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Advantage of a Lantern Toolpost?

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  • Advantage of a Lantern Toolpost?

    The Atlas Manual of Lathe Operation is adamant that the tool should be set at such an angle so that it cannot swing into the work under heavy cuts. With the slender lantern toolpost the tool is in line with the toolpost pivot and this is easy to do as illustrated in the Atlas Manual pages shown below, but how do you follow these guidelines with a QC toolpost. With a QC toolpost if you have the tool at rightangles (or angled slightly back) from the workpiece it is still offset to the left of the pivot point and can still swing into the work. If the tool is suitably ground to be set at an angle such that the point of contact with the work is in line with the toolpost pivot then the corner of the toolpost is angled too close in to the the chuck and headstock.

    Am I missing something?

    "Patriotism is the last refuge of a scoundrel"

  • #2
    I move my tool holder about almost as frequently as I change tools (dickson) so don't really get the issue....never would occur to me not to as I'm not in production and don't need repeatability. I've a Drehblitz for the small lathe and it takes things to the next level - its indexable. lets you move about with repeatability...lost on me as repeatability just doesn't matter (Drehblitz is superior to the swiss Multifix imo as its not too hard to make holders for it....you don't want to have to go buy 30 holders for either!)

    The lantern tool post is superior in many ways - very nimble. Quick to set and doesn't get in the way of the tail stock barrel or centre. If all I was using was turning and facing tools I'd tempted to go back to it....its all the other tools that make a QCTP worthwhile: threading, boring, parting, knurling....these a first class pita on a lantern style
    in Toronto Ontario - where are you?

    Comment


    • #3
      The other side of that argument is that a QC holder is a lot more rigid than a lantern style. Just look at them: the QC holder has a simpler design with fewer places where it can rotate or flex. The lantern style is a study in flexibility.

      When I designed my own QC holder, I took rigidity to another extreme. It has a bare minimum of parts and in use it acts much like a single, solid hunk of metal. The changeable holder can NOT pivot on the post and I have never seen the post rotate on the compound. The two are tightly connected with a 360 degree contact/clamping area, unlike the commercial dovetail designs which only have two narrow areas of contact. The worst case for flexing is the tool bit itself as it must stick out of the holder by a certain amount. I generally work with the tool bit perpendicular to the work axis so if it flexes it will rotate away and not dig in.

      My rock solid holder:







      In short, such a QC holder is a lot better than any lantern holder. And it saves time even if you don't need the repeatability. I can change tools in a few seconds using only ONE HAND and NO TOOLS. I never have to search for that ##*!#* wrench. The tool is instantly at the correct height and angle with no adjustments needed. Just change and cut. But it does have very good repeatability to boot.

      I do have a lantern style holder but it is only used on very rare occasions.
      Paul A.
      SE Texas

      And if you look REAL close at an analog signal,
      You will find that it has discrete steps.

      Comment


      • #4
        Thanks for the post and those pics Paul A. but I have two questions.

        When you say "I generally work with the tool bit perpendicular to the work axis so if it flexes it will rotate away and not dig in." - the tool although at rightangles to the work is still situated to the LEFT of the toolpost pivot and any flex will rotate the tool INTO the work as I see it.

        Secondly with all this talk about rigidity is there any point in using a run of the mill QC toolpost on an 10" or 12" Atlas for straight turning considering the above issues - won't the lantern be better?
        "Patriotism is the last refuge of a scoundrel"

        Comment


        • #5
          Paul Alciatore that is one beautiful, simple and functional QCTP. I hope you post an article on making it in HSM someday.

          John

          Comment


          • #6
            If you get your toolpost to actually swing under cutting forces, then it is just too small for your machines power. I'm using daily 10 kW lathe and haven't had the toolpost (4-position QC) rotate even once, even though the alignment pin is missing and only one bolt holding it down.

            I do have gotten the lathe to stall and/or the tool to dig in (the whole compound twists to the left and thus in to the work, as the tool & its height from the bed will act as a lever), but rotating QC? Not once.
            Amount of experience is in direct proportion to the value of broken equipment.

            Comment


            • #7
              I think the advice in the Atlas manual just addresses (and underscores) one of the weaknesses inherent in lantern tool holders.

              Just look at the surface area clamping to the compound visa-vee the QC tool post and a lantern tool post, also the mass of each. The lantern has a ring, a rocker, an HSS piece of tooling, and a small bolt; add all those movable components together and the whole is more flexible than the sum of the parts.

              After I got my QC tool holder, I never looked back.
              Gary


              Appearance is Everything...

              Comment


              • #8
                Advantages of the lantern style toolpost?

                None...
                Keith
                __________________________
                Just one project too many--that's what finally got him...

                Comment


                • #9
                  Many have the misconception that a QCTP is always more rigid than a lantern, when in fact it depends upon the toolposts and holders youre comparing themselves. When comparing a similar diameter lantern to a QCTP with a post of similar diameter, I would in fact say that the lantern is very likely to be more rigid. Having a big block of QC steel is not important, its the stickout (distance) of the toolbit from the post that affects the strength of the post, not the total surface area of the base bottom (similarly, flange width on an I beam isnt necessarily important, but the web size is very much so). Also of important consideration are the parts of the post at or above toolbit level - joints that can flex, which a QCTP has several more of.

                  I have a small collection of lantern tool posts from tiny up to those accepting a 1" bit, as well as AXA and BXA mixture of Aloris and Dorian. I used to use the QCTPs pretty exclusively until I worked in a prototype shop. Now, the most frequently used tool posts for me are the lanterns, as they are the most versatile, and ~30% of the turning I have done would not be possible with a QCTP. Speed wise, I can change a toolbit out of a lantern just as quick as a QCTP, not that time is of much consequence in a hobby shop anyway. If I had to have only one, it would be a lantern hands down.

                  As to the original point, it is a simple safety consideration to never have a tool bit that will dig into the work should it flex or rotate, and this is an important consideration for either style of tool post. This is the reason why we have right and left handed turning tools, to prevent the tool bit from becoming a bullet lodged in your chest as has happened to others in the past. A lathe is rather forgiving in many of these situations, but a shaper is not and will snap a bit like a pretzel given the opportunity.
                  Last edited by justanengineer; 06-06-2012, 03:19 PM.
                  "I am, and ever will be, a white-socks, pocket-protector, nerdy engineer -- born under the second law of thermodynamics, steeped in the steam tables, in love with free-body diagrams, transformed by Laplace, and propelled by compressible flow."

                  Comment


                  • #10
                    Originally posted by jhmiii
                    Paul Alciatore that is one beautiful, simple and functional QCTP. I hope you post an article on making it in HSM someday.

                    John
                    Check out the Feb/Mar 2010 issue of Machinist's Workshop. Paul has written several articles for both HSM and MW, this being one of them.

                    George
                    George
                    Traverse City, MI

                    Comment


                    • #11
                      Originally posted by justanengineer
                      Many have the misconception that a QCTP is always more rigid than a lantern, when in fact it depends upon the toolposts and holders youre comparing themselves. .
                      yup, all these people who don't think the lantern is solid .... i wonder how much time they've spent with them?

                      when set up properly, you've got a large forged bar almost directly taking the load to the compound. No cantilevered action off to the side like QCTP

                      to repeat, there is a very clear advantage in how little room they take up when machining close to the tailstock and rotating centre.

                      I too have joined the flashlight crowd because lanterns are a pita for lots of tooling types and I wouldn't go back....but they're being trashed here for the wrong reason.
                      Last edited by Mcgyver; 06-06-2012, 03:46 PM.
                      in Toronto Ontario - where are you?

                      Comment


                      • #12
                        Originally posted by Paul Alciatore
                        The other side of that argument is that a QC holder is a lot more rigid than a lantern style. Just look at them: the QC holder has a simpler design with fewer places where it can rotate or flex. The lantern style is a study in flexibility.

                        When I designed my own QC holder, I took rigidity to another extreme. It has a bare minimum of parts and in use it acts much like a single, solid hunk of metal. The changeable holder can NOT pivot on the post and I have never seen the post rotate on the compound. The two are tightly connected with a 360 degree contact/clamping area, unlike the commercial dovetail designs which only have two narrow areas of contact. The worst case for flexing is the tool bit itself as it must stick out of the holder by a certain amount. I generally work with the tool bit perpendicular to the work axis so if it flexes it will rotate away and not dig in.

                        My rock solid holder:







                        In short, such a QC holder is a lot better than any lantern holder. And it saves time even if you don't need the repeatability. I can change tools in a few seconds using only ONE HAND and NO TOOLS. I never have to search for that ##*!#* wrench. The tool is instantly at the correct height and angle with no adjustments needed. Just change and cut. But it does have very good repeatability to boot.

                        I do have a lantern style holder but it is only used on very rare occasions.




                        I don't readily see how you adjust tool height..

                        Comment


                        • #13
                          I wouldn't be without a lantern in my kit, even though I too use qctp tooling frequently. The biggest issue, I think, behind the Atlas manual's instruction is that often the tool or tool holder used in the lantern is narrower than the slot through the lantern. If that is the case, only the small contact area under the clamp screw provides the frictional resistance to the tool rotating within the rigid and unmoving toolpost until it hits the edge of the slot in the lantern. This doesn't take a lot of force and can move the tip quite a bit. In the past, I always tried to bias the tool such that it contacted the edge in the direction resisting the force, but more recently, I took the time to machine a simple U shaped yoke that was carefully fitted to both the width of the slot and the 3/8 inch cutter. The resulting rigidity was excellent.

                          Comment


                          • #14
                            Originally posted by George Bulliss
                            Check out the Feb/Mar 2010 issue of Machinist's Workshop. Paul has written several articles for both HSM and MW, this being one of them.

                            George
                            Thanks George, I have moved and still have stuff in boxes. I couldn't remember the issue.
                            Paul A.
                            SE Texas

                            And if you look REAL close at an analog signal,
                            You will find that it has discrete steps.

                            Comment


                            • #15
                              I spent about 10 years using nothing but a lantern tool post before I purchased an Import QC tool post. My experience is that the QC is far more rigid than the lantern, particularly for operations like parting and knurling. When I did those operations with the lantern I replaced the rocker assembly with a solid ring and improved rigidity tremendously. Even so it wasn't as rigid as the QC post. I guess this means I respectfully disagree with McGyver with regard to his remarks about the cantilevered offset issues. The base of the QC post is much wider and thicker than the concave ring of the lantern post and I believe this offsets the negatives of the cantilever. I still have the lantern tool post for those times I need to get closer to the chuck and can't grind a tool for the QC post. 99% of the time the QC post is being used with the tangential tool holder installed in it.

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