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    Default Lathe, mysterious taper

    Acquaintance bought an older logan in apparently decent shape, no visible wear, turns a fairly significant taper.

    Like .015 in 6 inches.

    Head isn't kicked, not wildly out of level.

    Chuck and collet same


    Just trying to think of something I am overlooking.

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    Old Logan's have the head casting aligned via one of the V-ways, so it would take a serious hit to throw it off IMO. Is the bed level?

    Logan's have thin bed castings. They do well for their class of machine but IMO they are one of the best examples for doing a 2 collar test.

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    Can we assume chuck mounted only and not tailstock supported?

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    Quote Originally Posted by gustafson View Post
    Acquaintance bought an older logan in apparently decent shape, no visible wear, turns a fairly significant taper.

    Like .015 in 6 inches.

    Head isn't kicked, not wildly out of level.

    Chuck and collet same


    Just trying to think of something I am overlooking.
    "Not enough information."

    Six inches, diameter and alloy not stated, centre support ELSE NOT, unstated?

    Might not be the lathe's fault? Collet's on a Logan are not so large as to accept material stiff at six inches out.

    Look for spaghetti-noodle material deflected by tool-tip rather than being cleanly cut.

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    Thing is its th'uther way round, small at the far end.

    C'mon, Im not trying to take a test cut hundred thou in 316

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    Quote Originally Posted by M.B. Naegle View Post
    Old Logan's have the head casting aligned via one of the V-ways, so it would take a serious hit to throw it off IMO. Is the bed level?

    Logan's have thin bed castings. They do well for their class of machine but IMO they are one of the best examples for doing a 2 collar test.
    Figured that, it could be bed level,but I haven't seen that much from simply level personally

    I mean, my first lathe was a 6 inch atlas on a wooden bench and it didn't give me that hard of a time.

    But I went straight to Monarch and they don't move much

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    Small at the far end means the tailstock end is wiggling, no?

    1. Maybe try thicker diameter stock just to rule out stiffness of the material as the problem.
    2. Maybe headstock bearings are loose, and the angular slop is magnified the farther out you go.
    3. 6" from the headstock is definitely far enough out that if the bed is badly worn near the chuck, the carriage will start to ride up on the less worn area of the ways.
    4. Ways could very well be twisted and the bed is light-enough that without bolting the feet down you may not be taking out all the twist. Maybe level it but give it some time to settle.

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    The adjustable hold-downs under the logan carriage aren't great. Particularly in the front (where it's really only the carriage lock that keeps the front down).

    Is it possible your friend is getting a chip under the carriage as he traverses towards the tailstock and it's lifting the carriage?

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    I have a Logan 10" (photos here for the curious).

    I would quick check the bed to make sure it's not twisted. That's possible if this is one of the models with a countershaft assembly behind and to the left of the headstock, and the weight of that wasn't or isn't properly supported with the "fifth leg" post or ledge. You can see that on the photos in the link above, the weight is taken up by a small "ledge" on the wall behind the lathe. (I think that direction of twist would make the test bar fat at the tailstock end.) Easy to check for level with a machinists level in between the ground flat tips of the two V ways. Or put it onto the carriage and run that back and forth.

    If the bed is not twisted, then I would take off the headstock. This is easy, it's just clamped onto the flat and V way with one bolt accessible at the left (headstock) end of the lathe and the other accessible under the chuck area. 10 minutes of fussy work with a ring wrench or ratchet ring wrench. Hopefully the headstock was removed at some point to move the lathe and not put back correctly so you'll find a chip there or some other obvious thing that's easy to fix.

    Last thought, there is an active Logan Lathe group here:
    [email protected] | Home
    which is moderated by Scott Logan, whose grandfather started the company. Scott still provides parts and manuals for these lathes and owns and uses three of them himself. He and others on that group can probably provide other ideas, if this isn't something obvious.

    PS: the compound on these lathes is a weak spot. It might be rocking. Make sure it's locked against rotation and tighten the gib screws for your test bar cuts. Also make sure that the cross slide lead-screw nut is not flopping around. It's held on with the flat head screw visible just behind the compound rotation circle on the cross slide. Just tighten that screw.

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    Quote Originally Posted by gustafson View Post
    Thing is its th'uther way round, small at the far end.
    I did say "not enough information?"

    OK, NOW you tell us...



    So.... is a TS centre being used for support at all?

    And if so, whyinthehell has it not been CHECKED for wear or OFFSET, intentional or not so much.

    Setting the TS centre toward the operator (small-end generated TS-ward) or away from the operator (large end generated TS-ward) IS how long tapers are intentionally generated, "time-immemorial, onward", after all.

    IF NOT supported, and small-end is TS-ward, then the "usual suspects" have been covered arredy.

    "Inspect and report back". Getting close. Someone will final-sort it.

    Light lathes, but not BAD at it, the Logans. Should be able to hit half a thou, that run-length, coupla spring passes "as new" condition, with no special effort.

    "Worn", OTOH, is whatever it is...

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    Just a little disclosure on my part: I hope nobody thinks that when they are leveling a bed they are seriously torq-ing it into an abnormal position. Ideally, you are just trying to re-establish how the lathe sat when it was plained and ground/scraped at the factory. Once it has some mileage on it, you can further "pick-up" the front right corner to compensate and get it cutting closer to true, but even then you're not pushing it that far away from "normal." I agree that you may need to adjust it up on 3 legs and let it settle for a day or two so it can relax back to normal. If it sat for an extended period OUT of level, it might not spring back to being factory true right away. An example would be a Taiwan engine lathe of ours that was used for a few decades without ever being leveled even after being moved around a few times. After we started expecting more from it and actually leveled it, it took a couple of weeks of leaving one leveling screw a little loose in the air before it settled down and starting holding a straight cut. The ways have fairly even wear of less than .01.

    If it's cutting a consistent taper side to side, I'd doubt it was from wear or a chip under something. Even if it was wear, a consistent taper should be able to adjust away. If it was a big jump due to the carriage climbing out of a hole in the ways, Not much you can do there, but I think you'd be able to see/feel the damage in the ways.

    The tool room lathe beds I've adjusted saw significant movement when I shimmed the legs or adjusted the leveling screws. Most had enough wear else-ware that I didn't bother chasing tenths, but .015 in 6" is a well within the range a tool room lathe can twist.

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    Quote Originally Posted by M.B. Naegle View Post
    .015 in 6" is a well within the range a tool room lathe can twist.
    ?? I submit you meant: "trade-school training / hobby / general repairs economy-grade light lathe". Even then, 0.015" seems too much for a mere 6".

    I'll refrain from saying "spaghetti bed" or "cursed with Iron deficiency anemia", but Gustafson having mentioned his own mount is a 10EE?

    By comparison he may be laughing his ass off about now?



    If a "toolroom" or "tool & gage" lathe were to be defined more or less in alphabetical order, as an appropriately optioned and selective-fitted example of:

    ATW Pacemaker, Axelson T&G, Hendey T&G, LeBlond Heavy-Duty with the 25-millionths TIR Timkens, L&S Powerturn / AVS, Monarch 10EE, Nebel Microturn, Rivett 10XXS, just to cover US Made marques?

    "No Fine Way" yer twisting a bed by enuf to deliver 0.015" taper in six inches.

    Some of those have kinematic 3-point suspension. Most have massive "base" castings, fully integrated, stress-wise. Some have carriages as mass as much as the entire Logan does, and "long" enough they'd smooth-out a twisted bed even if one COULD twist their heavy beds + serious support structure, integrated or otherwise.

    Just not happening.

    The portion of Texas under the "legs" would bend first!

    And that ain't EASY! Texas ain't as "vague" as the Kalifornikyah SSR.


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    You might find this video useful to understand how adjusting the lathe bed can minimize the taper:

    YouTube

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    Quote Originally Posted by M.B. Naegle View Post

    The tool room lathe beds I've adjusted saw significant movement when I shimmed the legs or adjusted the leveling screws. Most had enough wear else-ware that I didn't bother chasing tenths, but .015 in 6" is a well within the range a tool room lathe can twist.
    OK, I'll buy that, I have not seen that personally, but it is within the realm of possibility.

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    If theres one thing we know about a new to us machine, its that we just dont know, imo.
    .015" over 6" id call serious taper if the obvious isnt involved.

    Start with the bed, its the foundation of the machine. Run a level (through X and Z) up and down riding the carriage, a bit of plate in the tool post will work if youre struggling for a mount. If youre good both ways thats a strong indication your beds level and in decent shape. This isnt a last word check, but its quick and simple and gets you in the ballpark.

    Take a 2" odd slug of whatever you have and turn two equal diameter collars over 6". Indicate top and side to see where the spindle is pointing in relation to the bed. If that number confirms your taper then its time to pull the headstock.

    Has someone been in there with a shim pack? Has the bed got a dirty great crack in it? Or......? The above is 20 minutes work and can save a pile of tail chasing.

    Cheers
    D

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    Some Bubba with shims may hev done sonething like stuffed some under the V way contact surface "to fix the taper" while it was set on HIS crappy floor that looks like the Appalachians. Check that, yes.

    A bed twist would have to be pretty bad to do that, but it is possible, the actual tool movement is 0.0075, which is almost possible from a combo of some wear, AND a bed out of level. The common 10" size has a fairly tall carriage/compound asembly, and can tilt if the v way is worn more. Check that against the TS ways to see what you are dealing with there.

    A quick wear indicator is how sharp the corners of the V-ways are. if rounded, I bet 2 or 3 thou are coming from wear, at least. Note: A Logan generally will NOT show the soort of ridge that an SB will show from wear, so do not go by that.

    A decent level, like a Starrett 98 will show that amount of bed twiat fairly well. While they are nominally 0.005" , that is for an entire division.... you can see 20% of that easily. So check the bed with something around that sensitivity. Just set it on the compound, and watch the change as the carriage is moved. No need for fancy stuff. Also wiggle the compound, to see if it develops "rocking horse" corner wise tilting movement anywhere.

    A lathe on a bench may avoid the worst twist, but one on the Logan legs is definitely affected by the floor. Needs checked out for twist. Actually, so does a bench-mount, but the bench usually does not let the floor have as much effect.

    Logans are light for lathes in general, but they weigh double what the "lathes that shall not be named here" do. Beds are deeper and wider than similar SB, so they are not out of line. They are nice little machines, and can take a good cut if you can get the power to the spindle.

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    or something changed and the carriage is now riding on a V and a flat instead of a worn out V and V. maybe someone swapped carriages from another lathe?

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    Quote Originally Posted by johansen View Post
    or something changed and the carriage is now riding on a V and a flat instead of a worn out V and V. maybe someone swapped carriages from another lathe?
    Logan lathe beds have the carriage riding on a V on front and a flat on back. The tailstock rides on a V in back and a flat in front. Photo below.


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    Quote Originally Posted by ballen View Post
    Logan lathe beds have the carriage riding on a V on front and a flat on back. The tailstock rides on a V in back and a flat in front.
    The flat allows for thermal effects & stresses of work to move sideways whilst not fighting the "master" source for longitudinal location - the Vee, each case.

    Monarch 10EE is the same, just bigger, more finely fit and finished and harder. Also heavier and more expensive, of course.

    Logan need not apologize. They were/are decent value for small money and usually had a tad more long-axis daylight than a 10EE's mere 20" as well.

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    Quote Originally Posted by JST View Post
    ..see if it develops "rocking horse" corner wise tilting movement anywhere.
    THIS.. is one of the few places "gross motion" can hide out of sight.

    There may not be any significant wear on the visible, measurable, Vee or flat.

    There may be VERY significant "rocking horse" on the UNDERSIDE of the softer Cast-Iron matching surfaces of the carriage. Ball type oilers if it has those usually got poor attention, may also have let swarf in, even if carefully cleaned before oiling.

    Tool loading puts any slack into play.

    Five to seven times as much underside wear as is on the bed's Vee, less on the broader flat, is not uncommon, and more of it is at the ends than towards the center, hence "rocking horse".

    Borrow something like barbell weights to shift to each corner in turn and go a-hunting.

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