Checkered Disc Rotors

C

CB750 Cafe Racer Fan

New Member
These are the brakes on my CB750K7 build in progress. It has a dual disc rotor set up in front. Chris from MotoGP Werks dreamed up the idea of laser cutting checkers instead of conventional round holes. Given the thickness of the stock stainless steel rotors, the shape of the holes should not compromise the structural strength of the discs. Let me know what you think. Other mods to the front end include: transplanted K6 front end (with gators), polished and
ribbed (machined) lower forks, new Excel rims and stainless spokes, and (of course) checkers.

Honda750008.jpg


Here she was BEFORE the current re-build commenced:

014.jpg
 
CB750 Cafe Racer Fan said:
Chris from MotoGP Werks dreamed up the idea of laser cutting checkers instead of conventional round holes. Given the thickness of the stock stainless steel rotors, the shape of the holes should not compromise the structural strength of the discs. Let me know what you think.
Click to expand...

Wow, that is a horrible idea. I wouldn't expect those rotors to last more than a year before cracking when you are breaking hard. There is a very good reason nobody puts square holes in things that need to be strong. The stress concentrations at the corners of those holes look like they will be at least 20 times the normal disc stress. The stress concentration factor for round holes is around 4. You have basically just put about 80 little cracks into your rotors. It looks cool though.
 
Mike,

Wow! I would have shared the concern if they were not stock rotors or dual rotors (to share the stopping load), but given the 1.5-2 X thickness of Honda stainless steel rotors compared to conventional rotors, I'm not so sure. That said, if I start seeing stress cracks in my rotors, I'll be sure to switch them out to conventional hole-drilled rotors in a hurry.

Chris is no amateur wrench. He was a MotoGP Team Redbull Grand Prix Tech, Yoshimura Research & Development Engineer, Kawasaki Factory Race Master Tech and worked as a mechanic on Isle of Man TT teams and Britten Motorcycle Development during the last 15 years, so I'd like to think he knows his trade.
 
Looks damn cool. If anything atleast keep the center checkered if you have to switch rotors. I wanna see a rolling picture of that bike.
 
Chris may know more about this than me, and may have done it before.  I am admittedly no expert in motorcycles or brakes.  But when I saw the square holes, I gasped.  I've been doing structural analysis on aircraft for over 10 years now and this goes against everything I've learned.  Please keep a very close eye on them and look for very small cracks in the corners.  Most likely from the upr right or lwr left corners of the holes (looking as you are in the picture), between adjacent holes.  Hopefully, you will be able to see any cracking before it fails when you need it most.

The guys that designed the de Havilland Comet knew their trade too and look what happened to it.
http://en.wikipedia.org/wiki/De_Havilland_Comet
Lesson learned:  Square holes are bad.
 
I agree with everyone else... they look cool as hell... BUt with 12 years of machining experience, and working for a company that sells, engineer,s and builds very heavy duty overhead cranes(mostly 100 ton plus) i can tell you this much.... Anything that will will have any kind of a load on it needs a radius in every corner possible... Square corners are major stress points.... though what could be done would be to cut the holes but have a .01" to .02" radius in each corner... Not large enough to make a big difference visually, but it will make a HUGE difference structurally..
Just my .02 worth....
 
As a mechanical engineer I have to agree with Kodiak and Flugtechnik. Nothing worse on a part than square edges. Stress will concentrate there and cracks will start small and propagate over time.
 
Well, those holes do have some corner radius, the radius of the laser beam, but it is very small. As you see by the chart I posted, as the corner radii decrease in size with respect to the hole width, the stress concentration goes up exponentially. The fact that the worst corners of the holes are right next to each other makes it even worse.

If they do crack, hopefully Chris will man up and give you a new set of rotors. But I hope they don't.

(Flugtechnik, roughly translated means Aerospace Engineer)
 
Mike,

Thanks for the response. I'll keep a close eye on the rotors. I'm sure Chris will help me out with fitting replacements, if any stress cracks develop.

If you think the painted rotor hub checkers are cool, wait until you see the paint on the rest of the bike: Black with silver metallic ghost checkers on the tank, fenders and side covers; gold leaf 750 emblems; hand-masked black and white checkered rear brake, handlebars, grab rail and gauge housings; and black chrome details. Pics to come later.
 
+ 1 on the square corners = bad. same thing thing with our structural composites - big rads if you please.

I question the ribbed condom look at the bottom of the forks. i assume the ribs came from removing material? normally the engineering types don't add a lot more material (thickness) than needed especially when trying to keep weight down on a bike. i'm not an eng. but I would think close to the axle mounting point would be an area that's highly loaded. just my two pennys.
 
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