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Differences - SB 9" versus 16"

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  • Differences - SB 9" versus 16"

    Somebodys gonna call me stupid, but I checked it, and it's true. Now, I am a newbie, but hear me out. Big question is, "why is this so?" When I indicate on the cross or compound dial on my 16" SB a full inch, it only actually moves the cross or compound 0.500. When I indicate on the cross or compound dial on my 9" tool-room, it moves it the true indicated amount. Found it out when I was doing my first single pointing on the 16", a half inch shaft @ 28 TPI. At first, I could not figure out why, when I dialed in a total diameter reduction of .020", it was only taking off 0.010". Hmmm... Then I cranked the cross a full indicated 1.00". Only moved the cross 0.500! Them smart guys back in 1959! I only wish someone had told me! Pretty cool anyway! OK, now "why?"

  • #2
    Southbend 16

    So when you're turning a diameter you can dial in the exact amount you want the diameter reduced without dividing by two. I wish my lathe was like that.
    The other way, you dial the amount you want to reduce the radius. Two radii equal one diameter.

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    • #3
      The lathe that moves the cross slide a full inch USED to be called the American type. The slide that moves half the distance was called the Continental type. It is easier to use,as it eliminates the need to divide the distance you need to move by 1/2. My HLVH is the Continental type.

      My terminology dates from the 1950's,and may have changed.

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      • #4
        Direct reading dials is what I have heard them called. My Monarch has them too. But I dont look at them with a DRO...

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        • #5
          post deleted
          Last edited by J. Randall; 06-30-2010, 01:03 AM.

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          • #6
            Depends on what you consider 'direct reading' to mean. If you see it as meaning that the compound moves the same amount that you dial in, then it doesn't make sense. If you see it as the amount a diameter reduces as you machine it, then it does make sense. If the Americans wanted to see the mechanism move by the amount that the dial indicated, then they'd have to do the mental math each time to recall that a turned diameter would not directly correspond-

            My preference is to see the mechanism move by the indicated amount, because the 'double' diameter reduction is just another fact about using the lathe that the operator should know. What would it be otherwise- let's say if you're facing using the compound adjustment to tweak to the dimension you're looking for- do you have to automatically remember that you're only going in half as much as the dial indicates? That's the other side of the coin.
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #7
              Think yourself lucky.

              My Harrison L5 had been in a school machine shop and at some time an attempt had been made to upgrade it to Metric spec. There were a set of Metric threading gears still in their packing grease and the topslide leadscrew and dial had been changed. However, on the cross-slide just the dial had been changed, probably because the telescopic leadscrew that is used with the taper turning attatchment is very expensive. So I have a 4mm dial on a 0.2" pitch lead screw. It took me a while to figure that one out!
              Paul Compton
              www.morini-mania.co.uk
              http://www.youtube.com/user/EVguru

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              • #8
                Fit a Digital readout !!

                then you can work -
                mm or " ( or both )
                in absolute or incremental steps.
                no worries about wear or backlash (turns a crap machine into a precision Machine. well almost)

                You just take a cut, measure & enter it, then just cut to the size you want.
                Simples.
                john
                John

                I used to be indecisive. Now I'm not so sure , but I'm not a complete idiot - some bits are still missing

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                • #9
                  By-pass

                  Originally posted by jugs
                  Fit a Digital readout !! then you can work mm or " (or both) in absolute or incremental steps. no worries about wear or backlash (turns a crap machine into a precision Machine. well almost)

                  You just take a cut, measure & enter it, then just cut to the size you want.

                  Simples.

                  john
                  Not so sure about that John (Jugs).

                  If the DRO has an accuracy of +/- 0.0002" (plus or minus two-tenths) - as many of the common ones do- on the cross-slide it will have a compound effect.

                  If you "dial in" say 0.002" to take 0.004" off the diameter the cross-slide movement will be 0.002" +/- 0.0002" = 0.0018"/2.0002" which when doubled is 0.004" +/- 0.0004" = 0.0036"/0.0044" (a difference of 0.0008" ie 8 "tenths") off the diameter.

                  There would be few "dialed" measurements that could not beat that even with a badly worn lead-screw.

                  With a DRO like that and tight tolerances, I'd be using a good dial indicator on the tool post for the "last little bit" so as to ensure accuracy and to by-pass both the DRO and the lead-screw.

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                  • #10
                    The glass scales supplied with the 'budget' DROs are mostly 10um resolution, but there's often an option for 5um, which would give you the 10um 'diameter resolution' on the cross-slide of a lathe. Jenix scales go to 1um, but at considerably greater cost.
                    Paul Compton
                    www.morini-mania.co.uk
                    http://www.youtube.com/user/EVguru

                    Comment


                    • #11
                      With a DRO like that and tight tolerances, I'd be using a good dial indicator on the tool post for the "last little bit" so as to ensure accuracy and to by-pass both the DRO and the lead-screw.
                      I made a little setup like that for my SB9a that I enjoy using. The lathe has direct reading dials which I do prefer. The cross slide lead screw even though it is quite worn is still accurate once the backlash is removed.

                      The D.I. rig just makes it easier for me to monitor the actual movement of the tool bit. The D.I. rig is mounted to the backside of the carriage using the existing bolt holes I think may be there for a taper attachment.
                      It can be positioned easily with the slide rails and then locked tight.
                      A pillar with a magnetic base sits atop the cross slide and acts as the reference stop for the D.I.

                      Steve



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                      • #12
                        Originally posted by EVguru
                        The glass scales supplied with the 'budget' DROs are mostly 10um resolution, but there's often an option for 5um, which would give you the 10um 'diameter resolution' on the cross-slide of a lathe. Jenix scales go to 1um, but at considerably greater cost.
                        Hi,
                        All of mine (Sino, Miester) are 5um with 1um being optional. Also the budget glass scale ones on ebay below are also 5um with 1um being optional. I think the only ones that are 10um these days are the caliper type scales.

                        http://cgi.ebay.com.au/DRO-PROS-3-Ax...item439bddb6fc

                        http://cgi.ebay.com.au/NEW-2-axis-EA...item335e68d283

                        Dave

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                        • #13
                          Scale conversion metric>inch

                          For those who use or "know" inch and not metrics.

                          5um = 5 micrometers = 5 millionths of a metre.

                          1um x 40~ 40 micro-inches = 40 millionths of an inch = 0.000040" = "0.4 tenths".

                          5um x 40~ 200 micro-inches = 200 millionths of an inch = 0.000200" = "2 tenths".

                          1um scales are quite often reserved for or used on surface grinder grinding head down-feeds.

                          https://www.machineryhouse.com.au/Pr...tockCode=D7142

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