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Precisely moving the carriage

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  • Precisely moving the carriage

    My lathe carriage moves .010"/division which is fairly coarse.
    I sometimes put a dial indicator in my carriage stop in order to face to a final dimension and have a hard time getting it set where I want it.

    I found , quite by accident, that if I have the lathe motor running, the vibration allows me to set the dial indicator with ease. I bet if I had a tenth reading one I could split a tenth.

    Just posting this in case any of you with Chinese lathes haven't stumbled across it.

    I can face to 1/2 a thou without trying very hard.
    Mike

    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

  • #2
    Lock your carriage down and use the compound set parallel to the ways and use the compound to take fine cuts. I forget what the angle is to get .0005" per .001" feed in with the compound but someone will speak up without me going to the shop to look it up.

    Using a dial indicator or a carriage stop may not be as accurate as using the compound.
    It's only ink and paper

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    • #3
      Originally posted by Carld
      Lock your carriage down and use the compound set parallel to the ways and use the compound to take fine cuts. I forget what the angle is to get .0005" per .001" feed in with the compound but someone will speak up without me going to the shop to look it up.
      60 degrees from parallel with the axis of the lathe, AKA 30 degrees from square. It uses the sine function so the short leg is one-half of the hypotenuse.

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      • #4
        Use way oil over your entire carriage drive train and ways, it will really help for small movements.
        Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

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        • #5
          Actually, how often do you need to face with that kind of accuracy? I can see sneaking up on a diameter to get a certain fit, but find an indicator works very well for most facing operations.Bob.

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          • #6
            Facing accurately

            Most of the time I prefer the lock the carriage and move the compound technique.
            Sometimes a micrometer stop works better.


            It is not allways facing. Reaming a chamber, drilling or boring a hole to depth all require accurate movement of the carriage or tool.
            Last edited by Boucher; 04-12-2012, 10:49 PM.
            Byron Boucher
            Burnet, TX

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            • #7
              Micrometer stop works very well. The longer the screw, the better.

              You can make a pretty nice one by threading to 20 TPI, and putting 50 div on the dial.

              The one in the pic says 0.01 inch per division..... seems very coarse. Is that numbered divisions or the smallest?
              1601

              Keep eye on ball.
              Hashim Khan

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              • #8
                You've described
                1. an "indicator stop" where a dial indicator is used to register motion of a machine element like a lathe carriage having no micrometer dial; and

                2. "dithering" where an imposed mechanical vibration is used to settle a tensed mechanisim (like a dial indicator) to a least energy state.

                When an extended indicator set up is unavoidable a wiley machinist will gently tap (dither) the set-up with a pencil or a scribe. Even the best indicators exhibit some hysteresis whereby the internal spring exerts slighly less force as the stem extends than when it retracts. In a limber set up the elasticity of the system will store this half gram of force as several thousandths of deflection.

                Back in the day when I worked turbine driven forced draft blowers on a 5 ft vertical boring mill indicator set-up were unavoidably extended sometimes for four feet. Even purpose built tubular indicator tooling posed problems because it had to be made slender so we could see around it. The standard trick was to jog the traverse motor. The pulse of vibration made the indicator needle disappear in a blur but as the traverse motor coasted down it settled to a reading we could have confidence in.

                MotorMike: yours was a keen observation well described.
                Last edited by Forrest Addy; 04-13-2012, 12:13 AM.

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                • #9
                  FWIW

                  Setting the compound at 5.7 degrees (6 degrees is close enough) (from the horizontal) results in a movement toward the part of 0.0001" when using the compound only.

                  Jim B.
                  Jim B

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                  • #10
                    Thanks for the input guys.
                    If I need more accuracy I'll try some of your suggestions but the parts I'm making now need to be +/-.002" and I don't think I'm spending extra time getting them within .001".
                    Mike

                    My Dad always said, "If you want people to do things for you on the farm, you have to buy a machine they can sit on that does most of the work."

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                    • #11
                      Originally posted by J Tiers
                      Micrometer stop works very well. The longer the screw, the better.

                      You can make a pretty nice one by threading to 20 TPI, and putting 50 div on the dial.

                      The one in the pic says 0.01 inch per division..... seems very coarse. Is that numbered divisions or the smallest?
                      That would be the numbered divisions so the lines are 0.001

                      This makes for farily easy fine adjustment.
                      Byron Boucher
                      Burnet, TX

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                      • #12
                        Gauge trays...

                        For *precise* control of length (up to 18", anyway)...

                        My lathe has an 18" long gauge tray in the front way cover, with a 0.001" 1/2"-range micrometer dead-stop built into the carriage end of it - a heftyish (5/8") rod clamps up in the tool-tray in front of the headstock, so it can work to tenths (or better? How accurate are affordable gauge blocks?) on length if necessary - hasn't been necessary yet! It's a pretty damn rigid setup, so it can also be used to trip the carriage feed... Handy

                        The cross-slide has provision for micrometer dead-stops (T-slot and fixed block) and gauge blocks too, excellent for threading or repetitive work (once I've made the stops...) and these can trip the crossfeed too...

                        I really *must* buy some gauge blocks! Anyone know a source of inexpensive sets in the UK? Other than Ebay, that is...

                        Dave H. (the other one)
                        Rules are for the obedience of fools, and the guidance of wise men.

                        Holbrook Model C Number 13 lathe, Testa 2U universal mill, bikes and tools

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                        • #13
                          For my lathe I added a piece of threaded rod attached to the carriage at the right, and extending parallel to the bed. Then I made a forked contraption that clamps to the front way. The threaded rod passes through holes in the fork. Between the forks there's a disc with a nut pressed into it. When you turn the disc, the rod is pushed or pulled, moving the carriage along with it.

                          The rod is 10 tpi, so one full revolution of the disc moves the rod .1 inch. The disc is marked out for 100 divisions, and there's a reference spot marked out as well. When you turn the disc 1 division, the carriage moves by 1 thou.

                          The forked clamp can be loosened so it can slide along the front way when you're moving the carriage via the handwheel or under power. It's made in such a way that it doesn't interfere with the leadscrew or the tailstock.

                          My use for it is mostly for facing. If I'm facing a part to thickness, I'll take a cut, measure the thickness of the part, then determine how much remains to be removed. It's then a simple matter of turning the dial to drive the carriage the right amount.

                          The threaded rod is long enough to give a range of about 3 inches. For maximum range, I could have moved the tailstock all the way to the right, then moved the carriage all the way it can go, then made this rod long enough to extend to the rightmost end of the bed. This might have given me another two inches of range, but it's not needed.

                          It's a simple device, but it should be made well to give a smooth and tight action. Also, I would recommend to anyone building something like this to use a section of real leadscrew, or cut your own threads to make your own leadscrew. I took pains to select a section of threaded rod that was accurate as far as the threads go, and perfectly straight. It was not easy to find that, and I also spend considerable time cleaning up and polishing the threads so they could work relatively smoothly. I also had to shrink the nut to lessen the play. Best would have been to turn my own leadscrew and nut to work as a pair.
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            Originally posted by Hopefuldave

                            I really *must* buy some gauge blocks! Anyone know a source of inexpensive sets in the UK? Other than Ebay, that is...

                            Dave H. (the other one)
                            Hi Dave,

                            I'm Not sure how inexpensive you're after?, J&L (MSC) have some on offer, in their Advantage offers check out page 33.

                            Cheers
                            Brian

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                            • #15
                              Go to e-bay bid on a Trav A Dial. Mount to lathe and be done with it.
                              http://www.ebay.com/sch/i.html?_nkw=...:MEFSRCHX:SRCH
                              Every Mans Work Is A Portrait of Him Self
                              http://sites.google.com/site/machinistsite/TWO-BUDDIES
                              http://s178.photobucket.com/user/lan...?sort=3&page=1

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