Vented and Cross Drilled Rotors

[Gigsworth]

sorry for the mistake. meant to say vented and drilled rotors. maybe it will get more views!

are there any CNC Machinists here that have drilled and vented their own rotors? wanted to know if there is a formula for the spacing of the cross drilled holes between each other, and how to space the vents. maybe i should be asking the engineers on the site too. looking for speeds and feeds for the rotor material as well.
btw, anyone have the dimensions of the rotors on hand.

travis

[GTJIM]

Road cars inevitably crack rotors at the holes drilled in them and wear away the pads much faster with the grooves. OK for racing where every bit of braking counts but in the long term on the road it just causes problems.

Discs drilled by the manufacturer have special radiused edges to the holes and specially curving grooves to try and minimise these problems - not a DIY job!

The 'best' rotors to use on the street are un-drilled, non-grooved, but ventilated rotors which 'pump' air through their open cores to remove heat. These are typically much thicker than solid rotors to maintain mass that will absorb and transfer heat. They still 'warm-up' during heavy breaking but cool quickly once braking ceases for rapid recovery - ready for the next braking episode.

The nicest rotor I have found for my GT are the front ones from and Isuzu Impuse - slightly larger in diameter than the Opel solids but ventilated and 18mm thick with ventilated centres. So they weigh about the same as the '75 large rotors and have similar diameter. Their single piston sliding calipers are much lighter though and so reduce unsprung weight.

[RallyBob]

It should be mentioned that cross-drilling brakes does NOT make them more heat-resistant, in fact the opposite is true! They will overheat faster. What you have done by drilling them is reduced the mass of the rotor, and the rotor's mass is all you have to prevent heat build-up.

Think of it this way, if you held a piece of thin sheet metal to a bench grinder, it would get hot fast....hot enough so you'd probably have to drop it or burn your fingers. If you held a piece of 1/2" thick steel to the same grinder with the same pressure applied, it would take quite some time for that piece to get hot enough to burn your fingers. What you've got there is a better heat sink. Drilling holes or lessening the mass of the item allows it to get hot faster.

And as Jim said, you've also potentially given the rotor new stress points to crack from.

The only strong point for drilling rotors is the pedal response is a bit better, but at the expense of faster pad and rotor wear. Good for autocrossing or hillclimbing where the brakes are only used for short durations with modest intensity, and not in a situation where brake fade might factor in.

HTH,
Bob

[Gigsworth]

what about you rallybob, what do you use?

[RallyBob]

Originally Posted by Gigsworth what about you rallybob, what do you use?

Vented, but not cross drilled.

I've used modified/adapted 1977 BMW 320i vented front rotors.
I've used 246 mm factory 'Carlton' vented front rotors.
I've used custom adapted 1984 Dodge Omni Turbo rotors (260 mm).
I'm working on a new setup for my Opel wagon right now using Wilwood racing rotors that are 266 mm in diameter x .75" thick, which will fit inside the stock 13" wheels. I just need to find the proper caliper for adequate clearance. The Wilwood Dynalites *just* rub inside the wheels right now, I need to find a lower profile caliper body.

Bob

[Manta Rallier]

Ditch the drilled rotors for the street. Time and time again, guys put these on cars for rallying and then complain about how fast the pads dissappear. They usually dissappear after a couple of events.

Regards,
Mark B.