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  • Why so down on lantern toolposts?

    Why does everyone get so down on lantern toolposts?

    I have been driven to madness by the 4 way toolpost on my 12x48 lathe. I feel I can honestly say, I would rather have a single station, that I could easily adjust on to center, than four stations with all the adjustment finesse of a sledgehammer.

    I have considered swapping out to one of the ubiquitous Aloris type posts, but as always my lathe makes life difficult - the compound isn't t-slotted, but has a threaded in stud on which the original toolpost rotates. People always complain about the lack of rigidity in a lantern style post, and I would agree when you are sticking a great big Armstrong type holder in there to hold your bit, on top of a rocker - the moment arm is huge. But when I look at your typical Aloris type holder, the moment arm seems equally huge; it is just that the toolpost itself is more massive, but the holder itself is not, and is generally supported in tension only by a single screw.

    I was browsing Tony Griffith's lathes.co.uk site the other day when something caught my eye - Looking at the page for the Atlas 6" mark 2 was this toolpost:

    It seems so simple - threaded on the outside; a hex nut on the bottom to pull up the T nut, a knurled nut in the middle with which to set tool center height, and in my view, above the tool should be a washer, and then another hex nut with which to fix the tool.

    Can anyone see obvious fault with a toolpost built to this pattern, of approximately an inch in diameter, designed to hold the half-inch HSS tools I invariably use on this lathe? Holding the toolbits directly in the toolpost, I cannot see how it could be less rigid than an Aloris type holder; the moment arm would be equal, if not smaller. And it would be far more manouvreable than the equivalent Aloris.

  • #2
    Where does the force come from to clamp the Tee slot?

    --Doozer
    DZER

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    • #3
      Originally posted by Doozer View Post
      Where does the force come from to clamp the Tee slot?

      --Doozer

      Looks like the force comes from the screw inna middle pushing down on the toolbit, etc. At least that's how my lantern toolpost works...
      Design to 0.0001", measure to 1/32", cut with an axe, grind to fit

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      • #4
        Looks good; only issue I see is sharpening the tool bit. Changes the height a little, which is where the rocker comes in handy. I t looks like you would have to change washer thickness, which makes it every bit as fiddly as anything else.
        I'm here hoping to advancify my smartitude.

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        • #5
          Originally posted by Doozer View Post
          Where does the force come from to clamp the Tee slot?

          --Doozer
          I believe the T-nut is machined integral to the top (threaded) section of the toolpost. You can see on the very bottom of the threaded section of the post, there is a hex nut - I believe this nut would be threaded down against the top of the compound, which would force the toolpost writ large upwards, and the T-nut would then pinch the T-slot between the top surface of the 'T-nut' and the bottom of the hex nut.

          At least, that is how I planned to implement it.

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          • #6
            Originally posted by gizmo2 View Post
            Looks good; only issue I see is sharpening the tool bit. Changes the height a little, which is where the rocker comes in handy. I t looks like you would have to change washer thickness, which makes it every bit as fiddly as anything else.
            Ah but thats the beauty of the design - you aren't using a washer to set center height, you are using a knurled nut on the outside of the toolpost, so the center height is nearly infinitely finely adjustable. To adjust center height you only have to loosen the tool clamp, finger-adjust the nut to be on height, then re-tighten the clamp.

            You can also adjust the toolpost angle without changing center height - just loosen the bottom hex nut, rotate to position, and retighten.

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            • #7
              The design looks similair to the fantastically designed unimat tool post. The post isn't threaded, there's a sleeve going over the post and its threaded (with a cut out for the tool bit). Nut goes on that sleeve. This lets you adjust the height and the tightening the screw from above clamps everything.....I've often thought of making a larger one.

              QCTP are good but their bulky designs often get in the way of the tailstock so a post like this could be very useful
              in Toronto Ontario - where are you?

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              • #8
                Originally posted by Mcgyver View Post
                The design looks similair to the fantastically designed unimat tool post. The post isn't threaded, there's a sleeve going over the post and its threaded (with a cut out for the tool bit). Nut goes on that sleeve. This lets you adjust the height and the tightening the screw from above clamps everything.....I've often thought of making a larger one.

                QCTP are good but their bulky designs often get in the way of the tailstock so a post like this could be very useful
                Got any pics of the unimat post? I'm always keen for inspiration. Had a google, but no luck.

                Clearance is probably my biggest reason for wanting this; was doing a big turning job on the weekend and the 4-way post was seriously fouling the live center. Very irritating.

                What was even more irritating, was realising after turning off a lot of diameter at high SFM, low DOC with carbide tooling, I had specifically ground a knife type HSS tool for situations like this just a few weeks before, that would have done the job in a fraction of the time. I swear, those things eat diameter for lunch.

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                • #9
                  I'll take some today. I hear on the interference.....you end up havnig the tool sticking out to compensate (that sounded wrong!) or the tails stock barrel extended further....all of which increases overhang and is a good practice to avoid.
                  in Toronto Ontario - where are you?

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                  • #10
                    Originally posted by Sun God View Post
                    People always complain about the lack of rigidity in a lantern style post, and I would agree when you are sticking a great big Armstrong type holder in there to hold your bit, on top of a rocker - the moment arm is huge. But when I look at your typical Aloris type holder, the moment arm seems equally huge; it is just that the toolpost itself is more massive, but the holder itself is not, and is generally supported in tension only by a single screw.
                    I would agree that the lantern post is a quick and handy way to attach a cutting tool to a lathe, and one of the reasons is that Armstrong type toolholder that generates those major moment arms. They allow access to some confined places that would be difficult with other means. However, possible feed rates and DOC will be limited when compared with other types of toolposts. This may not be as great an issue for the average HSM, but we all seem to like taking one pass instead of 2 or 3.

                    The moment arm is essentially identical for either tool post. The difference being, a toolholder/bit held in the quick change or even the 4 way post has a much better chance of staying put while being subjected to this moment arm. As far as that goes, the above mentioned posts will probably cause greater forces as they will allow the use of heavier feeds and greater DOC.

                    One of the major culprits contributing to the instability of the standard lantern post is the rocker wedge that is used under the tool bit/Armstrong holder. One solution I have seen to this problem is to replace the wedge ring with a ring that has a series of flat steps of different heights milled into it for the Armstrong holder to rest on. Multiple rings can be made to increase the range of height adjustment.

                    Dave
                    Last edited by becksmachine; 03-21-2013, 10:28 AM.

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                    • #11
                      I've been using a "threaded sleeve" design as described by Mcgyver for the last few years. Somebody posted this idea on "the other" site, and I made a copy for myself. Here's a pic of mine in use.



                      I like it much better than the half-moon key and washer that it replaced!

                      Jim

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                      • #12
                        The only real advantage of the lantern style tool post is its ability to get in tight places. Otherwise it is a pain. Hard to adjust center and maintain cutting tool alignment (think threading tool), much much less holding power. If you're running a short run of even just two parts you're spending a lot of time just setting up the cutting tools. With the drop in style holders you can set the tools and just swap out the holder. The last time I used a lantern style TP was on the USS Coral Sea back in 1975 or so and I do not miss them. My Logan came with one and its just sitting on a shelf and will probably stay there until my estate sale.

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                        • #13
                          To the responses critical of the lantern tool - this isn't you're gramma's lantern tool post . I just notice Jim's is a large version similair to what I've posted below. He had enough room he didn't have to cut out a section of the threaded sleeve like below.

                          This style is worlds better than the tradition lantern and williams/armstrong tool holder. imo it goes a long way toward removing most of the faults ot the lantern style. The moment and overhang are minimize, it creates a solid base, and is easily adjusted without frustrations of the old style. Making a larger version would be a nice additional bit of kit for when the big QCTP holder is in the way.

                          In the follow pics the black parts are from a Unimat DB. The silver I made because I adopted to a Unimat 3. Lots of pics so you can see how it works and replicate. That one on Tony's site has way to coarse a thread imo. Fine would be both stronger, give a finer adjustment and make tightening easier





                          Last edited by Mcgyver; 03-21-2013, 07:56 PM.
                          in Toronto Ontario - where are you?

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                          • #14






                            in Toronto Ontario - where are you?

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                            • #15
                              Originally posted by Mcgyver View Post
                              This is a very nicely made toolpost, but I have personally avoided using any toolholder with only a round button in the topslide t-slot for fear that a catch would break out the slot. I try to use only large T-nuts or bolts in the slide to provide the most strength possible.
                              The way around it in a lantern like this is to use a T-shaped washer at the bottom and a short bolt up into the lantern post that has a thinned head.
                              Last edited by Gary Paine; 03-21-2013, 10:06 PM.

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