Turning brake rotors

How many of you resurface your brake rotors on your lathe?

Do you just chuck them up from the ID of the rotor?

I chucked one up last night just for kicks and put a dial indicator on it. I measured and got .005 of runout on the disk surface. Tapped the high spot and tightened it up again, getting closer to .001.

I do it all the time works great. Sometimes it is hard to get them to run true to their mounting surface, but its doable. There was a recent thread on the subject and well worth reviewing. Be sure to sand all the tools marks off before use though.

Measuring the surface of the rotor may not be what you want to do. You'd need to indicate relative to either the spindle bore through the center for integral hub types or off the flange where it mounts. Inner and outer faces also need to be parallel. In an ideal world you wouldn't re-chuck the rotor just to make sure the sides are parallel to one another.

and no I don't cut rotors on mine. 10" swing, nothing I own uses a rotor that small. I don't generally bother with resurfacing rotors. They're either fine when they come off and just need a light scuff with sandpaper, or they're trashed and get replaced. Seems like every time I've had one cut in the past it was either too thin to cut, or it warped quickly afterward and I had to replace it anyway.

I cut them on my 16" lathe. I grab the ID and indicate the inside of the flange that bolts to the hub. Bang it around to get <.001 runout and then turn the inside face. Flip the rotor and indicate the face I just machined to <.001 and turn the outside face. It's pretty quick when you get the hang of it.

I did one on my model 34 (13”) a few months back, not a hard job, I dialed It in off of the mounting surface and got that running true, faced it off and flipped it dialing in off of my just machined surface, it came out pretty well, been running it without any issues. I’d have no problem doing it again if the need arises.

I did it once and that was the realization I wouldn't do it again. You either drape every part of your lathe with covers or vacuum up for 2 hours. A real nasty job for the monetary return.

Stuart

atomarc said:

I did it once and that was the realization I wouldn't do it again. You either drape every part of your lathe with covers or vacuum up for 2 hours. A real nasty job for the monetary return.

Stuart

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Agree, but I do it for both convenience and quality. There is another reason for doing this. Both myself and others have suffered new disk warping after just a few miles of use. Once this occurs and becomes stable, refacing often saves the disks.

I know this is a lathe forum, but i get much better results on the mill. I center the rotor up on a rotary table and use a fly-cutter.

Relative to "warped" disks that cause a pulsating brake pedal:

Most commonly the pulsating or shaking brake is caused by an uneven "transfer layer" of brake pad material on the rotor friction surface and not warping of the rotor. The process of establishing a consistent transfer layer of brake pad material onto the rotor is called "bedding-in" the brake pads. Also called "burnishing" the brakes. Resurfacing the rotor does correct the uneven transfer layer by removing it entirely, but resurfacing is not necessary if the rotor is not warped.

Modern brake pads are designed to work most effectively when a portion of the pad material melts and adheres to the brake rotor. When new pads and new rotors are installed, that should be followed by a process of heating the rotors to the point where the brake pad surface is melted and some of it is evenly spread over the rotor surface. Once this is done, then the friction is caused not by friction between the rotor and the pad, but between the transfer layer and the pad. Brake experts say that when this is done properly, the brakes work much better and also last longer.

The first time I heard about this, I thought it was a nutty proposition. I did my homework, searching the web, and found ample support for it. A while later the brakes in my old Jeep began to develop the pulsating. I figured I had nothing to lose because it was bad enough to where I would normally do a brake job, so I'd give it a go. So I ran through the bed-in procedure to hopefully even out the transfer layer. I ran the start-stop cycles until I saw smoke coming up from the front brakes. (One youtube video I saw has a camera mounted on the side of the car watching the brakes and it actually shows flames coming out of the brakes during the last few stops.) In the past, this would have been alarming to me, but after learning about bedding-in brakes, it was what I was looking for. After that, my Jeeps brakes were perfectly smooth once again as if I had just done a brake job.

Here's one link that describes this process:
How to Bed-in Brake Pads - The Best Technique for Bedding in Brake Pads

There's ample info on the web about this topic, so I don't need to belabor the point.

DanMc77 said:

There's ample info on the web about this topic, so I don't need to belabor the point.

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That doesn't make any of it true. Many million new cars are built every year. Not one of them has the brakes "bedded".

Every vehicle I have ever worked on that had pulsating in the brakes was due to warping or uneven wear of the rotor. Truing up the rotors fixes the problem.