Custom crossdrilled rotors

[four_shot]

Does anyone cross drill their own rotors? My brother cross drills his purely for asthetics. I was wondering if any of you track day/drag guys did this for the braking performance gains.

I know there are many pre drilled products out there, and I am interested in hearing about the pros and cons, but I'm more interested in if certain patterns, sizes, and spacings make a real world difference.

(I'll get my fire extinguisher ready in the event that I get flamed )

[GregT]

Yep, we drill our own - for roadracing. i prefer an alternating 4/5 hole diagonal pattern so that the whole pad area is swept by holes.
From experience I can tell you that if the whole area is not swept you will rapidly develop ridges...
BTW we also thin them to 5mm....any weight reduction here helps the steering and suspension - and we're not doing huge mileages between inspections. Not recommended for road use though.
The rules we work under for our class of Vintage roadracing prohibit our using later floating discs so we've got to make the most of what we can use.

[bobthebiker88]

theres a good reason the manufacturers went to drilled rotors eventually. essentially the idea is that the holes will help bring cool air in, reduce the rotating mass a little, and carry off gases produced as byproducts of braking.

that rotating mass reduction alone is a worthwhile gain if you're used to performance oriented machines like high end superbikes.

[four_shot]

i prefer an alternating 4/5 hole diagonal pattern so that the whole pad area is swept by holes.
From experience I can tell you that if the whole area is not swept you will rapidly develop ridges...

I was wondering how to prevent those...

What diameter drill do you use, and would chamfering the holes have any benefit?

[GregT]

6mm or 6.5mm or 1/4in - depending which is newest in the rack - you'll have to resharpen several times too

I just deburr the holes -no actual chamfer.

[midnightcafe]

drilling them can be a PITA since rotors are stainless. Search for techniques with the search bar, or check out other forums for advice (Do The Ton should have a thread on DIY cross driling rotors)

[spyug]

I haven't done any Zuk disks so I can't speak to the hardness but I've done 4 or 5 pairs of Yammies.

Funny thing is some of them drilled like butter, easy peasy.....some were so hard I kept breaking bits. On the advice of some of the guys on the XS board, I now use "end mill" bits for drilling disks. The cut really well.

When drilling, I find it helps to use lots of cutting oil and, of course, it helps to set your drill press to the slowest speed you can get. You will get better control also if you clamp the disk to the drill press bed. Its time consuming to keep adjusting for each hole but it will help avoid "chatter" and skipping. Once you get good at it, you can do them free hand which is much quicker.

Usually I do them around 3/8" but I've seen some done in a combination of 1/4" and 1/2". Don't chamfer them as the square cut cleanly shaves the pad and helps keep them clean.

It is a fiddly job but worth doing as the guys have mentioned. Personall, I find it really does help improve braking performance.

Good luck with it.

cheers,
spyug

[fnkvn]

I've drilled lots and lots of them, and have never found a rotor that a normal drill bit wouldn't drill easily.

http://www.thegsresources.com/_forum/showthread.php?t=167895

[Texasgs]

Drilling

The proper speed is overlooked all the time, hard materials require low drill bit speeds. Cobalt bits help, especially if they have a split point. I bought a high end drill bit sharpener just to be able to grind the split point. Someone said oil, yes oil helps.