Hey, Jason,
<snip>As rumored, cross "drilled" rotors are crack susceptible. High
quality
rotors have the cross holes CAST into the rotor, not drilled.<snip>
I don't know where you got your information, but I disagree wholeheartedly.
I believe that most of the rotor holes are drilled AND reamed at CNC or DNC
machining centers at controlled speeds & feeds with plenty of coolant to
absorb heat build-up. This type of machining yields near perfectly round
holes & thus eliminates any possible "stress risers".
Stress risers would only result from the small striations resultant from too
fast a feed rate. This would also shorten tool life & add unneccessary
expense to both the process & the product.
Most round components (rotors) are made from either cold-rolled (CR) or hot
forged (HF) raw materials, which have uniform grain flow & as a result are
very strong.
Unless you are talking about "perfect" precision castings, which is an
oxymoron like "military intelligence" or "jumbo shrimp", all casting forms
are more subject to cracks and indications, especially those which undergo
repeated heating & cooling, such as a brake rotor.
There are a couple of reasons that castings tend to be weaker than bar stock
(billets):
1. Casting molds cannot be filled completely at one time. The molten steel
has to flow into the mold and while hot material is flowing in thru the
casting "gate," the material at the farthest part of the mold - away from
the gate - is already starting to cool. The differences in cooling rates
can lead to potential stress points.
2. Most molds are ceramic or sand & are only as true as the wax forms that
they were shaped over.
3. Even in aluminum or steel casting molds, the molten material will shrink
as it cools & there is no absolute guarantee that the resultant finished
casting will have round features without finish machining.
Actually, the strongest form of any iron/steel component is either a "drop"
forging or a rotary forging. The grain flow is uniform & unless heat
treat/quench is improperly performed, forgings are the least susceptible to
stress cracks. Even so, finish machining is still required.
I can't say that I know if any rotors out there are, in fact, forged - then
machined - but I bet some are.
WHEW!
Bob Smith (DAKSY2K on AIM)
(23 years in a machine shop)
Averill Park, NY
2K DAK SY CC Sport + V6 4X4 5 Speed
WebPage URL: http://home.nycap.rr.com/daksy/
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