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An electro-engraving project that needs development.

Discussion in 'CNC Mills/Routers' started by Tweakie, Jan 18, 2014.

  1. Tweakie

    Tweakie OpenBuilds Team
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    Two weeks ago a friend asked me “what could you do with one of these ?” http://www.lumaelectricco.com/product-description.php?products_id=13


    Well after a bit of research I found that these hand tools usually vibrate, as it perhaps makes it easier to draw lines and write text etc. but vibration would perhaps not be necessary if it was used on a CNC machine.

    I would not be everybody’s choice but being as I am related to Scrooge, in my distant past, I don’t buy anything that I can make so set about winding a suitable transformer with taps on a secondary winding to provide between 1.5 and 2.5Volts choosing a core size which would allow for 10Amps or so.

    The MkI used 2mm dia. wire for the secondary which was woefully inadequate (basically I did not know how much current I would need) so the MkII used rectangular section 5mm x 2.5mm wire – a much better choice. The next job was to make a pivoting holder for either a Tungsten or Copper electrode then to try it out and see what happens.


    Not exactly successful first time but, learning as I go, I am now starting to get to grips with the beast.


    Things I have learnt so far about the electro-etching process in general…
    Basically a tiny arc is struck between the tip of the electrode and the work and it is the extreme heat created by this arc which slightly etches and discolors the work surface.
    The voltage needs to be kept low. With a low voltage the arc is fairly stable beneath the electrode, as the voltage is increased the arc tends to wander from side to side and this spoils the appearance of the work.
    An arc creates electrical noise so it is important that the work is correctly earthed and any signal wiring (such as limit switches etc. and other input wires) are properly shielded otherwise this electrical noise may affect the correct operation of the CNC machine.
    Electrical resistance in the low voltage, high current wiring connections is to be avoided as even a fraction of 1 ohm can generate significant heat so take care.
    I have not managed to find (in my boxes of junk) a suitable shunt to be able to measure the output current directly but assuming my transformer is 50% efficient then measuring the transformer input current and voltage I can deduce the output current to be around 9-10Amps at 1.8Volts (but it could be more than 10Amps – it really needs to be measured properly).
    Considerable heat is generated in the electrode itself – this heat is being transmitted back to my pivot bearings and electrically insulated mount so I need to incorporate a ceramic or similar high temperature heat insulator to hold the electrode.
    The process is only really suitable for use with steel – the higher the carbon content the better but I have not yet tried steel alloys, tool steel etc - these may react differently.


    This is essentially a development project which needs more people, knowledge and experimentation but I think it has the potential to be a useful addition to a CNC machine, in particular for marking stainless steel (which easily work hardens and can be difficult to rotary engrave).


    Is anyone interested in perfecting this process and taking the project further ?.

    Tweakie. 7283775.jpg 2650125.jpg 7062984.jpg 0306669.jpg 6113720.jpg 4554383.jpg
     
  2. The Dude

    The Dude Veteran
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    Maybe you could etch copper PCBs to label where the parts go? Then you don't need silk-screening. Might be simpler to just use a pen but you never know.
     
  3. Public Do Omens

    Guest Builder

    Surround the electrode with a glass solid ring.Drill a very small hole for the targeting in this glass guide.
    The electrode then can sit inside the glass and then have a very small chance of the charge jumping in X & Y axis as the glass floats on the surface. The hole is the only place the charge can go, down in one direction Z.

    X & Y are minimised due to targeting.

    This is loads easier then trying to reduce current and target using nano electromagnetic focusing techniques.
    Avoid difficult tasks, reduce until simple.
     
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  4. Tweakie

    Tweakie OpenBuilds Team
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    That is a very interesting idea - exactly what this project needs, plenty of suggestions for improvement.

    Thanks,

    Tweakie.
     
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  5. Mark Carew

    Mark Carew OpenBuilds Team
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  6. The Dude

    The Dude Veteran
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    anything that is a good insulator and can withstand the heat will work. Good insulators are teflon, PET, fused quartz, air, sulfur, wood, hard rubber, diamond and glass. That ceramic is probably a kind of glass. Glass melts at 2300degC, quartz=1700deg, rubber=350, teflon=327deg, PTE=250. I think diamonds would be best but glass will work and costs pennies for a piece that small.

    Hey I bet you could get a syringe needle the size of a human hair from the medical industry and take to a glass blower and have them make a nozzle using the needle and glass then just remove the needle while the glass cools?
     
    #6 The Dude, Jan 22, 2014
    Last edited: Jan 22, 2014
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  7. Mark Carew

    Mark Carew OpenBuilds Team
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    I like the idea @The Dude
     
  8. Tweakie

    Tweakie OpenBuilds Team
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    I don't know but it is certainly worth consideration.

    Tweakie.
     
  9. Tweakie

    Tweakie OpenBuilds Team
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    Hi Guys,

    Thanks for all the input on this - it has given me further thoughts.

    I am now thinking along the lines of trying a much thinner electrode which is automatically fed, similar to a mig welding torch, and using a form of THC as the controller. This would overcome the existing problem of electrode erosion but, who know, may create it’s own set of problems :(


    Tweakie.
     
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  10. Public Do Omens

    Guest Builder

    Isolation used to stop steeper controllers burning out.

    Has anyone tried to use optical isolation on the motor to stop the feedback, if it happens?
    More important does it happen outside the lab in the real world?


    I think the motor would either have to be going very fast or have a large torque for this feedback.
    People have talked about speed controllers burning out.

    Would optical isolation work?

    Is this relevant as Tweakie shows the use in his brief?
    Do i start a new thread?
     

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