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Thread: Cutting shapes in HDPE

  1. #1
    Join Date
    Jan 2013
    Location
    West Columbia SC
    Posts
    83

    Default Cutting shapes in HDPE

    I need to cut a pocket in a sheet of HDPE the shape of the rocks in this picture picrocks.jpg I was thinking of tracing them on a piece of card board and scanning them into my computer and then do bitmap trace or is there a better way to do this?

  2. #2
    Join Date
    Dec 2005
    Location
    Pro Signs, Coal CIty IL
    Posts
    291

    Default

    When reproducing stuff like this I usually set the object(s) up on a contrasting background and take a picture of it, because most of the time the stuff I do is bigger than my scanner. Take the image as close straight on as possible to minimize distortion. I measure the X & Y overall dimensions and then make the image that same size in photoshop. For example, let's say tape an 18"x18" box around the group of shapes. So, if the tape box is 18"x18" and you skew the image in PS to match that same 18''x18'' that will help with any distortion and everything inside the box should at least be close, close enough that a little tweaking will get you there. I use the drawing tool, but if the photo is clean and contrasty I can sometimes auto trace and then clean up the vectors where needed.

  3. #3
    Join Date
    Mar 2013
    Location
    Memphis TN
    Posts
    691

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    I made up a sheet of plexiglas with a 1"x1" grid that I overlay on top of things or I use a similar grid on a large piece of cardboard and do the same thing from underneath. That way, the scale of the objects is included in the picture and any distortion caused by the camera can be compensated for. It also helps to line of the shot with the camera if the grid is in the image and to take the image from as far away as possible and use a zoom since that will minimize the distortion from being close up. Then, it's super easy to convert to an actual traceable bitmap since the scale is embedded in the picture.
    ShopBot Details:
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  4. #4
    Join Date
    Jan 2004
    Location
    iBILD Solutions - Southern NJ
    Posts
    7,907

    Default

    Mark each piece with a part number or letter. Trace around each shape onto a piece of white paper with a fine mechanical pencil. Write the part number on the inside & maybe some scribble marks in there too - depending on the flatbed it may ignore some fine lines. For scale, trace around a coin and mic out the diameter to left on the paper. Write that number inside the circle - in case you need to adjust for scale. Then scan the paper.

    Bring the image into CAD and manually trace it out using a polyline & then node editing (if you truly want professional result with the least number of nodes) - otherwise you can do the diet coke version where you just use the auto-trace and then spline it with a tolerance to reduce nodes.

    -B
    High Definition 3D Laser Scanning Services - Advanced ShopBot CNC Training and Consultation - Vectric Custom Video Training IBILD.com

  5. #5
    Join Date
    Dec 2005
    Location
    Pro Signs, Coal CIty IL
    Posts
    291

    Default

    I forgot to mention I do my layouts in Flexi Sign since it's what I have for the business. I've been using the same program for many years and anchor point editing/smoothing is relatively quick. I save as an EPS and import it to the CNC program.

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