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  • #16
    I found a manual for this lathe on-line, and it is described as a 12" lathe. I just wanted to see what it looked like to get possible clues on the problem. It shows a lantern type toolpost, and the compound is turned CCW about 30 degrees which would be a good position for turning close to the chuck as well as threading. If the compound is turned clockwise, I can see a mechanism where the toolbit might take off more material when traversing the tool toward the tailstock - if the compound twists CCW it will tend to push the cutting edge into the work. However, I will assume that it is set up as would be normal, and this would not apply.

    As others have noted, a light cut on return toward the tailstock is normal, and is called a "spring cut". If you perform this operation again, you should not see any more metal removed.

    I have friends and relatives in the Frederick area, Walkersville, Woodboro, Hagerstown, and Waynesboro, PA, and Gettysburg. I get out that way sometimes, so I could stop by to see your shop and maybe swap some ideas, experience, tools or materials. Also, you are not far from Lebanon, PA, where Cabin Fever will be happening again in mid-January. It's a really great show with lots of model engines and other machining marvels, as well as consignment shops, auctions, and tool vendors. Maybe I'll see you there.
    http://pauleschoen.com/pix/PM08_P76_P54.png
    Paul , P S Technology, Inc. and MrTibbs
    USA Maryland 21030

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    • #17
      Originally posted by Toolguy View Post
      Tool deflection. Just about every home shop lathe will do that. A lot of bigger ones too. The part pushes the cutting tool away when it makes the first cut, then there is less pressure on the tool and less deflection, so it cuts more on the second pass.
      +1.
      Wot he said.

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      • #18
        All the above posts are correct about tool or work deflection, insert or tool sharpness etc.

        There could be some play in the saddle meaning it rocks slightly when you change direction.

        One direction the pinion gear is pushing, the other way it's pulling.

        Try indicating the saddle wings with a dial. Push down on each wing and check for dial movement.

        JL..

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        • #19
          Originally posted by 754 View Post
          Generally for most work, if you don't want to leave a mark back the tool off.
          So it helps to know your last setting number on the dial.
          If you are not worried about appearance, just run the carriage away from chuch, as quick as you can.

          The next thing you need to know, is if you set your lathe to cut 20 thou, it won't always be 20 thou
          Yes its a machine, but, big but... the machine does little by itself, You have to do the setting.
          .
          Good point and here's an addition. I have two lathes, a 10 inch in the garage where it is too cold to work in winter and a mini lathe in my heated basement. The 10 inch lathe removes .010" when the dial is turned to that setting, reducing the stock by .020. The mini lathe removes .005" when the dial is turned to .010, reducing the stock by .010". When the weather changes rapidly I might use one today and the other tomorrow. Do I ever get confused and make a wrong cut?

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          • #20
            Originally posted by RMinMN View Post
            Good point and here's an addition. I have two lathes, a 10 inch in the garage where it is too cold to work in winter and a mini lathe in my heated basement. The 10 inch lathe removes .010" when the dial is turned to that setting, reducing the stock by .020. The mini lathe removes .005" when the dial is turned to .010, reducing the stock by .010". When the weather changes rapidly I might use one today and the other tomorrow. Do I ever get confused and make a wrong cut?
            Paint a big R on one and a D on the other. :-)
            ...lew....

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            • #21
              Problem with Lathe

              Originally posted by BCRider View Post
              Dipstick, are you running with carbide insert tooling or HSS? And did you sharpen the HSS if that is what you have?

              I've found that when newly sharpened and provided I don't use a feed rate that bunches up on the metal coming off the workpiece that I don't see that same "track" being cut on the return. I use mostly HSS though.

              Some carbide inserts are supplied deliberately dull to some degree to reduce erosion during heavy cuts. And if that is what you use it too can result in some work piece deflection.
              I am using a tool that I ground myself from a piece of 3/8 HSS tool steel. The shape is a 3/16 radius and probably not truly round since I ground it by hand. Am using the slowest power feed rate available (can't remember what that is). The tool is held in one of those square indexable holders that can hold four cutting tools mounted on the compound slide.

              After reading all of the much appreciated comments, I think the problem is spring back. The shape of the tool is going to push the work piece away while I am making the cut but when I move back toward the tail stock there is no longer any force perpendicular to the work piece and it therefore springs back against the cutting tool. A proper tool for a left hand cut would probably minimize this effect.

              I don't use the lathe continuously and also suffer from CRS (can't remember stuff) so I don't know when I first noticed this issue. It may all have been the result of using this tool.

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              • #22
                Most craftsman are flat bed
                It may just be lose or some play with head stock or bed was reground and no shims add for grinding

                The best flat bed simple to grind the bed and keep going

                Dave

                Originally posted by Dipstick View Post
                I have a Craftsman 13" lathe (101.28950 SN 002192). I make a light cut toward the headstock on a short piece of round stock which is centered in the four jaw chuck and supported with a dead center in the tail stock. If I return the cutting tool to the tailstock end of the work piece without backing out the crossfeed, I get additional material removed from the workpiece. It is not much material (< 0.001 ???) but I don't understand why there should be any contact between the cutting tool and the workpiece.

                Can someone tell me what could most likely be the cause of this issue. I can't feel or measure any slop in the saddle and have tightened up the gibs a little with no improvement. There is a lot of backlash in the crossfeed but I don't see how that could cause this problem. Tried returning with the hand wheel and with the power feed and got the same problem both ways.

                Thanks,
                Mark

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                • #23
                  Originally posted by RMinMN View Post
                  Good point and here's an addition. I have two lathes, a 10 inch in the garage where it is too cold to work in winter and a mini lathe in my heated basement. The 10 inch lathe removes .010" when the dial is turned to that setting, reducing the stock by .020. The mini lathe removes .005" when the dial is turned to .010, reducing the stock by .010". When the weather changes rapidly I might use one today and the other tomorrow. Do I ever get confused and make a wrong cut?
                  Well there is that too, but what I meant was say you just took 100 thou off. Now you got 20 to go, so you cut 10 and want to do 2 passes....but surprise it does not cut 10.. that sort of thing.. and worse if you decide to change feed at that tine to get a better finish.

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                  • #24
                    If your cut allows it (and most do), you can back off your cut depth and return the tool to the end of the work. Then advance it the distance you need for the next pass. It wouldn't hurt to back off the same distance each time, say .020", and that way you've got a second memory aid as to what the original position was.

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                    • #25
                      For machines that have spring-back issues that cause trouble, you can use a grind that has a straight radial cutting edge and very small nose radius. That puts virtually all of the force in the axial direction, which usually helps.

                      If the carriage is twisting, you still need to correct that, however, since the axial force is generally off-center vs the carriage.
                      CNC machines only go through the motions.

                      Ideas expressed may be mine, or from anyone else in the universe.
                      Not responsible for clerical errors. Or those made by lay people either.
                      Number formats and units may be chosen at random depending on what day it is.
                      I reserve the right to use a number system with any integer base without prior notice.
                      Generalizations are understood to be "often" true, but not true in every case.

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                      • #26
                        Not only sharpness but also tool grind style has a lot of effect how big the deflection is.
                        Easy also to end up with "hogging" tool geometry where force vectors are such that toolpost and workpiece are bending towards each other.
                        Large DOC, large back&side rake angle and soft material.
                        Usually chatter-prone at least on my lathe but you get zero spring-cut as the cutter is cutting air with 0.001" gap on a spring pass..

                        edit: J Tiers got before me about more or less the same idea..
                        Location: Helsinki, Finland, Europe

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