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  • Threading Problem

    I was cutting a part with 1.5"x8 tpi thread on my lathe. I was using a carbide threading tool and when I was almost done with the thread, the tip broke off the tool. I filed a bit on the threads to try "finish" them and took the part out to try to fit it into the hole. It didn't fit. The threads need to be cut just a tad deeper.

    How does one put the part back in the lathe and pick up the threads to cut them deeper? I've looked through all of my refenence books and they have nothing on it. I did find a method listed in "The Machinist's Bedside Reader" but in that method, the part has not been removed and replaced in the lathe.

    I'm sure it is a rather complicated process getting everything back into alignment. The settings on the dials have been moved since the part was removed so there is absolutely no reference to go back to. Appreciate any assistance. Thanks.

    Bill
    Bill

    Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

    Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

  • #2
    The way I do this is to set the compound rest to 29 degrees, back off the cross slide, start the lathe, engage the thread half nut, run the carrage until the tool is over the threads, shut off the lathe motor, don't move the carrage or disengage the thread split nut lever, while the lathe motor is stopped move the cross slide forward and adjust the compound to realign the tool. As I said this works for me I'm sure there are methods that work for other people that will work also. my two cents worth
    re
    Herm Williams

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    • #3
      Simple as pie! Mount the work back in the chuck. With the treathing tool backed off from the threads turn the lathe on and engage the half nuts then turn the lathe back off. Loosen the work in the chuck and crank the cutting bit mack into the work. Turn the work in the loose chuck until the thread groove lines up with the bit. Tighten the chuck back up and you are off to the races. Gary P. Hansen
      In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

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      • #4
        Well I been Drinkin But

        Here Goes. Same setup as before. Keep too; aAWAY fro your threads already cut. tHEN STOP LATHE MOVE THE TOOL BACK INTO THE PREVIOUSLY MACHINED THREAD GROOVE USING THE CROSSLIDE AND COMPOUND. wHEN ALL MATES CONTINUE AS BEFORE. No problem easy eh?? Excuse me cap lock on 11 hour day and some beers /

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        • #5
          Herm beat me to the answer. His way is another way to skin the same cat. Gary P. Hansen
          In memory of Marine Engineer Paul Miller who gave his life for his country 7-19-2010 Helmand Province, Afghanistan. Freedom is not free, it is paid for with blood.

          Comment


          • #6
            Bill,
            One thing to consider though it may or may not apply.

            If your part was rough stock (not concentric) to begin with, and was mounted in your chuck that way, then you turned the section to be
            threaded to the proper diameter, did you also turn any spot nearby
            concentric?

            If so, then you should be able to mount in a 4 jaw and indicate in
            from that true spot.
            That will get you pretty much where you were before you started to thread.

            Then follow Herm's procedure.
            I'm in my mid fourties and have to use magnifiers to see where the edges of the cutter are actually touching, to get it right.
            Mike green
            Mike Green

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            • #7
              I do it like Herm mentioned in his post.

              Comment


              • #8
                One other observation. Make sure you've removed the broken tip from your part. Hitting a chunk of carbide would probably yield another broken tip.
                The early bird may get the worm but the second mouse gets the cheese.

                Comment


                • #9
                  Starting as above, line it up close with the machine off. right side is most important, on RH thread. set zero on cross slide. my first couple passes under power, I use the cross slide (not compound) to advance the tool until the trailing edge just skims the right side of thread. Left side of tool (compound) is held away from thread. set zero on cross slide when right side touches. Then on progressive passes, advance the compound until it cuts to size. go easy, a couple thou per pass 'til you get a feel for it. threading is fun- I just love screwing things up!

                  Comment


                  • #10
                    Another vote for herm William's method, with a definite "yes" to MGREEN as well, that is an excellent point.

                    And, ditch the carbide threading tool for the moment. HSS works great, and has much less tendency to chip. Grind one if you don't have one. In fact, grind two or three. That way you have a spare if something messes up another time.

                    Now, I'm going to bet you were NOT advancing with the topslide (compound) at 29 deg...... Going straight in with the crosslide puts a lot of force on the tip, which has to cut a groove. Going in at 29 deg puts the force on one side of the tool, with just a bit on the other to keep things alined. Even better to do with a coarse thread like that.
                    Last edited by J Tiers; 04-11-2007, 12:06 AM.
                    1601

                    Keep eye on ball.
                    Hashim Khan

                    Comment


                    • #11
                      Excellent suggestions above, but I would perhaps add one final step. When you have done the method you choose and are close to the final position, you can loosen the tool in the tool holder and press it into the existing thread to get the final alignment. Then carefully tighten the tool down and back it out a bit before trying to cut again. This should align the tool almost perfectly with the existing thread.

                      It is important to actually engage the feed with the tool backed out in any of these methods to take up any backlash in the feed screw/half nut. This relation of the screw and nut should not be disturbed while getting the tool into the thread.

                      Magnifiers and good light can be very helpfull in operations like this. A white card held under the tool will show any misalignment better.
                      Paul A.
                      SE Texas

                      Make it fit.
                      You can't win and there is a penalty for trying!

                      Comment


                      • #12
                        I'll just add one more suggestion to the excellent ones already given. As you haven't done this before practice a few times on a cheap bolt.
                        Free software for calculating bolt circles and similar: Click Here

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                        • #13
                          I don't know what kind of threading tool you are using.

                          If you are using one of the brazed tip 60 degree jobs,
                          you will frequently have a break up.

                          These tools don't have enough front clearance, no rake,
                          and will chip when running too slow.

                          A proper threading tool "insert type", or hand ground "high speed tool"
                          will give better results in my opinion.

                          Kap Pullen

                          Comment


                          • #14
                            Thanks to all Responses.

                            I printed all of the responses and have filed them in a box I keep in my shop called "Good Ideas." Using the information in all of the suggestions, I was able to replace the part and cut the threads deeper. The part now fits just like it was made for it!! It turned out very nice as I was expecting it to end in the scrap metal box.

                            What I was doing was making an adaptor to fit a 4-jaw chuck to my rotary table. My rotary table has a MT3 hole in its center and I had a 4-jaw chuck that didn't fit my lathe. The 4-jaw chuck has 1.5" by 8 tpi mounting threads. My solution to the adaptor was to buy a taper extesion that has a MT3 shank and MT4 socket. I cut about 1.5" in length of the outside of the socket end to 1.5" dia. and threaded the end closest to the MT3 shank. I left a 1/4" lip between the end of the shank and start of the threads. I then cut off the unused potion of the MT4 socket end. The adaptor screwed into the chuck mounting plate and the other end drops into then center hole of the rotary table, mounting the chuck to the rotary table.

                            Bill
                            Bill

                            Being ROAD KILL on the Information Super Highway and Electronically Challenged really SUCKS!!

                            Every problem can be solved through the proper application of explosives, duct tape, teflon, WD-40, or any combo of the aforementioned items.

                            Comment


                            • #15
                              thread file

                              There is a file made to do just this chore. It is a square file about 5/8 sq and about 10 inches long and has 8 different pitches.You find the pitch that need
                              then file to size.
                              jimsehr
                              If you want I will post pic.

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