You might want to recess the hat so that the rotor can/will retain
concentricity without relying only on the hat mounting bolt shear
limits. Speaking of the bolts, if you can't use JetNuts with NAS1586
hi-temp bolts you may need to consider good old fashioned lockplates on
NAS1588 hex bolts. Safety first. -Bill
> Attached are some screen shots of a disc brake setup I'm modeling in R2011 and some quick FEA results.
I really appreciate the reply and feedback. I'll definitely consider using Jet Nuts for the fasteners! Even using red locktite, the fasteners may work themselves out, or perhaps galling will occur. More often than I'd like, I've had caliper mounting bolts work themselves out through NVH on my Datsun 280ZX Turbo. The roads in Southern California seem to shake our cars to pieces much more than up here in the Pacific Northwest. I need to purchase a safety wire-tie setup so that this won't happen again:
I'll rework the design to recess the hat as you recommended. I think you're right about ensuring concentricity via "hub-centric" with the hat versus "lug-centric" with the bolts.
I was relying that a majority of the shear load would be taken up by the friction between the rotor and hat mating surfaces. If there was no preload or "pre-torque" in the bolts, I would definitely be concerned about the bolts shearing off.
Brakes are special 'cause they produce huge amounts of non-linear,
multi-directional, high frequency vibration. Enough so that tightly
clamped rotor/hat mounting surface can become a tiny air gap under
almost any type of use any time they feel like it. The wheels that steer
also bring gyroscopic forces to the party. Mysterious, umm, stuff.
You're working with three distinct and two simultaneous shear forces.
Acceleration of the rotor, deceleration of everything, and the
centrifugal tug of the rotor itself. Recessing the rotor into the hat
pretty much eats number three. The expensive race brakes sometimes
(weight related) use little mild steel or stainless top-hat bushings
thumb-pressed into the rotor mounting holes. Then a torqued bolt/nut
binds those little top-hats solidly to the hat. The rotor is still
locked in place but it's allowed to squirm and slide about allowing the
rotor to find it's own happy place. The shear loads remain the same, but
the rotor is no longer a stressed participant which keeps the mounting
holes rounder longer. Less cracking of the rotor mounting areas result.
Don't really remember the real numbers, but I think the rotor/hat
mounting area temps can reach 900°F under extremes. Any non-aerospace
extreme heat locking compound goes to liquid, slings onto the base of
your pads, lets the bolts loosen, and collects dirt wherever it lands.
Safety wire isn't a good idea on the rotors. Centrifugal force on even a
short length of twisted stainless at 1600~4000 RPM can send out broken
lengths of wire like an expensive weed eater. It's primary target will
be your calipers, pads, and to a lesser extent - brake lines and cooling
systems. Safety wire loves caliper mounting bolts and other stationary
You don't want to go "lug-centric" on the hat/hub mounting surface
either. The center of the hat needs to tightly fit the hub itself - that
silly concentricity again... The lugs or drive pins should just slip
through the hat holes. Wheel clamping forces will usually take care of
I've included a shot of my last automotive brakeset design (R.I.P
Mechanical Desktop). The hat was segmented to allow heat and vibration
variables to work themselves out. Rotors were riveted to the hats per
the manufacturers specs. My job was the machining specs on an existing
Just think, if you had uploaded your Friday Pictures next Friday all
they would do is collect dust where news:discussion.autodesk.com used to
> Even using red locktite, the fasteners may work themselves out
> I need to purchase a safety wire-tie setup so that this won't happen again:
> I was relying that a majority of the shear load would be taken up by the friction between the rotor and hat mating surfaces.
after reading Bill's response and looking at his image, note the slotted hub/hat section, this will allow the hub to expand following the rigidly mounted rotor, I dont believe you will ever find a rigidly mounted high performance rotor mounted to a solid non dished hub.
As Bill stated the temperatures are high, the hub will be cool, something must give due to thermal expansion, the heating cooling cycles are many on each drive.
As for safety wire, I believe you will not have a problem if you follow normal wiring conventions. Safety wire just doesn't weigh that much, it will not have that great of a force on it, nor are the radius' that great.
Reference 2000 rpm on a 24" od tire is 143 mph.
I forgot to mention, your venting holes should not break into the cooling webs.
Edited by: email@example.com on May 29, 2010 3:48 AM