Tool For Setting Angle of Compound on 9": RETRY :-)
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  1. #1
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    Default Tool For Setting Angle of Compound on 9": RETRY :-)

    Hello crew; I hope all is well.

    First and foremost, I appreciate the responses on my first thread about setting the
    compound angle…lots of great ideas and information…thank you.

    But I find that I didn’t frame my question very well, and hence, a variety of answers.
    Rather than being a putz that doesn’t respond to his own thread, I thought I’d make
    my question a bit more concise with a few parameters and better explanations.
    Sorry to have taken you down this rabbit hole to begin with. This is NOT a problem I’m
    experiencing nor anything that requires immediate action or response. It’s just an idea, thought,
    or exercise in problem solving.


    As we all know, a digital readout (DRO) that measures movement in the X and Y axis
    is a popular add-on. Even mounting dial indicators (digital or dial versions) on an
    analog lathe by means of holders that go onto a V-way (or magnetic bases elsewhere)
    are great options. Clearly, a poor man’s CNC machine so to speak; the meeting of
    an analog machine with digital measurements.

    So my basic thought was if the X & Y axis can be so closely monitored (even to the thousandths), why not the angle of the compound using inexpensive handheld digital protractors? Although I said so in my first thread, it was really never about how to better see the degree graduations on the backside of the compound. Yes, lots of light, mirrors, magnifiers, and even camera snapshots are good ideas and I
    rely on all of those heavily. But for the sake of this discussion, let’s take the degree stampings out of the loop, and say they are simply not there.

    Let’s now add that a client has specified a 39.6 degree angle on the end of his/her product. Let’s also add that you must use a digital protractor to physically make this measurement. The tool post can be removed if necessary. Also, for the sake of discussion, let’s remove
    all issues regarding the +/- tolerance of said digital protractors (to avoid splitting hairs).

    It seems to me that there is really only one reliable machined surface on the compound,
    that being the very small sliver of flat on the backside of the compound (see photo).
    Clearly, the only other reference point can be the ways, the workpiece, or perhaps the
    side of the chuck (or tailstock?).

    First order of business will be to arrive at 'absolute zero' on the compound, be it perpendicular
    or parallel. Like Patv mentioned, one could even use a machinist angle gauge to arrive at, say,
    a true 45 degrees, and then any measured movement could be added or subtracted from that 45 degree
    setting.

    So the task at hand is to develop a quick way to set the compound digitally, and with any luck,
    in real time as you are moving the compound. I would assume that a decent digital angle finder could be
    modified somehow to be able to reach the two critical reference surfaces.

    PS: Yes, I did look for applications on-line, and found mostly protractors, but these will be of little use until ZERO is found. I could not see if they could be zeroed either. There is a compass on my phone in degrees, but can only assume it is referencing magnetic North.
    I doubt it would be accurate enough for machine work, but just thought I would mention applications.

    Doing a quick web search, I have found many “digital angle finders”, some of which are very expensive. But I believe that a lot of these are inclinometers as opposed to a “lay-flat” protractor type.

    Again, this is NOT a problem I’m experiencing nor anything that requires immediate action or response.
    Please don’t bother to respond if you don’t have the time or interest.

    I’ll live.

    Thank You For Your Thoughts


    PMc

    lathe-reference-surfaces.jpg digital-angle-finder.jpgphone-compass.jpg

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    You are oversolving the problem IMO. The compound is adjusted infrequently and does not warrant a huge investment in digital gizmos. If you need better than 1º accuracy just dial it in with an indicator. Or make a test cut and take some measurements.

    The whole operation is analogous to tramming a vice on a mill table.

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    Quote Originally Posted by jwearing View Post
    You are oversolving the problem IMO.
    Thanks; you are probably right.
    The digital angle finder in the photo is only 20 bucks on Amazon, so not a huge investment.

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    Use the phone app to align your lathe on a perfect east/west axis, then set the compound to north.

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    Admit to being confused.

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    I've been down this road and it doesn't work because I wasn't and your not visualizing how a movable slide and specifically how the top slide operates under real world conditions. For any object to move, it has to have X amount of clearance to do so. The more accurate the object is machined, ground and/or scraped as well as the better surface finish is, the closer the parts can be fitted, but that non optional clearance is still required. An exact 1" shaft can not fit in an exact 1" hole without it being a press fit. Setting a top slide by any method is still a static alignment. As soon as the cutting tool enters the cut the forces reacting against it are transmitted throughout the machine.

    Depending on the amount those clearances happen to be, then one of the effects are it pushes the one end of the top slide into the fixed dovetail closest to the tool point and opens up the same side at the other end. Those clearances allow the movable part of the top side to very slightly pivot. No it's not much, only part of a degree, but were talking precision here and it's going to change your settings no matter what you do, and it will throw off any preset angle the machine is cutting. Setting an angle by using a pre existing parts angle while using a DI or DTI only gets you almost to the correct angle. To get even close to exact match such as a Morse taper as one example, further very minor adjustments need to be made to compensate for those clearances between the top slide parts as well as how much deflection happens within the rest of the machine. And that's on the very best manufactured manual machines in brand new condition. On a worn machine those clearances can vary along the dovetails a lot. There is NO method of setting exact angles unless they also replicate the forces acting against the lathe parts your trying to set to an exact angle. Try cutting any male and female taper with the exact same top slide angle. Check there fit between the parts with something like Hi-Spot blue and you'll then see what I mean. Thinking you can easily set any high precision angle you want no matter how precise the tools being used happen to be is an exercise in futility. It can't work due to the limitations within the machine itself that allow it to operate.

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    As far as a dro or digital reader for setting degrees. I'm not sure, I haven't wrapped my head around it enough.

    Finding your zeros and reference points I have put more thought into.

    My first thought is, its like running alignments on the lathe. But to get a really good zero, you would need to run an alignment first, or be aware of the discrepancy to compensate.

    I'm not really in love with the reference points in the pic, in part because I don't know where they are at, unless you have recently scraped things in and done readings. The closest one I like is off the chuck face, but not by itself, but using a parallel on it. There are more modern examples and threads, particularly if you search the "reconditioning section". But one I remember is here, if you scroll a few pics down:
    Another New Toy

    To further explain, let me back track into things you may already have done, or know the number to. First, all things serve the ways, including the head stock. So headstock must be aligned using a test bar.

    With headstock aligned, you would check carriage/saddle to headstock, via the parallel in chuck. With two options for getting cross slide aligned. Scraping saddle ways, or scraping dovetail for cross slide until you get a good reading on parallel in chuck.

    Now assuming you got a zero on test bar for headstock alignment, and a zero for cross slide on the parallel. . .

    Well now can use both the test bar, and the parallel in chuck to set/check both zero and 90 degrees on your compound. Put dial indicator where tool post normally goes. Indicate off parallel for the zero reading, and run only the compound back and forth on it. Switch to 90 degrees, and put test bar in spindle taper. Run compound back and forth indicating off test bar.

    That would give you a zero degree and a 90 degree mark to within a thou or two I bet.

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    As Neander mentioned, the reference is the work, and the slop & dynamic conditions of the machine.

    However,if, as you mention, there is DRO on the lathe with Z & X axis scales, you could add one to the compound for sine bar reference.

    Put a test bar between centers. Verify it is parallel to the ways. Use a DTI to register -0- advance or retract the cross slide a defined distance, verify X displacement by moving cross slide to return DTI to -0-.

    Somewhat iterative, but accommodates some of the motion in a section of the ways.

    After that, adjust for conditions. The 3 axis DRO would make it easier to calculate & register small changes, and/or return to baseline.

    When it matters, i never use the degree scale, but use gage blocks or a mic standard to a stop, and a long travel DI, or another stack of blocks to the work for sine reference. That still only gets to within blue-up distance for fitting the parts. But close enough that moving the work to between centers on the tool & cutter grinder makes it easy to finish. Or for some parts, close enough to stone/polish the rest of the way on the lathe if the part will match a good master.

    smt

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    Quote Originally Posted by neanderthal mach View Post
    .... Thinking you can easily set any high precision angle you want no matter how precise the tools being used happen to be is an exercise in futility. It can't work due to the limitations within the machine itself that allow it to operate.
    Now that is an excellent response and makes total sense to me. Thanks so much for the explanation which will no doubt save me a lot of effort in discovering
    the futility of the exercise. I had not taken any of that into consideration. I often dwell in the realm of futility, not realizing that a solution isn't always as black and white
    as my mind tells me, but rather clearly in a gray area or Twilight Zone full of a lot of variables.
    I appreciate your taking the time to respond. You Sir, are a sharp tool in the drawer!

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    Thank you Texas Gunny and Mr. Thomas; those are excellent points you bring to the discussion.
    Makes me appreciate more the efforts and experience of MASTER machinists during the early days and during the wars.
    You guys are two more very sharp tools! I appreciate your passing along your outstanding knowledge.

    I recall attempting to make a morse taper for a local oilfield tool company a long time ago on a heavily used 10"
    SB lathe with taper attachment. Boy was THAT a humbling experience!
    Last edited by mcload; 05-06-2021 at 12:26 PM.

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    I don't think it would be difficult to retrofit such a device (I have a few ideas in mind) but like others have noted I question the necessity of it. A simple logarithmic pot under the compound could do it, controlling a v/f converter. Scaled to read in degrees. No absolute zero, you just zero off the part or put zero wherever you want it. It may not make much sense to do all that on an old SB though.

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    That link to the hobby site was a pretty good looking implementation. If it were me I’d want to use the microcontroller to output over to my DRO and scale degrees to inches and show it on a fourth axis.

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    Compass + large Iron = forget it, actually thought you where kidding.

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    How about a laser mounted on the compound with a target on a far away wall?


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