Anyone done this with a QCTP ?

[754]

Luther, I did not try it , at the time I built it , I got into other things. Now that I have a shop again I shoukd give it a test .
i designed it to work with the heavy thick early style Japan bike rotors.

[Arcane]

Yeah, brake rotors are really not that expensive brand new for the most part. The ones that are expensive may be better off being machined by a properly equipped shop. Keep in mind that there are specs defining the maximum amount that can be machined off drums and rotors which are for safety reasons. Many drums & rotors that came through my shop were below spec in the first place & couldn’t be machined safely. Remember, safety specs are for everybody as we all use the hi-ways & someone’s failed brakes can involve innocent bystanders in a fatal way.
Through the years in the mechanical repair business I have run into many instances of brakes on vehicles that were so bad I wouldn’t allow the vehicle to be driven any further unless repairs were properly made. The repairs didn’t have to be made at my shop but the vehicle could only leave on the back of a tow truck. I have seen rotors worn through to the inner cooling ribs & drums that literally came off in pieces.
I can appreciate a diy situation & trying to save a few bucks but ultimately safety for oneself & others must come first!

Brand new rotors barely meet "spec" and those so called safety specs are designed to force people - by law - into buying new when a simple machining job would suffice.

Back in the day when Stock Car racing was a big part of my life, we would often have the disc brakes turned if they were pulsating/grabbing and since they were Stock Car parts, and if the mechanic knew they were going on a Stock Car, they had no qualms about turning them down to well under the so called safety spec and I never once saw any failures. There's nothing harder on brakes than Stock Car racing except maybe a long downhill slope with a heavy trailer pushing you.

I've also seen work trucks that had the rotors worn into the cooling ribs and they never actually failed per se, but they didn't provide the proper braking effort either. That tells me you can take an incredible amount off a rotor and it will still be safe.

[A.K. Boomer]

It's more than just structural safety - there has to be an allowable amount of thermal mass to begin with or else the things will go up like a tooth pic,,, you have to have enough mass to absorb the immediate thermal energies that even one high speed panic stop can produce,,, if you cannot do this you can actually "float" the pads on gasses and create severe brake fade,,, I live in the mountains and im an auto tech.so not only do I strictly follow the discard thickness guidelines - I take my thinking a step further for people who routinely tow or haul firewood loads in the back of their trucks ect/ect/ect...
lots of times discard thickness is not good enough for certain customers of mine and they appreciate me looking out for them that way...

[Doc Nickel]

Yeah, brake rotors are really not that expensive brand new for the most part.[...]

-Shortly after the '08 recession, my income pretty much collapsed. Home-shop niche-market custom work, for which people simply didn't have the money to pay for anymore.

I had a little savings, and thought it a wise move (spoiler: It wasn't) to buy a few additional machines to be able to do a wider range of general work, as opposed to the specialty stuff I'd been doing. One of them was a restored Aamco brake lathe. In great condition, fully functional, nearly all the accessories.

I had, only a few years before, tried getting new rotors for a large GM car, only to find replacements were something like $125 each. I'd heard that the bigger truck rotors were even more.

I started advertising around for more general-machine work... and got bupkis. I had that brake lathe for nearly ten years, turned exactly one set of drums for a friend of mine. Made $20.

In the time between my looking for a set of rotors and picking up the brake lathe, the Chinese had started flooding the market with cheap rotors. It was now easier to just buy new ones than to have the old ones turned. Throw on the fact that a lot of small cars these days come from the factory with rotors that are don't have enough spare metal to bother turning in the first place, there's of course no money at all in doing so.

I found out later that the auto parts stores were getting rid of their lathes, because even at $15 apiece, they hardly ever got used. The only people around here that actually used their lathes are the full-service mechanic shops.

I finally basically gave mine away, and have since seen many others sold for basically scrap price.

Doc.

[luthor]

Luther, I did not try it , at the time I built it , I got into other things. Now that I have a shop again I shoukd give it a test .
i designed it to work with the heavy thick early style Japan bike rotors.

Yes, I thought that it would only be suitable for solid type rotor not the ventilated ones.

[754]

Luthor, rotors for bikes were not ventilated in the denter till into the 80s, abd i dont think many did.
any stainless rotor i tried turning starts to sing and vibrate, but cuting both sides, I would think should eliminate that..

yeah rotors tebd to be cheap, but like i mentioned, sometimes you dont want to wait , or cab yse the money for other things.. i have a lathe...it gets used..

[mikey553]

I have just resurfaced 4 rotors for my son's Subaru Forester. They are almost 12" in diameter and my lathe is 12 x 36. I have used almost the same setup as OP, but without tailstock. Clamped the rotor hub in the soft jaws, indicated the internal hub face to .001" and turned both sides at one setup. In my case I actually used a QCTP, but it does not matter. I have made a special tool holder, the left hand cutter is bolted to it to form a letter "L". The holder is massive, I made it out of 2.5" diameter bar. The benefit - there is no vibration at all with a sharp insert for aluminum.

New cars have bigger wheels and bigger rotors as years go by. 12" rotor is about the limit for me. Pretty soon my little lathe will be useless for brake jobs. I may need a bigger lathe!

[Tillie's in a bottle]

Luthor now that looks like a real solid setup

[754]

One thing J sould mention on our old bikes. Thinning discs, is pretty popular. On say CB 750 SOHC, and Z1 and KZ 900 and 1000.
early rotors were so overbuilt... in 40 years I have never seen a worn out one. Stainless steel they get marked up, but dont lose much thickness.
weight is the big problem, moreso after adding a second front rotor. Drilling is common, and thinning. Generally or often this involves removing the rotor from its alloy hub, so more cost involved. I Guess , I should finally try out my tool I made..

[luthor]

Luthor now that looks like a real solid setup

Thanks Tillie, yes it is quite solid and produces very good results when used as I described.

[old mart]

I seem to remember that the early Yamaha 900 fours had twin ventilated front discs which were found to warp. Later models had conventional solid drilled discs.
Using sintered pads give better braking, but tends to wear the discs faster.