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  • Working small, joystick etc

    I've been busy exploring the limits of my CNC mill. One of the things I am interested in is the accuracy, precision and repeatability of the machine. I went to great lengths in the design and construction to make it as precise as possible and it seems to have been worthwhile.

    I did some repeatability testing using an Interapid dial indicator mounted to measure table position. The indicator is able to measure to .oo1 mm per division. That's one micron per division or 0.00003937 inches. Preliminary testing shows repeatability to +- one micron 10 times out of ten. This is taking the table off the dial indicator, running it about in X and Y and then returning it to home. In theory the minimum step size on the machine is 790 nanometers which is the wavelength of deep red/near infrared light.

    With this information I decided to try a little stunt which worked. That's an ordinary straight pin. :=)



    I have been working to produce very fine ruled gratings with the idea of perhaps even being able to use the machine as a ruling engine for diffraction gratings. So far with some careful attention to the scribing head I built I have been able to sucessfully rule 40 lines per mm or 1000 lines per inch. This is an example ruled on a cube of 7075 aluminum. I used this alloy because it has a hardness slightly greater than mild steel. This sort of grating is known as a "blaze grating". The drill bit is 1/16".



    I very carefully sharpened the carbide graver to a very sharp but slightly radiused point. The radius is perhaps .0005". The point was highly polished using two grades of diamond dust in a brass lap and a final polish using cerium oxide. I don't have a pic of it but the carbide tip is mirror finished. The biggest obstacle is providing consistent downforce because the amount required is so small. I have removed the spring and am using small weights or even just the weight of the graver itself. To go finer I will have to lighten it further or counterbalance the graver tip. The multiplication of pressure becomes extreme when the tip is only .001" across. One ounce per square inch pressure becomes 62,500 psi on the tip.

    With that in mind it is obviously not a problem to engrave steel. This bar of square key stock has been polished and a 1000 line per inch blaze grating inscribed on the left end. I also scribed a much finer resolution hologram, the most complicated one yet.



    Also, the machine will easily inscribe lettering on glass.

    I have been having problems jogging the machine from the keyboard. I become confused which arrow keys to press for the X axis jog. I decided to interface a joystick as that is something I know I won't have a problem with. I use an old switch joystick originally intended for machines such as the Commodore 64 and Amiga. I had a look through my pile of old computer keyboards and finally found one with a real circuit board that can be soldered to easily. The joystick switches for the four stick directions are simply wired across the appropriate switches in the keyboard. The leads are brought to a D sub 9 pin connector on the back of the keyboard. The fire button is wired to the ALT key to provide rapid jog control. This is much nicer than pushing keyboard buttons and makes it easy to manually control the mill for a simple job.

    Last edited by Evan; 01-22-2008, 08:44 AM.
    Free software for calculating bolt circles and similar: Click Here

  • #2
    WOW Evan, that's remarkable. To think, I'm happy to work in .0005" increments.
    It's only ink and paper

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    • #3
      So that's one more step towards the $500 printing plates

      .
      .

      Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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      • #4
        Oh, come on Evan - you need to engrave dancing angels on that pin!
        "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

        Comment


        • #5
          Try the keyboard emulator boards that the gamers use. They go in series with your keyboard cable and you can program to generate any key sequence you want when the contacts close.

          Data on the emulators (and other boards to interface with CNC) here:

          http://www.cnccookbook.com/CCBreakoutBoards.htm

          Here's a bunch of panels to get ideas from:

          http://www.cnccookbook.com/MTCNCPanels.htm

          Mach3 makes it easy to support a lot of these things too.

          Lastly, if you're gonna mess with tiny stuff, you need more rpm. Better build a strap on high speed spindle using a laminate router or other 20-30K rpm motor.

          Cheers,

          BW
          ---------------------------------------------------

          http://www.cnccookbook.com/index.htm
          Try G-Wizard Machinist's Calculator for free:
          http://www.cnccookbook.com/CCGWizard.html

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          • #6
            You're out of control aren't you? I have to admit, 6 capital letters on the head of a pin is abit beyond impressive for someone working in their garage........in Canada to boot
            - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
            Thank you to our families of soldiers, many of whom have given so much more then the rest of us for the Freedom we enjoy.

            It is true, there is nothing free about freedom, don't be so quick to give it away.

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            • #7
              Yeah, what's with those coarse engravings on the head of a pin? What about the entire contents of machinery's handbook

              Nice work. I'd be inclined to celebrate if I found that degree of accuracy on one of my creations. My green is showing again
              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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              • #8
                I know about the various keyboard wedges. An easy way to do it is to use a USB and PC keyboard at the same time. It's easy to rip the controller out of an old keyboard and use it however you want. XP happily supports multiple keyboards and mice wherever they are plugged in. By using an old controller you can connect switches across the keyboard matrix and then remap it however you want using a simple tool from MS.

                You can download the Windows Server 2003 Resource Kit Tools here, no verification required.
                http://www.microsoft.com/downloads/d...displaylang=en

                It includes Remapkey.exe which allows the keyboard to be remapped. The resource kit also contains a slew of other tools, some of which are actually useful and AFAIK they all run on all versions of XP.


                The problem I found is that the USB controller causes missed steps in TCNC if it is enabled in DOS. Another reason to switch to something else, Mach 3 most likely.
                Free software for calculating bolt circles and similar: Click Here

                Comment


                • #9
                  I have to admit, 6 capital letters on the head of a pin is abit beyond impressive...
                  I had to make them that big because I don't have a more powerful microscope.

                  Lastly, if you're gonna mess with tiny stuff, you need more rpm. Better build a strap on high speed spindle using a laminate router or other 20-30K rpm motor.
                  I have already built and tried two high speed spindles, neither of which is satisfactory to me. I am now designing a third that I am pretty sure will do what I want.
                  Last edited by Evan; 01-19-2008, 08:02 PM.
                  Free software for calculating bolt circles and similar: Click Here

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                  • #10
                    Evan

                    Since I’ve been lurking around this site I’ve always looked forward to your posts, I’m especially intrigued with your CNC mill, I like the way that you’ve incorporated a lot of engineering into this thing, things like the use of prime numbers for lengths and spacing of components to avoid harmonics, and a whole lot of other things that a lot of machine tool manufacturers might not even consider.

                    I must admit, when I learned that you’d chosen to use Acme leadscrews and Delrin nuts my first thought was “Gee…………… after all that, I wonder why he scrimped on the leadscrews”. Your latest demonstration (engraving on the head of a pin) has shown that your machine has some incredible positioning and repeatability accuracies. I suspect this was no “Happy Surprise” to you, and a lot of thought probably went into your choice of leadscrew and leadnut materials. Would you share some of that with us and maybe the pros and cons you’ve come to understand between Acme leadscrews and the different grades of ballscrews.

                    Thanks

                    Chandler

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                    • #11
                      Originally posted by Evan
                      I had to make them that big because I don't have a more powerful microscope.



                      I have already built and tried two high speed spindles, neither of which is satisfactory to me. I am now designing a third that I am pretty sure will do what I want.
                      Evan, try looking at the Sherline high speed spindle.

                      TMT

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                      • #12
                        Evan...when you get some time I would like to see some pictures of that CNC mill.

                        thanks

                        TMT

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                        • #13
                          Originally posted by Evan
                          With this information I decided to try a little stunt which worked. That's an ordinary straight pin. :=)
                          For anybody who grew up in Seattle, your pin engraving immediately recalls the oddity at the Ye Olde Curiousity Shoppe (which still exists). It has the Lord's Prayer engraved on the head of a pin. It's on display, under a magnifier -- I think it is a larger pin head than you engraved.

                          So I'm curious, with your known CNC accuracy, how big a pin head would you need to match this feat?

                          I'm trying to think of more practical applications. How about a branding iron, for a flea circus.
                          Allan Ostling

                          Phoenix, Arizona

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                          • #14
                            And this is why cnc mills are so much fun. CNC turns an ordinary mill into a wonder tool that can do things you never even thought a mill could possibly do.

                            I use a USB gamepad with a lot of buttons on my x3. Mach 3 has an add-on called key grabber. It's easy to assign functions to any of the gamepad buttons and directional controls.
                            Steve

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                            • #15
                              Wow! I'm impressed. I can think of a few things I could use from that machine. Hey Evan, you taking orders for custom metal stamps? I need a couple. Not to mention some 1/32" thick fiberglass pieces cut to shape.

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