Using shop lathe to turn rotors

[Kestas]

We have a lathe available to us where we work. We've been toying with the idea of using it to turn rotors ourselves. This idea comes from a quest of not only saving money, but making sure our rotors have no more metal taken off than is necessary.

Naturally, I'm concerned with keeping the rotor prependicular to the mounted surface. Has anybody done this successfully themselves? Should we shop for a scrap half-shaft from a solid rear axle to use as a fixture?

 

[T-Keith]

I believe a special lathe is used so that both sides can be machined at once. I would not try it on your own. What does it cost to turn them, $12?

-T

 

[SyntheticShield]

I worked in a shop that had a couple of lathes as well a few years ago and toyed with the same idea but was told wht T-Keith mentioned that both sides should be turned at the same time. However, no one has ever explained why. I can see that you want to keep both sides the same thickness, but what if you have had a issue with abnormal wear? One side is worn more than the other due to a brake problem. You correct that, take your rotors in to have them turned. Arent they just going to turn them until both sides are smooth and straight? Of course there is a limit to how much they can be turned, I think minimum thichnesses are stamped on the rotors.

In that case I could see any benefit to turning them at the same time. With a good quality micrometer you could keep the thicknesses on both sides within a couple thousands and I cant see that little making much of a difference. Admittedly though, Iam no expert on this just reasoning things out.

Anyone have any input.

 

[HerkyJim]

Gee, Kestas, sounds like a super idea. Lucky you, to have access to an engine lathe. Last time I did was school 1966. I believe the deal would be a couple of tapers that locate off the bearing races and fit closely on an arbor between centers. Maybe such a setup exists for sale somewhere? Any good genearl machinist should be able to show you. This might be a good project for a talented kid in trade school class? I'm sure I could have done it easy back in the day. In fact the motorcycle shop where I hung out when I was a teenager asked me if I could make up some front wheel spools for flat track racing. Maybe you remember, back in the day, AMA professional flat track racing motrocycles were 30 cu. in. OHV or 45 cu. in. sidevalves and no brakes! Thats right, zero brakes, except compression or drag your foot! When I asked Smitty the shop teacher about it, he nixed it straight away. Didn't say why, but liability concern undoubtedly. Why don't they grind the rotor surfaces instead of using a lathe tool. Would produce a finer surface wouldn't it?

 

[Mike242GT]

Maybe I'm nuts, but for my cars, I don't think that turning rotors is ever worth the effort. If the brakes aren't pulsating, leave the rotors alone. Once turned, they'll warp again much sooner, and then you'll have to replace them anyway, probably long before you need pads, so add the extra labor for that. Brembo rotors for my cars are $32 front, $28 rear, vs. turning them for $10-12 apiece, plus you have to make two trips to the machine shop to drop off and pick up the rotors, and you're without the car for usually a day or so in the meantime.

 

[Eddie]

Just mount the rotors on a heavy face plate and do it taking light cuts on every pass. This is no big deal for a good lathe operator.

 

[XS650]

It can be done and some people do. Take a look at the specs for runout and parallelism on brake disks. They are pretty tight considering how big and flat the disks are. The tolerances are well within the capabilities of a decent engine lathe but work like that require some machinsist knowledge. You can't just slap the part in the lathe and start cutting.

Practice on some old disks first until you can turn them within spec without trouble.

One friend at my old job who is an accomplished home machinist used to alway turn his own disks on a regular engine lathe. I rode with him several times and his brakes were always smooth.

He said their were three advantages to turning his own disks.

1. He took off less metal than the pimply faced kid running the brake lathe at the auto machine shop did.

2. It took him less of his time to do them himself than to take them to ashop and have them done.

3. It helped justify the expense of his 2 ton lathe in his garage.

 

[kenw]

turning the wife's Highlander rotors last Saturday cost me all of $18 total for the pair. No, you don't have to do it every time and shouldn't but it's still chaper than buying new. Most rotors can be turned several times before they get too thin. I've never had any warp faster after multiple turns.

I have had one warp so badly (and these had never been turned) that they couldn't be turned and stay above the min thickness, however. When the ABS locks up one rotor many times over a year, it happens....

XS650, I've used his reason #3 many times. I think she's getting wise to me tho....

 

[1sttruck]

In general, use a dial indicator on the surface that the discs will be mounted/bolted to, to make sure that your 'reference surface is true, or do a finish cut on your fixture if one is being used to true it up. Mount your disc, remove material to clean up the surface, and then do the other side. Measure you results with a mic for thickness amd thickness variation, or a dial indicator and surface plate for flatness, parallelsim, and thickness (if you have gage blocks or a height gage). Note that lots of rust, nicks, burrs, etc. on your monting surface will affect your results.

 

[mechtech]

I like replacing them instead of cutting them.

 

[road_rascal]

I agree with Mike242GT. I had a set of returned rotors go bad within 3000 miles. These were Raybestos brand with new metal (apparantly you can get these with recycled metal). The rotors only had about 30,000 miles when they began to warp so I had a local machine shop resurface them. I'll never machine a set of warped rotors again.

 

[Kestas]

1sttruck's answer is what I was looking for. Eddie and XS650 also gave good answers.

Whether it's worth it is a personal decision. I like to think I can do a better job than the pimply faced kid with the store's lathe. Since I always have a summer car and a winter car, logistics is rarely a problem.

SyntheticShield, I believe T-Keith means both sides of the rotor need to be turned in the same chuck (without removing it from the lathe). This essentially guarantees perfectly parallel surfaces. I wouldn't do it any other way.

 

[JohnBrowning]

Both sides do not need to be turned at the same time. Your fixture is what is going to be important. Take a good look at a comercial brake lathe. Look at all the adapters. Their is no reason you can not make your own fixture and adapters especialy if you also have a mill! The speed control on your lather might be an issue though. you normaly do a slow cut and a fast cut.Some of the cheaper modern lathes do not turn slow enough for some operations. THe old cast iron lathe's from the 1920-1960's are about as good as it gets for things like cutting threads at slow speeds by hand, deep gun drilling, rifleing etc........ Remember heat is the enemy in any resurfaceing operation to go faster you have to have some way to get rid of the heat!!

P.S. Some vechiles require that the rotors be turned on the vechile wich is gaining in popularity! GM has some vechiles now that require this if it is to be done by the book. Thier are a lot of imports that recomend the on car method as well!