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any tips for "turning" a lathe carriage that is facing convex? (scraping)

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  • any tips for "turning" a lathe carriage that is facing convex? (scraping)

    my lathe project has the worst fit carriage I have ever seen - the cross slide(which is good) is facing convex by about .002-.003" in 6 inches.

    this is on my Yamazen Lancer project(the first wave of Taiwanese imports- mid 70`s)
    it was apparently that way when new.

    the saddle is too big me to mill it, so I am hand scraping the v way of the saddle.

    I am about 5 cycles in and have seen no appreciable change yet.

    any tips for getting it "turned"?

    thanks!

  • #2
    3" is a lot to scrape by hand, luckily the surface area is quite small.

    If you're real careful you might find you could use a file to bring a thou or two off it and save you some time.

    Are you sure it's that the cross slide ways being out of perpendicularity to the bed, rather than the spindle being out of parallelism with the bed? You would want to be 100% sure about that before you scrape it!

    Comment


    • #3
      you are absolutely correct!

      when i first checked the cross slide to spindle i freaked out- .010" in six inches convex!!

      then it dawned on me the headstock is adjustable.

      that was my incentive to ditch the vari-speed sheave and hook up the direct drive VFD conversion - so i could get it turning straight before i did anything else - it will now turn a 2" aluminum bar to within .0005" over about 10 inches - more than good enough for my needs, now i just have to get it facing flat.

      this machine is the reason early imports got such a bad rep! very poorly fitted, but with decent quality castings.

      the good news is the bed is hardened and shows no appreciable wear.

      if i can just get it facing flat it will be a great home shop machine.

      Comment


      • #4
        Yes I read alot abought this and its common new out of the box, you have to
        go all over everything seems those over the pond none are turn key and have
        to be tweaked now and then over time. .0005 is close enough for govt. work,
        but then when facing some lathes needs the carriage locked and then some
        lathes dont care------ nature of the beast.

        Comment


        • #5
          That was one of the first things I checked on my 7 X 12 lathe when I first got it. It's kind of hard to make anything on a lathe that cuts tapers and faces convex (or concave)

          I guess I was lucky. The spindle and tailstock were nearly perfectly aligned (.001" over 10 inches) The lathe bed and carriage were perpendicular and square (.0005" in 6")
          I did have the tailstock centerline a couple of thousandths high, but a good cleaning and a couple passes with a file cured that. The machine has held its accuracy for quite a while, even though I have had to adjust the gibs on all of it's sliding surfaces a few times. The only major change I've made was replacing the plastic change gears and drive gears with steel gears. I did find out something interesting during the time I've owned and used the machine. Normally, I used hydraulic oil to lubricate everything. But, last year, after changing the oil on my motorcycle, I had some full synthetic oil left over. I put some in my oil can and set about oiling all of the sliding surfaces....Bad idea. The first problem that arose was the cam-lock on the tailstock wouldn't hold, and the tailstock would slowly back away from whatever it was that I was turning. This didn't register, for some reason. I soon found my carriage saddle backing off, all by itself while facing a part. This led me to fabricate a carriage stop...which soon began to slither down the ways. Eventually, my feeble mind connected the dots. I carefully washed the synthetic oil off of the machine with acetone, and re-oiled it with non-detergent hydraulic oil. Problem solved. Uh, until the carriage drive rack almost fell off...
          No good deed goes unpunished.

          Comment


          • #6
            "I soon found my carriage saddle backing off, all by itself while facing a part."

            that sounds weird.

            Comment


            • #7
              "....convex by about .002-.003" in 6 inches." So, the surface is spherical (or curved), and the center is closer to the tailstock by .002-.003"?

              Seems to me the surface would be conical ( a very shallow cone in this case) if the spindle was not perpendicular to the cross-slide travel.
              Any products mentioned in my posts have been endorsed by their manufacturer.

              Comment


              • #8
                The first thing you want to do is to make sure the scraped cross slide has been properly fitted to the scraped cross slide ways.

                Looking at the saddle from the top, you have to turn it counterclockwise, which means that you have to scrape the left inside V slide end and the right outside V slide end. This will get confusing when you turn the saddle upside down, so make sure to mark the ends that you want to concentrate on. As you progress you will start scraping further down to the other ends. Don't forget to scrape the flat slide at the same time, just be careful how much you take off. All the while, you will have to run accuracy checks to keep the saddle level front to back and left to right. It's a tall order, and one of the most difficult alignments to obtain, but if done with care will be easy to obtain.

                The entire sequence is shown starting at post #147 in this topic.
                http://www.practicalmachinist.com/vb...update-146913/
                Harry

                Comment


                • #9
                  How about removing the jaws from the chuck, and placing a magnetic level horizontally across the center. Put your dial indicator on the cross-slide with the tip against the level as you run the cross-slide back and forth. Rotate the chuck 180 degrees, and repeat. This should tell you if the cross-slide travel is perpendicular to the spindle.
                  Any products mentioned in my posts have been endorsed by their manufacturer.

                  Comment


                  • #10
                    Originally posted by beckley23 View Post
                    The first thing you want to do is to make sure the scraped cross slide has been properly fitted to the scraped cross slide ways.

                    Looking at the saddle from the top, you have to turn it counterclockwise, which means that you have to scrape the left inside V slide end and the right outside V slide end. This will get confusing when you turn the saddle upside down, so make sure to mark the ends that you want to concentrate on. As you progress you will start scraping further down to the other ends. Don't forget to scrape the flat slide at the same time, just be careful how much you take off. All the while, you will have to run accuracy checks to keep the saddle level front to back and left to right. It's a tall order, and one of the most difficult alignments to obtain, but if done with care will be easy to obtain.

                    The entire sequence is shown starting at post #147 in this topic.
                    http://www.practicalmachinist.com/vb...update-146913/
                    Harry

                    this is exactly what I`m trying to do, and is also how I was thinking I should do it... I guess it`s just going to take a while- it`s about 14" along the v way and it is sooo tempting to try to mill off the bulk, but it exceeds the travel of my mill and would take 2 separate set-ups - very easy to mess up, so I`ll stick to scraping it.

                    better get some more hi-spot!

                    thanks!

                    Comment


                    • #11
                      12oorpm:
                      then it dawned on me the headstock is adjustable.
                      that was my incentive to ditch the vari-speed sheave and hook up the direct drive VFD conversion - so i could get it turning straight before i did anything else - it will now turn a 2" aluminum bar to within .0005" over about 10 inches - more than good enough for my needs, now i just have to get it facing flat.
                      Take care when performing the "turn bar over length". It DOES get you the right (repeatable) diameter for that size of bar; however it does not address the possibility that the headstock is tilted high or low at the spindle end.

                      At the end of the day the headstock alignment to ways setup stands alone (must be done by itself) and is the FIRST thing that should be done when aligning lathe. Once the headstock is aligned side-to-side and up-n-down the tailstock can be altered (aligned) to match.

                      Now the above said; I started doing my head in envisaging what would be the result of (change to) the concave/convex cut of the headstock being high or low at the spindle end. My conclusion (and I do stand to be corrected) is that high or low will cause the spindle end to be needed to be twisted INTO the cutting tool in order for the cutting tool to travel across the work cutting at constant diameter. Hence high or low is going to result in greater CONCAVE.

                      12rpm has a CONVEX issue so ... flame me.

                      Cheers,
                      Norman

                      Comment


                      • #12
                        Originally posted by winchman View Post
                        How about removing the jaws from the chuck, and placing a magnetic level horizontally across the center. Put your dial indicator on the cross-slide with the tip against the level as you run the cross-slide back and forth. Rotate the chuck 180 degrees, and repeat. This should tell you if the cross-slide travel is perpendicular to the spindle.
                        Easier is to just put a mark on the chucks face, zero a dial indicator to it, then rotate the chuck around and move the DI with the cross slide on the mark again. It is now showing you the error in perpendicularity, granted that your bearings are not destroyed.
                        Amount of experience is in direct proportion to the value of broken equipment.

                        Comment


                        • #13
                          You do use the saddle lock to lock the saddle to the bed when facing don't you? Not just leave the saddle free relying on friction to stop it moving, or just use the half nuts? I'm not familiar with your particular lathe, but some manufacturers put the saddle lock near the end of the saddle, so if the adjustment of the saddle is a bit slack, applying the saddle lock can cause the saddle to twist slightly on the bed. You can check this by putting the faceplate on, and running a dti across using the crosslide, first with the saddle locked and then with it unlocked. If there is any difference in the readings, then the saddle gibs need adjusting. If you know that the faceplate is flat, then this is also a good check for squareness of the crosslide.

                          Richard
                          'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

                          Comment


                          • #14
                            i have not actually checked a part after facing it - I bought this machine with the understanding that it would need some re-building and other than getting the headstock trued up to the bed by actually turning a piece my checks for the cross slide have been by 2 methods- a parallel held in the chuck in the zero to zero condition, and by a square on pins clamped to the cross slide guiding way - both ways show the same thing.

                            from what I can gather it was a common thing on the early imports.

                            Comment


                            • #15
                              so far i have not seen a chuck, that has a face running really true.

                              "My conclusion (and I do stand to be corrected) is that high or low will cause the spindle end to be needed to be twisted INTO the cutting tool in order for the cutting tool to travel across the work cutting at constant diameter. Hence high or low is going to result in greater CONCAVE."

                              i dont see how a spinde axis not aligned vertically can lead to convex/concave facing. anybody?
                              Last edited by dian; 06-08-2013, 11:15 AM.

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