Yes its another DIY question

When people such as Zimmerman and alike sell cross drilled brake discs, are they drilled in any special manner or are they excatly that - drilled discs ?

I've heard of some people experiencing cracking from the holes on drilled discs where Porsche etc. forge theirs (so I read on briskoda).

What I'm leading to is this............ I quite like the idea of some 312mm cross drilled discs but I have non-drilled discs in my posession - would it do any harm to drill them myself ?

EDIT: Before anyone says it - I'm not going to drill them in my garage with a Black and Decker

EDIT: Before anyone says it - I'm not going to drill them in my garage with a Black and Decker

THAT would be hilarious though!

I'm guessing probably not. Do you have a metalurgy (sp) person to advise you? I'm guessing the type of metal would differ for each application. TBH I wouldn't want to try it.

I see awesome sell grooved and dimpled discs - the dimples are just "shallow holes" that dont go through. The idea being that they avoid the cracking issues.

But how do the dimples work ? i thought the whole idea of cross drilled discs was to get the heat away from the pad surface , it wont do that with no holes . The grooves are to scrape the glaze off the pad , but they fill up if too narrow and require the pad material to be removed to work again properly .

Dimples would increase the surface area for dissipating the heat I suppose.

I dont see the need for anything other than solid disks if you have decent pads.

A chap I once spoke to said the holes and grooves also helped dissipate the "liquid gas" :confused: that often builds up between the pad and disc and can lead to brake fade.

He was on the Elise design team.

I dont need cross drilled discs at all, the Z diddnt have them - I just think they'd look nice

I personally wouldn't do it, why not just groove them to give a nicer look. If you check my recent thread there'll be a pic of my grooved disc shortly. I specifically avoided cross drilled due to issues of cracking.

I would think they have to be drilled in the right places to avoid 'hot spotting' the disc leading to warping..??? (oh and forged porsche discs crack too)

i had no issues of cracked discs on my last car but have heard it can happen.

i would like some but seems nobody does them for the S4 or A4 apart from US companies

A normal disc is better for everyday use, than a drilled one.

when a disc manufacturer drill holes in a disc they dont just drill them willy-nilly all over the place... the drill the holes in carefully selected places so as to not affect the structuraly integrity od the disc

when a disc manufacturer drill holes in a disc they dont just drill them willy-nilly all over the place... the drill the holes in carefully selected places so as to not affect the structuraly integrity od the disc

:orb_lol:

Sorry.

If you can get then on a CNC Miller you could copy the plotting of other manufacturers drilled holes and grooves.

If you can get then on a CNC Miller you could copy the plotting of other manufacturers drilled holes and grooves.

As long as the vents between the disc surface are the same angle/spacing on both discs.

:orb_lol:

Sorry.

i would have thought they would use some form of stress analysis on them?

As long as the vents between the disc surface are the same angle/spacing on both discs.

Mirror image the plot. Might give this ago tommorrow at work.

i would have thought they would use some form of stress analysis on them?

You could stress relieve them after you had put drilled holes and grooves in, to take out the stress on machining them.

Sorry if this is a little long-winded, but this is what I've gathered on the subject (as an extremely amateur hobby machinist investigating drilled/grooved discs):

Simply drilling holes creates "stress risers" - drilling may cause disc distortion, needing complex heat treatment afterwards to do it right. Also in use, the edges of the hole cool down faster than the surrounding metal - more prone to cracking. Putting in a bevel around the holes with a countersink decreases the stress. Porsche discs are cast with the holes in - not machined in afterwards.

Dimples are less stress-inducing (blind holes).

Grooves are a far better idea, but need to be done right.

In all cases, the idea is to dissapate the initial vapourised pad, and perhaps to scrub off any formed pad glaze (making pads last shorter). Modern pads are supposed to give off less gas on initial contact (the gas has to escape before the brake actually starts to work. And glaze less often.

Even with a lot of work, special rotors - translate into between 3-6m shorter stopping distance at 60mph.

Most modern discs are already ventilated, so cooling is not as big an issue as it once was.

Better buy a good set of grooved discs.

Cheers

Bas

After running some grooved and cross-drilled "unwarpable" discs and warping them with my regular road driving, I'd always go with just grooved in future I agree they looked very cool though!

Chris

i notice alot of mercs have them standard

Most motorbikes have drilled discs with no cracking issues. Would not fancy it

on my car though. Grooved yes.

Most motorbikes have drilled discs with no cracking issues. Would not fancy it

on my car though. Grooved yes.

also motorcycle discs are solid and not vented

I think grooved discs look nice than drilled.

Had several variations. IMO Drilled are a waster, Grooved is better & if the Grooves are curved in Elevation it works a tadge better but the big plus is it greatly reduces the rumble you normally get.

If youe anywhere near Godspeed (Bridgend0 Ian has all his own milling & drilling machines & you can have whatever you think is "prettiest"

If youe anywhere near Godspeed (Bridgend) Ian has all his own milling & drilling machines & you can have whatever you think is "prettiest"

My "unwarpable" discs were Godspeed........!

Chris