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Making 4'x8' sign inkjet printer - need nozzles - help?

  1. Nov 6, 2009 #1
    Hi all, hope I'm not intruding or posting in the wrong place, and I apologise in advance if I have.

    1st, I am not a grad student, simply a guy with the desire to invent things and fix stuff till it's broken.
    A few of my projects include a solar tracking system, which analyses webcam images and aligns dishes toward the sun, and also many smaller projects, many of which never leave paper.

    Here is a project I am trying to get into motion - a giant printer, for printing signs.

    I have everything planned, and pretty near what I believe will work, except the sprayer nozzles.

    Using air brush pens is not an option because the overspray will not render a crisp image.
    I had considered first to use diesel fuel injectors, but there are many reasons why that will simply not work.

    I have settled on making 4 high speed valves, probably driven by voice coils from a large speaker, to control flow from a high pressure paint line. (Driven by speaker coils, connected to amp, connected to computer which would use the sound card to manipulate the spray duration and intensity.)

    Now, where on earth can I ever find small nozzles, that will put tiny 1/8th inch dots on the board in a perfect and even circle? They need to be very small, and also able to handle very high pressure.

    Any clues or ideas on this would be awesome.

    Thanks in advance.
     
  2. jcsd
  3. Nov 6, 2009 #2
  4. Nov 6, 2009 #3
    LOL :)

    I thought of that, but I want to print with oil based paint, on wood boards.

    I sell solar lighting kits for roadside signs, so I though if I had a solution to make them, it would be better than cutting vinyl.

    Sorry, but I'm dead set on making one, although it will probably take hours to print a single 4x8 piece of plywood, it is what I want.

    LOL
     
  5. Nov 6, 2009 #4
    Should be a fun project, good luck!
     
  6. Nov 6, 2009 #5
    I thought of using a ribbon , such as an old impact printer, which would be a lot easier, but would require 4 seperate runs, with drying in between so the paint doesnt transfer to the other print heads.
     
  7. Nov 6, 2009 #6
    This isn't exactly what you asked for, but it might still work for your purpose.

    An array of hypodermic needles can be used to deposit directly on a surface.
    With proper viscosity, the capillary forces will prevent dripping.
    Deposition is accomplished by piezoelectric vibrator + gravity & hydrostatic pressure.

    I made a color wheel for 2 sets of acrylic paints with each sample composed of 256 parts made of different proportions of each to test color gamuts with a mind to a similar project but to paint murals on rolls of linen.

    It should be a heck of a lot of fun- please post pics when you finish or maybe do it somewhere you can post a whole series of your progress. Have fun!
     
  8. Nov 7, 2009 #7
    I plan to mix and use cyan, magenta, yellow, and black oil based paint.

    I thought of the "needle deposit" method, but I'm sure it would be a constant fight against streaking.

    My most recent thought is that an inkjet printer basically squirts a "blob" of ink on the paper, leaving gaps between injections to reduce intensity of a given color- this is possibly what I should be thinking, is to leave series of different sized "puddles" under the print head, as opposed to trying to actually spray it on such a tiny area. Leaving a controlled sized blob of paint could be as simple as a print head being a tiny rubber hose, with a pinhole pointed towards the board, and using sudden but controlled pressure spikes to make the desired amount of paint jump on to the sign.
     
  9. Nov 7, 2009 #8
    Just had to add this/ ask this as well-
    Going from RGB images on the computer, I need to know how hard to "punch" the paint injectors to paint the same image, but using CMYK paints.
    I stole this formula from an online calculator:
    RGB to CMY:

    //RGB values from 0 to 255
    //CMY results from 0 to 1

    C = 1 - ( R / 255 )
    M = 1 - ( G / 255 )
    Y = 1 - ( B / 255 )

    Now that seems simple enough, but wait...what happened to black?
    Another conversion, CMY to CMYK:

    //CMYK and CMY values from 0 to 1

    var_K = 1

    if ( C < var_K ) var_K = C
    if ( M < var_K ) var_K = M
    if ( Y < var_K ) var_K = Y
    if ( var_K == 1 ) { //Black
    C = 0
    M = 0
    Y = 0
    }
    else {
    C = ( C - var_K ) / ( 1 - var_K )
    M = ( M - var_K ) / ( 1 - var_K )
    Y = ( Y - var_K ) / ( 1 - var_K )
    }
    K = var_K

    I have a feeling the black will take a bit of adjustment, and less of such a precise calculation, but we will see.
     
  10. Nov 8, 2009 #9
    If you want no guessing, print out a color wheel in real paint, by the numbers, and then code them into a lookup table.

    Raise and lower the applicator to eliminate streaking.

    Absorption can be tweaked and drying can be assisted with a hairdryer mounted on the printhead- or something more elegant.

    You'll find a way to get what you want cuz you can.

    I chose to mix paints and make solid colored dots rather than deal with this kind of thing.
    http://en.wikipedia.org/wiki/Halftone
     
    Last edited: Nov 8, 2009
  11. Nov 8, 2009 #10
    Why not use UV cured pigment based inks. I own a hp 35100 flatbed and love the fact that 2 arc 500w lights cure the inks in about a minute. Consider your health. BTW, the inks remain fluid.
     
  12. Nov 8, 2009 #11
    addendum, liquid until zapped by UV, that is...
     
  13. Nov 8, 2009 #12
    Sounds expensive....

    Most rural communities around here will even hire someone to paint the sign by hand...trying to recoup major equipment costs or expensive inks are options that are not in the cards presently. I plan to build this entire thing for under 5000$.
     
  14. Nov 9, 2009 #13
    how about a variation of the needle solution. If the hypo was the pump, 2 check valves, then you could drive them with a low power electric motor with a cam on it (kinda like how the fake smoke in your model train gets the puff effect). Then a certain amount of the "stroke return reversion" could be what pulls the paint back to prevent drips
    or you could use high speed pulse modulated valves like we use in our pressure controller products, and pressurize the reservoir. those valves provide very precise control of gas flow)

    dr
     
  15. Nov 10, 2009 #14
    How about the faucet nozzles used on the sinks in chemistry labs? I seem to remember them being able to deliver one drop at a time for obvious reasons. Not sure where you could find them, but they should be able to handle high pressure. I would image the hard problem is going to be controlling the paint flow that exactly.
     
  16. Nov 11, 2009 #15
    Most printers I know of alter the colour using small dots of ink, the more sparse or dense the dots of each colour gives you the mix you are after. I can't see this being possible to do on a home built machine with a great deal of resolution.

    One possibility would be to have a mixing chamber prior to an air brush or maybe multiple air brushes if its possible to control the quantity of paint leaving easy enough. A somewhat translucent paint would assist as well, a white under coat would obviously be required.
     
  17. Nov 12, 2009 #16
    maybe we're going about this backward, could you use the ink delivery systems that already exists and then mount it on a new frame. also, how about the old plotter style, where they used a pen and just lifted it. have to do each color by itself, but use a pressurized paint brush. good luck

    dr
     
  18. Nov 12, 2009 #17
    I could see an airbrush method working for huge signs, with a 1/4 inch to 1/2 inch resolution.

    My favorite route so far is simply spitting different sized puddles of paint on the sign, creating the image that way.
     
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