MrBenjamonkey
MrBenjamonkey Reader
8/18/10 4:53 a.m.

So today we worked on upgrading the brakes. Obviously, Daewoo's don't enjoy huge aftermarket support so off the shelf rotors were out of the question. Not a big deal, because I want to give my kids as many opportunities to engineer stuff as possible.

With this in mind I bought a fresh set of stock rotors from Daewoo. The kids decided on 8 slots 45 degrees apart. The slots are rotated 60 degrees from perpendicular. They specified a 90 degree square cut 3 mm deep.

Is this safe?

44Dwarf
44Dwarf HalfDork
8/18/10 6:05 a.m.

square cut = stress riser Stress riser = crack

You be better off with a radiused cut or ball end. Most of the time slot numbers is equal to the number of the cast vanes inside the rotor and located in the middle of that area and angled to match.

Personaly i don't like sloted rotors, if your realy worried about gas planing the pads off the rotor grove the pads as many aftermarket pads are.

44

Dashpot
Dashpot New Reader
8/18/10 6:20 a.m.

In reply to MrBenjamonkey:

You will reduce your thermal mass and greatly increase the chances of cracking, for no apparent reason. Slotted rotors, like "lowering springs" are mostly cosmetic and mostly detrimental to performance.

snipes
snipes Reader
8/18/10 7:57 a.m.
Dashpot wrote: In reply to MrBenjamonkey: You will reduce your thermal mass and greatly increase the chances of cracking, for no apparent reason. Slotted rotors, like "lowering springs" are mostly cosmetic and mostly detrimental to performance.

Dashpot I hear what you are saying and your are right. However I think you have missed the point of what MrBenjamonkey is doing here. It seems to me this is an educational machining exercise first and a performance upgrade second. He is trying to make it fun to learn and kids love car projects. So who cares if slotted rotors are a little like lowering springs. In addition I think it is likely that stock Daewoo pads are going to off gas like its 1963 when driven hard (just a guess. I have never driven a Daewoo and was not born in 1963).

I would think the rotors are the non-directional straight vane type, so I would not worry about lining the slots up with the vanes, but I second 44Dwarf on the ball end. As for the depth I think it would be safer to just cut down to the minimum safe rotor depth. That way when the slots are worn off you know the rotors are at minimum spec and need to be replaced.

Good luck with the kids....

MrBenjamonkey
MrBenjamonkey Reader
8/18/10 8:40 a.m.
Dashpot wrote: In reply to MrBenjamonkey: You will reduce your thermal mass and greatly increase the chances of cracking, for no apparent reason. Slotted rotors, like "lowering springs" are mostly cosmetic and mostly detrimental to performance.

Really? I've heard stories about drilled rotors cracking, but slotted/grooved/dimpled ones not so much.

BTW, I am doing this because a) it's an engineering excercise b) the most aggressive pads I can find (already purchased) for a Nubira are mildly performance oriented street pads and c) I'm going to do track days.

The thermal mass difference is going to be minimal. Eight narrow channels 3mm deep. That's less than 1/8th inch. Each rotor probably weighs 20 lbs.

The vanes are straight and there are a kajillion of them. If I ran a slot for each vane it would look like a cheese grater.

I completely forgot about stress risers ... doh! I guess I'll do a ball/radiused cut.

Thanks for the info guys.

MrBenjamonkey
MrBenjamonkey Reader
8/18/10 8:52 a.m.

In reply to snipes: We just finished some pretty cool fabrication. Updates and pictures coming soon.

turboswede
turboswede SuperDork
8/18/10 1:13 p.m.

I'd cut a single, circular radiused groove in the rotor using a rotary table offset so that the cut ends up being a circle offset from the face of the rotor. Looks neat, is a single cut reducing the potential for stress cracks and helps with water on the rotors and keeping the pads fresh (which is what slotted rotors are for these days)

Just make sure to go slowly and make sure the brake pads are bedded in properly.

Appleseed
Appleseed SuperDork
8/18/10 1:59 p.m.
turboswede wrote: I'd cut a single, circular radiused groove in the rotor using a rotary table offset so that the cut ends up being a circle offset from the face of the rotor. Looks neat, is a single cut reducing the potential for stress cracks and helps with water on the rotors and keeping the pads fresh (which is what slotted rotors are for these days) Just make sure to go slowly and make sure the brake pads are bedded in properly.

I've never seen that. Would be cool looking.

klipless
klipless Reader
8/18/10 2:13 p.m.

I don't know if it's in your plans or not, but you should look at using some flexible tubing to make low-buck (low-won?) brake coolers.

oldeskewltoy
oldeskewltoy Reader
8/18/10 4:02 p.m.

take a look @ what comes on exotics....

you NEVER see slotted rotors.... only drilled

Oh... drilled as far as I know was invented for mass savings, NOT pad gas venting

As far as I know the 1st car with drilled rotors was the Porsche 917. Remember the time(60s) big rotors meant HUGE unsprung weight. Drilled rotors removed a decent amount of mass

Jerry From LA
Jerry From LA HalfDork
8/18/10 4:25 p.m.

Outgassing hasn't been a problem since the '70s but my wife would beg to differ.

turboswede
turboswede SuperDork
8/18/10 4:27 p.m.
Appleseed wrote:
turboswede wrote: I'd cut a single, circular radiused groove in the rotor using a rotary table offset so that the cut ends up being a circle offset from the face of the rotor. Looks neat, is a single cut reducing the potential for stress cracks and helps with water on the rotors and keeping the pads fresh (which is what slotted rotors are for these days) Just make sure to go slowly and make sure the brake pads are bedded in properly.
I've never seen that. Would be cool looking.

Yeah, a friend had a set made up for his 740 turbo. He would cook the brakes on it regularly in his commute and needed to keep the pads fresh. He took the rotors to a buddy of his that does machine work and he expected to get back the normal style of slots, instead they did the offset circle and it worked pretty well on that car.

ReverendDexter
ReverendDexter Dork
8/18/10 4:31 p.m.
turboswede wrote: I'd cut a single, circular radiused groove in the rotor using a rotary table offset so that the cut ends up being a circle offset from the face of the rotor. Looks neat, is a single cut reducing the potential for stress cracks and helps with water on the rotors and keeping the pads fresh (which is what slotted rotors are for these days) Just make sure to go slowly and make sure the brake pads are bedded in properly.

I'm a visual person and having issues picturing what you mean by that... got any pics?

turboswede
turboswede SuperDork
8/18/10 4:41 p.m.
oldeskewltoy wrote: take a look @ what comes on exotics.... you NEVER see slotted rotors.... only drilled Oh... drilled as far as I know was invented for mass savings, NOT pad gas venting As far as I know the 1st car with drilled rotors was the Porsche 917. Remember the time(60s) big rotors meant HUGE unsprung weight. Drilled rotors removed a decent amount of mass

What comes on exotics is based partly on looks and partly on the fact that the engineers know the average person driving them doesn't know how to make full use of the capabilities of the car. So to make the car work with the huge diameter rotors, they drill them to reduce surface area (and unsprung weight) and for the ones that are raced and abused, they use carbon ceramic solutions and/or they switch to more aggressive pads and solid rotors with slots.

Nissan GT-R for example:

Race:

Stock:

wbjones
wbjones Dork
8/18/10 8:02 p.m.

according to several sites I've been reading (brakes content) drilled are out/bad but slotted still help quite a bit.. ???

MrBenjamonkey
MrBenjamonkey Reader
8/19/10 12:14 a.m.
klipless wrote: I don't know if it's in your plans or not, but you should look at using some flexible tubing to make low-buck (low-won?) brake coolers.

I have the ducting on order. We're going to run them from what used to be the fog lights to what used to be the dust shields.

MrBenjamonkey
MrBenjamonkey Reader
8/19/10 12:17 a.m.
ReverendDexter wrote:
turboswede wrote: I'd cut a single, circular radiused groove in the rotor using a rotary table offset so that the cut ends up being a circle offset from the face of the rotor. Looks neat, is a single cut reducing the potential for stress cracks and helps with water on the rotors and keeping the pads fresh (which is what slotted rotors are for these days) Just make sure to go slowly and make sure the brake pads are bedded in properly.
I'm a visual person and having issues picturing what you mean by that... got any pics?

^Me too

fast_eddie_72
fast_eddie_72 New Reader
8/19/10 12:46 a.m.
ReverendDexter wrote: I'm a visual person and having issues picturing what you mean by that... got any pics?

Something like this I think:

http://www.tirerack.com/brakes/brakes.jsp?group=PremiumOne+Slotted+Rotor&model=PremiumOne+Slotted+Rotor&make=ATE&cat=Rotors

MrBenjamonkey
MrBenjamonkey Reader
8/19/10 4:41 a.m.

I don't know if I have the knowledge/tools/ability to make a shape that complex symmetrical.

44Dwarf
44Dwarf HalfDork
8/19/10 6:11 a.m.

I've seen those ATE before nice units funny they even list them for Mr. Ben's car! at $35!!

If it were me i'd start pouring over paper catalogs and find a rotor with same bolt pattern, same offset and bore with bigger diameter then machine a bolt on spacer to move the caliper out. Just make sure you can still fit the wheels on. Funny some people pay huge $$ for big brake kits that are off the self parts.

44

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