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Joined: Dec 2001
Posts: 49
New CEG\'er
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New CEG\'er
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Posts: 49 |
My point is not that stress concentrations don't exist but that they can be minimized to a point where other things become a problem. If you only wanted to minimize stress concentrations, you would run solid rotors and avoid the stress concentrations caused by the manufacturing process and the geometry of the webs in a hollow vented rotor. Since people successfully run hollow discs, the small effect of increase stress concentration is more than offset by the advantages of hollow disc rotors.
My rotors are machined at a local shop that has done contract work for the corporation I work for. The shop has world class equipment for doing aerospace work. Sometimes I do the machining myself at the shop after hours. The rotors are heat treated after machining based on the work I've done over the past 25 years. A very light final cut is taken on the rotor faces after heat treating, to true up the faces.
The quality of work is nothing I would consider special, anything a first class race team or someone working in the aerospace field could do. I have never had a rotor crack. If I see signs of significant corrosion or damage around one or more holes after a few years I may decide to replace the rotor.
Much of what I learned over the years was from deliberately machining or processing parts incorrectly to determine the effect of poor manufacturing. If there is a way to manufacture a part so it will fail, I have probably done so. The knowledge has been applied to learning how to make parts that don't fail, regardless of whether they are aerospace, elevator/escalator or my own automotive components.
I'm sure that there are many educated and experienced people on this board, such as yourself. My intent was to share that the manufacturing process can significantly affect the durability of a component. The same design can be robust or fail depending on how it was manufacturered.
I get the impression that some people here are not interested in information that conflicts with their opinions. At the risk of getting flamed, I don't plan to contribute any further to this discussion. Different people have different opinions and each of us needs to get the job done the best way they know how.
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Joined: Oct 2000
Posts: 3,867
Hard-core CEG'er
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Hard-core CEG'er
Joined: Oct 2000
Posts: 3,867 |
Originally posted by Rara:
Quote:
Intuitively it seems to me that the holes would tend to act as an inlet to the central venting, and that if the rotor is spinning at a decent speed the center vents will produce a bit of a vacuum that would pull air in through the holes. Wouldn't this contribute some cooling?
Not nearly as much as you think. A vented brake rotor works much like a centrifugal air pump, as the rotor spins, it creates low pressure areas behind the vanes, and air is drawn in from the center of the rotor to fill that low pressure area. So basically air is pumped from the center of the rotor radially outward (this is why you direct the ducting to the center of the rotor, for it to pick up the colder air, though, because the contour is vented on the outer face at the center, its a bit tough). When you drill holes in the face, it takes a lot away from the centrifugal pump effect by not allowing the low pressure area to build up nearly as effectively.
And proper ducting is always useful, well, as long as you are moving anyway.
What he said. "Intuitively," it seems to me that drilling holes in the rotor for extra cooling is like drilling holes in the water pump for the same reason.
With solid discs, your intuition is more accurate, but with modern, vented discs... well... what Rara said.
Function before fashion.
'96 Contour SE
"Toss the Contour into a corner, and it's as easy to catch as a softball thrown by a preschooler." -Edmunds, 1998
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Joined: Oct 2000
Posts: 3,867
Hard-core CEG'er
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Hard-core CEG'er
Joined: Oct 2000
Posts: 3,867 |
First of all, Jon, thanks for the extra info. Too bad your feathers got ruffled, but remember that you fired the opening shot with your "layman" comment. (I would be classed as such a layman, but some of the other people in this thread would not.)
Anyway, to sum up for those of you joining late:
1. Cross-drilling has no known performance benefit with modern braking systems, and may even detract from braking performance by a) reducing heat-sink mass and b) reducing cooling airflow through the vanes.
However,
2. It is possible to resurface (machine, turn, etc.) them with the proper technique.
3. They may be more prone to cracking, but
4. The manufacturing process has a lot to do with that. IOW, not all cross-drilling is created equal.
5. A lot of people still think they look cool.
Function before fashion.
'96 Contour SE
"Toss the Contour into a corner, and it's as easy to catch as a softball thrown by a preschooler." -Edmunds, 1998
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Joined: Jan 2002
Posts: 75
CEG\'er
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CEG\'er
Joined: Jan 2002
Posts: 75 |
you guys are retarded. chris was just trying to tell people that if they have the rotors they can be machined. Who cares if there is no improvement in braking. It doesnt make the car brake any worse and they look nice. I never bought mine but the previous owner did had them installed. They were machined without a problem. You guys start the same argument about this crap every week.
1998 SVT #95: Toreador Red - SHM headers, SHM custom tuned chip, K&N Filter, Energy Suspension MM inserts, Cross Drilled Rotors,Redline Tranny Fluid, Custom Billet Aluminum Shift Knob, Edelbrock RPM 5503 resonator,15.441 @ 91.66 mph
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Joined: Sep 2002
Posts: 3,632
Hard-core CEG'er
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Hard-core CEG'er
Joined: Sep 2002
Posts: 3,632 |
Originally posted by SVT#95:
you guys are retarded. chris was just trying to tell people that if they have the rotors they can be machined. Who cares if there is no improvement in braking. It doesnt make the car brake any worse and they look nice. I never bought mine but the previous owner did had them installed. They were machined without a problem. You guys start the same argument about this crap every week.
Although perhaps it happened in the wrong thread I would be hard pressed to say this conversation has been "retarded".
I have learned more about brakes in reading through these many pages then I have in my previous 23 years of existence on this planet. I would say that is one of the most informative CEG threads I have ever come across.
For your comment you get this: 
"Cobb - It's not just for corn anymore!"
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Joined: Jan 2002
Posts: 75
CEG\'er
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CEG\'er
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Posts: 75 |
I think this is one of the most informative threads also. All I am saying is that this argument about cross drilled vs. slotted vs. stock must have been brought up a 1000 times by now. I posted almost a year ago that my rotors were machined without a problem. Chris is just restating this but anytime someone brings up anything about cross drilled rotors the same argument pops up again and again. If anybody wanted to know about performance of cross drilled vs. slotted vs. stock then all they have to do is a search. there will be a ton of results for them to search through. But to post the same facts every post about drilled rotors just gets rediculous.
1998 SVT #95: Toreador Red - SHM headers, SHM custom tuned chip, K&N Filter, Energy Suspension MM inserts, Cross Drilled Rotors,Redline Tranny Fluid, Custom Billet Aluminum Shift Knob, Edelbrock RPM 5503 resonator,15.441 @ 91.66 mph
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Joined: Sep 2002
Posts: 3,632
Hard-core CEG'er
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Hard-core CEG'er
Joined: Sep 2002
Posts: 3,632 |
How hard is it to not look at the thread?  Its not like people are sitting on your front lawn arguing about it....its the internet. Anyhow....thanks for the good brakes information guys. Cross drilled rotors are definately never coming close to my car.
"Cobb - It's not just for corn anymore!"
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Joined: Sep 2000
Posts: 3,223
"Absolut Rara."
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"Absolut Rara."
Joined: Sep 2000
Posts: 3,223 |
Originally posted by JonsZX2SR:
I get the impression that some people here are not interested in information that conflicts with their opinions. At the risk of getting flamed, I don't plan to contribute any further to this discussion. Different people have different opinions and each of us needs to get the job done the best way they know how.
Jon,
I take offense at that. You as an engineer should understand the concept of hashing out a technical discussion better than most here. Can you tell me that you have never had a technical disagreement with another engineer? and further that you have never discussed it? Your only risk of getting flamed is for being a pansy and walking out just when the technical discussion is getting good. "Iron sharpeneth Iron . . ." This sort of debate is how the knowledge base of the CEG community is increased, at least for those willing to read and learn and not piss and moan about "can't we all just get along?" (Yeah, that was aimed at you SVT#95, and others like you)
Fwiw, I am in fact a degreed engineer as well, and I actively work in the automotive brake area. Does that mean I know all and can nail every single detail related to brakes? No, certainly not, but it does net me some credibility, just as your manufacturing experience does for you, and others have thier own education and experience in areas applicable. And I expect all who can add something to this technical table to do so, as a benefit to all of us. I absolutely love to see some actual tech come to this board, rather than the typical "that looks tite, Yo!" So common on boards like this. I love it when people like Todd TCE come here; a vendor that won't just spout BS to make a buck, but will disseminate REAL technical advice to his potential customers. I love to see folks like you (Jon) on here, that will actually engage in a public technical discussion that will benefit all willing to read and learn, regardless of thier experience level, or education (assuming the minimum of being able to read and operate a PC  ) I'm so sick and tired of BS tech propogated by ignorant fools regurgitating what they read on a sales brochure for something from APC products or the like; let's try to get some real tech out there for those willing to learn!!!!
I'm really sorry for my rant, but I hate to see someone just give up on something worthwhile, just because someone disagrees with them. Disagreement does not mean hatred, I wish people would get that through thier thick skulls; Most of the world's greatest discoveries only happened because someone disagreed, and didn't play the "can't we all just get along" game.
All that said, you will notice, I never disagreed with your comments on the manufacturing process. In fact I think you are right on about them. I honestly was taking the initial assumption that satisfactory manufacturing processes were used in manufacturing the cross-drilled rotors we are discussing, and that additional stresses were not "processed" into them.
I still maintain that the geometric discontinuities, especially when combined with thermal issues caused by the dissimilar cooling around the holes, are enough of a stress concentration to make cross-drilling a bad idea in all but the most specialized applications. Combine that with the poor manufacturing techniques you describe, and you create downright dangerous parts.
I can find numerous photos of cross-drilled rotors, that were manufactured to satisfactory levels that still have failed under use (or at least started to fail). I seem to recall even seeing photos of failed porsche "holed" rotors due to cracking around the cast-in holes.
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Joined: May 2001
Posts: 682
Veteran CEG\'er
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Veteran CEG\'er
Joined: May 2001
Posts: 682 |
Originally posted by JonsZX2SR:
Paul -- if you are experiencing severe fade during mountain descents, it is likely that overheating of the pads is the root cause of fade.
Or ultimately, overheating of the fluid, through overheating of the calipers, through overheating of the pads.
I've got 500 degree fluid in there but I've still overdone it once or twice.
Originally posted by JonsZX2SR:
Using stock drilled rotors will only help a small amount with stock pads. I would suggest that you look for pads that start to fade 100-200F higher in temp.
I currently have the KVR carbon fiber pads and for next time have been attracted to the glowing reports about Bendix titanium.
Originally posted by JonsZX2SR:
If that doesn't work, unfortunately the next step would be larger diameter rotors and pads with a larger surface area, also selecting premium pad materials. You need to spread the heat generating surface over a larger area and increase the ability of the rotor to dissapate heat. A larger caliper structure will also help increase heat dissapation though that path.
Another question which I've been asking about, and nobody has yet produced an answer to, is whether Focus SVT rotors will fit, with stock Tour calipers, inside an E0 SVT 16" rim. Apparently it's close; either barely fits or barely doesn't.
Of course, using these rotors would require me to either get a different spare, or always keep drum brakes in the back and deal with front flats by moving a rear wheel forward.
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Joined: May 2001
Posts: 682
Veteran CEG\'er
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Originally posted by Rara:
And proper ducting is always useful, well, as long as you are moving anyway.
So what does proper ducting consist of -- is it basically just a pipe that scoops up air from the front and feeds it to the middle of the rotor? Could I fake it with dryer hose?
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