Rong-fu (round column) mills

I was looking at a Rong-Fu clone today (RF30). Unlike the dovetail column mills that I am used to this one has a round column. The head can be moved
up and down and swivelled 360 degrees, however one loses the X-Y position doing it. The spindle (quill, really) has a maximum range of movement of only 5".
My small mill manages 9" and I need every thou of it on some occasions, particularly when changing for larger cutters, e.g reamers or simply changing holders.
Furthermore I thought it was a good practice to mill with the quill retracted as far as possible to improve rigidity. This would make it rather difficult to change even shorter bits let alone change, say, a mill-holder for a drill chuck.
What am I missing? How are these issues dealt with on these machines?
--
Michael Koblic
Campbell River, BC
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<snip>

You aren't missing anything. You have to find a way to re-register after moving the head on the column. Some people modify the mill to have the head keyed to the column. I read somewhere (HSM probably) Someone drew a plumb line on the wall opposite the mill. They had a laser pointer mounted on the mill head with the laser dot pointed to the line. When the head was moved the alignment was good as long as the dot remained on the plumb line on the wall (and the mill level). It's suprisingly accurate if you do the math.
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Charles U Farley writes:

This laser alignment idea is someone's ill-conceived fantasy. You don't get any accuracy without projecting the spot a long distance. But laser pointer spots are big blobs over such a distance (many thousandths), so there's no accuracy to eyeballing a blob onto a plumb line.
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A)    You can reduce the size of the dot with a tiny hole in a thin     metal plate. (Also the brightness.)
B)    Consider that the spindle is perhaps 8" away from the column     (not too unlikely, given the size of the machines which     typically have round columns).
    Assuming that the wall is perhaps five feet from the column     (60") then 0.001" at the spindle becomes 0.060" at the wall.     (And five feet to the wall behind the operator is not that     unreasonable, especially if there is another machine tool, such     as a lathe, on the other side of the aisle.
    Enjoy,         DoN.
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Uh no. The accuracy of the spindle is the ratio of the column to spindle divided by the column to wall. For your example of 8" and 60", .001" on the spindle would be .0055" at the wall.

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    [ ... ]

    O.K. -- not my 0.060", but not your 0.0055" either. I get 0.0075" when I recalculate it a couple of different ways. So -- add a mirror on the wall behind the operator, and bounce it to another wall more distant. Sum the distances.
    Enjoy,         DoN.
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The mirror has to be *very* flat over the height of the column travel. You might find one that's good enough in a scrapped scanner.
jsw
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DoN. Nichols writes:

Don't be naive. Pinholing a big blob of light doesn't make it any more pointy. You can't improve coherence outside the device, at best you preserve what exited the laser device aperture. A pinhole will just diffract and degrade coherence.
All of the follow-ups to date of my critique ignore the optical principles that prevent this entire scheme from working. Specifically, Gaussian beam optics, beam waisting, and beam divergence. Laser beams are narrow but they still start at millimeters wide and spread out to inches as they project. Have a friend stand 50 feet away and see what kind of spot you get on a target from a good-quality laser pointer.
A simple scribed vernier scale with mechanical pointer lever and magnifier would work better.
Lasers do not create precision out of nothing. They have to be attached to precision mechanisms, which isn't the case for this axis on a round- column mill-drill.
You're essentially trying to build a precision transit or goniometer without a mechanism or scope. You need more than just a laser pointer.
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The one I tried was about 0.2" wide at 10 feet. The spot wasn't too far from circular and its intensity fell off sharply at the edges, so I was able to align both edges with marks on the scale the same distance from the 1" line, in this case the lines at 0.920" and 1.080". The alignment only has to be repeatable, not absolutely accurate.
jsw
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    I've done the experiment, and observed a significant shrinkage of the projected point on the wall. Granted, it is most likely a loss in brightness so the *visible* part of the Airy disk resulting is significantly smaller. But it *does* make the visible spot smaller. After all -- the more distant from the center, the less energy concentration.

    But it will make the visible (to the naked eye) portion smaller.

    Of course. Even with a HeNe laser we get significant beam spread, actually more than with a solid-state laser level of similar brilliance.

    Note that if you mount a mirror on the mill head, and bounce the laser pointer off that so you get double the angular deflection from a given motion of the head as well as doubling the distance. Then select a pinhole based on the tradeoff between perceived spot size and brightness (you need sufficient brightness so you don't lose the spot. :-)
    Add a second mirror as the target of the first but if it has a cylindrical surface (with the axis properly vertical, of course), you get more angular magnification for a given beam length. (You find this sort of setup in the old projection galvanometers.)

    It at least will get you closer than just eyeballing the end mill itself. Better is a machine which doesn't have a round column, but rather proper dovetailed ways -- and even better with the table on the vertical dovetails instead of the head.
    Enjoy,         DoN.
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[on alignment recovery using a laser and target]

So, has anyone put a good scope-with-reticle onto a suitable mount point on their mill? Artillery aiming is routinely done this way, you dial in a deflection angle and move the big tube until your crosshair is on the reference stake. There's some realignment called for, each time the big tube ... shakes.
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I do the same thing - my small level - 18" - has a laser and either a point or a cross. I use the cross and have a tape line edge that I can shoot. Tape is sharp edge vs. a pencil or pen.
Martin
whit3rd wrote:

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DoN. Nichols writes:

I don't think you get the point.
Making a pinhole shadow of a big blob doesn't make the blob any more accurate. The blob moves around and the pinhole stays illuminated.
The whole approach just defies elementary principles. You can't improve on the beam divergence angle, and that is many thousandths of an inch at the spindle distance scale.
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    It makes the blob (Airy disk) dimmer, and thus makes the part *visible* to the user smaller. If the disk is full brightness, you see the peak, and several rings of minor peaks surrounding it. If you make it dimmer, you limit what you can *see* to the central peak only.
    And -- if the pinhole is mounted rigidly to the front of the laser, you are selecting the same portion of the blob as the laser and pinhole move as a unit.

    The beam, through a pinhole, is producing an Airy disk -- a central peak surrounded by rings of diminishing brightnesses. Make the pinhole small enough, and you can see only the central peak.
    Have you *tried* the experiment, or are you working purely from your own understanding of the underlying optics laws? Remember -- those laws are not taking into account what is visible to a human eye, just the overall distribution of light.
    I tried it with a series of pinholes mounted in a turret (designed for adjusting the energy content of IR from a black body source while retaining the same color temperature). Granted, these were quality pinholes, made in very thin metal, blackened, and with absolute minimum reflection through the bore (because of the thin construction). The pinhole was mounted about an inch in front of the laser pointer, and was projected on a wall about five feet away.
    Down to a certain size, the visible dot got smaller, then the diffraction started making things worse and spreading it out. FWIW, this was a red laser pointer. A green one would probably behave somewhat differently.
    Enjoy,         DoN.
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DoN. Nichols writes:

Both. As an optical engineer, I approach this problem all the time in many different forms.
Photons travel in straight lines. The childish gee-whiz notion about a laser is that its photons are also traveling in *parallel* from a nearly point source, because that is the casual impression when you wave the spot from a pointer around. The beam divergence is less than the angular resolution of your eye, so the beam *looks* perfect. That is the essence of the mistake that a laser is some magic mojo for this goniometry.
While laser light looks well-collimated compared to ordinary sources, and indeed looks indistinguishably like a perfect source to the naked eye, in reality it is not collimated to the kind of angular precision required for resolving 0.001" spindle travel on a radius of 12 inches on a mill-drill, or 17 seconds of arc, which is to say 0.08 milliradians. Compare this precision to a typical far-field beam divergence of about a milliradian for the best laboratory lasers, and you see why this hasn't a chance of working.
In fact, using a laser has nothing to do with this purported optical alignment gimmick. One could just as well use a flashlight with a pinhole, or just an alignment scope viewing ambient light. The laser is just a red herring. Which is what makes this laser-solves-all attitude even sillier.

Your pinhole notion is just wrong from the start. Study the basic laser principles like beam divergence and diffraction limits. Stopping a beam makes it diverge more, not less.
When you perfect your 0.08 mrad beam, please call me. We'll be rich.
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That is why you use a Cross + split beam that draws a line up and down. I have a short level that shoots that out the end. I mount it on the head once I have it trammed - My professional vice is set - I set a marker.
The real trick is looking 30' for a line. I figure spotting scope or binoculars.
Martin
Richard J Kinch wrote:

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On Sat, 19 Dec 2009 00:49:11 -0600, "Martin H. Eastburn"

Mirror on a stable stand or wall (the surface table would do in my shed). Then you can look at the wall close to the mill :-)
Mark Rand RTFM
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A mirror that reflects the beam back to a target attached to the laser should work, with doubled sensitivity, and be visible up close while you are tapping and tightening the head. You could confirm the flatness of the mirror by double checking with a square and test indicator as you move the head down the column.
I just tried it over a 10' path using a 50ths ruler as the target and equalizing the spot width on both sides of a 1" line, which is easier than estimating the center. I have to hold the button on this laser pointer so it wasn't as steady as possible, but I could align it within 0.050 easily, translating to about 0.005" at the quill. I think with a clamped instead of hand-held laser I could center the beam repeatably to 0.020", 0.002" at the quill.
I should have written that the RF-31's Z axis clamping shift was 0.1mm, not 0.5.
jsw
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Depends on the laser, of course. One can get under .050" spot size, and with two yards distance to wall (there should be at least one wall that far away) that angle accuracy is 0.04 degrees. I'd be tempted to use one of those hologram-symbol pointers, and get all the lines in a star to match up to the wall engraving; when it's spread over a large viewing area, the alignment would be easier to eyeball.
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Light Tool Supply had written this in response to http://polytechforum.com/metalworking/re-rong-fu-round-column-mills-215164-.htm : Hello I have a manual for the RF-30 Milling machine I can send you in pdf form if you like. Please email me for free copy
snipped-for-privacy@lighttoolsupply.com
Michael Elson President Light Tool Supply 100 Bayview Dr Suite 1029 Sunny Isles Beach FL 33160 800-526-4956 ext. 107 http://www.lighttoolsupply.com/ ------------------------------------- Charles U Farley wrote:

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