Brake rotor machining on a lathe.

[GoceKU]

I've machined many rotors and brake drums on my lathe but over the weekend i come across something strange, those are rear rotors from an mk3 mondeo and one had 0,4mm the other 0,25mm runout but it did not shake or make noise, in the past i've had discs with 0,10mm runout produce a shake, what's yours experience with brake rotors.

 

[T Bredehoft]

Hmm. when I worked for Kelsey Hayes (major US mfgr) they rejected rotors with .003 run-out. that's .08 mm. If those were no-shake at that run-out, (.015 to .009) that's unusual.

 

[middle.road]

I tried that - once, on the Kid's '97 Lincoln, rears. Hit a void and all h*ll broke loose.
At which point I went and grabbed a Cerveza and sent him off to the parts store.
That Continental had a appetite for rear rotors for some odd reason...

Might get my nerve up to try it again on my truck. 170K on the original front brakes. Might be time to check them again.

 

[bfd]

I have machined rotors in the past they need to run real slow. I made a special tool so I could cut both sides without removing the rotor from the lathe. I got less than .002 runout on an 11" disc. it took a while to indicate bith the taper roller bearing races in on that type. took a while but as many things in our hobby It saved me little money bill

 

[RandyWilson]

I've found that single piston floating calipers are much less sensitive to rotor runout than they are to thickness variations. Thickness you feel as a pulse in the pedal. Runout goes through the suspension and mostly gets dampened by the insensitiv overly numb steering.

 

[GoceKU]

I still haven't finished this job, i'm waiting on a new handbrake but last night wanted to fit the new brake pads but the old ones were really stuck, on one side to the point where i had to put the bracket on the hydraulic press and press the old pads off, which explains why the brakes did not work right and whay there was no vibration, it's really surprising that the brake pads can get so stuck on such a small surface.

 

[Firestopper]

I've turned rotors with success, but it took way to long to indicate after flipping. I turn around 200 RPM and used a radius tip insert cutter. I'll just take them to Merle's automotive and pay the $12 each for turning.
You got a nice finish though.

 

[GoceKU]

Yeah it really takes long time to refinish them right, i usually only cut the surface where the pads press against, but on bent discs i cut all the surfaces and make them with in 0,01mm, and as i'm machining them for me i'll rather spend the time and know they are done right.

 

[middle.road]

The last time I took the kid's fronts to the 'machine shop' they were going to machine off .035" / side.
At which point they would be under spec. Asked them to adjust the machine and received a blank stare...
Took them to the next shop down the road and thankfully there was a Gray Beard behind the counter and understood.

 

[cg285]

it actually goes by thickness variation not run-out. doing that on an engine lathe is time consuming. nowhere near cost effective.
however which ever way you do it you are losing much stopping power if it is a lathe finish -
http://www.oeqf.com/techinfo/scratching/scratching_lg.htm
i always knew what to do but never had it explained why like this does