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Thread: Rookie lathe user needs some advice

  1. #31
    Join Date
    Jan 2004
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    Something like this, with a rectangular base to sit of the ways, would allow setting close enough to be just fine. This one is from a grinder, but the same idea would work well for a lathe.

    The height setter itself. Reference surface is the straight underside at the end.


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    Sitting on the T&C grinder setup (A Greeenfield T&C base, with a TP grinder head in use as a jury grinding head. Works well enough that a real head is down the list)



    The "blade" has a setscrew in the side to hold it in position, and two up from the bottom to set the correct height, and adjust to be horizontal as seen here.

    Last edited by J Tiers; 02-04-2019 at 06:28 PM.
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  2. #32
    Join Date
    Oct 2013
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    I don't believe that the tool height is all that critical for turning. The cutting is done on the left edge of the tool, so it should cut well enough if above or below the center line of the spindle axis. If it is slightly above, the cutting forces will tend to bend the tool or the work so that the forward edge of the tool will cut a little deeper, and could cause chatter. Below the center point, the tool and work will tend to move away from each other, reducing the forces. But this applies only to the turned surface, where the only cutting will be a "clean-up" behind the left edge that is doing the cutting for turning.

    For parting, grooving, or facing, however, the tool height is more critical. I think it is better to be a little bit low, so cutting forces will move the tool down and away from the work, whereas if above center, it will cause the edge to dig in. Also, as the remaining diameter grows smaller, the face of the tool will begin to rub, rather than cut, and can cause heat build-up and work hardening. Here is an image showing the effect of various distances above and below center on a 1" diameter rod, IIRC:


  3. #33
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    Dec 2015
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    I like the idea of it extending to the side from a base like that. Be it on the flat of the bed or a flat spot on the moving parts often the tip of the tool is not directly over one or more of those flat spots. So an arm that extends out from the base on the reference surface is a good idea. Makes using the gauge a lot more flexible.

    I'd want more of a flat surface at the top of the gauge so I could run my finger over it and feel the step up or step down where it touches the top of the tool being set and not have it be confused by the edge of the gauge. But the idea of extending it out so it can reach over other things in the way is stellar.

  4. #34
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    Setting the tool more closely to center isn't so much to ensure that the geometry of the cut is right as it is for a number of other things.

    Paul, your sketch shows how the cutting point changes with height. And it also shows how the cutter "inwardly leads" the resulting diameter of the part.

    One thing it does not show is that as the diameter of the part becomes smaller any displacement above or below affects the size of the part resulting from a cut more. That's because the value of the tangent of the triangle between the center and horizontal extension line and the height of the point of the cut becomes greater. So if I take a .005 DOC off a larger size diameter I get what looks like a proper .010 change in size like I expect. But if I'm working on down to a small diameter the cut is made above the line of the feed in direction and the tangent value of the resulting triangle gives me less than my .010 change in diameter I expected. So that makes it tough to do accurate work. I've had far more predictable results since I started using my gauge to set my tool heights. Before I would set it by eye but if working on a small stuff that I wanted to be, say, .250" and working down from .320 I'd set my DOC to .035 to get the .070 change and find that I was still at .028 or something like that and I needed another cut to get to the desired size. Which left me scratching my head thinking of all manner of deamons that might be possessing my machine. And all the time it turns out it was small errors in setting my tool height.


    Second is that I don't want to deal with a bad center pip. If low it leaves one. If high it cuts in to a nub and then pushes said nub out of the way leaving a slightly domed center pip. And in the case of carbide tooling produces the risk of a pressure flaked tip due to the pressure being from the wrong direction and pushing the carbide up and out.

    And finally I've found that since using the height setting gauge to set my boring bars that the high pitched singing is pretty much a thing of the past. I might still get a slight background "whistle from longer skinny setups but the eardrum piercing shriek I often used to have and lousy finish quality is gone.
    Last edited by BCRider; 02-04-2019 at 07:07 PM.

  5. #35
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    Jun 2009
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    san jose, ca. usa
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