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Anyone done this with a QCTP ?

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  • #16
    OK my simple mind has a question here. Why not just flip the rotor 180* and cut the other side from the front? I'm probably missing something? I too have seen the older style brake lathe machines that cut both sides at the same time and have dial adjusters to set the DOC for the rotor. From what I've read before you do not get the cut real smooth or you get the pulsing like a warped rotor which is something to watch out for.
    I have a classic car that uses solid rotors from another make of car, I have to cut the diameter down to fit my car, but I have never done the sides so far.

    Good post to learn from.

    TX
    Mr fixit for the family
    Chris

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    • #17
      Originally posted by Mr Fixit View Post
      OK my simple mind has a question here. Why not just flip the rotor 180* and cut the other side from the front? I'm probably missing something? I too have seen the older style brake lathe machines that cut both sides at the same time and have dial adjusters to set the DOC for the rotor. From what I've read before you do not get the cut real smooth or you get the pulsing like a warped rotor which is something to watch out for.
      I have a classic car that uses solid rotors from another make of car, I have to cut the diameter down to fit my car, but I have never done the sides so far.

      Good post to learn from.

      TX
      Mr fixit for the family
      Chris
      By cutting each side while on the one setup, you are assured that both sides are parallel. It could be done by flipping the rotor, but this way is easier and more likely to be parallel, not .002 or .003" out of parallel. If out by that much, it will be felt. Just need to be careful about minimum thickness when done.

      Sarge41

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      • #18
        Its a video from Instagram... the rotor has a lot of runout on the side it is cutting, like 20 thou or more, very visible. It seems to be cutting it fine.
        turning a disc around, easy to end up with runout, and 3 thou, you will feel it at least on a bike, and longterm it will wear a tire unevenly.

        I posted it with that title for a reason... due to recent QCTP discussion. Although they are easy to use, and generally quick to use.. there are a few situations that they may not work as well.., this appears to be one of them.
        Why turn your rotors.. a few reasons.. you dont want to spend the money or dont have it. Because you can.. and for me at times, you are working on a vehicle, you have the brakes off, you realize the rotor needs turning..... then you realize too late in the day to get it done, or you have no way to get them back and forth... and now you have a vehicle sitting apart.
        I could not count the number of times, I just make something or just deal with it, so you can continue and get finished.
        If you are going to invest 10 or 20 K in machining stuff.... imo... you better be able to produce things..

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        • #19
          Originally posted by 754 View Post
          I posted it with that title for a reason... due to recent QCTP discussion. Although they are easy to use, and generally quick to use.. there are a few situations that they may not work as well.., this appears to be one of them.
          What? It's literally no different. You just turn the toolpost 90°.

          Explain. Please explain how it functions any different.
          21" Royersford Excelsior CamelBack Drillpress Restoration
          1943 Sidney 16x54 Lathe Restoration

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          • #20
            Not having turned one, i dont know what is involved.., if it indexes.. not a problem.. if it doesnt it may need clocking ir alignment. .

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            • #21
              Loosen top nut. Turn 90° Tighten top nut. Indicate it if you care.
              21" Royersford Excelsior CamelBack Drillpress Restoration
              1943 Sidney 16x54 Lathe Restoration

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              • #22
                Local college machine shop had a setup for exactly that same reason. Big U-shaped burnout made from 1" plate, with some extra bits welded on for both the mounting and the tool bit holding.

                Tool bits were typical cheap 1/2" shank triangular-insert lathe bits, like you use to see in the sets from Enco and the like.

                It was ugly, but it worked, and every time I took a semester of class, it was used at least once, usually two or three times.

                And yes, it was built to plunk right onto the CXA posts fitted to each of the big Colchesters.

                Doc.
                Doc's Machine. (Probably not what you expect.)

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                • #23
                  This post from a few years ago explains the process that I use with the double tool holder.
                  https://bbs.homeshopmachinist.net/fo...iscussed/page4
                  Last edited by luthor; 06-19-2021, 07:05 PM.

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                  • #24
                    Originally posted by The Metal Butcher View Post
                    Loosen top nut. Turn 90° Tighten top nut. Indicate it if you care.
                    LIKE!

                    --Doozer
                    DZER

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                    • #25
                      Originally posted by 754 View Post
                      Not having turned one, i dont know what is involved.., if it indexes.. not a problem.. if it doesnt it may need clocking ir alignment. .
                      Mind blown.

                      -Doozer
                      DZER

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                      • #26
                        Originally posted by The Metal Butcher View Post
                        Loosen top nut. Turn 90° Tighten top nut. Indicate it if you care.
                        TMB nails it in one. The position of the tool post means nothing, because the tool path is determined by the carriage, cross feed, and compound feed. I generally leave my compound feed at 30 deg. and the tool post "square" to the lathe... but the actual tool mounting surface can be spun around to the rear, or any angle in between to reach difficult spots, etc. None of that changes which way the lathe is going to move, though.
                        25 miles north of Buffalo NY, USA

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                        • #27
                          Heres my setup Click image for larger version

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                          • #28
                            Originally posted by 754 View Post
                            Heres my setup Click image for larger version

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                            Any pictures of it in use?

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                            • #29
                              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!

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                              • #30
                                Originally posted by JoeLee View Post
                                Doesn't that inside cutter chatter ?? That's a lot hanging out there plus going around the rotor. Looks like one big torsion bar setup to me.

                                Are you turning both sides at the same time ? if so how are you adjusting it ? Or are you doing one side at a time ?



                                JL................
                                If it works it works but that was my thinking --- in fact - set crews are not designed to work that way! it's very flimsy in both the combined length but especially torsioning a square bit inside a holder like that with the set screws having no real leverage on the piece at all...

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