techniques in mass production are can exemplary here the group brake disk developed by SHW of automotives, which connects extreme maximum stress with highest security. Here the grey cast iron friction ring is connected by steel pins with the aluminum pot and can expand when high heating up freely. A precision part, on that hardly a High end Fahrzeughersteller, hardly a sport or a rennsportwagen do without through brake disks do not only know appropriate manufacturing plants worked on and geometisiert, butby the integration by perforation drillings, Duppen or slots to be also further refined. This serves not only the rising optical requirements, but also the purposeful optimization or as wear indicator
Additonally, there are several photos of castings and molds on their website, none of which have any indication of them casting rotors with perforations in the disk.

Basically, if casting rather than drilling holes in the rotor face were easy, common, possible, and/or technologically advantageous, manufacturers would be both doing it and bragging about it. It should be easy as pie to confirm that somebody is making rotors in that fashion rather than impossible.

Last edited by jpr; 03-14-2007 at 04:18 PM.
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