Has anyone "dimpled" their own brake discs?

[Ducklakeview]

As my car has pretty much brand new discs and pads all round, if somewhat corroded and manky looking, I wanted to clean them all up and also paint the calipers and hub areas...

This got me thinking, as a while back I drilled a set of discs for my brother's R19...

Now I know drilled discs are inherently weaker, BUT dimpled or grooved ones offer a lot of the benefits without the loss of strength..

So, I have a drill press, and have ordered a 12mm ball ended mill bit.... But has anyone done this, if so, did you download a template or make your own?

Comments welcome...

Mike

 

[Paulwirral]

There's a good argument that by drilling or dimpling your discs your removing friction surface from your brakes , especially on a road car , that said they look nicer . For what they cost your better off doing a couple of hours overtime and buying them from mtec ready done and not risk causing any problems

 

[domsz4]

I'm not sure if drilling or dumpling your own discs is a stupidly dangerous thing to do or not?

I'd go with probably not a good idea unless you know what you are doing.

 

[Ducklakeview]

I'm not sure if drilling or dumpling your own discs is a stupidly dangerous thing to do or not?

I'd go with probably not a good idea unless you know what you are doing.

Perfectly safe.. Done it several times.

Mike

 

[no fit state]

If I was going to it, I would first draw it up and programme it on one of our cad/cam systems so everything was perfectly symmetrical and balanced once machined. Then put it on CNC Mill and set it up true to within 0.01mm, again to keep the balance of the disc.

....but after all that it would easier to do a couple of hours over time to give me the extra money needed to buy discs that came dimpled, drilled or grooved in the first place. It would only make sense if 1, it's a little project you wanted to do or 2, you were doing many sets at once.

 

[DB89]

I would not retrospectively drill the discs after OEM have designed the disc to meet a specific standard. True - you're removing the net brake surface area and may have to apply more brake force to get the same performance - but the issues lie deeper and are not obvious to the eye.

Drilling: Depending on how old and aggressively they have been used, over time the brakes will have undergone many heat cycles and could therefore exhibit microstructural fractures between the metal's structure on the brake surface. By 'tapping' in to the brake you could mechanically propagate existing fractures deeper in to the disc thus potentially compromising the disc integrity and ultimately crack the brake during use (i.e. under high stress).

Another issue is with the existing disc design there are the veins to consider. These are strategically designed not only to allow air flow through the inside surface of the disc, but are there to provide structural (lateral) strength when the brake calipers apply the braking force thus preventing disc flex. If you tap or drill in to the disc you cannot guarantee you can bypass the veins with enough clearance to distribute the stresses around the localized stress points (unless you had the OEM drawing showing the design giving you the exact locations of the veins beneath the disc plate). Unless you have this, you run the risk of weakening the disc.

I would just order an OEM spec'd disc that has been engineered to be vented to prevent anything unfortunate from happening.

Regards,

DB.

 

[Machine monkey]

As others have said I wouldn't be doing it on a drill press I have groved discs but on a milling machine so I know exactly where the holes and groves are going.

I guess you could mark it out and centre punch them but that won't work well with a bull nose cutter. Plus .1 is fairly good going with a punch and drill press. But you can start getting a cumulative errors and then your discs may not be balanced?

The other thing a ball nose cutter is technically a milling cutter and there fore not designed to be held in a drill chuck. For what you will be using it for it will be ok as your only going to be using it in a vertical axis. But if I was ever caught (I wouldn't be it was/is a big no no in workshops) well I would get a telling off from someone.

 

[Rialas]

This is a wind up right? oke:

Dirt cheap at eurocarparts. Safe, hassle free.

 

[Darkangelv2]

I'm not sure if drilling or dumpling your own discs is a stupidly dangerous thing to do or not?

I'd go with probably not a good idea unless you know what you are doing.

Perfectly safe.. Done it several times.

Mike

I'm confused. If it's perfectly safe and you've done it several times - what were you hoping to find out from this thread?

There are a fair few YouTube videos of guys doing their own discs on mills. Not sure I've seen one with a drill press.

 

[DB89]

What's the technical reason for wanting to drill the old brakes? You may need to get NDT using magnetic particle method just to confirm you haven't cracked the disc given the technical reasons above. This may cost you some amount of money per disc. May as well just buy some new OEM spec'd vented discs.

 

[Ducklakeview]

Didn't bother in the end, went for slotted and dimpled M-Tech discs..

Mike

 

[Machine monkey]

Didn't bother in the end, went for slotted and dimpled M-Tech discs..

Mike

Dont blame you its far easier. I have skimmed a few discs in the past and working on discs is a PITA!!

 

[Artful-Bodger]

Drilling discs is fine provided you mark them out properly.

Ferrari and Porsche to name but two regularly fit drilled discs to their cars.

I buy good quality discs and drill them myself, Dimpling does not have the same effect as drilling, the whole point of drilling is to delay the onset of brake fade, when your brakes overheat the pads begin to combust creating a gas/debris layer between the disc and pad that drastically reduces the friction, the holes allow the gas and debris to escape and delays the onset of fade.

I use a 4mm drill bit and a radiused centre bit to chamfer the holes, usually 1 hole per vane dependant on use.

 

[Steve84N]

Have a search on YouTube for Engineering Explained + Brake Discs as there's an interesting video on the subject of whether plain, drilled or slotted are best. The conclusion is that holes are more for show and under serious use are prone to crack propagation around the holes. The best for most people is plain but slotted are good for aggressive braking. This is backed up by true race applications where you see plain or slotted but not drilled. He also suggests that the whole gas layer thing is hardly an issue anymore as compounds have improved over the years.

 

[mmm-five]

Drilling discs is fine provided you mark them out properly.

Ferrari and Porsche to name but two regularly fit drilled discs to their cars.

I buy good quality discs and drill them myself, Dimpling does not have the same effect as drilling, the whole point of drilling is to delay the onset of brake fade, when your brakes overheat the pads begin to combust creating a gas/debris layer between the disc and pad that drastically reduces the friction, the holes allow the gas and debris to escape and delays the onset of fade.

I use a 4mm drill bit and a radiused centre bit to chamfer the holes, usually 1 hole per vane dependant on use.

You'll probably find that 'drilled' discs in Ferraris and Porches are actually cast with the holes in, so that the stresses flow around the hole and not across it.

If you drill a blank disc, then you're effectively weakening the disc.

 

[Artful-Bodger]

The Porsche Boxter discs I have in the garage are drilled, Drilling wont weaken a disc to any extent where it becomes a safety issue, neither will slotting, but it does reduce mass to absorb heat so you can't overdo it, they wouldn't sell them if they were insurance and warranty nightmares and I have never had a disc fail even during race conditions!

The surface cracking is temperature shock, you can mitigate this by bedding in differently, it's caused by the sudden increase in temperature of the surface, so you need to heat the disc without overheating several times to condition it, I have had a set of drilled disks turn blue they got so hot without any cracks, but also had a set crack by overheating with very grabby pads on a hillclimb car.

 

[Artful-Bodger]

Have a search on YouTube for Engineering Explained + Brake Discs as there's an interesting video on the subject of whether plain, drilled or slotted are best. The conclusion is that holes are more for show and under serious use are prone to crack propagation around the holes. The best for most people is plain but slotted are good for aggressive braking. This is backed up by true race applications where you see plain or slotted but not drilled. He also suggests that the whole gas layer thing is hardly an issue anymore as compounds have improved over the years.

Well that's a bit dubious as if gas layer issues had gone away we wouldn't get fade anymore!

I drilled my discs on a hillclimb/sprint car because you can't use a harder high temp pad in sprinting as the brakes are cold for the first few applications, so you have to use a softer pad that lights up from cold, and then you have to manage the heat to prevent them fading, to do this we drilled the discs and directed an air supply into the centre of the disc from the front splitter, even in testing this gave us three or four very fast laps before you felt the brakes start to fade, so I would have to disagree that drilling is for looks, it serves a purpose and made a difference on our cars.

One thing to remember about slotted discs is they should be machined with a chamfered cutter to prevent sharp edges at the bottom of the slot, this is a stress point, on drilled discs I always use a radiused centre bit to eliminate any sharp edges as this is where cracks can start due to localised overheating!

Race applications
https://upload.wikimedia.org/wikipedia/commons/thumb/6/6b/Ferrari_F430_Challenge_Brake.JPG/1280px-Ferrari_F430_Challenge_Brake.JPG
http://www.strikeengine.com/porsche-tuning/997_gt3_race_car_rear_brake_setup.jpg
https://s-media-cache-ak0.pinimg.com/564x/f8/72/63/f87263089182af159f4adb695573cdce.jpg

 

[Artful-Bodger]

dp

 

[Artful-Bodger]

Dp

 

[Ducklakeview]

Drilling discs is fine provided you mark them out properly.

Ferrari and Porsche to name but two regularly fit drilled discs to their cars.

I buy good quality discs and drill them myself, Dimpling does not have the same effect as drilling, the whole point of drilling is to delay the onset of brake fade, when your brakes overheat the pads begin to combust creating a gas/debris layer between the disc and pad that drastically reduces the friction, the holes allow the gas and debris to escape and delays the onset of fade.

I use a 4mm drill bit and a radiused centre bit to chamfer the holes, usually 1 hole per vane dependant on use.

You'll probably find that 'drilled' discs in Ferraris and Porches are actually cast with the holes in, so that the stresses flow around the hole and not across it.

If you drill a blank disc, then you're effectively weakening the disc.

They will be drilled after being cast, but possibly before any heat treatment. I've drilled plenty and never had a problem.

Mike