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Thread: Machinable epoxy

  1. #1
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    Default Machinable epoxy

    I want to make a non-conductible prototype that will eventually be made of injected plastic. Making and modifying the injection mold is the hard way to do it, so I want an epoxy prototype that can be altered easily if I want to change design details. It would just require mixing up some more 2 part epoxy and filling the holes, then re-machining.

    Is 2 part epoxy easily machinable? Use low speed or high speed? Is it tough on cutting tools?

  2. #2

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    Belive it or not I have had really good results using Bondo to make prototypes. It is really soft right out of the can but I mix in a bit more polyester resin and it machines pretty well. Still soft but easy to add to and cheap. I have used it to make sand castings and latex moulds. I dont' know if it is conductive.

    Wayne

  3. #3
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    There are so many different forms of epoxy about, that it would be difficult for someone to tell you ...
    I've had some stuff that is like boiled sugar sweats (candy).......same as, in every way ...very brittle and shatters as soon as you look at it.

    and there is other stuff that never quite sets,,,,,,,,,it would be like machining rubber.

    so epoxy is different and varied.

    all the best.mark

  4. #4
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    I'll second the bondo.

    Check boating sites for various fillers used for epoxy and polyester resins, they've got hundreds of different types.

    Bondo itself is pretty machinable, easily filed and sanded, but should use water for a cutting fluid as it will get sticky sometimes when warmed up. Very easy to add material or fill unwanted holes when desired.

    I think the typical filler in bondo is talc so you can essentially tailor it to your needs by adding more talc or resin.

    Ken.

  5. #5
    J.Ramsey Guest

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    Two that I've used are Devcon Epoxy( F) Aluminum and Devcon plastic steel(A) both cure over night and machine quite well dry.

  6. #6
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    Default Epoxy

    Duct Taper:
    One thing you did not mention is size of the Item. Hercules brand epoxy plumbers putty should work for small items. For larger stuff go with the bondo.
    I worked 6 years in and R&D shop at a yacht yard . we made all of the patterns of bondo wood and polyester paint. We built with wood added fillets and filled screw holes with bondo sanding was done at 80 grit. We then painted with gray primer. The form was refined with 180 grit and small inperfections were filled with evercoat a 100% talc filler polyester putty. The form was then painted black and wet sanded with 320, 400, 600 some areas were buffed and everything was waxed with five coats of mold release wax. Some of the proto type patterns were 50 foot long .
    If you are making something of all bondo consider a fiberglass reinforced formula. A Stanley sure form plane AKA cheese grater is great for roughing the shape when the bondo is half kicked. Be careful if you mix a lot or have a heavy cross section it can get real hot. Also piles of shavings can smoke DAMHIK .
    There are lots of formulas of polyester putty. Basically it is a mixture of casting resin laminating resin and various fillers; ground walnut shell,micro-beads ,fumed silica ,fiberglass chop,talc etc
    Another trick is making your own putty of aerosil Fumed silica and gel coat to touch up small holes and low spots. http://www.aerosil.com/aerosil/en/solutions/default

    And as the others have mentioned it is possible to customize the putty by adding fillers or thinners like resin or styrene monomer.
    Tin Falcon
    Last edited by Tin Falcon; 08-13-2007 at 09:01 PM.
    Ad maiorem dei gloriam - Ad vitam paramus

  7. #7
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    Default

    Quote Originally Posted by kendall
    I'll second the bondo.

    Check boating sites for various fillers used for epoxy and polyester resins, they've got hundreds of different types.

    Bondo itself is pretty machinable, easily filed and sanded, but should use water for a cutting fluid as it will get sticky sometimes when warmed up. Very easy to add material or fill unwanted holes when desired.

    I think the typical filler in bondo is talc so you can essentially tailor it to your needs by adding more talc or resin.

    Ken.


    Ken : Talc is one of the fillers it is considered a premium filler. A premium product with 100% talc typicaly cost 4 times as much as regular bondo. It is twice the money for a can half the size . However for filling small inferfestions it is well worht the extra expense it cures fast 5 minutes as apposed to 20 and it sands easily with less loading of the sandpaper. A premium bondo such as evercoat would be excelent for filling inperfections in fabricated steel assemblies that are being painted.

    Water would be OK for a coolant on a marine grade bondo . Automotive bondo uses filler that absorbs water. that could be a problem if filling holes with more bondo or painting.
    Tin
    Ad maiorem dei gloriam - Ad vitam paramus

  8. #8
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    Default

    Thanks for the input. My prototype will be small, 3" x 2.5" x 1" and box shaped. There will be electrical wiring in a recess on one side of the bottom that will then be filled with epoxy when complete. I will start with a block of material a little larger than the finished item and mill out all the recesses with my Bridgeport. The box is limited to those outside dimensions so I need to try different configurations of the components so that everything fits inside the box. Once I know that then I can make the injection mold.

    I mentioned epoxy because I have 15 gallons of the stuff and the Part A is coagulating in the jug so I want to use it up. But I do also have automotive polyester filler and have used that for a few things. Tonight I mixed up some epoxy and put it into a square container to let it harden. I will check it tomorrow to see if it has hardened enough to mill. If not, I guess I will try the bondo.

    Then I will make my million bucks... or just have fun making the thing!

  9. #9
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    old epoxy has a crystallised marzipan substance on the surface.
    important.... do not skim this off.

    mix this in well.

    put epoxy container into hot water ...as hot as you can get it ...
    if you don't, the stuff that makes it work will be crystallised in the mix ...and separated out .

    if spraying you may loose the chrystals content by filtering ...you dont want to do that either.

    when the mixture has warmed up stir ....and change the surrounding hot water for another batch.

    the Chrystal's will melt and be absorbed into the stuff....they are needed to make it set-up.


    this is the way of reviving old epoxy


    all the best.mark
    Last edited by aboard_epsilon; 08-13-2007 at 09:47 PM.

  10. #10
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    Dec 2004
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    Default

    Thanks Mark! I was ready to throw the crystalized stuff away. I could see $$$ going to the dump. One of my 5 gallon jugs has about 3 gallons of crystalized epoxy left. I poured off about a gallon of it that was not crystalized and gave it to a friend. I will try the hot water bath to see if I can save it.

    You said the crystals were on the top, but this stuff is on the bottom of the jug. If that matters. My second jug has about 3" of white crystals on the bottom so I will give that the hot water treatment too.

    The jug of Part B seems to have no problem.

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