Rotor Chamfering

[Rick Iverson]

Gents;

I am installing new rotors on the car, but I have been led to believe without chamfering the holes, I’ll go through pads as though they are sticks of butter. Prior to being sent to Mike for Cryogenic treatment, need to get this done.

Q: how deep?
Q: reputable sources to do it

[R. Pare]

You can do it yourself in a drill press with a decent single flute 90 degree champhering bit. .020-.025 deep should do nicely.

The reason for champhering is to get rid of the sharp edges - they are massive stress risers that will cause cracking rather quickly.

The holes will still eat the pads faster than without the holes.

[Rick Iverson]

RP;

Any recommendations on a decent single flute, 90 degree champhering bit?

[glenn cooper]

Those holes look awfully close together.
What class car are these for?
The last time I had a set scalloped, thinned, drilled it was a pile of money and they cracked between holes in VERY short order.
I hope you have a different result than I did, but I was kicking myself in the ass for being talked into doing that.

[R. Pare]

MA Ford makes some good one, and you can get them from Manhatten Supply Company:

https://www.mscdirect.com/browse/tn/...vid=4287924387

[BeerBudgetRacing]

Can't find 90.... But 100 like this?
https://www.browntool.com/Listview/t...0/Default.aspx

What is the significance of the single cutter?

My instinct would be to use something like this depending on the hole size to it's centered:
https://www.browntool.com/Listview/t...1/Default.aspx
They don't seem to leave any edge.

Trying to extract knowledge - I'll probably need to do this soon.

[R. Pare]

Single flute cutters will not try to chatter or wobble off center - no pilot needed.

90's are listed - you just have to either go through the list, or set up the search criteria.

[Rick Iverson]

Those holes look awfully close together.
What class car are these for?
The last time I had a set scalloped, thinned, drilled it was a pile of money and they cracked between holes in VERY short order.
I hope you have a different result than I did, but I was kicking myself in the ass for being talked into doing that.

Glenn, FC.

[stonebridge20]

Gents;

I am installing new rotors on the car, but I have been led to believe without chamfering the holes, I’ll go through pads as though they are sticks of butter. Prior to being sent to Mike for Cryogenic treatment, need to get this done.

Q: how deep?
Q: reputable sources to do it

There's no need to chamfer these prior to Cryo treatment. It's not a problem doing them afterwards.
I was planning on getting these and your CW&P into Tuesdays Cryo run so box those suckers up !

[problemchild]

Those are common rotors that I have seen used on many cars, at both ends of the grid. They seem to be well-engineered and durable. Why would you assume that they were not supplied with a suitable design that you need to modify them before use?

[DaveW]

I looked closely at the photo and the holes appear to already be chamfered...or at least any sharp edges rounded.

So as Greg said, they probably don't need or want further chamfering.

[Rick Iverson]

On closer inspection, there appears to be a slight chamfer. RP recommended 0.020”-0.025”, probably will follow his advice.

I looked closely at the photo and the holes appear to already be chamfered...or at least any sharp edges rounded.

So as Greg said, they probably don't need or want further chamfering.

[DaveW]

On closer inspection, there appears to be a slight chamfer. RP recommended 0.020”-0.025”, probably will follow his advice.

Since I can see the chamfers in that photo, I'd think they are already close to or at those dimensions and they look very smooth.

If it were me, I'd just leave them alone. Of course, I don't use drilled rotors, so that's an academic opinion.

[t walgamuth]

Since I can see the chamfers in that photo, I'd think they are already close to or at those dimensions and they look very smooth.

If it were me, I'd just leave them alone. Of course, I don't use drilled rotors, so that's an academic opinion.

I drilled my rotors with about 4 times that many holes with no problem....autocrossing. The chamfering is easily done on a drill press. its not rocket science.

[DaveW]

I drilled my rotors with about 4 times that many holes with no problem....autocrossing. The chamfering is easily done on a drill press. its not rocket science.

Autocrossing is a whole different animal from road racing. The temperature peaks are usually much less in autocrossing because of the short runs. And it's the temperature spikes and rapid cooling combined with stress-risers that cause rotor cracking.

[t walgamuth]

Autocrossing is a whole different animal from road racing. The temperature peaks are usually much less in autocrossing because of the short runs. And it's the temperature spikes and rapid cooling combined with stress-risers that cause rotor cracking.

Of course.

[problemchild]

I still am having trouble understanding why one would buy parts that were engineered and manufactured for a specific application, have a proven record, but are considered in need of modification before use. Deburring 480 holes by hand is not a 5 minute job.

If one cannot trust their brake rotor supplier, then time to buy your rotors somewhere else..

[Rick Iverson]

Since I can see the chamfers in that photo, I'd think they are already close to or at those dimensions and they look very smooth.

If it were me, I'd just leave them alone. Of course, I don't use drilled rotors, so that's an academic opinion.

agreed

I still am having trouble understanding why one would buy parts that were engineered and manufactured for a specific application, have a proven record, but are considered in need of modification before use. Deburring 480 holes by hand is not a 5 minute job.

If one cannot trust their brake rotor supplier, then time to buy your rotors somewhere else..

going on the car as is

[Rick Iverson]

Of course, I don't use drilled rotors, so that's an academic opinion.

Dave, my curiosity is piqued. Why not?

[DaveW]

Dave, my curiosity is piqued. Why not?

One of my posts from another rotor thread, link: https://www.apexspeed.com/forums/sho...l=1#post597624

"And I will not use drilled rotors for 2 reasons - the fact that (1) they crack more easily and (2) they have less heat capacity than solid rotors. The heat capacity is important for consistent brake performance (maintaining more consistent rotor temperature) over a long lap. Another reason I don't like drilled rotors is that they eat pads too fast, but that's not as big an issue as the previous two."

[Rick Iverson]

One of my posts from another rotor thread, link: https://www.apexspeed.com/forums/sho...l=1#post597624

"And I will not use drilled rotors for 2 reasons - the fact that (1) they crack more easily and (2) they have less heat capacity than solid rotors. The heat capacity is important for consistent brake performance (maintaining more consistent rotor temperature) over a long lap. Another reason I don't like drilled rotors is that they eat pads too fast, but that's not as big an issue as the previous two."

Masterful, as usual.

[BrianT1]

Rick,

Where did you purchase these from if you don't mind me asking.

Brian

[Rick Iverson]

Rick,

Where did you purchase these from if you don't mind me asking.

Brian

Brian, Primus. And Brad gave me a smoking deal.

[2BWise]

One of my posts from another rotor thread, link: https://www.apexspeed.com/forums/sho...l=1#post597624

"And I will not use drilled rotors for 2 reasons - the fact that (1) they crack more easily and (2) they have less heat capacity than solid rotors. The heat capacity is important for consistent brake performance (maintaining more consistent rotor temperature) over a long lap. Another reason I don't like drilled rotors is that they eat pads too fast, but that's not as big an issue as the previous two."

Dave, what about the benefit of reduced unsprung mass? Not arguing your point, as I agree with it, but just curious if you've considered the mass portion of the decision.

[Pop Chevy]

I agree with all Dave said but it's not all about unsprung mass, it's about rotating weight which is much more important. However as Dave said, if your brakes are over heating it just doesn't matter. It's up to you to keep an eye on rotor temps. For autocrossing it's a no brainer for road racing it's a trade off.

[DaveW]

I agree with all Dave said but it's not all about unsprung mass, it's about rotating weight which is much more important. However as Dave said, if your brakes are over heating it just doesn't matter. It's up to you to keep an eye on rotor temps. For autocrossing it's a no brainer for road racing it's a trade off.

You are, of course, correct. However, the good thing about rotor weight is that it is relatively (compared to the tire) close to its center of rotation, so its rotational inertia is not very large. Of course, it adds unsprung mass, so that's also a disadvantage. And as Gregg says, for autocrossing, rotational inertia is much more important than in typical road racing, since with very low gears, the rate of acceleration is much higher. So he's absolutely correct that it's a compromise, as are most things about a racecar.

And another point - it's not just rotor/pad overheating that's important. The rotor can actually get too cool on long straights. Some pad compounds lose some % of friction coefficient at lower temperatures making getting max G's in deceleration when downforce is highest (mostly in winged cars) at top speed at the end of a straight with too-cool rotors difficult.

[BeerBudgetRacing]

Brian, Primus. And Brad gave me a smoking deal.

I bought a pair for the rear on my FC. We'll see...

[Rick Iverson]

One of my posts from another rotor thread, link: https://www.apexspeed.com/forums/sho...l=1#post597624

"And I will not use drilled rotors for 2 reasons - the fact that (1) they crack more easily and (2) they have less heat capacity than solid rotors. The heat capacity is important for consistent brake performance (maintaining more consistent rotor temperature) over a long lap. Another reason I don't like drilled rotors is that they eat pads too fast, but that's not as big an issue as the previous two."

We have celebrity in Minnesota’s named Joe Soucheray, the mayor of Garage Logic. As in one of their mottos, “You learn more here by accident than elsewhere by design”.

[DaveW]

Dave, what about the benefit of reduced unsprung mass? Not arguing your point, as I agree with it, but just curious if you've considered the mass portion of the decision.

Yes, as I said in a previous post, that is an issue. But considering the weight of the Hoosier radials we use in the FRP F2K series, wheel, upright, a-arms, pushrods, etc. (30+ lb), I don't think less than a lb of drilled holes would make a measurable difference, at least at my level of measurement. BTW, 60 3/8" dia holes in a 3/8" thick iron rotor is ~0.71 lb.

[john f]

And another point - it's not just rotor/pad overheating that's important. The rotor can actually get too cool on long straights. Some pad compounds lose some % of friction coefficient at lower temperatures making getting max G's in deceleration when downforce is highest (mostly in winged cars) at top speed at the end of a straight with too-cool rotors difficult.

Another point to too cool rotors is after a long straight with hard braking at end can heat shock rotor, increasing the chance of cracking.
Road America has three spots every lap for this.

john f

[stonebridge20]

Rick, your rotors and CWP found their way into the Cryo chamber.

[stonebridge20]

On segment 2 of 8 in the Cryo treatment.
Cycling between -295F and -305F for 14 hours and then +295F and +305F for 3 hours in the 3 day process.

[10rmotor]

I worked at a fab shop in the Bay area that drilled porsche rotors for Automotion (don't know if they're still around). Anyway, we used radius cutters instead of a countersink tool. They still cracked, but the rotors lasted a bit longer, and were probably a little more friendly with the pads.